week 4: nutrient transport Flashcards
what is the function of the cytoplasmic membrane
-diffusion barrier
-only site of active transport
what are the mechanisms of how molecules cross the cytoplasmic membrane?
osmosis
simple diffusion
facilitated diffusion
active transport
what is osmosis
the movement of water from low solute to high solute environments that are separated by a semi-permeable membrane
can be aided by aquaporins
describe an isotonic solution
same solute concentration as the bacterium’s cytoplasm
no net movement of water by osmosis
describe a hypertonic solution
higher solute concentration than the bacterium’s cytoplasm
net movement of water out of the cell resulting in shrinkage
describe a hypotonic solution
lower solute concentration than the bacterium’s cytoplasm
net movement of water into cell by osmosis causing cell expansion
what is simple diffusion
-diffusion of molecules directly through lipid bilayer of cytoplasmic membrane (high concentration to low)
-usually uncharged molecules because charged cannot pass through
-passive
what is facilitated diffusion
-facilitated involves a substrate-specific permease/transporter
-involves membrane proteins called permeases that form channels
-substrate-binding and conformational changes mediate transport
-passive
what is active transport?
-requries energy and membrane proteins
-transports molecules against concentration gradient
3 mechanisms:
- coupled transport
- ATP binding cassette transporter
- group translocation
what is coupled transport?
moves one molecule down its concentration gradient providing energy to move a second molecule against its
what is a symporter
energy is released as one substrates moves down its concentration gradient which moves a second substrate against its gradient and into the cell
same direction
what is an antiporter
one molecule moves against its concentration gradient while moving the second molecule down its gradient
opposite directions
ATP binding cassette transporter
-hydrolysis of ATP to ADP provides energy active transport
-some may require a solute binding protein in the periplasm that binds to and delivers the solute to the ABC transporter in the cytoplasm membrane
-hydrolysis causes conformational change to release into cytoplasm
group translocation
chemically modifies the molecule as it enters the cells so the concentration gradient is maintained for diffusion
group translocation process
- phosphate from PEP is passed along common elements of the PTS (only for transporting certain sugars) to the enzyme II proteins
- substrates are transformed by phosphorylation during transport
