**Biology 220**
06/24/02:
Part I: Cellular Physiology
Comparing between plants and animal (I will put this into a chart, as soon as I figure out how to do it...)
Plants:
sessile ("fixed" in one place)
non-motile (therefore evolved to tolerate non-favorable conditions)
maximize external surface area
gas exchange through stomatas; need carbon dioxide to produce oxygen by photosynthesis
plant defense mechanism (poisonous chemicals, blah blah blah...)
indeterminate growth (mostly from the tips)
new organs produce all the time
easy to clone
have cell walls, chloroplast, and vacuole
storage via starch
Animals:
mobile
motile (can seek out more favorable conditions)
maximize internal surface area by complex internal folding
respiration (take in oxygen and release carbon dioxide)
immune system
proportional growth
organs formed during development
cell fate determined in early development
storage by glycogen
Some definitions.........
diffusion: tendency of molecules to spread out to equalize their concentration
molecules diffuse down their concentration gradients
osmosis: passive movement of water to equalize its concentration
semi-permeable membrane: water can pass, but other molecules can't pass
Structure of cell membrane
lipid bilayer
glycoprotein: protein attached to carbohydrate
glycolipid: lipid with carbohydrate attached to its polar head
oligosaccharide chain: carbohydrate
cholesterol: controls fluidity of membrane
06/25/02:
Permeability of Cell Membranes
water yes
gasses yes ie. oxygen, carbon dioxide
small uncharged polar molecules yes ie. ethanol, urea, anaesthetics
large uncharged polar molecules no ie. glucose
ions no ie. K+, Na+, Cl-
charged polar molecules no ie. ATP, amino acid
Diffusion cont'd........
hypotonic: with lower ion condentration
hypertonic: with higher ion concentration
isotonic: both side of the semi-permeable membrane have equal ion concentration
animal cell in hypertonic solution:
ion concentration inside cell is lower
water molecules diffuse from the inside through cell membrane out into the solution
cell shriveled
animal cell in hypotonic solution:
ion concentration inside cell is higher
water molecules diffuse from outside into the cell
cell bursts
plant cell in hypertonic solution:
ion concentration inside cell is lower
water molecules diffuse from inside the cell into the solution
plasmolysis: cell collapse from the cell wall
plant cell in hypotonic solution:
ion concentration inside cell is higher
water molecules diffuse from outside into the cell
cell swell until confined by the cell wall, and does not burst
Therefore, animal cells are normally isotonic with surrounding environment (except in kidney), and plant cells are normally in hypotonic solution.
calculating osmolarity:
1 mol glucose = 1 osM
0.5 mol Nacl = 0.5 mol Na+ and 0.5 mol Cl- = 1 osM in total
membrane potential: separation of charge across membrane
06/26/02:
after receptor receive signal, the cell can then...
activate genes
increase enzymes and other proteins
regulate ion channels or proteins
activate enzymes directly
plastids have:
2 membranes ]
own DNA/RNA ] proplastid
some of own proteins ]
3 functions:
1. chloroplast
chlorophyll gives the green color
photosynthesis: generate ATP and make carbohydrate
2. chromoplast
contains lipid-soluble pigments
ie. lycopene and B-carotene (give orange-red color)
3. amyloplast
stores starch (become visible in purple when stained with iodine)
vacuole
can be over 90% of volume of matured plant
single membrane
contains water, ions, some proteins or none
functions:
1. spreads cytoplasm into thin layer
increase surface area, good for diffusion of gasses
plant cell is 5 to 10 times in diameter, 10 to 100 times long as animal
increase cell size, competing for resources (light and water)
2. stores waste and toxin that potentially damage cytoplasm
short-term storage of organic acids to be use later ex. lemon
to combat herbivores, long-term storage for chemicals such as tannins, nicotine, oxalic acid(chili), sulfuric acid(algae)
cell wall
not selectly permeable
let almost everything through, ie. water, ions, proteins
built from carbohydrate
cellulose: beta-1-4-linkage glucose
take about 6000-10000 glucose nomomers per chain
microbibril: 40 chains, parallel bundle together by hydrogen bonding
matrix: amorphons carbohydrate; more complex chain
pectin: soluble
hemicellulose: variety of polysaccharides
primary cell wall: all plant cells have this
strong but flexible, can withstand 200 pound per inch square pressure
"cell wall solution"
secondary cell wall:
extremely rigid
with lignin (contains aromatic chain) for stiffening
"glue" cells together
plant cells can't move as animal cell
06/27/02:
more about cell wall:
"wrap" around cell, cell elongate to grow
useful to change direction of growth when cell expand
what's great about it?
1. cell shape and support
2. regulate water uptake by cells
cell wall solution, the fluid inside and around cellulose, is hypotonic
balance between osmotic pressure and force of cell wall push back
Resources plant need:
from air: carbon dioxide
from soil: inorganisc minerals and ions
synthesize everything else that is needed, ie. nucleotides, amino acids, lipids
in plant's food factory: leaf
respiration: glucose + oxygen --> carbon dioxide and water
carbon was reduced and oxygen was oxidized in the process
to reverse the above reaction, supply energy and reduce carbon dioxide
"fixation of carbon dioxide"
need a source of energy
Structures that link cells
animal only:
tight junctions
water-proof layer, separate the two sides
found in the epithelial sheet
no intracellular space, no cell-to-cell connection
"stitched" together at the junction
desmosomes
cell adhesion proteins and keratin fibers that cross gap between cells
liquid can still flow between cells
gap junctions
mostly in specialized cell type
very rare, for communication between cells
hydrophilic channel between cells so solutes can flow freely
found commonly in muscle and nerve tissue
small gap, about 2 nm, only allow ions and small molecules to pass
plant only:
plasmodesmata
just like gap junction, but much larger, approximately 30-100 nm
larger molecules, such as glucose and hormone, and sometimes even RNA and proteins, can also pass through
most cells in plant have this
used by plants to replace circulatory and nervous systems
07/01/02
Respiration:
take organic material
carbohydrate + oxygen --> carbon dioxide + water + energy
to reverse reaction, apply energy
light + carbon oxide + water --> carbohydrate + oxygen
**To plant, oxygen is a by-product (waste), except in the root system
Leaf "food factory"
the plant's organ which main purpose is make sugar (fig. 10.2)
usually arranged perpendicular to plane of light
spread out so leaves shade each other at minimm
epidermal layer: for protection from water vapor loss
secrete cuticle (water-proof, waxy, prevents water vapor loss)
