Unit 1.4 - Communication and Signalling

Question 1

What are receptor molecules?

Answer 1

Proteins with a binding site for a specific signal molecule

Question 2

What response does binding create?

Answer 2

It changes the conformation of the receptor, which initiates a response within the cell

Question 3

Why do only target cells respond to a specific signal?

Answer 3

Only target cells have receptor molecules for the signalling molecule

Question 4

Describe a hydrophobic signalling molecule (lipid-soluble? passes through cell membrane? location? types of signals? examples?)

Answer 4

Lipid soluble - yes
Passes through cell membrane - yes
Location - cytosol
Types of signals - steroid hormones
Examples - oestrogen and testosterone

Question 5

Describe a hydrophilic signalling molecule (lipid-soluble? passes through cell membrane? location? types of signals? examples?)

Answer 5

Lipid soluble - no
Passes through cell membrane - no
Location - extracellular membrane
Types of signals - peptide hormones
Examples - insulin

Question 6

What is a hormone-receptor complex?

Answer 6

When a steroid hormone binds to a specific receptor

Question 7

What is a hormone response element?

Answer 7

The DNA that the hormone-receptor complex binds to when it enters the nucleus

Question 8

What protein is involved with transduced hydrophilic signals?

Answer 8

G-proteins

Question 9

Describe the stages of signal transduction.

Answer 9

1 - Hydrophilic signalling molecule binds to the receptor. The signal is transduced.
2 - Binding of a ligand causes a conformational change, activating a G-protein. This can now bind to the target protein.
3 - Intracellular signalling pathway is now activated.

Question 10

What is an action potential?

Answer 10

A wave of electrical excitation along a neurons plasma membrane

Question 11

What are neurotransmitters?

Answer 11

Ligand-gated ion channels on synapses

Question 12

How do neurotransmitters initiate a response and what does this cause?

Answer 12

1 - binding to their receptors
2 - changing conformation
3 - opening their channel and allowing Na+ ions through
This causes depolarisation of the resting potential

Question 13

How can an actional potential take place?

Answer 13

If sufficient ion movement occurs the entry of positive ions triggers the opening of voltage-gated sodium channels, leading to depolarisation of neighbouring regions and so in, in a domino effect

Question 14

What happens when the action potential reaches the end of the neuron?

Answer 14

Vesicles containing neurotransmitters fuse with the membrane, the neurotransmitter is released and stimulates a response in the connecting cell

Question 15

How is the resting membrane potential restored?

Answer 15

When the voltage reaches a high level, the voltage-gated Na+ channels close and return to their original conformation. Voltage-gated K+ channels then open allowing K+ ions to diffuse out of the cell, restoring the resting membrane potential. Na+ channels are in their original conformation and can respond to further depolaisation

Question 16

How are blood glucose levels maintained?

Answer 16

By a negative feedback system

Question 17

How does glucose pass into the cells?

Answer 17

By travelling (facilitated diffusion) through transporter proteins called GLUT4 glucose transporters

Question 18

What does the binding of insulin to its receptor cause?

Answer 18

A conformation changes that triggers phosphorylation of the receptor, this starts a cascade of kinase phosphorylation which eventually leads to GLUT4-containing vesicles to be transported to cell membranes

Question 19

What effect does the extra GLUT4 transporters have on glucose levels?

Answer 19

It allows them to be controlled

Question 20

Describe type 1 and 2 diabetes

Answer 20

Type 1 - caused by failure to produce insulin and is often genetic
Types 2 - caused by loss of receptor function and generally associated with lifestyle

Question 21

What part of the eye is responsible for detecting light?

Answer 21

The retina

Question 22

Describe the function of rods and cones in the eye

Answer 22

Rods - function in dim light but don’t allow colour perception
Cones - responsible for colour perception but require bright light to function

Question 23

Where is rhodopsin embedded?

Answer 23

The membranes of rod cells

Question 24

Why do rod cells have high sensitivity at low light intensities?

Answer 24

The protein cascade provides a high degree of amplification

Question 25

Describe the process of rhodopsin and nerve impulse

Answer 25

1 - photon of light is absorbed by retinal, conformation change in rhodopsin
2 - changed rhodopsin activates hundreds of G-proteins (transducin) — each one actives a PDE
3 - Each activated PDE catalyses hydrolysis of cGMP so the Na+ channels close
4 - If there is a sufficient build up of the Na+, the membrane becomes hyperpolarised and a nerve impulse is generated

Question 26

In cone cells, what gives a range of photoreceptor proteins? (each with a particular sensitivity to specific wavelengths)

Answer 26

Different forms of opsin.