Key Area 3

Question 1

Integral membrane proteins:

Answer 1

Interact with the hydrophobic tail of phospholipids in membrane to hold it in the bilayer.

Some are transmembrane proteins.

Question 2

Transmembrane proteins.

Answer 2

When integral protein spans the entire width of the membrane.

E.g. Channels, transporters and receptors

Question 3

Peripheral membrane proteins.

Answer 3

Have hydrophilic R groups on their surface.

Bound to the surface of membranes by ionic and hydrogen bonds.

Many interact with the surfaces of integral membrane proteins.

Question 4

The phospholipid bilayer:

Answer 4

Barrier to ions and most uncharged polar molecules.

Small molecules (oxygen, carbon dioxide) pass through the bilayer by simple diffusion.

Question 5

Facilitated diffusion:

Answer 5

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

Question 6

To perform specialised functions:

Answer 6

Different cell types have different channel and transporter proteins.

Question 7

Channel proteins:

Answer 7

Highly selective.

Multi-subunit proteins.

Subunits arranged to form water-filled pores across the membrane.

Some are gated and change conformation to allow or prevent diffusion.

Question 8

Ligand-gated channels:

Answer 8

Controlled by the binding of signal molecules.

Question 9

Voltage-gated channels:

Answer 9

Controlled by changes in ion concentration.

Question 10

Transporter proteins:

Answer 10

Bind to the specific substance to be transported.

Undergo a conformational change to transfer substance across the membrane.

Alternate between two conformations so that the binding site is sequentially exposed on both sides of the bilayer.

Question 11

Active transport:

Answer 11

When protein pumps transfer substances across the membrane against their concentration gradient.

Requires metabolic energy (ATP).

Question 12

Protein pumps:

Answer 12

Transporter proteins coupled to an energy source.

Question 13

ATPases:

Answer 13

Protein pumps that hydrolyse ATP to provide the energy for the conformational change.

Question 14

Electrochemical gradient:

Answer 14

Formed from the concentration gradient and the membrane potential.

Determines the transport of the solute.

Question 15

Membrane potential

Answer 15

Electrical potential difference.

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

Question 16

Ion pumps

Answer 16

Use energy from the hydrolysis of ATP to maintain ion gradients.

Question 17

Sodium-potassium pump

Answer 17

Transports ions against a steep concentration gradient using energy from ATP hydrolysis

Actively transports sodium ions out of the cell and potassium ions into the cell.

Establishes both concentration gradients and an electrical gradient.

Question 18

Sodium-potassium pump steps:

Answer 18

1. High affinity for sodium ions inside the cell.
2. Binding occurs
3. Phosphorylation by ATP
4. Conformation changes
5. Affinity for sodium ions decreases
6. 3 sodium ions released outside of the cell
7. Potassium ions bind outside the cell
8. Dephosphorylation
9. Conformation changes
10. 2 potassium ions taken into cell
11. Affinity returns to start

Question 19

Sodium-potassium pump in small intestine:

Answer 19

Sodium gradient (made by pump) drives the active transport of glucose.

In intestinal epithelial cells, the pump generates a sodium ion gradient across the membrane.

Question 20

Glucose transporter:

Answer 20

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

Sodium ions enter the cell down their concentration gradient.

The simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.