Cell Signalling 2

Question 1

What causes a secondary messenger to be released when a molecule binds to a receptor?

Answer 1

The protein binds to a G-protein coupled receptor and causes a conformational change situating the secondary messengers.

Question 2

What are the 4 types of receptors?

Answer 2

G protein coupled receptors (single chain of amino acids), intrinsic receptors (2 come together to form a dimer), ion channel receptors and DNA binding receptors (a dimer)

Question 3

Briefly describe the process when a ligand binds to a receptor

Answer 3

The ligand binds to a receptor and a conformational change occurs, exposing the G - protein. The G - protein bind to the receptors once the agonist has bound. Exchange of GDP for GTP on the G - protein. Secondary messengers are released.

Question 4

What are the 7 cellular location of receptors?

Answer 4

1) Nuclear receptors = interact with DNA aiding transcription and translation
2) Intracellular receptors
3) Plasma membrane receptors e.g. ligand gated ion channels, G-protein coupled receptor
4) Intrinsic enzyme receptor (tyrosine kinase receptor)
5) Ion channel receptors (allow ions to enter the cell once a chemical messenger is present)
6) DNA binding receptors

Question 5

What is the insulin receptor an example of?

Answer 5

A tyrosine kinase receptor (intrinsic enzyme receptor)

Question 6

What are the three parts of an insulin receptor? What is the form of the insulin receptor?

Answer 6

Ligand binding, transmembrane, enzyme.

It is a dimeric form as two monomers are joined up by disulphide bonds.

Question 7

How does an intrinsic enzyme receptor work?

Answer 7

Ligand joins to the ligand binding site, two monomers come together to form a dimer. Autophosphorylation and substrate phosphorylation occurs leading to conformational changes.

Question 8

What are 3 things that RTK (receptor tyrosine kinase) does?

Answer 8

• causes phosphorylation = phosphorylated tyrosine bind to kinase and signalling proteins bind to this
• activates RAS (G - protein) = signal molecule binds and G - protein is activated. Exchange of GDP for GTP activating it.
• activates MAP kinase signalling = G - protein from RTK activated kinase. Phosphorylation of transcription factor which activates it,

Question 9

Outline the steps in the action of receptor tyrosine kinase signalling.

Answer 9

1. Ligands binds to receptor
2. Conformational change for receptor results in autophosphorylation at tyrosine residues
3. Recruitment of RAS (G-protein)
4. Exchange of GDP for GTP on RAS results in a conformational change
5. Activation of MAP kinase by phosphorylation
6. Further protein phosphorylation in cell signalling

Question 10

What are the forms that receptors can come in?

Answer 10

Pentameric, tetrameric, trimeric

Question 11

How does the ion-channel coupled receptors work?

Answer 11

Signal molecule binds and this causes a conformational change to make the channel hydrophilic and ions can therefore pass through.

Question 12

What type of receptor is an acetylcholine receptor? How does it work?

Answer 12

It is a ligand gated ion channel receptor. When closed, hydrophobic amino acids side chains keep pore closed. Acetylcholine binds to receptor leading to a conformational change. The gate opens and ions enter

Question 13

What is the structure of a DNA binding receptor?

Answer 13

Ligand binding at top, zinc fingers in middle, co-activator region at bottom

Question 14

How does a DNA binding receptor work?

Answer 14

Ligand floating in the cytoplasm where the receptors are. It binds to the receptor and recruits another receptor to become a dimer. The dimer goes into the nucleus and binds to the promoters in the DNA causing a conformational change in the DNA leading to transcription.

Question 15

What do glucocorticoids do?

Answer 15

Anti-inflammatory as they inhibit transcription of cytokines interleukins.

Question 16

Compare the structure and speed of all the receptor types

Answer 16

Ion channel - multiple subunits, very fast
GPCR - Single protein, fast
Intrinsic enzyme - dimer, slow
DNA binding - dimer, very slow