Hormone Receptors (G Protein-Coupled Reactions and Receptor Tyrosine Kinase Receptors)

Question 1

The large diverse family of G protein-coupled receptors respond to a variety of extracellular signals and activate _________.

Answer 1

G proteins

Question 2

How do G proteins function?

Answer 2

They function as on or off switches for intracellular signalling pathways by activating or inactivating ion channels or effector enzymes that generate second messenger molecules.

Question 3

GPCR signalling pathways regulate a wide range of cellular activities including: ????

Answer 3

• Metabolism
• Cell division
• Gene expression

Question 4

The structure of G-protien coupled reactions contain how many transmembrane alpha-helical regions?

Answer 4

Seven

Question 5

In the structure of G-Protien Coupled Receptors where is the N-termimus is found? The C-terminus?

Answer 5

N-terminus: On the OUTSIDE (ectoplasmic face)
C-terminus: On the CYTOSOLIC face

Question 6

Ligand-binding site located in a groove located in the _______ of the plane of the membrane.

Answer 6

Middle

Question 7

Ligand interacts non-covalently with specific amino acids in the ______ - facing side of several membrane-spanning alpha-helixes.

Answer 7

Interior

Question 8

The G alpha and gamma subunits are linked to the membrane by ____________.

Answer 8

Covalently attached lipids.

Question 9

Ligand binding alters receptor conformation allowing the binding of the alpha G subunit causing the release of bound _______.

Answer 9

GDP

Question 10

Describe the six steps associated with the mechanism of GPCR signalling.

Answer 10

1. Binding of hormone induces a confirmation change in a receptor.
2. Activated receptor binds to the G alpha subunit.
3. Activated receptor causes a conformational change in the G alpha, triggering dissociation of GDP.
4. The binding of GTP to G alpha triggers the dissociation of G alpha both the receptor and from G bela, gamma.
5. The hormone dissociates from the receptor, and G alpha binds to the effector, activating it.
6. Hydrolysis of GTP to GDP causes the G alpha to dissociate from the effector and reassociate with the G beta, gamma.

Question 11

GEF is an ________ protein that is a guanine exchange factor.

Answer 11

Activator

Question 12

GAP is a GTPase _______ protein.

Answer 12

Accelerating

Question 13

Guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) regulate the activity of small ______________ to control cellular functions.

Answer 13

Guanine nucleotide-binding (G) proteins

Question 14

In the case of FRET: Fluorescence Resonance Energy Transfer, cAMP acts as a _________, NOT as a secondary messenger.

Answer 14

Hydrophilic homrone.

Question 15

True or False. In the case of FRET, activation of a G protein occurs within seconds f ligand binding to its cell-surface G protein-coupled receptor.

Answer 15

True.

Question 16

G proteins as ON-OFF switches for intracellular signalling pathways by activating ion channels or effector enzymes that generate __________.

Answer 16

Secondary messenger molecules.

Question 17

True or False? RTKs have a different mechanism action as compared to GPCRs.

Answer 17

True.

Question 18

Name two types of hydrophilic signalling molecules.

Answer 18

Hormones or peptides.

Question 19

Hydrophilic signalling molecules (hormones/peptides) activate Receptor Tyrosine Kinases (RTKs), which phosphorylate _______ targets and initiate a signal transduction cascade.

Answer 19

Downstream.

Question 20

In RTKs, the hormone or peptide leads to _______ of two kinase polypeptides.

Answer 20

Dimerization.

Question 21

What does the dimerization of RTKs lead to?

Answer 21

Cytoplasmic domain autophosphorylation, which recruits proteins that initiate intracellular signalling pathways.

Question 22

Describe the activation of RTKS in three steps.

Answer 22

1. Receptor tyrosine kinases (RTKS) are first found without a bound ligand.
2. The ligand binds. This causes dimerization and phosphorylation of activation loop tyrosines.
3. Then, phosphorylation of additional tyrosine residues takes place.

Question 23

FGF is a fibroblast growth factor. Describe what they are involved in and what they stimulate.

Answer 23

They are involved in wound healing and stimulates cell proliferation and cell spreading.

Question 24

Describe the two main points associated with activation of the EGF receptor by EGF binding.

Answer 24

When the EGF binds, dimerization alters the conformation of intracellular domain leading to kinase activation. Reciprocal phosphorylation of tyrosine residues on the two cytoplasmic domains of the activated receptor occurs.

Question 25

Activation of dimerized RTKs leads to _________________, which recruits proteins that initiate intracellular signalling pathways

Answer 25

Cytoplasmic domain autophosphorylation.

Question 26

There are four HER (Human Epidermal Growth Factor Receptors) that mediate signalling by different members of the ___________.

Answer 26

Epidermal growth factor of hormones.