Module 7 Intercellular Communication

Question 1

Why is cellular communication important?

Answer 1

Because cellular functions that are vital for life are regulated by other cells, thus producing a physiological response.

Question 2

What happens if cellular communication is disrupted?

Answer 2

A break in homeostasis

Question 3

Intercellular Communication occurs via: (2)

Answer 3

• Direct contact (eg. Gap junctions)

- Chemical messengers (eg. Hormones)

Question 4

What are integrins?

Answer 4

Transmembrane proteins that help in Intercellular packaging

Question 5

List the 3 membrane junctions

Answer 5

• Desmosomes
• Tight junctions
• Gap junctions

Question 6

What are the functions of each membrane junction?

Answer 6

Desmosome: Holds together cells by thin linker proteins (cadherins)
Tight junction: Prevents molecules from passing through (impermeable)
Gap junction: Allows small substances to pass through by hollow cylinders called connexons

Question 7

Give an example of the role of tight junctions in brain function

Answer 7

Blood-Brain Barrier
(Endothelial cells of the capillaries in the brain are attached firmly together, unlike other capillaries in the body) this is to shield brain tissues from toxins.

Question 8

What are the 5 basic components involved in Intercellular Communication?

Answer 8

1- Secretory cells
2- Communicating cells (ligands)
3- Specific receptors
4- Signal transduction process
5- Signal response

Question 9

What are paracrine agents?

Answer 9

Messenger molecules that act on neighbouring cells (eg. Neurotransmitters, histamine)

Question 10

What are autocrine cells?

Answer 10

Cells that releases a signal molecule on itself

Question 11

What are endocrine cells?

Answer 11

Cells that releases a signal molecule to blood vessels that will carry it to target cells.

Question 12

What are the 4 types of chemicals that can serve as extracellular signalling molecules?

Answer 12

• Amines (eg. Epinephrine)
• Peptides (eg. Insulin)
• Steroids (eg. Aldosterone)
• Other small molecules (eg. AA)

Question 13

What does the magnitude of target cells depend on?

Answer 13

• Concentration of messenger
• No. of receptors present on target cell
• Affinity of receptor for messenger

Question 14

What are the 2 types of receptors?

Answer 14

• Intracellular (Lipid-soluble)

- Plasma membrane (Lipid-insoluble)

Question 15

What is a signal transduction?

Answer 15

Events occurring after receptor activation

Question 16

Example of second messengers?

Answer 16

cAMP, IP3, DAG, Ca2+

Question 17

What are the 6 steps of signalling event?

Answer 17

Recognition, transduction, Transmission, modulation, response, termination

Question 18

What are the 4 groups of plasma membrane receptors?

Answer 18

• Receptors that function as ion channels (Ionotropic)
• Receptors that function as enzymes
• Receptors that interact with cytoplasmic JAK
• Receptors that interact with G-protein

Question 19

Ionotropic Receptors can be fast or slow. Describe each.

Answer 19

Fast channels: receptor is part of the channel

Slow channels: receptor couples by G-protein

Question 20

Examples for plasma membrane Ionotropic receptors

Answer 20

Receptors for Ach, GABA, glycine, serotonin

Question 21

What are the 2 major enzymes that are involved in receptors that function as enzymes?

Answer 21

• Tyrosine kinase

- Guanylyl cyclase

Question 22

What are the functions of protein kinases & Guanylyl cyclase?

Answer 22

P.K: Phosphorylase proteins (activating it)
G.C: Catalyses the formation of cGMP
These two act as 2nd messengers to activate signalling events

Question 23

What is JAK?

Answer 23

It is an Intercellular enzyme that is not a part of the receptor, but resides in the cytoplasm (PK is part of receptor)

Question 24

Mechanism of action of JAK

Answer 24

A first messenger binds to JAK & changes its confirmation to activate the kinase. This leads to phosphorylation of Tyrosine residues of receptors which, in turn, could phosphorylase many Intercellular proteins.

Question 25

When G-protein is binded with GDP, it is inactive.

What is exchanged with GDP to activate the G-protein?

Answer 25

GTP (binds to the alpha-subunit of G-protein & causes the beta and gamma subunits to dissociate) this stimulates Intercellular response

Question 26

What are the 3 classes of G-protein & their function?

Answer 26

G-alpha s: Stimulates adenylyl cyclase
G-alpha q: Stimulates PLC-beta which breaks bown PIP3 to DAG & IP3
G-alpha i: Inhibits adenylyl cyclase

Question 27

Example of GPCR

Answer 27

Catecholamine receptor

Question 28

Role of cAMP

Answer 28

Acts as a 2nd messenger to trigger events leading to cell’s response to 1st messenger

Question 29

How is the cation of cAMP terminated?

Answer 29

By its breakdown to non-cyclic AMP, which is catalysed by Phosphodiesterase

Question 30

Briefly explain the mechanism of action of cAMP

Answer 30

A messenger binds to a receptor > Several G-protein are activated > Each G-protein activates an adenylyl cyclase > Each adenylyl cyclase activates hundreds of cAMP > Each cAMP activates a PKA > Each PKA activates hundreds of proteins

Question 31

Function of DAG

Answer 31

Activates a particular PKC, which phosphorlyates a large number of other proteins leading to cell’s response to 1st messenger

Question 32

Function of IP3

Answer 32

Acts by binding to calcium channels & opens them. This increase in Ca2+ continues the sequence of events leading to cell’s response to 1st messenger. Eg. Muscle contraction

Question 33

What is the most widespread 2nd messenger?

Answer 33

Ca2+

Question 34

Explain the mechanism of action Ca2+

Answer 34

Calcium binds to calmodulin, changing its configuration. This activates a calmodulin-deoendant kinase and activates proteins.

Question 35

How does receptor activation cease?

Answer 35

By a decrease in the concentration of 1st messenger molecules in the region of the receptor.