1. Key Area 3- Membrane proteins

Question 1

Describe the fluid mosaic model

Answer 1

The phospholipid is the basis of the system. The phosphate group is hydrophilic which aligns towards the aqueous cytoplasm and external fluid whilst the fatty acids are non-polar and thus hydrophobic. This part sits inside the bilayer.

Question 2

What do the regions of hydrophobic R groups do?

Answer 2

They allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer

Question 3

What is the function of an integral membrane protein

Answer 3

They interact extensively with the hydrophobic region of the membrane phospholipids

Question 4

What is an example of an integral membrane protein?

Answer 4

transmembrane protein

Question 5

Which membrane protein has hydrophilic R groups on their surface?

Answer 5

Peripheral membrane proteins

Question 6

How are peripheral membrane proteins bound to the surface of membranes?

Answer 6

Mainly by ionic and hydrogen bond interactions

Question 7

What is the function of peripheral membrane proteins

Answer 7

They interact with the surfaces of membrane proteins

Question 8

What is the phospholipid bilayer?

Answer 8

A barrier to ions and most uncharged polar molecules

Question 9

How do small molecules such as oxygen and carbon dioxide pass through the bilayer

Answer 9

By simple diffusion

Question 10

Define facilitated diffusion

Answer 10

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

Question 11

In order to perform specialised functions, different cell types have different…?

Answer 11

channel and transporter proteins

Question 12

What are channel proteins?

Answer 12

Multi-subunit proteins with the subunits arranged to form water filled pores that extend across the membrane. In animal and plant cells, most channel proteins are highly selective

Question 13

Why are some channel proteins gated and change conformation?

Answer 13

To allow or prevent diffusion

Question 14

What are ligand gated channels controlled by?

Answer 14

The binding sequence of signalling molecules

Question 15

What are voltage gated channels controlled by?

Answer 15

Changes in ion concentration

Question 16

What is the role of transporter proteins?

Answer 16

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

Question 17

What is active transport?

Answer 17

It uses pump proteins that transfer substances across the membrane against their concentration gradient

Question 18

What is required for active transport to occur?

Answer 18

A source of metabolic energy

Question 19

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

Answer 19

hydrolyse ATP directly

Question 20

How does ATP hydrolysis provide energy?

Answer 20

By the addition of water to breakdown ATP to ADP and Pi releasing energy

Question 21

What components form the electrochemical gradient?

Answer 21

For a solute carrying a net charge, the concentration gradient and the electrical potential difference combines to form the electrochemical gradient

Question 22

What determines the transport of a solute which carries a net charge?

Answer 22

The electrochemical gradient

Question 23

How is an electrical potential difference (membrane potential) created?

Answer 23

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

Question 24

What is an example of an ion pump?

Answer 24

sodium potassium pump

Question 25

What is an ion pump?

Answer 25

Uses energy from the hydrolysis of ATP to establish and maintain ion gradients

Question 26

What is the function of the sodium potassium pump?

Answer 26

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.

Question 27

Describe the sodium potassium pump process

Answer 27

The pump has a high affinity for sodium ions inside the cell, binding occurs, phosphorylation by ATP, conformation changes, the affinity for sodium ions to decrease thus releasing sodium ions out of the cell. Potassium ions bind outside the cell, dephosphorylation, conformation changes, potasium ions taken into cell, affinity returns to start

Question 28

What happens for each ATP that is hydrolysed

Answer 28

3 sodium ions are transported out of the cell and 2 potassium ions are transported into the cell which establishes both concentration gradients and an electrical gradient

Question 29

How does the sodium potassium pump account for a high proportion of the basal metabolic rate in many organisms?

Answer 29

As it is found in most animal cells

Question 30

In the intestinal epithelial cells in the small intestine, what does the sodium potassium pump generate?

Answer 30

It generates a sodium ion gradient across the plasma membrane which drives the active transport of glucose

Question 31

Describe the transport of glucose through intestinal cells

Answer 31

Sodium ions enter the intestinal cells, down the concentration gradient through a glucose symport channel. The energy from the flow allows the simultaneous transport of glucose into the cell against the concentration gradient. Glucose and sodium ions are thus transported simultaneously (at the same time and in the same direction) by a glucose symport channel.