Microbiology Lecture Wednesday March 7, 2012 (Chapter 4)

Structure and function of prokaryotic and eukaryotic cells.For now, we are not going to review the structure of eukaryotic cells but we will talk about the clinical significant differences between eukaryotic and prokaryotic cells, their evolutionary differences and the two theories about them, namely endosymbiosis and something else.

BEGINNING OF CHAPTER 4

Okay here we area, structural function of prokaryotic and eukaryotic cells.

Central concepts slide

What are the clinical applications attendant to these differences?

Why you should know about bacterial cell structure?  Antibiotics are used to inhibit cell structure as a method of contorl.  Where do these antibiotics attack?  They must get into the cell wall, attack the membrane, protein synthesis, dna, nucleic acid replication, metabolic activity, etc.  If you have a bacterium that infects a human body, what’s the job of the antibiotic used?  To kill and inhibit the bacteria without having an adverse affect on the human.  The basis of “selective toxicity” for antibiotic treatment depends on the structural, physiological and metabolic differences between bacteria and eukaryotic cells.

Erlich pioneered the use of chemicals to inhibit bacterial reproduction. (“a moment with venus (love), a lifetime with mercury” b/c if you got syphilis and they were treating you, it would take a long time to make a difference)

We talked a lot about hte gram stain so the answer to that question about the gram stain is YES.  The preliminary result tells the clinician what the potential antibiotics are that could treat that organism depending on whether it is gram +/-.

How did eukaryotic cells evolve?  Bacteria are our ultimate ancestors!

The terms prokaryotic and eukaryotic apply only to organisms with cells (not applicable to viroids, prions or viruses because they are acellular).  Eukaryotes consist of cellular entities such as protozoa, fungi, worms, algae.

When we talk about prokaryotes we talk about bacteria but there are two groups of bacteria.
The true bacteria and the archaebacteria (ancient bacteria, such as halophiles, thermophiles, metanogens).  The existence of archaebacteria provides support for the evolution of the bacteria because they likely evolved first in different conditions of this world.  Archaebaceria are not clinically relevant because they are not pathogens and do not affect us.

Slide: Comparing cell size and organisation of pro and euk cells
WBC are eukaryotic.  Bacteria are typically much smaller than the average eukaryotic.
Typical eukaryotic cell: balantidum coli: 50-100um
Typical bacteria cell: escherichia coli: 1x 2-4um

Definition of terms:  Pro means first.  Prokaryote first formed, pre nucleur; lack membrane enclosed nucleus;
Eu means true :formed later, defined nucleus, nuclear membrane enclosing cells DNA; true nucleus.

Now turn to page 87, Table 4.1.

Notice surface area to volume ratio.  In bacteria it’s 6, in human cells its 0.3.  In bacteria, they could transport things much easier.  They don’t a complex organelle such as the endoplasmic reticulum to transport things. Material can pass in and out of the bacteria quite easily and rapidly and also multiply much more rapidly.  E.coli for example, multiply about every 20 minutes.  Your skin or mucosa cells take about 4-5 days to be replaced.  If you put a bacteria in water, transport is very simple.  If you a eukaryotic cell in the water, some of hte cell will be sticking out.  Imagine you put a little piece of paper and fold it up and you drop it in a beaker of water.  Take a roll of ppaer towel and stick it in a similar beaker.  The little peiece of paper will soak up water faster because stuff can get in and out easier.  The DNA is not even enclosed in a nucleus.  So if that’s the case… what do we need to happen in a eukaryote cell?  We need an internal compensatory transport system called the endoplasmic reticulum.

Eukaryotes evolved from prokaryotes by endosymbiosis and autogeny.

Eukaryotes more complex, greater internal membrane organization compared to prokaryotes, compensatory mechanism to overcome decrease surface area to volume ratio determining transport of material into/out of cell.

Materials pass rapidly by diffusion and other processed in/out of the very small bacterial cells; larger bacteria have internal membranes to faciliate transport (such as thiomargarita namibiensis).

Interestingly there are two bacteria that are larger than most eukaryotes and actually visible to the naked eye.  These organism are (page 265, giant bacteria), eupulopiscium fishelsoni and thiomargarita.  What’s interesting is that in thiomargarita you have internal vescicles and the organism of course is a chameroheterotroph and uses sulfur as a major source of energy.  This could be looked as a precursor or forerunner to endoplasmic reticulum because the bacteria is so large it needs internal organization and have internal membranes.  As a matter of fact, if you rupture an ordinary bacteria cell, the cell membrane will form vesicles that are equivalent to endoplasmic reticulum, particularly if the bacteria is dehydrated.  This provides support for the origin of the eukaryotic cells.

Nothing fancy, okay.

PROKARYOTIC CELLS
There are organelles but they are not membrane bound organelles: capsule, slime layer, flagella, fimbriae.  No internal membrane bound organelles.

Page 87, Figure 4.3, this is your typical prokaryotic cell.  The differences are monumental from eukaryotic cells.  There are not much things inside.

Shapes: cocci = round.  rods are well.. rods.

The shape and arrangement gives ideas for the potential identity to make a decision based on empiric theory.

