2.3 cell membrane and gram + cell wall Flashcards
(27 cards)
the plasma membrane
completely encloses the bacterial cell – phospholipids spontaneously arrange as bilayer in water.
- lipid ‘tails’ inward ; glycerol ‘heads’ outward.
composed of 60% protein and 40% phospholipid
lipid tails and glycerol heads hydro-
tails = fatty and hydrophobic – fear of water
heads = hydrophilic – mixes with water
these arrangements provide permeability for cell.
what is the plasma membrane model referred to
the fluid mosaic model
structures on the plasma membrane; inner leaflet
- peripheral protein – called that because embedded in the inner leaflet.
- transmembrane protein – called that because it spans the whole lipid bilayer.
- protein channel - transports specific chemicals through from outside the cell to inside and vice versa
structures on the plasma membrane; outer leaflet
- glycolipid; carbohydrate lipid – lipid embedded in outer leaflet and has carbohydrate chain attached.
- peripheral protein but anchored on outer leaflet
- glycoprotein: carbohydrate protein ;
simple diffusion; plasma membrane
passive mechanism
the structure of the lipid bilayer allows small uncharged substances, like O2 and CO2, and lipids, to pass through the membrane and down the concentration gradient by simple diffusion
– molecule moves from outside of cell to inside and concentration of molecule is now similar on both sides.
– high concentration to low concentration
facilitated diffusion
type of passive transport, because solute is moving down a concentration gradient.
– the diffusion of solutes through transport protein that are located in the plasma membrane
– allows polar and charged molecules (carbs, amino acids, nucleosides, some ions) across the plasma membrane.
– transmembrane protein used
active transport definition
energy is required, usually in the form of ATP – mediated by proteins in the membrane called carrier proteins
active transport steps
- sodium ions fill the channel (transmembrane protein channel)
- hyrolysis of ATP provides energy for the conformational change in the channel protein that result in the release of the sodium from the cell.
- ATP also allows for migration of potassium into the channel.
- second conformational change in the channel proteins that releases potassium into the cell.
membrane structure and function; functions
osmotic stability, premeability, transport, energy transformations, cell wall synthesis
membrane structure and function; structures
transmembrane transporter for proline,
transmembrane protein that actively transports only lactose from putside to inside (protein called lactose permease)
flagellar motor embedded in cell membrane – enables motility.
primary functions of the. bacterial cell wall
- a structure that completely surrounds the cell protoplast
- prevents rupture or osmotic lysis of the cell protoplast
- almost all bacteria have a cell wall.
- provides shape
- assists some bacterial cells to attaching to other cells or evading anti-microbial drugs.
what are most bacterial cell walls composed of
peptidoglycan
peptidoglycan is composed of two altnerating sugars
NAM and NAG
NAM = N-acetylmuramic acid
NAG = N-acetylglucosamine
NAG and NAM are ___ linked
covalently
the peptide portion of peptidoglycan is comprised of how many amino acids
4 = L-alanine, D-Glutamic acid, meso Diaminopimelic acid, D-alanine
what is the tetrapeptide chain linked to
covalently linked to NAM
gram positive peptidoglycan drawing
what interpeptide chain is unique to gram positive bacteria
glycine5 – 5 aamino acids – cross linked and provide rigidity
thickness of gram positive bacteria
very thick around 20-80 nm thick
linking arrangement between the tetrapeptide chain and interpeptide
the terminal glycine (both ends of interpeptide) are used to form interpeptide bonds between the third amino acid on one chain and the fourth (usually D-alanine) on the other.
sites of antibiotic action in gram positive peptidoglycan
– penicillin blocks the insertion of the interpeptide bridge – penicillin prevents cross-linking of the DAP and D-ala molecules on the side chain
– lysozyme breaks the glycoside bond between M and G
lipoteichoic acid
teichoic acids that are covalently linked to lipids. these lipoteichoic acids span the peptidoglycan layer to anchor it to the plasma membrane
teichoic acid
unique to gram positive – embedded in the peptidoglycan (covalently attached)
– polymers of glycerol, glucosyl, and ribitol phosphates.
