3a + 3b: Membrane Proteins Flashcards
How is the phospholipid bilayer arranged
The hydrophilic heads points outwards whereas the hydrophobic tails point inwards.
How are integral membrane proteins held in the phospholipid bilayer?
Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer.
Functions of proteins found within the membrane
Active transport proteins, channel forming proteins, enzymes, receptors, attachment proteins of the cytoskeleton.
What are peripheral membrane proteins
Proteins found on the surface of the membrane. They have hydrophilic R groups of their surface which bound to the surface of the membrane
How do peripheral membrane see bind to the surface of a membrane
Mainly by ionic bonds and hydrogen bond interactions.
The phospholipid bilayer creates a barrier for…..
Most ions an uncharged polar molecules.
What molecules can pass through the bilayer by simple diffusion
Small molecules like oxygen or CO2
What is facilitated diffusion
The passive transport of substances across the membrane through specific transmembrane proteins.
Eg channel proteins, transmembrane proteins.
Why do a different cell types have different channel and transporter proteins
To preform specialised functions.
What are protein channels
They are multi-subunit (quaternary structure) proteins with the subunits arranged to form water-filled pores that extend across the membrane.
In animal and plant cells, they are highly selective.
What are gated channel proteins
Some channel proteins are gated and change conformation to allow or prevent diffusion.
They respond to a stimulus which cause them to open or close.
- may be chemically (ligand- gated) or electrically stimulated (voltage- gated)
Ligand gated channels are controlled by the binding of…
Signal molecules
Voltage- gated channels are controlled by…
Changes ion concentrations
What do transporter proteins do
Bind to the specific substance to be transported and undergo a conformational change to transfer solute across the membrane.
Transporters bind between two conformations so that the binding site for a solute is sequentially exposed to one side of the bilayer, then the other.
What are protein pumps
Pumps that carry out active transport are transporter proteins coupled to an energy source.
Transfers substances against concentration gradient
What are ATPases
Some active transport proteins hydrolyse ATP directly to provide the energy for the conformational change required to move substances across a membrane.
Proteins which hydrolysis ATP directly are called ATPases
How is membrane potential (electrical potential difference) created
A membrane potential is created when there is a difference in electrical charge on the two sides of the membrane
Ion pumps use energy from ___________ to establish and maintain ion gradients
Hydrolysis of ATP
What does the Sodium-Potassium pump do.
Transports ions against the concentration gradient using energy directly form ATP hydrolysis.
Actively transports 3 Na ions out of the cell and 2 K ions in.
It is found in most animal cells and accounts for high proportion of basal metabolic rate.
Steps in Na-K pump
- Pump has high affinity for sodium ions inside of the cell
- binding with 3 Na ions occur
- Na+ binding stimulates the phosphorylation of ATP.
- The binding of the phosphate triggers a conformational change
- The affinity for Na+ decreases.
- Consequently, Na+ is released from the cell
- 2 Extracellular K+ binds to the protein
- Triggers dephosphorylation
- Conformational change occurs in the protein
- K+ ions are taken into the cell
- affinity returns to the start.
Function of the Na-K pump in the small intestine
In the intestinal epithelial cells (of the small intestine), the sodium potassium pump generate a sodium ion gradient across the plasma membrane
This gradient drives the active transport of glucose.
What is the electrochemical gradient
(Electrochemical gradient) is a combination of the concentration gradient.
AND
The electrical gradient (across the plasma membrane).
