3a + 3b: Membrane Proteins

Question 1

How is the phospholipid bilayer arranged

Answer 1

The hydrophilic heads points outwards whereas the hydrophobic tails point inwards.

Question 2

How are integral membrane proteins held in the phospholipid bilayer?

Answer 2

Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer.

Question 3

Functions of proteins found within the membrane

Answer 3

Active transport proteins, channel forming proteins, enzymes, receptors, attachment proteins of the cytoskeleton.

Question 4

What are peripheral membrane proteins

Answer 4

Proteins found on the surface of the membrane. They have hydrophilic R groups of their surface which bound to the surface of the membrane

Question 5

How do peripheral membrane see bind to the surface of a membrane

Answer 5

Mainly by ionic bonds and hydrogen bond interactions.

Question 6

The phospholipid bilayer creates a barrier for…..

Answer 6

Most ions an uncharged polar molecules.

Question 7

What molecules can pass through the bilayer by simple diffusion

Answer 7

Small molecules like oxygen or CO2

Question 8

What is facilitated diffusion

Answer 8

The passive transport of substances across the membrane through specific transmembrane proteins.

Eg channel proteins, transmembrane proteins.

Question 9

Why do a different cell types have different channel and transporter proteins

Answer 9

To preform specialised functions.

Question 10

What are protein channels

Answer 10

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.

Question 11

What are gated channel proteins

Answer 11

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)

Question 12

Ligand gated channels are controlled by the binding of…

Answer 12

Signal molecules

Question 13

Voltage- gated channels are controlled by…

Answer 13

Changes ion concentrations

Question 14

What do transporter proteins do

Answer 14

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.

Question 15

What are protein pumps

Answer 15

Pumps that carry out active transport are transporter proteins coupled to an energy source.

Transfers substances against concentration gradient

Question 16

What are ATPases

Answer 16

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

Question 17

How is membrane potential (electrical potential difference) created

Answer 17

A membrane potential is created when there is a difference in electrical charge on the two sides of the membrane

Question 18

Ion pumps use energy from ___________ to establish and maintain ion gradients

Answer 18

Hydrolysis of ATP

Question 19

What does the Sodium-Potassium pump do.

Answer 19

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.

Question 20

Steps in Na-K pump

Answer 20

1. Pump has high affinity for sodium ions inside of the cell
2. binding with 3 Na ions occur
3. Na+ binding stimulates the phosphorylation of ATP.
4. The binding of the phosphate triggers a conformational change
5. The affinity for Na+ decreases.
6. Consequently, Na+ is released from the cell
7. 2 Extracellular K+ binds to the protein
8. Triggers dephosphorylation
9. Conformational change occurs in the protein
10. K+ ions are taken into the cell
11. affinity returns to the start.

Question 21

Function of the Na-K pump in the small intestine

Answer 21

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.

Question 22

What is the electrochemical gradient

Answer 22

(Electrochemical gradient) is a combination of the concentration gradient.
AND
The electrical gradient (across the plasma membrane).