SC246: Microbiology Unit 1 Seminar

What do the terms Prokaryotic and Eukaryotic mean 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 Eukaryote Paired chromosomes, in nuclear membrane One (usually) circular chromosome, not in a membrane No membrane-enclosed organelles Peptidoglycan cell walls (usually) Binary fission 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.