Membrane proteins Flashcards
Give an example of a compound that require assistance when entering a cell?
For polar compounds and ions, specific membrane proteins are required. e.g glucose, water, ions.
Whereas…
Non-polar(hydrophobic) compounds can dissolve in the membrane and cross the barrier e.g. anaesthetics.
What is the affect of transporters and channels on activation energy?
The activation energy is reduced.
What do transporters do in cell membranes?
They span the entire membrane and provide a non-lipid passageway.
They replace hydration shell with non-covalent favourable interactions. or transports the water as well.
What needs to happen for some compounds to diffuse across the membrane?
Water needs to be removed which needs energy input. Compound must diffuse through lipid in which it is insoluble. Meaning ACTIVATION ENERGY IS HIGH.
What are the two methods of passage that allow substrate passage?
Channels(passive transporter)
Pumps(active transporters)
Give some points about CHANNELS allowing substrate passage?
- gated holes in the membrane
- very fast transport (almost diffusion limited)
- aka facilitated diffusion
- substrate only go down their gradient
Give some points about PUMPS allowing substrate passage?
- relatively slow transport
- often large-scale conformational changes
- multiple conformations required
- substrate can go down their gradient or be pumped against it by coupling transport to an energy source
What does the final equilibrium position depend on?
The electrochemical gradient.
The electrochemical gradient of a _________ can power its own ____________.
substrate, transport.
What transporter is used to move glucose into red blood cells?
GLUT1
How does GLUT1 come into affecT?
- The helices in this transporter have a hydrophilic surface that faces into the channel.
- The protein changes conformation to expose the glucose binding face.
- It accepts glucose from outside in the T1 conformation and from the inside in the T2 conformation.
Describe the steps of what happens when glucose transporter are left idle and inulin reaches the membrane?
Glucose transporters are ‘stored’ within the cell in membrane vesicles.
Inulin interacts with its receptor, vesicle move to surface and fuse with plasma membrane, increasing no. of glucose transporter in the plasma membrane.
When insulin levels drop, glucose transporters are removed form the plasma membrane by endocytosis, forming small vesicles.
the smaller vesicles fuse with a larger endosome.
Patches of the endosome are enriched with glucose transporters bud off to become small vesicle, ready to return to the surface when insulin levels rise.
What is the necessity of chloride in relation to cystic fibrosis?
It maintains viscosity of mucus in the lungs.
What is the CFTR?
Cystic fibrosis transmembrane conductance regulator
⬇️
The channel that enables chloride to be exported.
What is the issue that the condition cystic fibrosis causes?
People have a mutation that prevents correct folding and insertion of the channel into the membrane.
Leads to mucus build up in the lungs and ultimately-life threatening infections.
How is passive transport across the plasma membrane facilitated?
Exchange of ions across a membrane. e.g HCO3- is exchanged into red blood cell by exchange of chlorine.
Describe no.1 example of passive transport by carriers and ionophores……..
Gramicidin, antibiotic effective against G+,G- and fungi. Produced by bacterium. Enters membrane and forms large pores.
Causes haemolysis.
Describe no.2 example of passive transport by carriers and ionophores……..
Valinomycin
A K+-specific ionophore.
Produced by bacterial Streptomyces strains.
Dissipates membrane potential.
Very toxic to humans as well.
What is the difference between primary and secondary active transport?
Primary transporters
Use a primary energy source, e.g. ATP or sunlight
Secondary transporters
Use a secondary energy source, e.g. electrochemical gradients
Define paradigm
An example of something.
How are mitchondrion specialised for transport?
It is a mass of membranes.
Large SA to generate proton gradient.
Lipids and integral membrane proteins facilitate large SA.
Huge amount of membrane in a mitochondrion maximising reaction area.
Describe how the proton motive force comes about?
Protons mump across the membrane to generate a chemical and electrochemical gradient known as the ‘proton motive force’.
Active transports have what kind of binding site?
Single substrate
How do active transporters get substrates across the membrane?
Using airlock-like mechanisms.