guard cells: open and close pores/stomata for gas exchange
when guard cells swell, stomata open
control by water level inside cell
increase solutes inside cell, increase turgor pressure
Guard cells
1. H+ ATPase pumps H+ out more actively
2. membrane potential (inside) become negative
3. K+ enters cell through voltage-gated channels in response to decrease in membrane potential
4. Cl- pump into cell by co-transporter along with H+
-->H+ out and in; K+ and Cl- coming in
-->solute concentration inside increased, more water flow in due to osmotic pressure
-->cells swell and stomata open
generally, stomata open in presence of light or in the condition of low CO2 concentration inside cell;
and stomata close in dark or dry climate
light detection
photoreceptor: molecule that absorbs light and triggers a change inside the cell
in plant:
guard cell
photoreceptor triggers H+ ATPase
concentration of carbon dioxide in leaf relates to H+ ATPase
when sensing dry environment,
cells in root detect fluidity of water through cells
when dried, release homone ABA (abscisic acid) to leaf
-->deflates the guard cells and closes stomata
mesophyll: the cells which do photosynthesis, a part of ground tissue system
lots of them
top layer tightly packed in order to intercept more light
inside layer has air spaces for carbon dioxide to diffuse through
chloroplast double membranes with space between them
chlorophylls packed into granum, which make up to thykaloid
light energy:
wave spectrum
violet, indigo, blue, green, yellow, orange, red
high energy <-----------------------------> low energy
short wavelength <-------------------> long wavelength
particle: photon (quantum of light)
energy is quantized (come in as discrete package)
pigment: molecule that absorbs light
ex. chlorophyll an and b, carotenoids
none of these pigments absorb green light
--> green reflect and leaves are green
Chlorophyll fig. 10.8
made of C, O, H, 4 N, and one Mg
consisted of porphyrin ring and hydrocarbon tail
chlorophyll pigments clustered together and embedded in membrane
-->pack into chloroplast
-->made up to granum
->form thylakoids
reaction center: chlorophyll
Engelman - use prism to separate light spectrum physically
place algae filamet in
grow aerobic bacteria around the algae filament
use bacteria as a meare of oxygen produced
Photosynthesis
1. photo: light energy
driving a redox reaction uphill; acquires energy
2. synthesis: reducing power and energy used to convert carbon dioxide back into carbo hydrate
CO2 + H2O --------> (CH2O)n + O2
carbon dioxide reduced to carbohydrate; water oxidized to oxygen
07/02/02:
photosystem: the whole cluster
reaction centers
accessory pigment: ex. antenna
see fig. 10.19 for review of photosynthesis
Calvin Cycle
bring in carbon dioxide (carbon fully oxidized)
reduce carbon dioxide
output of sugar
regenerate receptor molecule to recept carbon dioxide
1. carboxylation ("carbon fixation")
2. reduction of carbon dioxide, require reducing power and energy
need to use 2 NADPH and 2 ATP
3. product G3P (glyceraldehyde triphosphate)
4. regenerate receptor molecule RuBP (ribulose bisphosphate)
enzyme: rubisco (ribulose bisphosphate carboxylase/oxygenase)
*take place in stroma, outside of thylakoid
stochiometry:
start with 3 5-C RuBP, + 3 CO2, form 3 6-C, rearrange into 6 3-C G3P
release 1 G3P, 5 G3P rearrange into 3 5-C RuBP and the cycle starts again
coupling "photo" with "synthesis"
light reaction + dark reaction
must have both working at same time for the system to keep running
Rubisco: catalyse reduction of carbon dioxide to RuBP
CO2 + RuBP --Rubisco--> 2 3-C compounds
the most abundant protein on earth, 10000000 tons per year produced by plants
every single carbon compound gone through Rubisco
evolved under conditions where there's lots of carbon dioxide
many years ago, carbon dioxide were abundant, oxygen were rare
does not work as well under oxygen abundant condition
C3 plants
photorespiration: consume oxygen to produce carbon dioxide
O2 + RuBP --rubisco--> 3-C + 2-C
the 2C compound is not useful, break down into carbon dioxide
"wasted" 2 fixed carbon atoms
reduced amount of carbon being fixed
can waste up to 50% of photosynthetic output
occurs only under presence of light
seems like "extra" respiration
high oxygen + low carbon dioxide --> photorespiration
rubisco has a higher affinity for carbon dioxide than for oxygen
ususlly the rate of photorespiration is very low
in sunny and dry environment
->closed stomata ==> increase oxygen and decrease carbon dioxide by PS
C4 plants see fig. 10.17
vascular tissue surrounded by bundle-sheath cells,then outside are mesohyll cells
mesophyll: doing photo part of photosynthesis
bundle-sheath cells: Calvin cycle; synthesize glucose and pass them into vessel
Summary of pohotosynthesis reactions
light energy capture reactions
1 NADPH requires 4 quantas of light
2 NADPH requires 8 quanta, 10 hydrogen ions
4 hydrogen per ATP, therefore, 2.5 ATP generated
need extra ATP by increase gradient and cyclic electron flow
carbon dioxide fixation reactions
1 quantum per hydrogen
4 quanta per ATP
==> 1 carbon dioxide, 10-12 quanta of light
Photosynthetic Pathways
C3 plants
carbon dioxide go through Calvin cycle
C4 plants
1. carbon dioxide diffuse into mesophyll cell
2. combine with PEP to form C4 compound (enzyme PEP-carboxylase)
3. C4 compound transport from mesophyll into sundle-sheath cell through plasmodesmata
4. C4 release carbon dioxide and left C3 compound behind
5. carbon dioxide go through Calvin cycle, sugar product transport into vessel
6. C3 compound transport back into mesophyll cell through plasmodesmata
7. C3 compound converted to PEP, ATP required in the process
07/03/02:
***important:
separate photo and synthesis into two cells
separate oxygen from carbon dioxide
extra energy involved: 2 cells doing 1 cell's work
evolved multiple times in many plant families
grasses (sugarcane, corn, sorghum, crabgrass)
C4 plants grow in high light environment, so do better in saturated light
CAM plants (Crassulacean acid metabolism)
1. stomata open, carbon dioxide diffuse into cell during night
2. react with PEP to form C4 acid
3. use active transport (ATP) to store acid into vacuole
4. daytime, stomata close, C4 acid diffuse out into cytoplasm
5. acid break down into carbon dioxide and C3 compound
6. carbon dioxide go through Calvin cycle with rubisco
7. during night, C3 compound converted back into PEP
***important:
require energy to active transport acid into vacuole
take enery to convert into acid and PEP
very efficient for conserving water
common in plants under unpredictable or dry conditions
cactus, bromeliads (pineapple), orchids
pineapple and orchids are epiphytes
Part II: Animal Organ Systems
Nervous System: senses and reacts to the environment
fast signaling
integrate lots of information and come up with response
Parts of a Neuron
1. dendrites: receives stimuli from adjacent neurons
2. nucleus: contains DNAs, etc.
