UPDATED SEPTEMBER 20TH!
Lecture # 1 Added!
Welcome, Environmental Health students. This entry is the first of weekly presentations of vocabulary words, study questions and other highlights from lectures and classes from the preceeding week. We hope that you will find it useful in helping your studies for this course.
At the conclusion of today's session, you should be able to:
1. Appreciate the many places that microorganisms are found.
2. Understand number concept and size.
3. Understand the structure of cells.
4. Know what a prokaryote and eukaryote are, and how to differentiate them.
5. Know the different types of microorganisms and their basic shapes (morphologies).
6. Know some of the methods of studying microorganisms.
WEEK 1: August 31 - September 4, 1998
microorganism -- A microscopic form of life including bacteria, fungi, viruses, protozoa, and some multicellular parasites.
prokaryote -- -- A cell whose genetic material is not enclosed in a distinct nucleus.
eukaryote -- -- A cell having DNA inside a distinct nucleus.
nucleus -- -- The part of an eukaryotic cell that contains the genetic material.
cell wall -- -- Rigid outer covering of most bacterial, fungal, algal and plant cells.
cytoplasmic (plasma) membrane -- -- Semipermiable structure enclosing the cytoplasmic contents of a cell
cytoplasm -- -- In a prokaryotic cell, everything inside the cytoplasmic membrane; in a eukaryotic cell, everything inside the cytoplasmic membrane and external to the nucleus.
organelles -- -- Membrane-bound compartments in eukaryotic cells that are the sites for various functions within the cells.
DNA-- -- The nucleic acid (deoxyribonucleic acid) of genetic material.
RNA-- -- A nucleic acid (ribonucleic acid) which serves many functions, including the code for the sequence of amino acids in protein synthesis and the transfer of amino acids necessary for protein synthesis
micron -- -- One-millionth of a meter (one-thousandth of a millimeter). A standard unit of measurement of microorganisms.
bacterium -- -- a prokaryotic living organism
virus -- Particles of nucleic acid, either DNA or RNA, surrounded by a protein sheath. Is NOT a cell; is neither prokaryotic nor eukaryotic.
fungus -- -- Non-photosynthetic eukaryotic organism, as a yeast or a mold.
protozoan-- -- Unicellular, non-photosynthetic eukaryote that lacks a rigid cell wall.
flagellum-- -- A long thin appendage, coming from one or more locations on a cell wall that is used for cellular locomotion.
pseudopod-- -- An extension of a cell, particularly seen in the protozoa, that aids in locomotion and feeding.
coccus -- -- Spherical bacterium
bacillus -- -- Any rod-shaped bacterium
spirillum -- -- A spiraled or corkscrew shaped bacterium.
yeast -- -- Unicellular fungal cell.
mold -- -- Fungus that forms large multicellular aggregates of long, branching filaments.
algae -- -- photosynthetic eukaryote that can be unicellular or massive (seaweed)
culture medium (media -- -- plural) -- The nutrient material prepared for growth of microorganisms in a laboratory.
colony-- -- Visible aggregate of cells on a solid medium, all descended from the same parent organism.
inoculating loop -- -- instrument used to apply microorganisms to a culture medium.
Week 1: August 31 - September 4, 1998
2. Arrange the following objects in order of DECREASING size: bacterium -- chicken egg -- hydrogen atom -- frog egg -- virus -- mushroom -- spore from bread mold -- ribosome
3. Which objects in question #2 can be seen with the naked eye?
4. Define prokaryote and eukaryote. Give three structures that they both contain.
5. In the list below, indicate whether the organism is a prokaryote or a eukaryote by placing a P or E, respectively, following each word:
6. Circle the item in the following list which is NOT part of a eukaryote:
7. Sketch the shapes (morphologies) of the following organisms:
8. Complete the following statements:
9. Which common group of microorganisms is not considered a living organism? Why?
10. Name two methods used to study microorganisms.
1. Intro Activity --- Micro Grab Bag (give to several students as they enter)
Microbes are around us all the time, and our lives would not, could not be without them. Several of you have examples of how microbes influence of lives in many ways. I would like for some of you to share these with us. (Ask for about 8 -10 volunteers to come up front, share.) At completion, have a couple of students collect the examples. Leave up front in case any want to look at them after class.
2. The Big and Small of it... Does size matter?
What is the smallest thing you can see? How big do you think that is? Can you give me the metric measure?
Most microbes are about 1-5 microns long. A micron is 1/1,000,000 of a meter, or 1/1,000 of a millimeter. And there are 25 mm in an inch! Kind of small, huh?
In your handouts is a lovely cheat-sheet I got from Carl Sagan’s book, Billions and Billions. It is probably the best illustration I have ever seen on explaining really big and really small numbers. Using exponents is such a simple way of describing size... all you have to remember is that that little superscript numeral tells you the number of zeros that come before or after a one. Isn’t it much easier to say 1015 than try to remember that 15 zeros after a one equals a quadradrillion? (You poli sci and econ folks will really learn to appreciate this, I’m sure!)
