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Lecture 7

MBIO 1010 Lecture 7: Lecture 7

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University of Manitoba
MBIO 1010
Christopher Rathgeber

Microbiology 1010 – Lecture Notes Role of the Cell Wall Cell wall prevents cell expansion – protects against osmotic lysis Protects against toxic substances – large hydrophobic molecules o ex. detergents, antibiotics Pathogenicity (when have a capsule) o Helps evade host immune system Helps bacterium stick to surfaces Partly responsible for cell shape. Why do we salt fish? It makes a hypertonic environment – which means the bacteria on the fish dehydrate and shrink. Peptidoglycan Species of Bacteria separated into two groups based on Gram stain Gram-positives and gram-negatives have different cell wall structure (Figure 2.24) Gram-negative cell wall Two layers: LPS and peptidoglycan o  Gram-positive cell wall One layer: peptidoglycan Endospores – only from gram positive (but not all gram positive) All gram neg. have lipid and sugar. Lipid is on the outer membrane and the sugar is then attached to that. Together it is called LPS (lipopolysaccharide) = endotoxin. LPS – is ‘o’ linked. It helps us to determine different features of bacteria. It’s called an exotoxin = secreted to the outside Endotoxin – is physically attached. Once LPS is released from the dead cell, it can cause shock from the vassal dilation and can cause the person to die. Which is why depending on the gram neg. bacteria infection, antibiotics won’t be given. 37 Microbiology 1010 – Lecture Notes Gram neg: Periplasmic space = Area of the interior of the outer membrane and the exterior of the plasma membrane. In between these two membranes, there is the thin layer of peptidoglycan 38 Microbiology 1010 – Lecture Notes Peptidoglycan (Continued…) Rigid layer that provides strength to cell wall Polysaccharide composed of: o N-acetylglucosamine (NAG) and N-acetylmuramic (NAM) acid o Amino acids o Lysine or diaminopimelic acid (DAP) o Cross-linked differently in gram-negative bacteria and gram-positive bacteria o Form glycan tetrapeptide There is many different variations that are found within gram neg and positive bacteria. NAM and NAG are the disaccharides when coupled together to make majority of the structure. Creating a lattice. The D form is unique to this case to the bacteria and few other exceptions. The 5 glycine there is alternative amino acid threads to bridge the gap between the structure – this glycine is specific for staphylococcus aureus. 39 Microbiology 1010 – Lecture Notes Betta (1,4)Is what joins the monosaccharides (covalent bond) Lysozyme- Natural enzyme (found in tears sweat Sylvia) has the acidity to destroy the linear chains. Tetra peptide that makes the chain strong. NAM and NAG is always consistent. Peptidoglycan (Continued…) More than 100 different PG structures identified Vary in peptide cros
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