3. cell body: cellular machinery
4. axon hillock (start of axon): integration and initiation of signal
5. axon: propagates the signal
6. node of renvier: signal jumps from node to node
7. Schiwann cells: insulation of axon (by producing myelin)
8. terminal branches
9. synaptic terminal: converts electrical signal to chemical signal and transmits it to the next neuron
Diversity of Neurons with different functions
1. take sensory imput --> sensory neurons
2. process information --> interneurons (contact with multiple neurons)
3. come up with reaction --> motor neurons (ie. stimulate muscle to contraction)
something about neurons:
1. they are excitatory
can change their own membrane potential when needed
2. adapted to carry signal
elongated cell; cell body : axon as tennis ball : 1 mile
membrane potential: separation of charge across membrane
depend on potential of all ions and the conductance of each ions
conductance: how easily the ion move across the membrane
ions move down concentration gradient until oppose by voltage
**Use Nernst Equation to get euilibrium potential
for normal animal cell
general membrane potential is approximately -70 mV
think about Na and K, which channel is open?
if open to potassium, it will move out until reach -85 mV in cell
-70 is more positive than -85 mV, so there's also some Na
but, K channels sets membrane potential
therefore, conductance of K is higher
if Na channel open, Na enters, membrane potential increase
if Na channel open for longer, MP can go as high as +65 mV
--> cells can control membrane potential by selectively control the opening and closing of ion channels
07/08/02:
equilibrium potential; Nernst Equation again:
Na (+65 mV) K (-85 mV)
balanced between concentration and electrical charge
membrane potential, for all ions
Em = conductance * equilibrium potential
= sum[(conductance of ion)/(total conductance)*(equilibrium potential of ion)]
to change MP:
depolarize: to make charge closer to 0
open Na or Ca channels
hyperpolarize: to make charge further from 0
open K or Cl channels
Action Potential: voltage change through membrane and pass through
as membrane potential reach threshold value for depolarization
opens the voltage-gated Na channel downstream
signal-propagation is self-generating
1. resting state
K move through the leaky K channel
inactivation gate of Na channel was open
2. depolarizing phase
in response to depolarization, activation gate of Na channel open
3. repolarizing phase
inactivation gate respond to timer
Na channel close
K channel open
--> hyperpolarization
4. undershoot
activation gate close, voltage once went lower than normal -70 mV
for summary of AP again:
both K and Na channels are voltage-gated, but K channel is leaky...
during resting,
Na act gate: closed
Na inact. gate: open
K V-gated channel: closed
--> ion flow: K out
during depolarizing,
Na act gate: open
Na inact. gate: open
K V-gated channel: closed (starts to open)
--> ion flow: Na in
during repolarizing,
Na act gate: open
Na inact. gate: closed
K V-gated channel: open
--> ion flow: K out
during undershoot,
Na act gate: closed
Na inact. gate: closed
K V-gated channel: open
--> ion flow: K out
Propagation of the Action Potential
1. Na enters
2. charge spreads inside membrane;
membrane "downstream" depolarizes
3. voltage-gated Na channel (downstream) opens in response to depolarization
rate of signal conducted depend on:
1. membrane resistance (the Schwann cells)
prevent signal decaying
increase membrane resistance, increase rate of transmission
ex: human and vertebrate can have myelination of nerves
->increase resistance and increase rate of conductance
2. diameter of axon
increase diameter, increase rate of transmission
ex: squids have giant axon and big neurons
->detect predator, sqirt water and escape
how signal pass across synapse
gap junction: directly transfer electrical signal
via fused membranes
in vertebrates:
electrical --> chemical --> electrical
AP neurotransmitter AP
advantage:
once action potential is triggered,
--> all-ore-none response
if with gap junction, one cell fired, next cell must fire
NT released at synapse allow possibility of graded response
ACH (acetylcholine)
connect neuron to skeletal muscle, also neuron-neuron interaction
ACH-esterase: enzyme in synaptic cleft to break-down acetylcholine
07/09/02:
review from 7/8
AP: 1. activation gate opens
2. inactivation gate close (timer) 1 milli sec. after depolarization
3. activation gate closes
4. inactivation gate opens
self-propagating (moves through/across axon)
amplitude of response is independent of intensity of stimulus
all-or-none (there would by a response as long as stimulus exceed threshold on axon)
only move one direction, because:
1. inactivation gate closed (absolute refractory period)
2. hyperpolarization (relative refractory period)
the graph look the same for every AP
if the signal was initiated at middle of axon, Na channel open
depolarization in middle of axon, then AP would move both ways
Neurotransmitters
ACH: can be broken down by ACH-esterase and inactivated
Biogenic amines
serotonin: makes people happy
Prozac can block uptake of serotonin
-->increases serotonin activity and fights depression
dopamine: lacked by Parkinson's Disease patients
neuropeptides + amino acids
**neuropeptides are derived from amino acids
endorphins: pain perception; reduced sensation of pain
morphine and heroine mimic function of endorphins
glutamate
At Synapse: see figure 48.4 for more detail
1. Ca enter in response to depolarization
Ca channels were only presented in synapse, not along axon
2. vesicles fused with membrane and released neurotransmitters
3. NTs bind to receptors on post-synaptic neuron membrane
4. NT will either hyperpolarize or depolarize the post-synaptic neuron
depolarization: EPSP (excitatory post-synaptic potential)
hyperpolarization: IPSP (inhibitory post-synaptic potential)
-->NT changes MP of post-synaptic neuron
may result in AP in post-synaptic neuron
at axon hillock: reach -50 mV, positive feedback, --> AP
at cell body or dendrite
signal enters
electrical signal move toward axon hillock
decayed/degraded over time
must be strong to start with in order to maintain the AP
temporal summation: pre-synaptic neuron fired more than one signals
from same neuron
high frequency of AP: E1 + E1 + ...
spatial summation
more than one excitary neurons interact with post-synaptic neuron
from different neurons
E1 + E2 + E3 + ...
