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Lecture 8

MBIO 1010 Lecture 8: Lecture 8

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University of Manitoba
MBIO 1010
Christopher Rathgeber

Microbiology 1010 – Lecture Notes LPS: The Outer Membrane (Continued…) Periplasm: space located between cytoplasmic and outer membranes o ~15 nm wide o Contents have gel-like consistency o Houses many proteins Porins: channels for movement of hydrophilic low-molecular-weight substances (Fig. 2.29c) The periplasm is between the inside the outer membrane and the outside of the plasma membrane (including the peptidoglycan). Outer membrane is none selective = generic protein channels and specific protein channels. Job to just get materials into the periplasm. The periplasm is very viscous because it has a lot of dissolved content within. You are going to have chaperons protein that collects the molecule or nutrient of interest and delivers it to the face of the plasma membrane at the expense of ATP can bring it into the cell. 3 polypeptide subunits – The pore is hydrophilic is relatively none selective and as long as you can fit, you can go through into the periplasm. Relationship of Cell Wall Structure to Gram stain In Gram stain reaction, insoluble crystal violet-iodine (CV-I) complex forms inside cell Complex is extracted by alcohol from gram-negative, not gram-positive bacteria Why? Gram-positive bacteria have thick cell walls consisting mainly of peptidoglycan Becomes dehydrated during alcohol step so pores in wall close Prevents CV-I complex from escaping Gram-negative bacteria – alcohol penetrates OM CV-I extracted from cell o cells appear nearly invisible until counterstained with second dye (safarin) 44 Microbiology 1010 – Lecture Notes The ability to form complex's inside the cell Provides colour (gram positive) allows the crystal violet to stick within the pores of the peptidoglycan. Archaeal Cell Walls No peptidoglycan Typically no outer membrane Pseudomurein o Polysaccharide similar to peptidoglycan (Figure 2.30) o Composed of N-acetylglucosamine and N-acetylalosaminuronic acid Found in cell walls of certain methanogenic Archaea Cell walls of some Archaea lack pseudomurein Waxy outer layer – Makes it impenetrable from the stains so it has be stained with a carboyl fussion dye. These guys have to have a plasma membrane and can adjust to temperatures by adding saturated to more saturated fatty acids to plasma membranes. Do not all have pseudomurein More a restraint linkage beta (1,3) than the other peptidoglycan. Instead of tetra there is a tripeptide 45 Microbiology 1010 – Lecture Notes 2.12 Archaeal Cell Walls (Continued….) S-Layers o Most common cell wall type among Archaea o Consist of protein or glycoprotein o Paracrystalline structure o Some Archaea have only S-layer (no other cell wall components) o Most have additional cell wall elements Glycoproteins Highly ordered in the array of molecules – Para crystalline structure Some archaea do not have additional cell wall structure or components Summary of Archaeal Cell Walls Variety of structures possible Some closely resemble peptidoglycan Others lack polysaccharide completely Most Archaea contain some type of cell wall structure – functions to prevent osmotic lysis and give shape Because they lack peptidoglycan, Archaea are resistant to lysozyme and penicillin The Cytoplasm Cytoplasm – material bounded by plasma membrane (PM) Protoplast – PM and everything within o Macromolecules – amino acids, nucleotides, etc o Soluble proteins o DNA and RNA (nucleoid) o Ribosomes o Inclusions Cytosol – is the fluid within the cytop
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