Communication between cells

Question 1

What are the 4 main reasons for inter-cell communication?

Answer 1

Information processing
Self-preservation
Voluntary movement
Homeostasis

Question 2

Explain an example of endocrine signalling

Answer 2

Glucose homeostasis - maintenance of correct blood sugar - Hypoglycaemia

1) Glucagon secreted by αcells in pancreas travels in blood vessels
2) Stimulates glycogenolysis and gluconeogenesis within liver to increase blood sugar levels

Question 3

Define endocrine cell signalling

Answer 3

Hormone travels within blood vessels to act on a distant target cell

Question 4

Define paracrine signalling

Answer 4

Hormone acts on adjacent cells

Question 5

Explain an example of paracrine signalling

Answer 5

Hyperglycaemia

1) Increased blood glucose causes insulin secretion from βcells in pancreas
2) Insulin has paracrine effects on inhibiting glucagon secretion

Question 6

Define autocrine signalling

Answer 6

Signalling molecule acts on itself

Question 7

Explain an example of autocrine signalling

Answer 7

1) Activated T cell receptor initiates cascade of reactions within T cell
2) Activated T cell expresses interleukin-2 receptor on surface and also secretes
3) Secreted IL2 binds to same cell’s IL2R

Question 8

Define signalling between membrane attached proteins

Answer 8

Plasma membranes of adjacent proteins interacting

Question 9

Explain an example of signalling between membrane attached proteins

Answer 9

1) Blood borne virus detected by antigen presenting cell
2) APC digests pathogen, expresses MHC class II molecules on surface
3) Circulating t-lymphocyte engages with MHC through TCR interaction

Question 10

Explain the signal transduction events involving ionotropic receptors

Answer 10

Ligand binds to receptor protein
Change in conformation of channel protein opens pore
Pore allows movement of ions according to their respective concentration gradients
e.g. Nicotinic Acetylcholine, GABAa

Question 11

Explain the signal transduction events involving g-protein coupled receptors

Answer 11

1)7-TM receptor and heterotrimeric G-protein inactive
2)Ligand binding changes receptor conformation and causes binding of the unassociated G-protein
3)Bound GDP replaced with GTP
4)G-protein dissociates and α and βγ subunits bind to their target proteins
5)Internal GTPase activity on α subnunit dephosphorylates GTP
6)α Subunit dissocates from target protein so inactive again
7)Receptor remains active as long as ligand is bound
it can activate further heterotrimeric G proteins

Question 12

Explain enzyme linked signal transduction

Answer 12

1) Ligand binds causing clustering of receptors
2) Activates enzyme activity within cytoplasmic domain
3) Enzymes phosphorylate receptor causing binding of signalling proteins to cytoplasmic domain
4) Signalling proteins recruit other signalling proteins
5) Signal is generated within cell
e. g. Insulin receptor, ErbB receptors

Question 13

Explain type 1 (cytoplasmic) intracellular signal transduction

Answer 13

In cytosolic compartment, associated w chaperone molecules

1) Hormone binds to receptor, chaperone molecule dissociates
2) 2 hormone bound receptors form a homodiner
3) Homodimer transolcates to the nucleus and binds with DNA
e. g. Glucocorticoid receptor

Question 14

Explain type 2 (nuclear) intracellular signal transduction

Answer 14

Binding of hormone ligand within nucleus causes transcriptional regulation
e.g.Thyroid hormone receptor