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.

One (usually) circular chromosome, not in a membrane

No membrane-enclosed organelles

Peptidoglycan cell walls (usually)

Binary fission

PROKARYOTE 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

Staining procedure:1.Crystal violet and Gram’s iodine: Primary stain2. Stain is decolorized with 95% ethanol3. Counterstain: Safranin4. Water rinse

Gram + retain CV and remain purpleGram – retain safranin

* Based on cell physiology

GRAM STAIN MECHANISM

DIFFERENTIAL STAINS: GRAM STAIN

Figure 3.11b

STREPTOCOCCUS

PYOGENES GRAM +

GRAM -

Spirillum volutans (harmless bacteria)

Polymer of disaccharideN-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)

Linked by polypeptides

PEPTIDOGLYCAN

Figure 4.13a

Figure 4.13b, c

Thick peptidoglycan

Teichoic acidsIn acid-fast

cells, contains mycolic acid

GRAM-POSITIVE CELL WALLS GRAM-NEGATIVE CELL WALLS

• Thin peptidoglycan

• No teichoic acids

• Outer membrane

GRAM-POSITIVE CELL WALLS

Figure 4.13b

Thick layer of peptidoglycan

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

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.