***important
No Voltage-Gated Channels Involved!!!
neuron
started with all-or-none electrical impulses
interaction between neurons
graded response, graded potential
electrical response that is "proportional to stimulus" because it built on each individual release of NT
at axon hillock
translated into all-or-none response
code intensity of stimulus by number of signals sent
at cell body
NT-gated channels translate chemical signal into electrical signal
see textbook figure 48.1
Overview of vertebrate nervous system
sensory receptor --sensory imput--> integration
effector <--motor output-- (brain and spinal cord)
peripheral NS central NS
Sensory receptors
sensory neurons: cells able to take imput from environment (stimulus)
and translate or convert it into electrical signal (MP)
respond to environment instead of other neurons
receptor potential: a graded change in membrane potential in response to stimulus (ie. light or pain)
can be mechanical or chemical
can distinguish levels of senses
---------------------------------------------------------
07/10/02:
sensory neurons: external stimuli are converted to electrical stimuli
receptor potential: proportional to stimulus
a graded change in membrane potential in response to stimulus,
refractory period: control maximum rate of action potential along the axon
regulated by Na channel
senses:
smell, taste, touch, vision, hearing, balance, blood pH, oxygen content
pain, stretch in muscle, magnetic orientation, proprioception (sense of where parts of body are located)
senses are divided into three types:
electromagnetic: sight and magnetic orientation
chemical: smell and taste and blood pH, oxygen content
mechanical: touch, pain, stretch
sensory structure
vision: rods and cones eye (retina)
hearing: hair cells ear
smell: olefactory neurons nose olefactory mucosa
taste: taste buds tongue
*****also, ears are responsible for detecting movement
Vertebrate eye
fovea: with sharpest acuity
peripheral vision field: sensitive to dim light
cone cells: color
rod cells: black and white vision
sensitive to low and dim light
Cone and Rod cells
contain stacks of membranes
pigments embedded in membrane
Rhodopsin--consisted of two parts...
retinal: photoreceptor molecule
opsin: G protein activation --> signal transduction
came in three different forms
red blue and green photopsin --> color vision
in light,
rod cell hyperpolarized
no NT released
-->no inhibitory post synaptic potential
downstream neuron are more likely to fire
trans-retinal absorbs quantum of light
activates opsin by changing conformation of retinal
G protein cascade --> cGMP --> GMP
no cGMP => sodium channel close
hyperpolarized --> no NT --> EPSP --> action potential in post-synaptic neuron
for contrast of color,
lateral inhibition:
amacrine cells
horizontal cells
light in one area will inhibit the adjacent area
-->enhancing contrast between light and dark
allows us to detect lines and changes in shade
Receptive field: total area on retina that can intercept and respond to light
larger field increases chance of light perception
adding receptor cells-----as adding pigment moleules for PS
one-to-one connection:
smallest receptive field
maximum visual acuity
in dark
cis-retinal, no light recepted
cGMP (cyclic GMP) keeps Na channel open
depolarization
NT released
IPSP in post-synaptic neuron
no action potential in post-synaptic neuron
07/15/02:
Movement
requires energy
2 ways of movement:
contraction by changeing conformation of molecules
polymer formation
ex. actin polymerization as in acrosomal reaction
cellular level
moving by growth and division
osmotic changes: guard cells
cellular projections:
cilia and flagella
both included microtubules
pseudopodia: occured in amoeba
focusing on contraction in muscle cells...
Muscle: soften/contract as a whole cell
see textbook figure 49.25
muscles come in set; one contracts while the other one relaxes
Structure of muscle
muscle: built of muscle cells
muscle cells: inside are bundle of myofibril
each myofibril divide into segments: sarcomeres
sarcomeres: working unit of the muscle
Mechanism of Sarcomere Contraction 49.26
striatum
Z line to Z line could be shorten
H zone also could be horten
I band could be shorten
A band always stays the same
myosin chain: bundle of myosin molecules with heads sticking out
myosin head: proteins coiled up in bean shape
during contraction, these heads moved as result of change in myosin conformation
"strength" of contraction controlled by number of myosin heads and the degree of overlapping
Molecular mechanism of Contraction -- Crossbridge Cycling
1. trigger cocked <-- where ATP consumed
heads in high energy state, ready for binding
2. heads bind to actin
3. conformational change, actin move
trigger pulled; ADP and phosphate leave
4. ATP used to release actin, heads go back to high energy state
**filaments sliding longitudinally
**movement resulted from conformational changes of myosin heads
**ATP is required for myosin to release actin
**every cycle used up 1 ATP for each myosin head
skeletal muscle: under control of nervous system
Neuro-Muscular Junction
1. ACH released into space between motor end-plate and myofibril
2. ACH-gated channels open
3. ACH cause depolarization of muscle fiber
4. trigger AP in muscle cell
1 AP in motor neuron --> 1 AP in muscle cell
***more sensitive than neuron-neuron communication
5. AP results in release of Ca from sarcoplasmic reticulum
sarcoplasmic reticulum: storage of Ca
Ca controlled movement of myosin
07/16/02:
Neuro-Muscular Junction vs. Neuron-Neuron Junction
similar
AP from pre-synaptic neuron
NT
NT cause channel open
different
AP move through T-tubules (T for transverse) to carry through the whole cell
this prevents asynchronous contraction
SR release Ca, and Ca controlled movement of myosin
sarcoplasmic reticulum
separate inside membrane from outside membrane
storage of Ca and release with AP
at rest, has high concentration of Ca
has 2 proteins:
1 pump Ca in constantly
1 channel pump Ca out
how muscle work
using energy and ATP
ATP use to
maintain ion gradients: Ca in muscle, Na and K in other cells
when out of ATP, ie. death, --> rigor mortis: muscle can't relax
no ATP --> Ca gradient collapse
increase in cytoplasmic Ca concentration
muscle contracted to maximum strength and then "stucked"
cannot complete Crossbridge cycle
=> stiffened muscle
at molecular level:
1. AP in motor neuron
2. ACH released
3. muscle AP generated and moved through T-tubules
4. Ca released from SR
5. Ca binds troponin
6. tropomyosin shifts
7. crossbridge cycling (ATP needed)
8. sarcomere shortening --> muscle contracts
9. Ca pumped back into SR
Regulation of Contraction
contraction depends on rate of Ca pumping vs. the number or freq. or AP's
tetanus
smooth contraction as a result of summation of Ca due to a high frequency of AP
temporal summation:
inc. contraction due to a high freq. of AP; resulted in inc. cytoplasmic Ca concentration
spatial summation:
inc. contraction due to recruitment of motor units
motor unit: all those muscle fibers innervated by a single motor neuron
other types of muscle:
smooth muscle:
no striation
less organized; less regular
has gap junctions and electrical junctions
cells layered over one another
adapted for longer-lasted contraction
arteries and veins; digestive system
for maintainance and homeostasis purposes
cardiac muscle:
gap junctions for ions to move through and carry AP
also electrical junctions: for synchronized contraction
Cardiovascular System
transport nutrients to cells throughout body
gas exchange in respiratory system
oxygen (used in mitochondria to generate ATP) to tissue
carbon dioxide away
important for regulation of body as well as transportation
why not diffusion?
