Chapter 7: 7.2 Receptors and Ligands

Question 1

What are the purpose of ligands? Where do they come from?

Answer 1

To trigger the signalling pathway by binding to a receptor
* Produced by a cell to be transported to the receptor

Question 2

What are the types of ligands?

Answer 2

1. Diffusible ligands
2. Surface-bound ligands

Question 3

Describe characteristics of:

Diffusible ligands

Answer 3

• Enter the cell directly by diffusion
• Small and hydrophobic
• Bind to an intracellular receptor

Question 4

Describe characteristics of:

Surface-bound ligands

Answer 4

• Bind to a receptor on the cell surface
• Cannot diffuse through the membrane
• Mostly small and hydrophilic

Question 5

Give an example of a diffusible ligand

Answer 5

• Steroid hormones
• Certain gases (nitrogen oxide etc.)

Question 6

Give an examples of a surface-bound ligand

Answer 6

• Protein ligands

Question 7

What is the purpose of receptors? Describe them

Answer 7

Bind to the ligand to activate the signal cascade that leads to the final response
* Can be in the cell (intracellular) or on the surface of the cell

Question 8

What are the types of receptors?

Answer 8

1. Cell-surface receptors
2. Intracellular receptors

Question 9

Describe characteristics of:

Cell-surface receptors

Answer 9

• Bind to small hydrophilic ligands
• Have 3 domains

Question 10

What are the 3 domains of cell-surface receptors?

Answer 10

• Extracellular domain: Faces the outside and binds to the ligand
• Hydrophobic domain: Spans the membrane
• Intracellular domain: Faces the inside of the cell and transfers the signal inwards

Question 11

Describe characteristics of:

Intracellular receptors

Answer 11

• Bind to diffusible ligands (small, hydrophobic) such as hormones
• Can often enter the nucleus to regulate gene expression
• Features include: DNA-binding domain, ligand binding domain

Question 12

How do Ligand-gated Ion Channels work?

Answer 12

Open when a ligand binds to it

Question 13

Give an example of a Ligand-gated Ion Channels

Answer 13

Neurotransmitters often bind to ligand-gated ion channel on neuron cells to transport the ions Na+ and K+ to create an action potential in order to send signals as electric pulses

Question 14

Describe characteristics of:

G-coupled Receptors

(5 points)

Answer 14

• One of the largest groups of cell-surface receptors
• 7 transmembrane domains (cross the membrane 7 times)
• Bind to many different types of ligands
• Receptor is bound to a G-protein on the interior of the cell
• G-protein triggers the response, it is also bound to three other subunits labelled alpha, beta, and gamma

Question 15

What are G-coupled Receptors involved in?

Answer 15

• Cell growth
• Motility
• Cell division
• Cancer

Question 16

Describe:

The signalling process of G-coupled receptors

(6 points)

Answer 16

1. When unbound to ligand, the G-protein (bound to the receptor) has a nucleotide guanosine diphosphate (GDP) attached. This is the OFF state
2. The ligand binds to the receptor
3. A phosphate group is added to GDP to become GTP.
4. This is the ON state
5. The activated G-protein breaks off from beta and gamma subunits, goes to activate response (e.x. gene expression changes)
6. GTP has one phosphate removed, making GDP, and reattaches to the receptor, resetting the system

Question 17

What are Receptor Tyrosine Kinases (RTKs)? Describe their characteristics

Answer 17

Enzyme-linked cell-surface receptors
* The kinase enzyme part adds a phosphate group to the amino acid tyrosine
* Two of the proteins are needed to actually work

Question 18

Describe:

The signalling pathway of RTKs

Answer 18

1. Two RTKs are present relatively close to each other on the membrane but not close enough to interact (OFF state)
2. When ligands bind to both, they come together until the receptor domains and intracellular domains are in contact
3. The intracellular regions which have kinase activity and tyrosine residues - cross modify each other by adding phosphate groups to the tyrosine of each other’s intracellular domain to activate them (ON state)

Triggers activation of the response

Question 19

What is the Dissociation Constant (Kd)?

Answer 19

Measures the affinity between the ligand (L) and the receptor (R)