Unit 1: KA3 - Membrane Proteins

Question 1

What is the accepted model of the plasma membrane called?

Answer 1

Fluid Mosaic model.

Question 2

Describe the Fluid mosaic model.

Answer 2

• Phospholipid bilayer held together by hydrophobic reactions
• Integral membranes held by hydrophobic reactions
• membrane can move making it ‘fluid’

Question 3

What are the two types of membrane protein?

Answer 3

• Integral: embedded within

- Peripheral: found on surface

Question 4

Describe peripheral membrane proteins’ interactions with the membrane.

Answer 4

Bound to the surface of the phospholipid bilayer with ionic and hydrogen interactions, due to hydrophilic R group

Question 5

Describe integral membrane proteins’ interactions with the membrane.

Answer 5

• Can be transmembrane (spanning entire membrane)

- Hydrophobic R groups allow strong interactions with hydrophobic tails of phospholipids.

Question 6

How do differing membrane proteins react?

Answer 6

Many peripheral membrane proteins interact with the surfaces of integral membrane proteins.

Question 7

What does the phospholipid bilayer act as a barrier to?

Answer 7

Ions and most uncharged polar molecules.

Question 8

What are examples of molecules that can diffuse straight through the phospholipid bilayer?

Answer 8

• Water

- CO₂

Question 9

Define facilitated diffusion.

Answer 9

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

Question 10

What do different cell types need to perform specialised functions?

Answer 10

Different channel and transporter proteins

Question 11

What is highly selective in plant and animal cells?

Answer 11

channel proteins

Question 12

Describe gated channel proteins.

Answer 12

• Voltage gated: controlled by changes in ion concentration

.- Ligand gated: controlled by the binding of signal molecules.

Question 13

Describe transporter proteins.

Answer 13

They bind to the specific substance to be transported and undergo a conformational change to transfer the substance across the membrane.

Question 14

Describe active transport across the plasma membrane?

Answer 14

Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
This requires a source of metabolic energy.

Question 15

What is a common source of metabolic energy for active transport?

Answer 15

Hydrolysis of ATP

Question 16

What enzyme hydrolyses ATP?

Answer 16

ATPase

Question 17

What forms the electrochemical gradient?

Answer 17

The concentration gradient and the electrical potential difference.

Question 18

Define the term membrane potential.

Answer 18

Difference in electrical charge on either side of a membrane, creating electrical potential difference

Question 19

What maintains ion gradients?

Answer 19

ion pumps

Question 20

How does the sodium potassium pump work?

Answer 20

• The sodium-potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
• It actively transports sodium ions out of the cell and potassium ions into the cell.
• It has a high affinity for sodium ions within the cell; binding occurs; the pump is phosphorylated by ATP and changes conformation; sodium affinity lowers and are released; High affinity for potassium; binding occurs; dephosphorylation; conformation changes back; potassium released into cell

Question 21

What are the concentrations of Potassium and sodium ions in the cell?

Answer 21

Potassium (K) - HIGH

Sodium (Na) - LOW

Question 22

How many potassium and sodium ions are involved in one cycle of the sodium potassium pump?

Answer 22

• 3 Sodium ions are pumped out

- 2 potassium ions are pumped in

Question 23

What is the importance of the sodium potassium pump in the small intestine?

Answer 23

the sodium gradient created by the sodium-potassium pump drives the active transport of glucose.

Question 24

Describe Glucose symport and the direction of the gradients involved.

Answer 24

The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time, in the same direction.
Sodium Ions enter the cell down their concentration gradient, while glucose is pumped into the cell up its concentration gradient.