Lecture 21: Cell Communication & Receptor Families

Question 1

why is cell communication important?

Answer 1

cells in the body need to communicate with each other in order for the body to function as a whole organism, the body to sense the environment and the body to respond to the environment.

Question 2

what are two types of local signalling, function and example?

Answer 2

paracrine signalling; one cell releases a signalling molecule that acts on nearby cells e.g this is used in the immune system to trigger an immune response.

synaptic signalling; the main method of communication between neurons e.g. to generate thoughts and memories in our brain.

Question 3

what is a type of long distance signally, function and example?

Answer 3

endocrine signalling; released from a cell into the blood stream, termed a hormone and travels around the blood stream until it finds a target cell. e.g. to signal to cells to take up glucose after a meal (insulin).

Question 4

what are the 3 stages of cell signalling?

Answer 4

1. reception; the signalling molecule binds to a specific receptor which is located on the cells surface.
2. transduction; a signalling pathway is initiated in the cytoplasm.
3. response; a cellular response is activated e.g. to activate an enzyme

Question 5

what are four types of receptors?

Answer 5

cell surface receptors;
ligand gated ion channels - neurotransmission, hormones

g protein coupled receptors; neurotransmission, hormones

tyrosine kinase receptors; hormones

intracellular receptor:
4. steroid receptor; hormones

Question 6

what are ligand gated ion channels?

Answer 6

they are ion channels in the membrane that are opened by the binding of a ligand i.e. a neurotransmitter/chemical messenger
- this generates a very fast response
- this changes the voltage across the membrane during synaptic transmission, triggering IPSPs and EPSPs.

Question 7

what is a G protein-coupled receptors?

Answer 7

a very large family of receptors that is involved in neuronal and hormonal signalling (for example, sensing light in the eyes and taste in the mouth). this receptor causes a cascade of effects within the cell and takes 100ms - 2s in duration.

Question 8

what is phosphorylation?

Answer 8

phosphorylation controls the activity of proteins as kinases are enzymes that add phosphate groups to other proteins.

Question 9

what are phosphatases?

Answer 9

phosphatases are enzymes that remove phosphate groups to other proteins.

Question 10

what is the process of G protein-coupled receptor-mediated activation of the adenylate cyclase/protein kinase A pathway?

Answer 10

1. signally starts through the binding of the neurotransmitter (or hormone) to the G protein-coupled receptor
2. a G protein is activated by the molecule GPT replacing GDP
3. the enzyme adenylate cyclase is activated by the G protein
4. adenylate cyclase converts ATP to cAMP
5. cAMP acts by opening or closing ion channels, activating enzymes, and activating gene transcription.

Question 11

what is signal amplification?

Answer 11

amplification occurs during G protein coupled receptor signalling. amplification enables a low concentration of the chemical messenger to trigger a pronounced cellular response.

Question 12

what are tyrosine kinase receptors?

Answer 12

they are membrane (cell surface) receptors that respond to hormones only. they are important for slower processes such as metabolism and growth. e.g. acted upon by insulin to trigger glucose uptake into cells. if this goes wrong, diabetes occurs.

Question 13

tyrosine kinase receptor process steps

Answer 13

1. tyrosine kinase receptors exist as two monomers in the inactive state
2. activation by signalling molecules causes the dimerization of the monomers
3. each part of the tyrosine kinase molecule phosphorylates the other part as tyrosine sites, activating itself
4. this then activates other proteins to cause cellular effects e.g. a phosphorylation cascade

Question 14

how do ion channel linked receptors mediate very rapid responses?