Microbiology 201: Week 3 Notes
Microbiology 201: Week 3 Notes MICRB 201
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This 5 page Class Notes was uploaded by Grace Spellacy on Friday January 29, 2016. The Class Notes belongs to MICRB 201 at Pennsylvania State University taught by Dr. Steven Keating in Spring 2016. Since its upload, it has received 29 views. For similar materials see Introductory Microbiology in Microbiology at Pennsylvania State University.
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Date Created: 01/29/16
Microbiology 201 WEEK 3 NOTES (1/251/29) 1/25/16 Osmosis continued… Isotonic o Concentration of solutes is equal inside and outside the cell o No movement of water Hypertonic o Outside solute concentration is less than inside solute concentration Water flows in the cell o Membrane expands outwards (Cell wall in bacteria prevents lysis) Lysis: bursting of the cell Hypertonic o Outside solute concentration is greater than inside solute concentration Water flows out of the cell o Membrane collapses which can stop metabolism o Bacterial species are vulnerable to a hypertonic environment o Hypertonic environments can be created to control microbes using salts and sugars Stops spoilage and metabolism (preserves foods) Some foods are naturally preserved (maple syrup) because of their high sugar content Some microbes can tolerate hypertonic environments Example: staphylococcus Grows on skin Adapted to high salt concentrations because it has a higher concentration of certain solutes in the cytoplasm than other calls o Solutes: proline (amino acid), glycine betaine (amino acid derivative) o Transport proteins move these solutes in and out of the cell Becomes a problem if found in high salt foods Bacterial Cell Walls Cell wall completely surrounds the cell membrane and cytoplasm Gives cells characteristic shapes Major component: peptidoglycan (murien) o Unique to bacteria, so it is a good target for antibiotics o Name describes composition: peptido amino acids, glycan sugars Together create a polymer biological plastic o Glycan (sugar) 2 amino sugars (glucose derivatives) 1. NAG (N acetyl glucosamine) 2. NAM (N acetyl muramic acid) Linked by glycosidic bonds to form long strands o Peptide part (short peptide strands) Linked to glycan part by NAM sugar Chains have 4 amino acids in final product Bridges are formed between amino acid chains to link sugar strands and to form a mesh like structure (check ppt) Bacterial cells depend on their cell wall for protection in a hypotonic environment o Cell wall expands, but if absent, then hypotonic environment could be fatal Cell wall structure is unique to bacteria so they are a good target for antibiotics o Examples 1 . Lysozyme Naturally present in tears, saliva etc. Attacks and breaks down glycosidic bonds in peptidoglycan 2 . Penicillin Prevents formation of cross link bridges between amino acid chains So sugar chains cannot link Dead cell wall = dead cell Cell Wall Synthesis Assembly of subunits in cytoplasm (check ppt for diagram) 1. NAM sugars are linked to short A.A. (amino acid) chains o This step can be blocked by the antibacterial cycloserine 2. NAM A.A. combo is linked to bactoprenol 3. NAG sugar is added to the complex Transfer through cell membrane *problem: sugars are polar, cell membrane has an oily interior o Bactoprenol (nonpolar) acts as a shuttle to carry the subunit across the membrane Outside cell membrane o Bactoprenol is released and cycles back through the membrane but needs to drop a phosphate first o Dropping a phosphate can be blocked by the antibacterial bacitracin Bacitracin isolated from a broken leg in the 1940s, produced by bacillus Each NAM NAG A.A. subunit can be added to existing peptidoglycan to increase polymer size o This step can be blocked by the antibacterial vancomycin Transpeptidation o Builds links between A.A. chains o This step can be blocked by penicillin 1/27/16 Types of Cell Walls Two types: Gram positive (retains crystal violet stain after alcohol rinse) and gram negative (does not retain crystal violet stain) o Discovered by Christian Gram in Germany in 1884 Wanted to stain bacterial cells to differentiate them from human cells and found that there are two types o Significance: very useful in identification and classification Reflects underlying structural differences in cells Affects nature of disease and response of organisms to antibiotics Gram positive cell wall o Thicker peptidoglycan layer than gram negative (90% of cell wall) o cross bridges in gram positive cell walls contain 5 glycines o Teichoic acid Negative charge, can bind cations Increases rigidity of cell wall Helps with attachment of bacteria to mucous membrane in animals Important in infection Prevents degradation of peptidoglycan (some degradation is necessary for remodeling and growth) If released from dead cells, stimulates immune response Triggers fever, blood vessel dilation Usually a good things If blood pressure drops too much could lead to shock Gram negative cell wall o Thinner peptidoglycan layer (1015% of cell wall) o Cross bridges directly link between A.A. chains, no glycine bridge o Outer phospholipid envelope Outside of peptidoglycan layer, lost during alcohol rinse Disagreement on whether this is part of the cell wall Attached to peptidoglycan by brain’s lipoproteins Function Acts like a molecular filter by restricting passage of molecules Entry of molecules (especially large polar molecules) depends on protein channels Provides protection and reduces vulnerability to drugs Example: most gram negative cells are not sensitive to penicillin Example: lysozyme is blocked so it cannot act on peptidoglycan Conversely, some antibiotics use porins to enter the cytoplasm Can be mutations that change porin shape and block drugs (drug resistance example) o Lipopolysaccharide (LPS) Unique to gram negative cells Embedded in outer envelope Plays a role in strengthening outer membrane Also called endotoxin Contrast to exotoxin which is secreted Released when the cell dies and circulates the body May occur if immune system cells kill bacteria There is a large LPS release when using antibiotics Response of the body depends on dosage Fever, blood pressure drop, vasodilation, shock Strong immune system stimulant Part of LPS called ospecific side chain Sugar chain part Composed of variable arrangements of various sugars Closely related strains differ in o specific side chains, so you can identify different strands (ex. E coli) 1/29/16 Periplasmic Space Filled with gel like material Between cell wall and cell membrane In gram negative cells (thicker) Functions o Synthesis and maintenance of peptidoglycan o Digestion of large nutrient molecules o Enzymes for detoxification and modification of toxins Other Bacterial Structures (table on angel) Ribosomes, endospores, capsule, slime layer, flagella, pili, bacterial chromosome, plasmids Bacterial Genetics Mutations o Permanent changes in DNA (genes) o Products of random mistakes, mostly during DNA replication o Background rate: rate of mutation under ideal conditions Example: E. coli: once in every 10^8 nucleotides copied, once in every 10^5 genes copied, once in every 10^2 genomes copied Rates can be increased by exposure to mutagens May deliberately expose bacteria to mutagens o To control by causing fatal mutations o To create certain strains of bacteria (industrial strains), to create a high yield Effects of Mutations o Depends on location 1. Mutation in a gene for mRNA Aka structural genes or genes for protein products May have no effect if the base change creates and codon for the same A.A. Example: change of DNA from CNA to CCC results in a change in mRNA from GGU to GGG. Results in the same protein If a codon change does change the A.A. sequence, the protein does change (example on ppt) Effects Loss of metabolic enzyme activity Death of cell if vital function is lost May get a new function, new metabolic pathways, antibiotic resistance and ability to cause disease 2. Mutations in genes for rRNA (used to build ribosomes) Change could be good (resistance to an antibiotic) or bad (ribosome does not work)
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