Cell Receptors

Question 1

What are chemical messages or molecules that bind to receptors called?

Answer 1

Ligands.

Question 2

What are receptors?

Answer 2

(Generally) proteins that bind with ligands to elicit an effect within the cell.

Question 3

What is a second messenger?

Answer 3

A chemical messenger separate from the ligand or receptor that provokes the intracellular response when a receptors binds to a ligand.

Question 4

What are the four main types of receptors?

Answer 4

Ligand-gated ion channel receptors.
G-protein coupled receptors.
Enzyme-linked receptors.
Intracellular receptors.

Question 5

What can ligand-gated ion channel receptors also be known as?

Answer 5

Ionotropic receptors.

Question 6

What do all ionotropic receptors have incorporated within their quaternary (3-D) strucuture?

Answer 6

A central pore (for things to pass through).

Question 7

How does the central pore of an ionotropic receptor open up?

Answer 7

When an appropriate ligand attaches to the ligand-binding domain on the external surface of the protein.

Question 8

What is the name given to the process of the receptor changing shape?

Answer 8

Conformation change.

Question 9

Do molecules pass up or down their concentration gradient through an ionotropic receptor?

Answer 9

Down.

Question 10

What are G-protein coupled receptors also known as and why?

Answer 10

7-transmembrane receptors as the channel protein snakes in and out the membrane 7 times.

Question 11

What are the channel proteins linked to in a G-protein coupled receptor?

Answer 11

An intracellular G-protein complex.

Question 12

What is a G-protein complex made of?

Answer 12

An alpha subunit, a beta-gamma subunit, and an associated GDP molecule.

Question 13

What part of the G-protein complex is the most variable?

Answer 13

The G-alpha part of the complex, allowing for alternative signal transduction pathways.

Question 14

What are the steps involved in G-protein activation?

Answer 14

1. Ligand binds, causing the G-protein complex to associate with the receptor, causing the GDP molecule to be phosphorylated to GTP.
2. The G-alpha subunit dissociates from the G-beta-gamma subunit.
3. The G-alpha and the G-beta-gamma subunit can act as second messengers.
4. Once the ligand dissociates from the receptor, internal GTPase on the G-alpha subunit hydrolyses GTP to GDP.
5. The G-alpha and G-beta-gamma subunits re-associate and are available to the receptor again.

Question 15

What do enzyme-linked receptors consist of?

Answer 15

These transmembrane receptors ordinarily only consist of one transmembrane domain, which has the ligand-binding domain on the outside and specialised enzymes (usually tyrosine kinase enzymes) on the inside.

Question 16

What is needed to activate the intracellular enzyme associated with enzyme-linked receptors?

Answer 16

Clustering of more than one receptor protein is needed.

Question 17

What happens when the intracellular enzyme associated with enzyme-linked receptors is activated?

Answer 17

The enzymes trigger a signalling cascade within the cell.

Question 18

What is the overall process involved in enzyme-linked receptor activation?

Answer 18

1. Ligand binding results in receptor clustering.
2. Receptor clustering activates enzyme activity within the cytoplasmic domain.
3. The enzymes phosphorylate the receptor.
4. The phosphorylation leads to the binding of signalling proteins to the cytoplasmic domain.
5. These signalling proteins recruit other signalling proteins and a signal is generated within the cell.
   6, The signal is terminated when a phosphatase dephosphorylates the receptor.

Question 19

What do intracellular receptors act as?

Answer 19

Transcription factors.

Question 20

What sort of hormones can act on intracellular receptors and why?

Answer 20

Steroid hormones as they are membrane-permeable thanks to their lipophilicity.

Question 21

How many classes of intracellular receptors are there?

Answer 21

2

Question 22

What is the structure of a type I receptor?

Answer 22

A receptor located within the cytosol and is associated with a chaperone molecule called a heat shock protein.

Question 23

How does a type I receptor work?

Answer 23

Once the hormone binds, the HSP dissociates allowing the hormone-receptor complex to form a homodimer with another identical hormone-receptor complex (two hormone-receptor complexes bind together). The homodimer translocates to the nucleus where it binds to DNA and acts as a transcription factors.

Question 24

How does a type II receptor differ from a type I receptor?

Answer 24

They are located within the nucleus of the cell (vs the cytoplasm) and are already bound to the DNA.

Question 25

How does a type II receptor work?

Answer 25

Binding of the hormone ligand to the receptor usually results in direct transcriptional regulation by the activated hormone-receptor complex.