11. Cell communication

Question 1

What is a receptor?

Answer 1

A molecule on the cell’s surface or within a cell that recognises and binds with a specific signaling molecule that may lead to a cellular response

Question 2

What are the basic steps in a signal transduction pathway?

Answer 2

1. A signalling molecule or land binds to a receptor
2. Transduction (conveying message to cell)
3. Response (effects)

Question 3

What is hormone action?

Answer 3

Where signaling molecules/ligands act at a distance, travelling via the blood to the cells or tissues

Question 4

What is autocrine action?

Answer 4

Signalling molecules bind to receptors located on the cell that secreted it

Question 5

What is paracrine action?

Answer 5

Signalling molecules that bind to receptors on nearby cells

Question 6

How do paracrine/autocrine action ligands travel?

Answer 6

They do not enter the blood and travel only in the interstitial fluid

Question 7

How can you classify receptors by location?

Answer 7

Intracellular receptors can be cytoplasmic or nuclear

Question 8

What are the characteristics of membrane bound receptors?

Answer 8

• extracellular domain (binds signaling molecule)
• A transmembrane region (anchors it to the plasma membrane)
• An intracellular region (which plays an important role in the response to signal)

Question 9

What are some examples of membrane bound receptors?

Answer 9

1. Ligand - gated ion channel receptor
2. G-protein linked receptor
3. Protein kinase receptor

Question 10

What is the way to activate a protein-receptor protein or cellular protein?

Answer 10

The exchange of GDP for GTP

Question 11

How does a g-protein linked receptor function?

Answer 11

• When a signalling molecule binds to the receptor, there is a conformational change in the receptor
• The intracellular domain of the receptor exchanges GDP for GTP and activates the G protein
• THe subunit of the G protein containing the GTP moves through the membrane and binds to an effector molecule
• GTP is hydrolysed back to GDP

Question 12

What does PKA do?

Answer 12

• Protein kinase a
• AN enzyme in the cascade that activated PPK (phosphorylase kinase)
• Also inhibits glycogen synthesise so there are two mechanisms that help released stored glucose quickly from he liver when needed

Question 13

What happens to the signal after a normal cell has responded?

Answer 13

Ras is a family of proteins, known as small GTPases found in most cell types

• Receptor activation leads to second messenger signalling that activates RAS via GDP/GTO exchange
• After a brief time in the activated state, Ras returns to its inactive form
• THE SIGNAL IS REGULATED/SWITCHED OFF UNDER NORMAL CONDITIONS