Cell Signalling

Question 1

Why do cells communicate?

Answer 1

Essential for survival:
-blood glucose
-infection
-wounding
-time to contract
-time to divide
-time to die

Question 2

What are ligands

Answer 2

Signalling molecules-> hormones, neurotransmitters, cytokines, chemokines etc

Question 3

5 different types of cell signalling:

Answer 3

• direct signalling
• paarcrine signalling
• endocrine signalling
• synaptic signalling
• autocrine signalling

Question 4

What is direct signalling?

Answer 4

Cells can share molecules between each other
(Plasma membrane- gap junctions)

Question 5

What is paracrine signalling?

Answer 5

Signalling molecule is released by a cell to an adjacent cell (immune system cell, eg. Vascular endothelial growth factor)

Question 6

What is endocrine signalling?

Answer 6

Gland secretes hormone directly into the blood, travels through the blood to an organ further away, target organ responds to stimuli (testosterone)

Question 7

What is synaptic signalling?

Answer 7

Nerve cell releases a neurotransmitter, acetylcholine travels across synaptic gap and binds to receptors

Question 8

What is autocrine signalling?

Answer 8

Cell will release a hormone/signal, and binds to receptors on itself. Immune cell releases cytokines- binds to receptors on itself as well as surrounding cells. Leads to changes within the cell itself

Question 9

What are the four receptor classes that a signal binds to:

Answer 9

• steroid receptor
• G-protein coupled receptor
• Ligand-gated ion channels
• Enzyme linked

Question 10

What are the responses to cell signalling?

Answer 10

Change protein production
Change protein activity

Question 11

What does changing protein production do?

Answer 11

Switch genes on and off

Question 12

What does changing protein activity do?

Answer 12

Turn enzymes on and off
Reorganise the cytoskeleton

Question 13

Outline steroids (testosterone)

Answer 13

-all come from cholesterol
-steroid binds to enhancer regions within the DNA
-made up of carbon rings
-hydrophobic
-lyophilic (can pass through cell membrane)

Question 14

Outline steroid receptors:

Answer 14

• when steroids bind to steroid receptors-> localised to the nucleus
• steroid receptors act as transcription factors-> move to nucleus-> turn on genes-> bind to enhancer region on DNA-> promotes formation of RNA polymerase complex-> production of mRNA
• leads to synthesis of proteins

Question 15

Outline G-protein coupled receptors:

Answer 15

-found in cell membrane
-1 in 20 human genes code for a GPCR/ 800-1000 receptors
-40% of pharmaceuticals bind to GPCRS
-serpentine receptors-> span the membrane 7 times
-heterotrimeric-> 3 different subunits

Question 16

Outline what adrenergic is

Answer 16

Contrasting effects on different receptors depending on the tissue - coupled with GTP- binding proteins
Beta receptors on the heart
Alpha one receptors found in the gut + sympathetic target tissues
Alpha two receptors mainly on the digestive organs

Question 17

Outline kinases role:

Answer 17

-kinases add phosphate to macromolecules
-phosphorylase specific amino acids within the protein- serine,threonine
-change activity of target proteins and lead to an effect in the cell

• tyrosine phosphotases are a subset of serine/threonine protein phosphotases

Question 18

How signals are turned off

Answer 18

cAMP gets broke down by enzyme called phosphodiesterase into AMP
Inhibit phosphodiesterase by enzyme PD3, switch processes off

Question 19

Outline ligand gated ion channels

Answer 19

Ligands bind to their receptor that has a pore/channel, when activated ions rush in.
All cells have a resting membrane potential due to ions travelling through pores through this membrane

Question 20

In a gradient potential how many sodium ad potassium ions are pumped in and out

Answer 20

3 sodium out
2 potassium in

Question 21

Outline enzyme linked receptors

Answer 21

Receptors signal for kinase cascades- enzymes that phosphorylase macromolecule, altered activity in the protein, add a phosphate group onto a transcription factor -> synthesis of a new protein