Download SC246: MICROBIOLOGY Unit 1 Seminar

SC246: MICROBIOLOGY
Unit 1 Seminar

What do the terms Prokaryotic and Eukaryotic
mean? What are some of the major differences
between Prokaryotic and Eukaryotic cells?
PROKARYOTIC CELLS

Comparing Prokaryotic and Eukaryotic Cells
Prokaryote comes from the Greek words for
prenucleus.
 Eukaryote comes from the Greek words for true
nucleus.

PROKARYOTE
One (usually) circular
chromosome, not in a
membrane
 No membrane-enclosed
organelles
 Peptidoglycan cell walls
(usually)
 Binary fission
EUKARYOTE

• Paired chromosomes,
in nuclear membrane
• Organelles
• Simple cell walls (IF
present)
• Mitosis

From an evolutionary prospective, Prokaryotic
cells are much less complex than Eukaryotic
cells. It seems that we wouldn’t have much of a
problem fighting them off, right? However, this is
obviously not the case. Offer an explanation for
this. WHY do you think we still get infections and
illnesses?

What is the Gram stain, and why is it a
fundamental part of identifying bacteria? What
are the major differences between Gram negative
and Gram positive cells?
GRAM STAIN




The Gram stain was developed by Christian
Gram in 1884
Primary stain of identification in microbiology
lab
Used to classify bacteria as either gram positive
or gram negative
Most, but not all, bacteria can be stained using
this method
GRAM STAIN MECHANISM
Staining procedure:
1.Crystal violet and Gram’s iodine: Primary stain
2. Stain is decolorized with 95% ethanol
3. Counterstain: Safranin
4. Water rinse

Gram + retain CV and remain purple
Gram – retain safranin
* Based on cell physiology
DIFFERENTIAL STAINS: GRAM STAIN
Figure 3.11b
STREPTOCOCCUS
PYOGENES
GRAM +
GRAM  Spirillum
volutans
(harmless bacteria)
PEPTIDOGLYCAN
 Polymer
of disaccharide
N-acetylglucosamine (NAG) & N-acetylmuramic
acid (NAM)
 Linked by polypeptides
Figure 4.13a
Figure 4.13b, c
GRAM-POSITIVE CELL WALLS GRAM-NEGATIVE
CELL WALLS
 Thick
peptidoglycan
 Teichoic acids
 In acid-fast
cells, contains
mycolic acid
• Thin
peptidoglycan
• No teichoic
acids
• Outer
membrane
GRAM-POSITIVE CELL WALLS

Thick layer of peptidoglycan
Figure 4.13b
GRAM-NEGATIVE OUTER MEMBRANE
 Lipopolysaccharides,
lipoproteins,
phospholipids.
 Forms the periplasm between the outer
membrane and the plasma membrane.
 Protection from phagocytes, complement,
antibiotics.
 O polysaccharide antigen, e.g., E. coli O157:H7.
 Lipid A is an endotoxin.
 Porins (proteins) form channels through
membrane
GRAM-NEGATIVE OUTER MEMBRANE
Figure 4.13c

The medical and scientific communities use their
knowledge of Prokaryotic cells to target infectious
microbes and clear out infections. Given just
what you have learned so far, how do you think
they might go about this?
QUESTIONS??
REFERENCES

Tortora, G., Funke, B., & Case, C. (2007).
Microbiology: An Introduction (8th ed.). San Francisco,
CA: Pearson.