Cell Signaling

Question 1

Why do cells need to communicate?

Answer 1

Process information

Self preservation

Voluntary movement

Homeostasis

Question 2

What are the 4 types of signalling?

Answer 2

Endocrine

Paracrine

Membrane attached proteins

Autocrine

Question 3

What is endocrine communication?

Answer 3

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

Question 4

Example of endocrine communication.

Answer 4

Hypoglycaemia

• glucagon secreted by alpha cells of Islets of Langerhans
• travels out of pancreas in blood vessels
• stimulates glycogenolysis and gluconeogenisis w/in liver
  —> increasing blood glucose levels

Question 5

What is paracrine communication?

Answer 5

Hormone acts on adjacent cell

Question 6

Example of paracrine communication.

Answer 6

Hyperglycaemia

• increased blood glucose - insulin secreted by beta-cells in Islets of Langerhans
• insulin has paracrine effects —> inhibiting glucagon secretion
• also has endocrine effects on the liver

Question 7

What is membrane attached protein signalling?

Answer 7

Plasma membrane proteins on adjacent cells interacting

Question 8

Example of membrane attached protein signalling

Answer 8

Blood borne virus —> detected in blood by antigen presenting cell

APC digests pathogen —> express major histo-compatibility class II molecules on surface

Circulating T-lymphocyte engages with MHC molecule through T-cell receptor interaction

Question 9

What is autocrine communication?

Answer 9

Signalling molecule acts on the same cell

Question 10

Example of autocrine signalling

Answer 10

Activates TCR will initiate a cascade o reaction within T-cell

Activated T-cell expresses interleukin-2 receptor on surface

Activated T-lymphocyte also secretes IL-2 which:
—> binds to IL-2 receptor on the same cell
—> binds to IL-2 receptor on adjacent activated T-cell

Question 11

Process of neurotransmission.

Answer 11

1. Propagation of the action potential
2. Neurotransmitter release from vesicle
3. Activation of postsynaptic receptors
4. Activation of postsynaptic receptors

Question 12

What are the 4 types of receptors?

Answer 12

Ionotropic

G-protein coupled

Enzyme-linked

Intracellular

Question 13

What is an ionotropic receptor

Answer 13

Ligand binding —> opens ion permeable pore traversing the membrane

Question 14

Events in an ionotropic receptor.

Answer 14

Ligand binds to the receptor protein

Change in conformation of channel protein —> opens pore

Pore allow soins to move in our out of cell

Question 15

Ionotropic receptor example

Answer 15

Nicotinic Acetylcholine
Ligand: ACh
Location: skeletal muscle
Physiological effect: muscle contraction

Question 16

What is a G-protein coupled receptor?

Answer 16

Ligand binding —> activates intracellular G-protein

Question 17

Events in a G-protein coupled receptor

Answer 17

7-TM receptor & heterotrimeric G-protein are inactive

Ligand binding —> changes conformation of receptor

Unassociated G-protein binds to the receptor —> GDP is exchanged for GTP

G-protein dissociates into two active components:
—> alpha - subunit
—> beta gamma - subunit
bind to their target proteins

Internal GTPase activity on alpha - subunit dephosphorylates GTP —> GDP

Alpha - subunit dissociates from target protein —> inactive again

Receptor remains active as long as ligand is bound and can activate further heterotrimeric G-proteins

Question 18

G-protein coupled receptor example

Answer 18

Gs protein linked receptor
—> stimulates adenylyl cyclase
—> beta-adrenergic receptor

Gi protein linked receptor
—> inhibits adenylyl cyclase
—> M2-muscarinic receptor

Gq protein linked receptor
—> stimulates phospholipase C
—> AT-1 angiotensin receptor

Question 19

What is an enzyme linked receptor?

Answer 19

Ligand binding —> receptor clustering —> activates internal enzymes

Question 20

Events of an enzyme-linked receptor

Answer 20

Ligand binding

Receptor clustering activates enzyme activity w/in cytoplasmic domain

Enzymes phosphorylate receptor

Phosphorylation —> binding of signalling proteins to cytoplasmic domain

These signalling proteins —> recruit other signalling proteins —> signal generated in cell

Question 21

Examples of enzyme-linked receptor

Answer 21

Insulin receptor

Question 22

What is an intracellular receptor?

Answer 22

Membrane permeable ligand binds to receptor inside cell

Question 23

Events in an intracellular receptor

Answer 23

Type 1 - Cytoplasmic

Located within the cytosolic compartment

Associated with chaperone molecules (heat
shock proteins, hsp)

Hormone binds to receptor ® hsp dissociates

2 hormone bound receptors form a
homodimer.

The homodimer translocates to the nucleus —> binds to DNA

Type 2 - Nuclear

Located within the nucleus

Binding of hormone ligand —> transcriptional regulation

Question 24

Example of intracellular receptors

Answer 24

Type 1: glucocorticoid receptor
Ligand: cortisol, corticosterone
Physiological effect: lower immune response, more gluconeogenisis

Type 2: thyroid hormone receptor
Ligand: thyroxine (T4), triiodothyronine (T3)
Physiological effect: growth and development