EUKARYOTIC CELL STRUCTURE
Golgi: packing, sorting, labeling destined for external transport or internal.
Ribosomes: Protein synthesis.  The ribosomes are different in the cytoplasm than the ones in the mitochondria.  In the cytoplasm you find 80 S ribosomes but you find 70 S ribosomes in the mitochondria.  The “S” is a measure of density.  When you put it in a centrifuge, the 80S will be more in the bottom than the 70S.  *The 70S ribosomes are identical to that found in a bacterial cell.*    This is evidence of the mitochondria evolving from bacteria.  Antibiotics that are meant to attack bacterial cells.  Some of the toxicity associated with antibiotic use may be due to the effect of these antibiotics on the mitochondrial 70S ribosomes which is also found in bacteria. (For example, chloramphenicol has the potential for creating anemia.  Blood cells come from stem cells.  If you have a decrease in mitosis because the mitochondria are not producing enough red and blood cells.)

A question I will ask you: In an actively phagocytizing macrophage (active macrophage gobbles up things), what organelles increase in numbers and activity?  (find out)

Surface area to volume ratio slide.  The volume increases dramaticall with surface area, nothing fancy about that, end of story

Endomembrane system in eukaryotes slide:  you could see here that you have thi snetwork that is consisten and it’s primary function is transport in and out of the cell (endocytosis/exocytosis).  This shows you the relative sizes of things.  YOu could see plant/animal cells are really large and viruses are really tiny.  YOu can’t use a light microscope to see a virus.

EUKARYOTIC CELL EVOLUTION SLIDE: How did eukaryotic cells evolve?

Two theories: endosymbiosis and autogeny.

Endosymbiosis: The central concept is that at the dawn of time, we had a large prokaryotic cell and a smaller prokaryotic cell.  Big fish eat little fish, right?  THis larger prokaryotic cell feeds on the smaller prokaryotic cell and that provides food and nutrition.  Overtime, the larger prokaryotic cell was able to take in the smaller prokaryotic cell and enclosed it and made it a functional part of the prokaryotic cell.  Now because energy production is so critical (just look at gas prices now) to any viable organism because metabolism is a basic necessity.  This small prokaryotic that was engulfed became a *endosymbiont* which became the mitochondria in the plants and animals or the chloroplasts in plants.  The chloroplasts evolved from photosynthetic bacteria.  We could explain the origin of mitochondrion and chloroplasts with this.  Now the eukaryotic can have its own personal attendant/assistant/maid/cook, like rich people, which becomes a mutually beneficial relationship.  Rich people get other people to work for them, right?  This mitochondria can produce ATP, allowing the eukaryote to form with more complex structures.

*Eukaryotic organisms only evolved when oxygen became available and accumulated to 21% in the earths atmosphere.*  That shows you how critical and important metabolism is.  In photosynthesis you produce oxygen.

Autogeny: Endosybiosis does not explain the origin of ER and the cell membrane. It explains the mitochondrion and the chloroplasts and to some extent the golgi.  So there’s another theory, called a default theory because if you can’t explain one by one theory, then you do it with the other with is ATOGENCY which is defined as “self induced internal re-organization.”

Evidence for endosymbiosis slide:  Naturally this is on the exam on Monday.

1. If you look at the bacteria membrane, we find the electron transport chain, which is embedded in the cell membrane of the bacteria.  If you look at the mitochondria, we have the inner crystal (foldings) where we find the electron transport chain which is analogous to the bacteria.  Functionally in the bacteria, we have glycolysis occuring in the cytoplasm and oxydative phosphorylation occuring in the electron transport chain.

In eukaryotic, glycolysis occurs in the cytoplasm of the cell.  Glycolysis occurs in the matrix of mitochondrion-similar site to that in cryoplasm of hte bacteria cell.  Oxidative phosphorylation occurs in the electron transport chain of hte mitochondria.

70s vs 80s, we talked about.

Next, we have not looked at anaerobes.  The mitochondria and bacteria have the same oxygen-protective superoxide dismutase enzyme (detoxifies free radicals, a prerequisite for eukarytoic evolution).  You could look at the evolution of SDE and find that SDE came about at the same time as the evolution of bacteria because these both happened when oxygen became present in the atmosphere, because the presence of oxygen produces hyperactive free radicals.   The mitochondria evolved from bacteria.

nucleur stuff

Antibiotics .. we talked about this already..

Autogeny Evidence Slide

There’s not a lot of evidence, but we already said the internal membranes are the same.  Electron micrographs of bacterias cell, particularly since electron micrograph requires dehydration, you’ll find that there are all kinds of, largely due to shrinkales, an extensive membrane network.  This may be an adaptive response to fix nitrogen in a n anaerobic environment.  If you break these up and rupture the cell, you get vesicles, so the membranes will actually form vesicles.  What that suggests is that the cell membranes of bacteria can spontaneously form vesicles.

In addition, spore formation suggests… in a bacteria you have a spore being formed… a cell membrane lays down a thick wall, some proteins and that spore is formed inside the bacteria cell, which tells you the bacteria has the POTENTIAL to reorganize its internal structure which provides for some evidence for endosymbiosis.

Which is the most dominant cell?  Eukaryotes, because of their ability to adapt and have a greater complexity.  The vast numbers of eukaryotes that we have, came obviously after the development of eukaryotes.  That’s when the tremendous increase in variance came in the biological world because of ht einherent complexity and ability to adapt.

SO WE STOP HERE.