KA3 - Membrane Proteins Flashcards
The phospholipid bilayer acts as?
A barrier to ions and most uncharted polar molecules
What can pass through the phospholipid bilayer?
Some small molecules such as oxygen and carbon dioxide
What do specific transmembrane proteins act as?
Channels or transporters
Specific transmembrane proteins act as channels or transporters. Why’s does this control?
Controls ion concentrations and concentration gradients
To perform specialised functions what do different cell types have/do?
To perform specialised functions different cell types and different cell compartments have different channel and transporter proteins
Passage of molecules through channel proteins is?
Passive
Eg. Aquaporin
Some channel proteins are gated. What does this mean?
They change conformation to allow or prevent diffusion
Such as, sodium channels or potassium channels
What can ‘gated’ channels be controlled by?
Signal molecules (ligand- gated channels) or changes in ion concentrations (voltage- gated channels)
Why do transporter proteins change conformation?
To transport molecules across a membrane
Transport can be facilitated.
Give an example of this
Glucose support
Active Na/KATPase
What does conformational change in active transport require?
Energy from hydrolysis of ATP
What do some cell surface receptor proteins convert?
An extracellular chemical signal to a specific intracellular response through a signal transduction pathway
What may signal transduction result in?
The activation of an enzyme or G protein
A change in uptake or secretion of molecules, rearrangement if the cytoskeleton
Or activation of proteins that regulate gene transcription
How does the sodium potassium pump transport ions?
Transports ions against a steep concentration gradient using energy directly from ATP
The transporter protein has high affinity for sodium ions inside the cell so binding occurs
Phosphorylation by ATP causes conformational change of the sodium potassium pump
Affinity for ions changes, sodium ions are released outside of the cell and potassium ions bind outside of the cell
Dephosphorylation occurs which causes conformational changes
Potassium ions are taken into the cell and the affinity returns to the start
What does maintenance of ion gradients by Na/KATPase account for?
A significant part of basal metabolic rate (up to 25% in humans)
Describe the functions of Na/KATPase
Maintaining the osmotic balance and animal cells
Generation of the ion gradient for glucose dumpiest in small intestines
Generation and long-term maintenance of ion gradient for resting potential in neurons
Generation of ion gradient in kidney tubules
What is nerve transmission?
A wave of depolarisation of the resting potential of a neuron
How can nerve transmission be stimulated?
When an appropriate signal molecule such as a neurotransmitter, triggers the opening of ligand-gated ion channels at a synapse
If sufficient ion movement occurs, then voltage-gated ions will open and the effect travels along the length of the nerve
What happens once the wave of depolarisation has passed?
These channel proteins close and others open to allow the movement of ions in the opposite direction to restore the resting potential
