Rigid Structure that lies just outside the plasma membrane Determination of

Rigid structure that lies just outside the plasma

This preview shows page 15 - 24 out of 35 pages.

Rigid Structure that lies just outside the plasma membrane Determination of cell shape Prevent bursting from osmotic pressure (lysis) Bacterial cytoskeleton
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Bacterial Cytoskeleton Involved in movement Cell Walls of Bacteria Divided into two major groups based on response to Gram-stain procedure
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o Gram (+) stain purple o Gram (-) stain pink Staining reaction due to cell wall structure The Mechanism of Gram Staining Involve constriction of the think peptidoglycan layer of gram + cells o Constriction prevents loss of crystal violet during decolorization step Thinner peptidoglycan layer of gram (-) bacteria does not prevent loss of crystal violet Cell Wall Important component of both gram + and gram - bacteria Unique to bacteria Peptido-glycan polymer o amino acids + sugars Sugars o N-acetylglucosamine (NAG) o N-acetymuramic acid (NAM) Amino acids cross link NAG and NAM
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Cell Wall: Gram (+) vs. Gram (-) ) Chapter 3: *No title* Teichoic Acids and LTA of Gram + Gram + only Polymers of glycerol or ribitol joined by phosphate groups
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Three components of LPS 1. O-antigen: repeating oligosaccharides 2. Core region: polysaccharide 3. Lipid A: toxic properties Importance of LPS Protection from host defenses (O antigen)
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Contributes to negative charge on cell surface (core polysaccharide) Helps stabilize outer membrane structure (lipid A) Also known as an endotoxin Functions of Cell Envelope Provides characteristic shape to cell Protects the cell from osmotic lysis May also contribute to pathogenicity May also protect cell from toxic substances Cell Envelope: Gram (+) bacteria Cytoplasmic membrane Thick cell wall No outer membrane TA and LTA Cell Envelope: Gram (-) bacteria Cytoplasmic membrane Thin cell wall Presence of outer membrane LPS
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The cytoplasmic matrix Substance between membrane and nucleoid Packed with ribosomes and inclusion bodies Highly organized with respect to protein location Inclusion bodies Granules of organic/inorganic material stockpiled by the cell for future use Some are enclosed by a single-layered membrane Ribosomes Complex structures consisting of protein and RNA Sites of protein synthesis o Prokaryotic ribosomes 70S (50S+30S) o Eukaryotic ribosomes 80S o S=Svedberg unit: a unit of sedimentation rate during centrifugation
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The Nucleoid (Chromosome) Irregularly shaped region Location of chromosome o Usually 1/cell Not membrane bound A closed circular, double stranded DNA molecule Supercoiled: looped and coiled extensively Plasmids Usually small, closed circular DNA molecules Exist and replicate independently of chromosome Not required for growth and reproduction May carry genes that confer selective advantage o E.g. drug resistance Capsules Discrete layer of polysaccharide surrounding the cells; outside the cell wall Usually composed of polysaccharides Well organized Not easily removed from cell
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Slime layers Layer of material lying outside the cell wall Diffuse Unorganized Easily Removied Function of Capsule Prevent harsh environmental conditions o e.g. desiccation Prevent phagocytosis and help invading host Aid the bacteria adhere to the host Assist in warding off attacks by phages
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