rate of diffusion: Fick's Law
J = P*A*(Ca-Cb)
J = rate of diffusion
P = permeability (cm/s); depends on substance and thickness
A = surface area
Ca - Cb = concentration difference
way too slow to move through large distance
Comparative Physiology
2 main types of circulatory system
open: hemolymph (body fluid, any fluid outside the cell) flows
ie. blood and interstitial fluid
closed: blood - fluid in vessels; the plasma; contains red and white blood cells
interstitial fluid
07/17/02:
2 systems:
open: invertebrates and earth worm
closed: squid and octopus and all other vertebrates
fish: 2-chambered
gills instead of lungs
single circuit
amphibian: 3-chambered (2 atria, 1 ventricle)
2 circuits (through lund and through body)
mixed (when diving can bypass the lung part of the system)
can gas exchange across surface of skin
turtles and lizard: 3 chambers, 2 circuits
still some mixing, but more separation
still okay with diving; shunting blood to body circuit
crocodile: 4-chambers
completely separated
shunt also
birds and mammals: different lung development???
completely separated circuits
Heart: pumping mechanism
arteries: act as a pressure reservoir
help maintain pressure of system during diastole
thick elastic walls
smooth muscle helps control diameter
arterioles: smaller version of arteries
capillaries: where exchanges actually take place
thin walls --> leaking fluid (fig. 42.12)
venules: smaller version of veins
veins: lower pressure than arteries, so have thinner walls
act as volume reservoir (accomodate extra volume of blood)
some smooth muscle, but not as much as in arteries
one-way valves: maintain movement of blood throughout system
vericose veins: enlarge when there's too much blood
The Human CV System
human hart:
atria: thinner muscle and smaller than ventricle
entry point for blood
ventricle: incredibly thick muscle, especially on left
valves: 2 major types
semi-lunar valves: between arteries and heart
one for pulmonary, one for aortic artery
prevent blood from back flowing
atrio-ventricular (AV) valve: between atria and ventricle
one at left and one at right of heart
left AV: mitral valve (Bishop's hat)
right AV : tricuspid (3 cusps)
all valves are one-way
controlled solely by pressure gradient
***no motor neuron involved***
Cardiac Cycle
diastole: rest
systole: contracting
heart sound: lub(AV valve closing)-dub(semi-lunar closing)
with one-way valve, aortic pressure stays higher range
Heart Muscle
myocytes (muscle cells):
striated
electrical gap junctions
occur at intercalated disks
point where one cell is attached to another cell
electrical signal pass on by movement of ions through electrical gap junction carrying AP
nodal cells: smaller
only contractile weakly
initiate electrical signal and being the "pacemaker"
self-stimulating (generate AP)
**self-excitatory
built-in timer --> sets the heart rate
advantage for 4-chamber
2 completely separated circuits
2 different pressure for 2 circuits
higher pressure: blood to brain
low pressure pulmonary circuit:
thinner membranes --> increase rate of diffusion of oxygen and carbon dioxide in lung
force liquid out of capillary walls
07/18/02:
Ventricular Myocite
1. Ca pump (using ATP)
2. Ca/Na exchanger (energy from Na gradient built by Na/K pump)
3. Na/K pump (uses ATP)
4. Ca channel that's triggered by Ca in cytoplasm
"Ca induced Ca release"
action of drug: digitalis
"cardiac glycoside"
blocks Na/K pump
collapse gradient
less Na
-->less Ca transport outside of cell
--> extra Ca store in SR
==> stronger contraction
Cardiac Output = stroke volume * heart rate
increase strength of contraction
--> increase stroke volume
--> --> increase cardiac output
Circulation
pressure = flow * resistance
inc. surface area of artery wall, inc. resistance due to friction
regulation of blood flow
smooth muscle
controls diameter of arterioles
vesoconstriction: dec. diameter
vesodilation: inc. diameter
nervous system and endocrine system
sphincter muscles at capillaries
force blood (when contracted) directly from arteriole to venule
->less blood flow through capillaries
Cardiac Action Potentials
ventricular myocyte
phase 0: initiation of AP; Na in --> depolarization
phase 1: Na channel starts to close; begins repolarization
phase 2: Ca enters cell (L-type channel); maintains depolarization
phase 3: L-type Ca channel closes, K channel opens --> repolarization
phase 4: fully repolarized to resting MP
**NO SUMMATION**
Sinoatrial Node Cell
phase 0: Na entering, Ca in for small amount --> depolarization
phase 3: close Na and Ca channels; K channel open --> repolarization
phase 4: Na channel leaky; K channel close "progressively" over time
--> slow depolarization
**SELF-STIMULATING**
Conducting System of the Heart
1. pacemaker generates wave of signals to contract
2. signals delayed at AV node
3. signals pass to heart apex
4. signals spread throughout ventricles
07/22/02:
Control of Heart Rate
sympathetic NS --> adrenaline --> excite and pump up body
increase heart rate: faster "drift" of pacemaker potential
increase force of contraction
-->increased blood pressure
->vasoconstriction (dec. in blood vessel diameter)
increase resistance --> increase pressure
parasympathetic NS --> ACH --> lower heart rate
lower MP to start with --> lower pacemaker potential
Control of Blood Pressure
baroreceptors: stretch receptors in artery walls (both aorta and carotid)
in brain: CV control center in Medulla oblongata and Pons
controls cardiac output
resistance of circulation
blood volume
SNS --> increase blood pressure
PNS --> decrease blood pressure
Respiratory System
gas exchange --> transported by CV system in mammals
breaking down the process into three parts
respiratory medium: source of oxygen
air, water
ventilation: movement of respiratory medium
flow of air or water current
gas exchange
between respiratory medium and blood
between blood and tissues
cellular respiration: occurred inside cells
using oxygen to generate ATP
diffusion rate, depending on...
concentration gradient = pressure gradient for gases
surface area
permeablility of membrane
thin (elastic in lung)
moist
faster blood flow to maintain pressure gradient as well as faster transportation rate
type of ventilation
tidal ventilation: in and out through the same opening
human and lungs of most of other animals
exception in bird lungs
dead space: volume of lungs that isn't completely emptied between breaths
some air left behind; can't force all air out
mixing of fresh and old air
reduced efficiency of gas exchange
continuous ventilation: continuous flow of respiratory medium
countercurrent: flows in opposing directions
done by maintaining a gradient
maximizes the amount of change
human lungs
trachea and bronchi
cartilege hoops: rings keeping the tube open and preventing from collapse
smooth muscle
cilia to keep clean (paralyzed in smokers --> coughing)
bronchioles and alveoli
no cartilege
elastic (elasticity also could be damaged by smoking)
thin and fragile
keep lung inside body --> keep moist and prevent water loss
-->adaptation for terrestrial life
07/23/02:
Partial Pressure PV = nRT
atmospheric pressure 760 mmHg
oxygen 21% --> 160 mmHg
nitrogen 78% --> 600 mmHg
CO2 <1% --> 0.3 mmHg
partial pressure: pressure exerted by a single gas if all other gases in the mixture were removed
amount gas dissolved in water is proportinate to partial pressure of gas
transporting gases throughout body...
