Week 2 cp 5 & 12 Flashcards
what does the cell membrane do?
- separates the cytoplasm from the outside environment
- prevents cytoplasmic proteins from leaking out, and it maintains concentration gradients of ions and nutrients
- also the site of oxidative phosphorylation (or respiration) process in which electrons pulled from food molecules yield energy to pump hydrogen ions (H+) across the membrane
- cell membranes is covered by a cell wall
- mediates exchange w/ the environment such as toxin secretions and communications w/ fellow pathogens
what is a cell wall?
-is a single interlinked molecule that encloses the entire cell
outside the cell membrane is the cell wall
-a rigid mesh-like structure called peptidoglycan. it is a single molecule that surrounds the cell like a cage
-peptidoglycan consists of sugar chains linked covalently by peptides
-highly porous to ions and small organic molecules
what constitutes the cell envelope?
the cell membrane, the cell wall, and outer membrane (for gram-negative species)
- it protects the cell from environmental stress and predators
- envelope protects pathogens from macrophage phagocytosis
what is a nucleoid?
not an enclosed membrane, so could of DNA can extend throughout the cytoplasm
- loops of DNA from the nucleoid are transcribed by the enzyme RNA polymerase to form MRNA
- MRNA transcribe and bind to ribosomes to start synthesizing polypeptide chains (proteins)
- protein synthesis occur
what is passive transport?
- no energy required
- moves nutrients with the concentration gradient from (high to low) across the membrane
what is active transport?
- energy required to move against the concentration gradient from low to high
ex. antiport pump- sodium and potassium pump
what is coupled transport?
the use of energy from one gradient to drive transport up another gradient
what are the two types of coupled transport systems?
symport and antiport
what is symport?
- two molecules travel in the same direction
1. energy is released as one substrate (red) moves down the concentration gradient
2. this energy moves a second substrate (blue) against its gradient and into the cell
what is antiport?
- actively tranported molecule moves in the direction opposite to the driving ion
1. antiporter binds substrate A (red) on the cytoplasmic side of the membrane
2. antiporter opens to the outside of the cell, where the concentration of A is lower
3. substrate A leaves its binding site and substrate B (blue) then binds to its site
4. antiporter opens to the inside of the cell. substrate B is released in exchange for substrate A.
what is ABC transported?
- uses the energy from ATP hydrolysis to move solutes “uphill” against their concentration gradient
1. solute binds to the substrate-binding protein and the complex then binds to the membrane transporter (green)
2. the ATPase activity of one component (yellow) powers the opening of the channel (green) and movement of the solute into the cell
what are siderophores?
-tightly bind whatever ferric iron is available in the environment
-these iron scavenger molecules are produced and sent forth by cells when the intracellular iron concentration is low
-the siderophores binds iron in the environment and the siderophore-iron-complex then attaches to specific receptors in the bacterial out membrane
-the complex may then be transported across the cell membrane by an ABC transporter
=iron is transported into the cell
what is peptidoglycan?
consists of parallel polymers of discarcchardies called glycan chains
- glycan chains are cross-linked w/ short peptides
- they are unique to only bacteria- never human cells
- spaces between links are open, porous to large molecules
gram positive bacteria
have a thick cell wall w/ multiple layers of peptidoglycan
-outside the cell wall, has an outer membrane
gram-negative bacteria
has a thin cell wall (single layer of peptidoglycan) enclosed by an outer membrane