Unit 1 - Membrane Proteins

Question 1

What is the name for the model that describes the structure of the cell membrane?

Answer 1

Fluid mosaic model.

Question 2

What holds integral membrane proteins within the phospholipid bilayer?

Answer 2

Strong hydrophobic interactions from regions of hydrophobic R groups.

Question 3

What R groups are on the surface of peripheral membrane proteins?

Answer 3

Hydrophilic R groups.

Question 4

What are peripheral membrane proteins bound to the surface of membranes by?

Answer 4

Ionic and hydrogen bond interactions.

Question 5

What is the phopholipid bilayer a barrier to?

Answer 5

Ions and most uncharged polar (hydrophilic) molecules.

Question 6

What molecules can pass through the phospholipid bilayer by simple diffusion?

Answer 6

Small molecules, such as oxygen and carbon dioxide.

Question 7

What is facilitated diffusion?

Answer 7

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

Question 8

What are channel proteins?

Answer 8

Multi-subunit proteins with subunits arranged to form water-filled pores that extend across the membrane. They are highly selective.

Question 9

What are ligand-gated channel proteins controlled by?

Answer 9

Binding of signal molecules.

Question 10

How do transporter proteins work?

Answer 10

Bind to specific substance being transported & undergo conformational change to transfer the solute across the membrane.
They alternate between two conformations so that the binding site for the solute is exposed equally on both sides of the membrane.

Question 11

What are the pumps that mediate active transport?

Answer 11

Transporter proteins coupled to an energy source.

Question 12

What is required for active transport?

Answer 12

Source of metabolic energy.

Question 13

What do some active transport proteins do to provide the energy for the conformational change required to move substances across the membrane?

Answer 13

Hydrolyse ATP directly using enzymes called ATPases.

Question 14

When is a membrane potential created?

Answer 14

When there is a difference in electrical charge on the two sides of the membrane.

Question 15

How many sodiums are moved out of the cell by the sodium-potassium pump and how many potassiums are moved in for each ATP hydrolysed?

Answer 15

3 sodiums out

2 potassiums in

Question 16

What does the sodium-potassium pump use to transport ions against a steep concentration gradient?

Answer 16

Energy directly from ATP hydrolysis.

Question 17

What are the 3 steps that occur for sodium to be transported outside the cell by the sodium-potassium pump with reference to affinity?

Answer 17

Pump has high affinity for sodium ions inside the cell.
Binding occurs and the pump is phosphorylated by ATP.
The conformation of the protein changes and the affinity for sodium ions decreases. This means that sodium ions are released outside the cell.

Question 18

What are the 3 steps that occur for potassium to be transported inside the cell by the sodium-potassium pump following the transportation of sodium outside the cell?

Answer 18

Potassium ions bind outside the cell.
Dephosphorylation occurs and the conformation of the protein changes.
Potassium ions are taken into cell and the affinity returns to start (high affinity for sodium).

Question 19

In the small intestine, what does the sodium gradient created by the sodium-potassium pump drive the active transport of?

Answer 19

Glucose

Question 20

What does the glucose transporter responsible for glucose symport do?

Answer 20

Transports sodium ions and glucose at the same time and in the same direction.

Question 21

How does glucose symport in the small intestine work?

Answer 21

Sodium ions enter the cell down their concentration gradient. The simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.