Cell Signalling

Question 1

Why do cells need to communicate?

Answer 1

Process information: sensory stimuli e.g. sight and sound
Self preservation: identify danger e.g. spinal reflex and sympathetic nervous system (fight or flight)
Voluntary movement
Homeostasis: thermoregulation, glucoses regulation

Question 2

What is the physiological response to hypoglycaemia?

Answer 2

Glycogen breakdown

Gluconeogenesis

Question 3

How does glycogenolysis occur?

Answer 3

Glucagon secrete by alpha cells of islets
Travels out of bloodstream into liver
Stimulates glycogenolysis and glucogenesis in liver

Question 4

What is endocrine signalling?

Answer 4

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

Question 5

Name 2 examples of endocrine signalling?

Answer 5

Insulin produced in pancreas acts of muscles and adipose

Adrenaline produced in adrenal glands acts in various places including airway

Question 6

What happens when you are hyperglycaemic?

Answer 6

More glucose uptake
Reduced glycogenolysis
Reduced gluconeogenesis

Question 7

How does the body respond to hyperglycaemia?

Answer 7

Insulin secreted by beta cells in islets of langerhans
Insulin inhibits glucagon secretion (paracrine effect)
Also has endocrine effects on the liver

Question 8

What is paracrine signalling?

Answer 8

When a hormone acts on an adjacent cell

Question 9

Give 2 examples of paracrine signalling?

Answer 9

Nitric oxide produced by endothelial cells in blood vessels causing vasodilation
Osteoclasts activating factors produces by adjacent osteoblasts

Question 10

What is the third type of signalling?

Answer 10

Signalling between membrane attached proteins

-plasma membrane proteins on adjacent cells interacting

Question 11

Give an example of membrane attached protein signalling

Answer 11

HIV GP120 glycoproteins + CD4 receptors on T-lymphocytes

Question 12

What is autocrine signalling?

Answer 12

Signalling molecules acts on same cell

Question 13

Give two example of autocrine signalling?

Answer 13

Acetylcholine –> presynaptic M2 receptors prevent further release
Growth factors from tumour cells, more and more produced

Question 14

What are the four types of inter-cellular signalling?

Answer 14

Endocrine
Paracrine
Membrane attached proteins
Autocrine

Question 15

What type of communication is transmission at a neuromuscular junction?

Answer 15

Specialised type of paracrine communication

Question 16

What is step one of neurotransmission?

Answer 16

Propagation of the action potential

Question 17

What is step 2 of neurotransmission?

Answer 17

Neurotransmitter release from vesicles

Question 18

What is step 3 of neurotransmission?

Answer 18

Activation of postsynaptic receptors

Question 19

What is an ionotropic receptor?

Answer 19

Receptor that binds ligands and opens ion permeable pore traversing the membrane

Question 20

what is a G-protein coupled reactor?

Answer 20

Ligand binds and activates an intra-cellular G-protein

Question 21

What is an enzyme-linked receptor?

Answer 21

Two hormones act on the external surface of the receptor cause clustering and activates internal enzymes

Question 22

What is an intracellular receptor?

Answer 22

A membrane permeable ligand binds to receptor inside cell

Question 23

How does an ionotropic receptor work?

Answer 23

Hormone acts on external surface
Conformational change of channel protein opening a pore
Pore allow ions to move in or out of cell according to respective conc. gradients

Question 24

Name an example of an ionotropic receptor

Answer 24

Nicotinic Acetylcholine binds to skeletal muscles causing muscle contraction
GABA receptor

Question 25

How do G-protein coupled receptors work?

Answer 25

GPCR and heterotrimeric (made of 3 different components) G-protein are inactive
Hormone binds causing conformational change of G-protein
Allows the heterotrimeric G-protein binds to the receptor
Bound GDP molecule is phosphorylated to GTP
Or more correctly GDP is exchanged for GTP
G-prtoein dissociates into two active components
1. alpha
2. betagamma
They bind to their target proteins
Activate a cascade

Question 26

What are the three types of G-protein linked receptors?

Answer 26

Gs- stimulates
Gi- inhibits
Gq

Question 27

How do enzyme-linked receptors work?

Answer 27

Two ligands bind to the outside of the receptor
Receptor clustering activated enzyme activity within cytoplasmic domain
Enzymes phosphorylates receptors
Phosphorylation causes binding of signalling proteins to cytoplasmic domain
Signalling proteins recruit other signalling proteins and a signal is generated within the cell

Question 28

Give an example of an enzyme-linked receptor?

Answer 28

Insulin receptor that stimulates glucose uptake

Question 29

How do cytoplasmic intracellular receptors work?

Answer 29

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

Question 30

How do nuclear intracellular receptors work?

Answer 30

Located within the nucleus

Binding of hormone- transcriptional regulation

Question 31

Give an example of a cytoplasmic intracellular receptor

Answer 31

Glucocorticoid receptor,
binds cortisol and corticosterone
decrease immune response
increases gluconeogenesis

Question 32

Give an example of a nuclear intracellular receptor

Answer 32

Thyroid hormone receptor
binds thyroxine and triiodothyronine
growth and development