Key Area 3: Membrane Protiens

Question 1

Which two molecules can diffuse directly across the phospholipid bilayer?

Answer 1

Oxygen and carbon dioxide

Question 2

Which molecules does the bilayer act as a barrier to?

Answer 2

Molecules that are too large or too polar

Question 3

What are three types of transmembrane proteins?

Answer 3

• channel
• transporter
• receptor

Question 4

What does a channel protein do?

Answer 4

Allows the passive transport of molecules down concentration gradients

Question 5

What does a transporter protein do?

Answer 5

Actively moves molecules across membranes against concentration gradients

Question 6

What does a receptor protein do?

Answer 6

Receives signals and brings about responses

Question 7

How do different cells perform specialised functions?

Answer 7

Different cell types and compartments must contain different channel and transporter proteins as the proteins expressed in the membrane are what the specialised function depends on

Question 8

What protein is involved in the passive transport of water?

Answer 8

Aquaporin

Question 9

How does a gated channel work?

Answer 9

Responds to signal molecules or electrical impulses and is open or closed to prevent or allow transcription

Question 10

What is a ligand-gated channel?

Answer 10

Channel is opened or closed following binding of a ligand

Question 11

What is a voltage-gated channel?

Answer 11

Responds to changes in ion concentration

Question 12

What is facilitated transport?

Answer 12

A passive process which involves a conformational change in the protein

Question 13

Does facilitated transport require energy?

Answer 13

No

Question 14

What is active transport?

Answer 14

A process that requires energy to bring about the necessary conformational change of the transporter protein

Question 15

Does active transport require energy?

Answer 15

Yes, it comes from hydrolysis of ATP

Question 16

What is the difference between intercellular and extracellular?

Answer 16

Intercellular occurs inside a cell and extracellular occurs outside a cell

Question 17

How is a signal passed?

Answer 17

Through a signal transduction pathway

Question 18

What are four potential responses of a cell to a signal molecules?

Answer 18

• activation of special enzymes or G-proteins
• changes in molecule uptake or release
• rearrangement of cytoskeleton
• activation of proteins that regulate gene expression

Question 19

How are ions pumped in Na/KATPase?

Answer 19

Against a steep concentration

Question 20

How do Na/NATPase work?

Answer 20

Three sodium ions bind and phosphate group form ATP binds to the pump then affinity changed back to potassium and sodium is released outside the cell, one potassium ion binds and the phosphate group is released

Question 21

What are four functions of Na/KATPase?

Answer 21

• maintenance of osmotic balance in animal cells
• generation of ion gradients for glucose symport in small intestine
• generation and long terms maintenance of ion gradient for resting potential in neurone
• generation of ion gradient in kidney tubule

Question 22

What is depolarisation of a neutron?

Answer 22

When the charge across the membrane becomes les negative

Question 23

What is nerve transmission?

Answer 23

A wave of depolarisation occurring when membrane potential changes

Question 24

How is nerve transmission initiated?

Answer 24

The binding of a neurotransmitter which opens ligand gated channels in the neutron membrane

Question 25

How do neurotransmitters move?

Answer 25

They diffuse across the synapse

Question 26

What is resting potential?

Answer 26

When the cell is not transmitting signals and is generated and maintained by the action of the sodium potassium pump

Question 27

What is the typical membrane potential in neurons?

Answer 27

60-80mV

Question 28

What are the steps in the transmission of nerve cell?

Answer 28

• resting potential of membrane is stable which is slightly negative inside the neuron
• neurotransmitter binds to ligand-gated channel
• ligand-gated channels open
• neuron becomes less negative
• if threshold is reached, voltage changes an voltage gated channels open
• more sodium ions flood into the neuron
• increases sodium ions causes a wave of depolarisation through the neuron