Another handout I’ve given you is seen here. It is a visual comparison of the size of “things”. Just remember... this is NOT drawn to scale! There’s quite a bit of space between that 1 um mark and 10 meters! (And no... the woman is NOT over 10 m tall!!!)
To the right of the chart, you will note what it takes to view objects of these sizes. What we are going to be talking about in lecture and working with in labs for the next few weeks are many of these organisms which cannot be seen with just your eyes, the world of microbes. We will be looking at them in a variety of ways: by use of microscopes; by growing enough of the organisms so that they form visible colonies or communities of millions of them. And we will be examining what microbes do that make our lives what they are today.
3. The mighty cell -- prokaryotes and eukaryotes
Before we can discuss microbes, we should understand a little something about their structures. Just about all living organisms are composed of one or more cells. A cell, of course, is the fundamental structural and functional unit of living organisms. Millions of cells, many specialized into organs and tissues, make up our bodies. However, in the world of microbes, a single cell is a complete functioning body all by itself.
In the microbial world, there are two types of cells, the prokaryote and the eukaryote.
“Karyote” comes from the Greek word for “nut” or “nucleus”. A prokaryote literally means “before nucleus”, and these cells do not contain a nucleus. The eukaryotes do have a nucleus, the word meaning “true nucleus”.
As you can see on the handout entitled “A spectrum of the World’s Organisms”, eukaryotes can be only one celled organisms, or they can be part of complex organisms -- try calling someone a bag of eukaryotes sometime!
There are several other ways these cells are different, and we should look at these differences.... and how they are alike.
By definition, the main difference in these cells is whether or not a nucleus is present. Other differences include:
4. Building a cell...
I have given you a handout that merely has the names of these two types of cells. I would like you to reconstruct a generic version of each of these cells by drawing as I draw. First off, all of these cells with only rare exceptions, contain a cells walll and a cytoplasmic membrane. These layers enclose a middle area called the cytoplasm.
(Use overviews to draw cells.)
All right... at the bottom of the comparison chart, under “Examples”, you see that microbes are listed in each category. We’re now going to examine what these microbes are, and what they look like...
5. Microbes and their morphologies
As I stated earlier, and as you saw on the size comparison chart, eukaryotes tend to be larger than prokaryotes. Most organisms considered to be microorganisms, i.e. ,those studied in microbiology, are prokaryotes and are smaller than a few microns. (An exception to this is a bacterium found in 1985 in the intestines of a tropical surgeonfish. This organism was more than 500 um long -- a little over 1/2 mm and visible without a microscope! After several years of study it was discovered to be a prokaryote> Based on what we described above, why do you think it was determined to be a prokaryote rather than a more complex eukaryote?)
In microbiology, we are generally studying four different groups of organisms: bacteria; fungi; viruses; and protozoa.
1. The bacteria (Singular: bacterium) are prokaryotes and are among the most numerous organisms on earth. One pinch of dirt contains billions of bacteria. They can be found almost anywhere on Earth, and next week, we will look at their importance in all aspects of life. Some cause disease. Bacteria come in a variety of forms...
How to remember names: cocci are round.. most of letters are, too. Bacilli - long rods, long or tall letters, resembling rods; spirilla -- ssssss curved form
2. Cyanobacteria --- Used to be known as blue-green algae. Are prokaryotes, with light-trapping pigments (chlorophyll).
3. Viruses --- not even prokaryotes. Look back at “Spectrum” handout.... viruses are not considered cells, but rather are naked DNA or RNA... they have no cell wall, no organelles, no nucleus. As such, they require other cells in order to reproduce. They invade many types of cells from bacteria to cells in your body, and there they disassemble, replicate, are repackaged and burst form the cell. This is one reason why antibiotics are not effective against viruses --- antibiotics cannot penetrate cell walls and kill the replicating viruses inside. (overheads... structures are similar to crystals or polyhedrons... usually very regular in form and structure)
4. Fungi (fungus -- singular) --- these organisms are eukaryotes, even in their one celled forms. When a fungus exists as a single cell, it called a yeast. Many fungi produce networks of filaments called hyphae, and in this stage are called molds. Fungi have cell walls, are non-motile (no flagella) and depend on outside sources for all its nutrition.... never can use sunlight as a form of energy. Fungi are important in food and industrial processes, as well as ecological cycles. In addition, several chronic diseases are caused by fungi. (overheads....)
5. Protozoa. (singular --- protozoan)... These unicellular eukaryotes lack a cell wall and must obtain their food from outside sources... thus the name “parasite”. They move by means of pseudopods, flagella or cilia. They are an important links in the food chain, although some do cause human disease.
6. Algae --- (alga -- singular) Eukaryotes that can be single celled photosynthetic organisms to multicellular seaweed. Algae are among the most important organisms on earth, from being primary sources in food chains to providing oxygen for us to breathe.
In your handouts, you have a sheet that illustrates some of the basic morphologies of microorganisms. (Show it here...) Take a few minutes to fill it in...
6. Ways we study microbes
Microbes must be amplified in order to be studied. This can be done in several ways:
We will be doing a combination of the first two methods in our laboratory sessions.
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