dissolved in plasma
carrier (molecule binds to gas, ex. hemoglobing)
chemical modification
Oxygen
low solubility in plasma; cost too much energy to maintain the need
use hemoglobin as a carrier
made from 4 protein chains, 4 heme groups (irons)
carry 4 molecules of oxygen at once
cooperative binding: affinity of hemoglobin for oxygen depends on how many oxygen are already bound
graph in signoidal shape due to cooperative binding
left shift: during pregnancy
fetal form of Hb has higher affinity for oxygen
enhances transferring from maternal to fetal Hb
right shift: can be caused by several reasons...
decrease in pH
muscle produce lactic acid --> lower pH
increase in carbon dioxide
increase in temperature
presence of 2,3 DPG (a product of glycolysis)
Carbon Dioxide
fairly soluble in plasma
carried by deoxygenated Hb
chemical modification occur inside red blood cell
Carbon Dioxide Transport in the Blood
from tissue to RBC:
diffuse through epithelial cells into plasma
some dissolved in plasma
others diffuse into RBC
in RBC, react with water with enzyme CA to form carbonic acid
carbonic acid disassociated into hydrogen cation and bicarbonate anion
bicarbonate anion transported out into plasma in exchange for chloride ion
from RBC to alveolus:
bicarbonate ion from plasma into RBC to exchange Cl out
bicarbonate react with hydrogen ion to form carbonic acid
in presence of CA, carbonic acid yield water and carbon dioxide
carbon dioxide diffuse out of RBC into plasma through capillary wall into alveolus
07/24/02:
Control of breathing: can be done both voluntarily and involuntarily
inc. CO2 => inc. H => acidic blood; shallow or infrequent breaths
dec. CO2 => dec. H => rapid or deep breath
1. breathing control occurs by monitoring CO2 (related to pH)
both in blood and cerebrospinal fluid (in contact with brain)
breathing control center receives information and sets breathing rate
2. stretch receptors in lungs
negative feedback
preventing overinflation
3. oxygen sensors in aorta and carotid arteries
Osmoregulation (Excretory System)
maintaining homeostasis; keep body balance within an active metabolic range
ion balance: tied up with osmotic balance
excretion of nitrogenous waste
ammonia: simplest form of N in body; highly toxic if built-up in quantity
used by aquatic animal for quick disposal via water
uric acid: good for organism in need to conserve water
Mechanisms of osmoregulation in various organisms
osmoconformers: conform to external osmolarity
common in marine invertebrates and lower vertebrates
tolerate higher concentration of salt
regulate which ions higher inside and outside cells
conform to osmolarity of their environment
osmoregulators: regulate internal osmolarity
freshwater and terrestrial animals
most vertebrate fish
general form of osmoregulatory structure
long tube, covered by epithelium cells joined by tight junctions
lumen inside of tube
substance diffuse through epithelium and its interstitial fluid (hemolymph)
if diffuse out, directly into capillary and carry away
wastes go down the tube and lead to outside of body
1. flame bulb system: flatworms in freshwater environment
bundle of cilia beating inside
end lead outside body wall to excrete through a pore
fluid flow through the slits
->isoosmotic urine
if water flow in --> diluted urine
reabsorption of solutes, ex. Na and Cl
2. malpighian tubules
insect in dried terrestrial area
hyperosmotic (concentrated) urine
3. metanephridia: earthworm
interstitial fluid (coelom) filter into nephrostome
nephrostome is ciliated
reabsorption of most solutes
close CV system; solute brought into capillary back into body
dilute urine regulated; sometimes hypoosmotic urine
excreted outside body wall through pores
07/25/02:
Kidney
one fourth of cardiac output
single organ packed with tubes called nephrons
with epithelial layer on top
ultrafiltration: filtration of blood driven by hydrostatic pressure
plasma move through into the tubules
large substances such as RBC remain in blood
function:
salt balance: regulate blood osmolarity and specific ions in blood
control blood volume
regulate excretion of nitrogenous waste (urea)
regulate pH of blood
regulate RBC density-----erythropoeitin
The Mammalian Kidney: Structure
filtration in nephron (counter current with blood vessel: vasa recta)
reabsorption in renal vein
cortex: the outermost layer
medulla: the center; salt built-up and hyper-osmotic
inner medulla: the innermost portion
operating principle of the nephron:
filtration
maximizes rate of exchange
regulates osmolarity of body
rapid removal of toxin, adjustment of osmolarity
reabsorption: up to 99% of volume and solutes were reabsorbed
Na, Cl, K, and GLUCOSE!!!
done by active transport
secretion: a selective process
drugs and toxins can be excreted back into urine
excretion
the end product urine can be hypoosmotic or hyperosmotic depending on diet and need
Mammalian Kidney: Nephron
1. glomerulus: filtration of plasma
2. proximal convoluted tubule (PCT): reabsorption and secretion
3. descending limb: create concentration gradient for urine
4. ascending limb: create concentration gradient for urine
5. loop of Henle: consisted of descending and ascending limbs
6. Macula dense (dark spot): sense NaCl and water flow
7. distal convoluted tubule (DCT): ion regulation
8. collecting duct: adjust total osmolarity of final urine
Events in PCT
Na/K pump: driving force; Na into blood and K into epithelial cell
co-transportor of Na and glucose
Na/H exchanger: Na into epithelial cell and H into tubule side
Cl channel into epithelial cell
07/29/02:
loop of Henle
1. hairpin design --> countercurrent
2. descending limb only permeable to water (adjust volume)
3. ascending limb only permeable to NaCl (adjust solute concentration)
2 and 3 in similar osmotic balance; spatially located next to each other
4. driven by Na/K ATPase pump in the thick part of ascending limb
DCT
Na and K regulated
reabsorption of Na and secretion of K
regulation depends on
activity of Na/K pump
membrane permeability of Na and K
hormone Aldosterone
regulation of the pump and channels
increasing transcription
increasing reabsorptin of Na
increasing secretion of K
K high in cell and low in blood, vice versa for Na
atrial nuturitic factor (ANF) --> balance between Na and K
collecting duct: reabsorptino of water in a regulated manner
regulates osmolarity of urine by controlling
how permeable is the wall to water
whether the water exit or not
aqua porins: water channels inserted in cell membrane
control blood pH by PCT
driven by Na/K pump
bicarbonate help to buffer the blood
initiation
pump H into lumen
react with bicarbonate yield carbonic acid then disassociate into water and CO2
reabsorption
carbon dioxide + water --> carbonic acid --> H and bicarbonate
bicarbonate absorbed into capillary
--------------------------------------------------------------------------------
07/31/02:
PLANT
Xylem Tissue
organs:
roots: uptake and storage of starch
stems: transport of water and minerals and glucose
produce and holding up new leaves and stems
leaves: photosynthesis and storage
tissues
epidermal: guard cells control stomata opening
ground
meristem
vascular
Vascular tissues
phloem
sievecells and companion cells
parenchyma
fiber cells
xylem
vessel elements
dead at maturity
hollow for water transportation
thick secondary cell wall
prevent cavitation (when water column is broken)
partially water proof; with gaps for transfer from tube to tube
tracheids: another way to carry water
water move by pressure gradient
water potential (psi)
predict the direction that water will move
take in account of...
