Intercellular Signalling

Question 1

What is a ligand and why is it result in cell communication? (2)

Answer 1

It is a signalling molecule which binds to its corresponding receptor.

This receptor is in turn coupled to an intracellular signalling pathway which is activated and leads to action within cell.

Question 2

Why might a receptor become unresponsive to a ligand? (3)

Answer 2

1. The receptor might be present but not functional.
2. The receptor might be inactivated by another signalling system.
3. The receptor might become unavailable following binding.

Question 3

What are the 3 main categories of Membrane Receptors?

Answer 3

1. Receptors linked to Ion Channels
2. Receptors linked to Enzymes
3. G protein coupled Receptors (GPCR)

Question 4

What type of molecules can cross the cell membrane to bind to receptors in cytosol/nucleus? (2)

Answer 4

1. Small Molecules e.g Nitric Oxide

2. Hydrophobic molecules (e.g steroid hormones, thyroxine)

Question 5

What is the difference of adrenaline action in smooth muscle cells in the vessels supplying gut compared to smooth muscle cells in blood vessels supplying muscles? (2)

Answer 5

The difference is due to different ADRENERGIC receptors in both areas.

1. In gut, adrenaline makes smooth muscle contract
2. In Muscles, adrenaline make smooth muscles relax.

Question 6

What is an example of a signalling molecule that can activate different receptor types? What receptors are involved? (3)

Answer 6

1. Acetylcholine can attach to Ion channel linked channels and GPCRs.

• In Salivary glands causes secretion (GPCR)
• In Heart pacemaker cell - Decreases firing rate
• In Skeletal Muscle - Causes contraction (Na+/K+ ion channel)

Question 7

What are the types of Signalling, are they long or short range (5)

Answer 7

Mneumonic: JAPEN

Endocrine Signalling is only long range (but slow).

1. Juxtacrine Signalling
2. Autocrine Signalling
3. Paracrine Signalling
4. Endocrine Signalling
5. Neuronal Signallin

Question 8

What type of substance is released in Endocrine Signalling, how do they work? (2)

Answer 8

1. Hormones
2. They are released into bloodstream, coming into contact with most cells. However, only act in cells with correct receptor to interpret signal.

Question 9

Give 2 examples of Endocrine Signalling and corresponding target cell (2)

Answer 9

1. Insulin (from beta cells in the pancreas) /glucagon (from alpha cells in the pancreas) in glucose control.
2. Cortisol in stress response - The glucocorticoid receptor on cells can suppress or activate gene expression which affects metabolic and immune response.

Question 10

For diseases that can trigger based on stress response (Psoraisis, Ulcerative colitis, Asthma, Allergic reactions); What are some drugs (synthetic hormones that can activate Glucocorticoid receptor)

Answer 10

1. Hydrocortisone
2. Dexamethasone
3. Prednisolone

Question 11

How does Paracrine Signalling work? Give some examples (2)

Answer 11

Signalling molecules are released and diffuse locally to neighbouring cells.

E.g Cytokines, Histamine, Nitric Oxide

Question 12

Nitric Oxide:
How is it produced? (1)

How does it work? (3)

Answer 12

1. It is produced in blood vessel endothelial cells when stimulated by acetylcholine.
2. It diffuses into nearby smooth muscle cells and activates GUANYLATE CYCLASE enzyme.
3. NO binding to Guanylate cyclase converts GTP to cyclic GMP.
4. This relaxes the smooth muscle, increasing blood flow. This is shortlived, with cGMP converted back to GMP.

Question 13

What causes Angina? (1) How is it treated? (2)

Answer 13

1. Inadequte blood flow to heart muscles.
2. Adminstration of NITROGLYCERIN
3. NITROGLYCERIN is converted into NO by mitochondrial ALDEHYDE DEHYDROGENASE in heart smooth muscles to improve blood flow.

Question 14

How does Neuronal Signalling work? Give some examples. (2)

Answer 14

Transport of Neurotransmitters across synpases.

e.g Adrenaline, noradrenaline, Acetylcholine, Endorphins etc.

Question 15

How does Autocrine Signalling work? What are some examples. (2)

Answer 15

1. When a cell secretes signals which act on its own receptors.
   e. g Positive feedback loop: Cytokines can activate autocrine signalling to produce more cytokines.

Epidermal Growth Factor (EGF) in cancer.

Question 16

How does Juxtacrine Signalling work? What are two ways this can happen? (2)

Answer 16

Cells signal by coming intact with another cell.

This can occur through an Ion channel in membranes (GAP signalling) or LIGANDS directly binding.

Question 17

Describe the structure of GAP junctions in Juxtacrine Signalling. What are examples of GAP signalling? (3)

Answer 17

1. Formed by channels called Connexons, which consist of 6 protein subunits (from a pool of up to 20 subunits).
2. Gap Signalling is used in heart cells to allow electric excitation to pass quickly through tissue.
3. Gap Signalling is used in pregnancy, to help coordinate uterine contractions.

Question 18

What is an example of Ligand binding in Juxtacrine signalling? (1)

Answer 18

T cell receptor in Antigen presentation.

Question 19

Why do cells need to communicate? (4)

Answer 19

1. Communication with neighbouring cells
2. Immune Response
3. To induce/stop Growth
4. Metabolism and nutrition.