4. Membrane Transport Flashcards
transferring specific water-soluble molecules and ions across their membranes
membrane transport proteins
allowing passive transmembrane movement, primarily of water and small inorganic ions. interact with the solute to be transported much weaklier
Channels
Passive transport
downhill
2 active transport
Secondary active transport
Primary transport
undergo sequential conformational changes to transport specific small molecules across membranes
transporters
Active transport
Uphill and uses ATP
2 passive transport
Passive diffusion
Facilitated diffusion
cannot transport certain amino acids (including cystine, the disulfide-linked dimer of cysteine) from either the urine or the intestine to the blood
cystinuria
their polypeptide chains traverse the lipid bilayer multiple times
multi pass transmembrane proteins
impermeable to ions
Lipid bilayers
“uphill”, against their electrochemical gradients
Active transport
uncharged molecule
concentration gradient
charged molecule
membrane potential
intermediate state, inaccessible
occluded
negative insided
electrical potential
three principal classes of ATP-driven pumps
P-type pumps
ABC transporters
V-type pumps
energy stored in concentration gradients
coupled transport
energy from light
light- or redox-driven pumps
hydrolysis of ATP
ATP-driven pumps
passive transport,
Uniporters
structurally and functionally related multipass trans membrane proteins. they phosphorylate themselves during the pumping cycle
P-type pumps
transfer of one solute depends on the transport of a second
coupled transporters
e the free energy of ATP hydrolysis is used to directly drive the transport of a solute against its concentration gradient.
primary active transport
transfer in the same direction
Symporters (co-transporters)
transfer in opposite direction
Antiporters (exchangers)
co-transported ion
Na+
The Na+ that enters the cell during coupled transport is sub sequently pumped out by an _____
ATP-driven Na+-K+ pump
ion-driven coupled transporters as just described are said to mediate
secondary active transport
pseudosymmetric
inverted repeats
T he first eukaryotic ABC transporters identified were discovered because of their ability to pump ___out of the cytosol.
hydrophobic drugs
differ structurally from P-type ATPases and primarily pump small molecules across cell membranes.
ABC transporters (ATP-Binding Cassette
turbine-like protein machines, constructed from multiple different subunits.
V-type pumps
intracellular storage of Ca2+ in muscle cells specialized type of endoplasmic reticulum that forms a network of tubular sacs
sarcoplasmic reticulum
present at elevated levels in many human cancer cells and makes the cells simul taneously resistant
multidrug resistance (MDR) protein or P-glycoprotein
use the H+ gradient across the membrane
F-type (ATP synthase)
pumps Ca2+ out of the cell
Ca2+ ATPase in sarcoplasmic reticulum
10 transmembrane α helices connected to three cytosolic domains
the nucleotide-binding domain (N)
the phosphorylation domain (P)
the activator domain (A)]
release of Ca2+ into the cytosol (Ca+-release channels)
muscle contraction
contains highly conserved ATPase domains
ABC transporters
established Na+ and K+ gradient across the plasma membrane
Na+-K+ pump
create an electric potential
Electrogenic
connects the cytoplasm of two cells
gap junctions
constitute the largest family of membrane transport proteins
ABC transporters
cystic fibrosis transmembrane conductance regulator protein (CFTR)
Cl- transport protein
displayed at the cell surface for scrutiny by cytotoxic T lymphocytes
TAP transporter
receive, conduct, and transmit signals
Neurons
causes malaria, pumps out chloroquine
Plasmodium falciparum
open briefly and then close again
Gated
tilting the inner helices
close K+ channels
actively pumps a wide variety of peptides from the cytosol into the ER lumen
transporter associated with antigen processing, or TAP transporter
membrane potential
K+ leak channels
active electrogenic pumping and from passive ion diffusion
Voltage-gated channel
3 types of gated channels
Voltage-gated channel
Mechanically gated channels
Ligand-gated channel
inorganic ion transport
ion channels
structural and functional diversity alternative splicing of RNA transcripts
voltage-gated Ca2+ channels
water channels which allow water to move more rapidly
Aquaporins
diffuse down electrochemical gradients
Channels
changes in the electrical potential across the neuron’s plasma membrane
action potential or nerve impulse
Ion channels that pass inorganic ions; selectivity filters
Ion selectivity
polypeptide chain that connects the two transmembrane helices forms a short α helix a crucial loop that protrudes into the wide section of the cone to form the selectivity filter
pore helix
An important subset of K+ channels opens even in an unstimulated or “resting” cell
K+ leak channels
K+ ion must lose almost all of its bound water molecules
selectivity filter
voltage-gated Na+ channels in skeletal muscle cells
Myotonia
Numerous proteins are known to be capable of responding to such mechanical forces, and a large subset of those proteins has been identified as possible
mechanosensitive channels
Na+ or K+ channels in the brain
Epilepsy
the glial cells that myelinate axons in peripheral nerves
Schwann cells
Myelin is formed by specialized non-neuronal supporting cells called
glial cells
The myelin sheath is interrupted at regularly spaced where almost all the Na+ channels in the axon are concentrated
nodes of Ranvier
photosensitive ion channels that open in response to light.
covalently bound retinal group * light-driven cation channel * revolutionized the study of neural circuits
Channelrhodopsins
mechanical stretching of the lipid bilayer
Hypotonic
allowing a small amount of Na+ to enter the cell down its electrochemical gradient.
Voltage-gated Na+ channels
arrangement allows an action potential to prop agate along a myelinated axon by jumping from node to node
saltatory conduction
glial cells that myelinate axons in central nerves
Oligodendrocytes
Increases the Speed and Efficiency of Action Potential Propagation in Nerve Cells
Myelination
neuronal signals are transmitted at?
Synapses
open Cl- or K+ channels, suppresses firing
inhibitory neurotransmitters
Process of synapsis
presynaptic cell – synaptic cleft postsynaptic cell
open cation channels, influx of Na+ or Ca2+; firing an action potential
excitatory neurotransmitters
Release of neurotransmitter from the
presynaptic cell
bind to and open _____in the postsynaptic cell
transmitter-gated ion channel
G-protein coupled receptors that bind to all other neurotransmitter
metabotropic receptors
Excitatory neurotransmitters
acetylcholine, glutamate, serotonin
Inhibitory neurotransmitters
γ-aminobutyric acid (GABA) and glycine
ion channels and feature at fast chemical synapses
ionotropic receptors
