Term
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Definition
| Rigid structure that lies just outside the plasma membrane |
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Term
| 2 groups of bacteria cell walls |
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Definition
gram (+) purple
gram (-) pink
*Staining rxn due to differences in cell wall structure |
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Term
| Cell Wall Functions (bacteria) |
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Definition
*Maintains shape of bacterium
-almost all bacteria have one
*Helps protect cell from osmotic lysis
*helps protect from toxic materials
*may contribute to pathenogenicity |
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Term
| Peptidoglycan (Murein) structure |
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Definition
*Meshlike polymer composed of identical subunits
*Each unit contains N-acetyl glucosamine (NAG) and N-acetylmuramic acid and (NAM) several different amino acids
*Links together to make chains
*Chains of linked peptidoglycan subunits could be cross linked by peptides |
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Term
| Cross-linking of peptidoglycan chains (check picture) |
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Definition
*Direct connection between amino acids in the peptide chain
*Peptide interbridge; mostly in gram (+) bacteria, rarely in gram (-) |
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Term
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Definition
*Composed primarily of peptidoglycan
*May also contain large amounts of teichoic acids
*Some gram(+) bacteria have layer of proteins on surface of peptidoglycan |
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Term
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Definition
*Polymer of glycerol or ribitol joined by phosphate groups
*Amino acids, sugars are attached to the glycerol or ribitol group
*Connected to the peptidoglycan or the plasma membrane (Lipoteichoic acid)
*Function not clearly known, thought to help confer a negative charge on cell surface |
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Term
| Periplasmic space of gram (+) bacteria |
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Definition
*lies between plasma membrane and cell wall and is smaller than that of gram (-) bacteria
*periplasm has relatively few proteins
*peptidoglycan is permeable, enzymes that stay in the periplasms of gram positive cells are attached to the plasma membrane (integral proteins)
*enzymes secreted by gram + baacteria are called exoenzymes (pass through the periplasm but are not retained)
*(ex.) Lipase is an exoenzyme that hydrolyzes lipids into fatty acids and glycerol. |
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Term
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Definition
*More complex than gram + cell walls
*Consist of a thin layer of peptidoglycan surrounded by an outer membrane
*peptidoglycan is ~2-5% of wall weight
*periplasmic space differs from that in gram + cells
-may constitute 20-40% of cell volume
-many enzymes present in periplasm Braun's lipoproteins connect outer membrane to petidoglycan
*Outer membrane composed of a lipid bilayer, lipoproteins, porins, and lipopolysaccharide (LPS)
*No teichoic acids |
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Term
| How are outer membrane connected to the cell? |
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Definition
| Braun's protein, adhesion sites |
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Term
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Definition
| To anchor peptidoglycan & outer membrane |
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Term
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Definition
| *Proteins w/pores. Different sizes for diff compounds |
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Term
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Definition
*on outer surface of bilayer. complex
-Lipid A
-Core polysaccharide
-O side chain (antigen) |
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Term
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Definition
Glucosamine phosphate units with long fatty acid chains
-Anchors LPS to the outer membrane
-Acts as an endotoin in pathogenic gram negative bacteria
(gram - infections from lipid A reaching your bloodstream) |
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Term
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Definition
| Substituted collection of sugars, including heptose and octose sugars |
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Term
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Definition
-Composition varies, but is made of polysaccharides
-Antigenic; antibodies bind to
-Cell shuffles the genes of the chain; changes composition
-Surface of antibodies |
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Term
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Definition
-Helps stabilize outer membrane structure (lipid A)
-Can act as toxin (lipid A)- inner layer of outer membrane
-Contributes to negative charge (due to polysaccharide structure) on cell surface (core polysaccharide)
-protection from host defenses (O antigen) |
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Term
| Other characteristics of the outer membrane |
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Definition
*More permeable than plasma membrane due to presence of porin proteins and transporter proteins
-porin proteins from channels through which small molecules (600-700 daltons) can pass |
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Term
| The mechanism of gram staining |
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Definition
-Thought to involve shrinkage of the pores of the peptidoglycan layer of gram-positive cells
--constriction prevents loss of crystal violet during decolorization step
-thinner peptidoglycan layer and larger pores of gram-negative bacteria does not prevent loss of crystal violet |
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Term
The cell wall and osmotic protection
(osmotic lysis) |
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Definition
*Osmotic lysis:
-can occur when cells are in hypotonic solutions
-movement of water into cell causes swelling and lysis due to osmotic pressure
*cell wall protects against osmotic lysis |
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Term
| Evidence of protective nature of the cell wall |
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Definition
*Lysozyme breaks the bond between N-acetyl glucosamine and N-acetylmuramic acid
*penicillin (antibodies) inhibits peptidoglycan synthesis
*If cells are treated with either of the above they will lyse if they are in a hypotonic solution (unless osmosis equal) |
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Term
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Definition
Protoplast: cell completely lacking cell wall (ex. G+ ccells treated w/penicillin)
Spheroplast- cell with some cell wall remaining (ex. G- cells treated with penicillin)
G+: in essence, peptidoglycan is whole cell wall |
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Term
| Capsules, slime layers, s-layers |
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Definition
Layers of material lying outside cell wall
-capsules: usually composed of polysaccharides
-Well organized and not easily removed from cell
-slime layers: similar to capsules except diffuse, unorganized and easily removed |
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Term
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Definition
-network of polysaccharides extending from the surface of the cell
-a capsule or slime layer composed of polysaccharides can also be referred to as glycocalyx |
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Term
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Definition
-regularly structured layers of protein or glycoprotein
-in bacteria the S layer is external to the cell wall
-common among archaea, where they may be the only structure outside the plasma membrane (is the cell wall of some archaea) |
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Term
| functions of capsules, slime layers and s-layers |
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Definition
-protection from host defenses (ex. phagocytosis)
-protection from harsh environmental conditions (ex. desiccation)
-attachment to surfaces
-protection from viral infecion or predation by bacteria
-protection from chemicals in environment (ex. detergents)
-facilitate motility of gliding bacteria
*protection against osmotic stress |
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Term
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Definition
*Lack peptidoglycan
*Cell wall varies from species to species but usually consists of complex heteropolysaccharides, glycoproteins
-Some bacteria have a layer of protein (S layer) as the only structure outside the plasma membrane
-Others would have additional layers external to the S layer (ex. proteins sheath, methanochondroitin (ex. methanosarcina
-many methanogens have walls containing pseudomurein (polymer has structure of urine-slightly same function)
-Few have no S layer, only thick homogenous lyaers of various polysaccharides
-Some stain gram + and some gram - |
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