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Lecture 5

MCB 3020 Lecture 5: microbiology lecture 5-- exam one

4 Pages

Microbiology and Cell Science
Course Code
MCB 3020
Abdolkarim Asghari

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8/30/2017 Microbiology Lecture 5—Exam 1 • Bacteria usually .5- 2 um • Glycocalyx—covers exterior of cell. Not every cell has it. Most prokaryotes and Eukaryotes may have this. • Bacteria Structure: o Divided into two groups of cells—gram positive and negative o Only cell wall and membrane is gram positive o Nam (N-acetylmuramic acid) and NAG(N-acetylglucosamine) are building blocks of peptidoglycan. Their layers are built up from peptide bridges. o Peptidoglycan is a polysaccharide that covers some bacteria in where the cell wall is made up. About 25 of these cover bacteria o For gram negative, have thinner layer of peptidoglycan. Gram negative has an additional layer called an outer membrane. Has only 5 layers of peptidoglycan. Gram negative has an additional membrane to cover cell. Because of this extra layer, it creates a periplasmic gap (compartment between). o Lipoprotein, porin protein (like a gate; an additional layer of protection) and periplasmic space unique to gram negative o Telchoic acid is unique to gram positive o Outer membrane has some phospholipids and lipopolysaccharide o Only gram negative has endotoxin—causes damages to the host fever, bleeding, coughing o Both gram negative and gram positive have cell wall (made of same thing, cell membrane, flagellum, peptidoglycan • Property Gram Positive Gram Negative • Color after Gram stain Purple Pink • Peptidoglycan content High Low • Outermembrane Absent Present • Lipopolysaccharide (LPS) Absent Present • Teichoic acid Present Absent • Sensitivity to Penicillin G Easy Difficult • Sensitivity to lysozyme High Low • Cell membrane Yes Yes ❖ Gram staining procedure helps predict other properties ❖ Penicillin and lysozyme damage cell wall ❖ Gram positive more prone to attack of penicillin than gram negative • Cell membrane o Key barrier between the cell and the outside world. Mainly composed of lipids and proteins o Phospholipids made of glycerol, phosphate group and fatty acid (long stretch of hydrocarbons. Fatty acids are Hydrophobic) o Phospholipid structure: Head (glycerol and phosphate) is hydrophilic and tails (fatty acid) are hydrophobic o Sometimes protein sticks out or in wall or runs through whole wall transmembrane protein. o Sugar molecules are sometimes attached to phospholipids and proteins. They act like a receptor; sense info outside o Embedded into cell wall is cholesterol which causes flexibility for cell membrane. Cholesterol may cause arteries to harden. Can also deposit between arteries and hardens it then ruptures and adds to blood pressure • Fluid Mosaic Model of Membrane Structure—phospholipids not solid; not grouped together o Any o Anything with charge cannot just go easily through o Conformational changes—protein 3- dimensional structure will shift and move o A signal can go from outside to inside from transmembrane protein— signal transduction o Lipid bilayer in which proteins float o Peripheral proteins loosely associated with the membrane and easily removed o Integral proteins embedded within the membrane a
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