1. solute concentration --> osmotic potential
2. physical pressure
pressure gradient --> pressure potential
08/05/02:
Psi continuum:
soil > root > stem > leaf > air
water move following water potential gradient
Mechanism for long-distance transport
1. leaf into air: moisture vapor diffuse out of stomata following water potential gradient
rate depends on environmental factors which influence either psi air or evaporatio rate
also depend on stomata open or closed
opening of stomata
1. inc. in H+ ATPase in presence of light and low CO2
2. membrane hyperpolarization
pump H out, inside of cell become more negative
3. K enters cell, co-transportors of H and Cl
increase in osmotic concentration
decrease in osmotic potential --> water enters from currounding cells
-->increase pressure potential
4. stomata opens
2. movement of water through stem
transpiration: evaporation of water from the leaves drives the movement of water up
column of water drien by tension
cohesion-tension mechanism:
1. tension from evaporation
2. cohesion: forces of holding one molecule of water to the next molecule
hydrogen bonding between water molecules
occurred in continuous column
3. adhesion of water to the vessol cell walls, which are hydrophilic
oppose force of gravity
movement of water up driven by solar energy to evaporate vapors
water move through vessels and tracheids (dead at maturity and contain no cytoplasm)
water movement not driven just by osmosis --> only water, no ion movement
bulk flow: driven by hydrostatic pressure
carry ions with it in solution
faster; pressure potential is negative inside vessel
no metabolic energy used
require continuous column
cavitation: continuous water column interrupted
water vapor and gas from solution formed bubble
caused by...
tension too breat and overcomes cohesion
freeze/thaw --> gases come out of solution and create gas bubble
to solve the problem...
isolate bubble and bypass it
refill bubble: live cells pump water in
08/06/02:
Function of roots
uptake of water
storage of starch
stability - anchoring in soil
-->soil retention
high surface area: active uptake via root hairs
root hair: not protected by cuticle; very delicate
extension of epidermal cytoplasm
mycorrhizal fungi: symbiotic interaction between plant roots and fungi
hypha: lon thin strands
mycelium: network of hyphae
pericycle: lateral neristem
give rise to branch roots
endodermal cells: surrounded by Casparian Strips
guarding the vascular cylinder
Casparian Strip: waxy layer for protection
ground tissue: cortex
vascular cylinder: contains xylem and phloem
epidermal cells: give rise to the root hairs
Soil Development and Structure
organic matters decomosed and create air spaces
dissolved minerals in soil water
soil particles are visible as small pieces of rock
organisms in soil; fungi and worms
oxygen in soil air
compacted soil in part has no air space, so plants can't live long
soil particles:
clay - very good at holding water and ions
silt - dec. surface are for exchange with root in comparison with clay
sand - not good at holding water; drains rapidly
soil characteristics depdn on proportions in mixture ----- soil texture
loam: equal mix of clay, silt, and sand
the ideal conditions for most plants
soils come from...
breakdown of substrate material ----- bedrock
freeze/thaw
tide action and erosion
glacial action --> glacial silt
wind
organisms on rock:
roots
lichens: secrete organic acids to "dissolve" rock in slow process
accumulation: depressions; river valleys and flood plains; wind deposit; volcanic ash
Root Uptake
sources:
1.from dissolving rock - slow but ultimate source
except N (very soluble, lost from rock already)
2. decay of organic matter - faster
dead organism --> --> --> water and carbon dioxide and inorganic ions
3. fertilizer
rate of release is important; depend on...
organic fertilizer - slow release
chemical fertilizer - fast release
in deserts, the soils are low in nutrient
dry --> decomposition rate is slow
decomposition rate depend on both moisture and temperature
-->low biomass
08/07/02:
Abundance of ions in soils
1. climate
influence decomposition rates
leaching: loss of ions due to excess water and runoff
2. substrate: tpype of rock
serpentine soil: low in Ca, high in Mg and heavy metals
very selective for plants adaptive for that area
dec. in diversity --> lots of endemic or rare plants
name indicate greenish soil
3. clay content of soil: determines drainage and aeration
clay particles are negatively charged and hydrophilic
attracts cations and not holding onto anions very well
tight H > Ca > K > NH4 loose
the loose one is easiest to lost and easiest to uptake
cation exchange: replace bound cation by another cation
->by adding Ca in soil, ie. lime
making other cations available to plant
in acidic soil: lots of H+ in soil solution
other cations were stiped away and lost in leaching
can be improve by liming (adding CaO)
in basic/alkaline soil: lots of OH-
OH- are reactove and form insoluable compounds
-->precipitates cations ie. FeOH3
result in iron deficiencies
more on root uptake
cations
driven by H+ ATPase
pump H out
RMP becomes very negative -----electrochemical gradient (about -200 mV)
cations come in (even against concentration gradient)
in addition, H+ into soil and cation exchange for other cations in
slowly acidify the soil
when CO2 diffuses into soil solution --> releasing of H+
anions: phosphate, nitrate
negatively charged, not bound by clay
active transport
driven by co-transport with H, bring anions into root
precipitated cations
can be solublized by chelators
chelator: molecule that bind ions and make them soluble
Transport in Root
root cells were connected by plasmodesmata; result in continuous cytoplasm
symplastic route:
movement through cytoplasm and plasmodesmata
roothair to epidermal cell to cortex thru. Casparian Strip into endodermal cell into vascular cylinder into vessel element
apoplastic route:
movement through cell wall solution
blocked by Casparian Strip and moved into cytoplasm
exclude toxins and prevent ions from getting back out
Symbiotic mutualists
1. mycorrhizal fungi
fungi take water and inorganic ions
provide advantage for plant in dry or low nutrient soils
land plants coevolved with mycorrhizae
plant gives out sugar
myecelium do the uptake
root tip and fungal sheath exchange materials
ectomycorrhizae: fungal sheath visible
penetrate into cortex cells, not into vascular bundle
endomyccorrhizae: fungal material branched inside root
apoplastic symplastic
selective? no yes
accumulate? no yes (result of active transport driven by H+ ATPase)
08/08/02:
Nitrogen-fixingbacteria
break triple nitrogen bond and reduce N
sources:
1. indurstial fixation: require lots of energy
2. lightning
3. biological 95%
occurs at ambient temperature and pressure
using enzyme nitrogenase
nitrogenase - catalyzer
affected by oxygen just as Rubisco
oxygen blocks nitrogenase's activity
