transport across cell membrane (2) Flashcards
membrane function
control composition of space surrounded by membrane
providing route for polar and large molecules - cross membrane
proteins in the membrane
channels, transporters, receptors, structural protein
peripheral transmembrane protein
loosely associated to bilayer
bound by electrostatic interaction
integral transmembrane protein
embedded in bilayer
alpha-helical in membrane
cross HP core of bilayer
R group of side chains interact with bilayer - anchoring
what favours aqueous in cells
hydrophilic groups
charges in centre of bilayer
no charge
makes VdW forces between HP lipids and side chain
max H bonding function in protein
neutralise charges NH and CO in protein backbone
what can peptide adopt
finding lowest energy conformation
transmembrane helices anchor membrane protein
protein sequences is HP
R group project out - face lipids - anchored
producing path for polar solutes
amphipathic helices cluster together - route
at least 4 helices
entry of channel - function
charged
determine types of charges approach channel
glycine - in producing path of helices
help packing amphipathic helices together
polar channel - transport ion
alpha helices charged residue on one side and HP on other side
simple gated ion channel - closing
helices rotate - larger side chains towards centre
ligand gated ion channel - conformation
focused on N2 transmembrane domain
closing and opening conformation is triggered by binding of acetylcholine
neurotransmitters
what channels can’t do
move ion against electrochemical gradient
facilitated diffusion like glucose and amino acids
use of transporters - towards substrates and function
reduction in affinity for substrate
has solute recognition site = large conformational change
opens gated below and closes above - never both
passive transport
down gradient
example of passive transport
facilitated diffusion - binds to substrate = conformational change moving substrate down concentration gradient
active
against gradient
energy from electrochemical gradient or energy rich substrate - ATP
example of active
active transport - bind to substrate - provide energy causing conformational change
atomic resolution structure of Ca2+ pump
10 alpha helices across bilayer
calcium ATPase
assimilating Ca2+ in sarcoplasmic reticulum pump Ca2+ into calcium store - muscle tissues
process of Ca2+ pump (1)
calcium ATPase binds to Ca2+ from cytoplasmic side with high affinity
Using ATP hydrolysis (2)
conformational change - close access of cytoplasmic side
conversion of high to low affinity site - opening hydrophilic cavity to lumen of sarcoplasmic reticulum
energy released by ATP hydrolysis (3)
weaken grip of high affinity from Ca2+ by conformational change around amphipathic helices