anaerobic bacteria: don't need oxygen to generate ATP, but very slow
to protect nitrogenase, bacteria form a nodule in root
oxygen free environment provided by plant (leghemoglobin)
actinomycetes: found in trees like alder (in disturbed soil or after fire)
rhizobium associated with legumes
mutually specific
proliferating inside root cells; intimate interaction
Development of a root nodule
1. root signals to rhizobium
chemotaxis: moving toward a chemical compound
rhizobium move toward root
2. rhizobium signals root hair
elongation of root hair and formation of infection thread
3. bacteria enters the cortex
both bacteria and plant cells divided
4. proliferation of vascular tissue
exchange of sugar and nitrogen
leghemoglobin - protect activity of nitrogenase by reversely bind oxygen
Sugar Transport
phloem tissue
sieve cells: form sieve tube
no nucleus, few or no other organelles
allive because of companion cell (smaller diameter, same length)
sieve plate: join sieve cells together
callose plug: prevent sugar loss when stem damaged
in sieve tube: contain highly concentrated sugar, generally glucose
sometimes some amino acids and some hormones
sieve cells have to be alive --> active process and require ATP
mechanism for sugar transport:
pressure flow hypothesis: sugar transport occurs by bulk flow
driven by hydrostatic pressure
process controlled by active transport
Phloem loading with sugar
H+ ATPase
H+/sucrose co-transporter
inc. conc. of sucrose in sieve tube
water enter from surrounding cells
inc. pressure because volume can't increase
transfer of sugar occur at region of high pressure
Phloem uploading
uptake of sugar
-->dec. in sucrose concentration
-->inc. osmotic potential (less negative) --> inc. potential of the sieve cell
-->water OUT
result: decrease in pressure
Sources and sinks
source: where sugar coming from
sink: where sugar is going to
new growth and root
xylem carrying water from roots to leaves
sugar flow control by source and sink
review of loading and uploading
1. sucrose diffuse or active transport from source into companion cell
2. sucrose active transport into sieve cell
3. osmotic potential in sieve cell increase, water from vascular tissue come in
4. volume cannot increase, so pressure potential in cell increase
5. this region is now region of high pressure
6. sucrose solution flow from region of high pressure to region of low pressure
7. region of low pressure is where water flow from sieve tube back into vascular tissue
8. sucrose active transport from sieve tube into companion cell
9. sucrose active transport or diffuse from companion cell into sink for storage
08/12/02:
plant life cycle
seed germination
growth and organogenesis
flowering (pollination and fertilization)
fruit and seed production
there are 2 types of plants
annual: complete life cycle in one year or one growth season
perenials: more than one year
woody to persist during winter
persistant roots
primary growth: production of new organs and growth from the tips
secondary growth: increase in girth of plants
stems and roots get wider
plants are able to change the way they grow in response to environment
respond to conditional changes by growth instead of movement
Stem Apical Bud
for elongation and growth of stem:
apical meristem: division of cells
sub-apical meristem: derived from apical meristem daughter cells
adding cells that are going to be differentiated in stem
zone of elongation: where cells elongate
zone of differentiation: where cells start to differentiate
for organogenesis:
leaf primordium: derived from apical meristem; become leaf in future\
embryonic lear: cells divide and elaf arches over and protect apical meristem
axillary bud primordium: cells give rise to the bud
axillary bud: arrested apical dominance
apical bud supress growth of axillary bud
Root: apical meristem and organogenesis (branch root)
branch root: formed from edidermis and pericycle
extend from vascular dylinder out and burrows through cortex of parent root
started at oldest region of root near the stem
differentiation and formation of epidermis and new apical meristem at tip
Regulation of primary growth
hormones
simple organic molecules
from ordinary cells; not from dedicated organ/gland
active at low concentrations
second messenger system; amplified at cellular level
specific receptors on specific type of cell --> effects depend on cell type
auxin: IAA is the natural form
produced from shoot apical bud and young leaves
IBA: rooting hormone
agent orange: weed killer
CK: 4~5 natural forms
produced from root apical meristem
GA: more than 110 natural forms; GA1 is the active form
produced from shoot apical meristem and yound leaves
ABA: seen in stomata
produced by root cortex cell, leaves' mesophyll cells, and green fruit
ethylene gas: control fruit ripening
08/13/02:
Regulation of divisino and elongation
division
promoted by several different hormones
IAA and CK
GA (stem only)
inhibited by ABA
elongation
promoted by IAA in stem and GA in stem
inhibited by ABA and ethylene; also IAA in root
MEchanism of elongation
1. cell wall must yield according to direction of microfibrils
reduce strength of hydrogen bonding
orientation of cellulose microfibrils control direction of elongation
2. turgor pressure psi pressure
Hormones
1. IAA promote elongation in stem
in presence of IAA, H+ ATPase more activated
H into cell wall solution, decrease pH and cell wall soln. become acidic
enzyme activated by low pH and break hydrogen bonds between microfibrils
walls loosen, allow elongation to occur
2. ABA inhibits elongation
directly opposing action of IAA
3. ethylene (gas) inhibit elongation
promotes widening
in presence of ethylene, add microfibril in random orientation
no specific direction to expand, cell just get bigger
4. GA promotes elongation
NOT via pH but involve wall loosening
normal effect: rapid elongation of flowering stems
dwarfism when defective in producing GA
Organogenesis
take pith cells: adult cell in parenchyma
in water, minerals, and wugar: no growth
above plus IAA: cells engarged but no cell division
IAA and CK: division and enlargement (callus), but no differentiation
changing ration:
high IAA : CK roots
low IAA : CK bud and new shoots
-->cells can reverse differentiation and gave rise to any cell type
Regulation of organogenesis
1. branch root initiation
no IAA ==> no branch root
with IAA ==> normal formation of branch root
with IAA and removal of root tip ==> branch roots near tip
as going from root tip and up, reduce CK and increase IAA : CK ratio
->initiation of branch roots
2. apical dominance
apical bud suppresses axillary growth
after apical bud removed, axillary buds grown into new stems
cut apical bud but add IAA ==> dormant axillary bud
keep apical bud and add CK ==> axillary bud grow
therefore...
high IAA : CK ratio: buds remain dormant
low IAA : CK ratio: growth of axillary buds
Environmental Regulation of Growth
gravitropism
effects of light