Cell Signalling II

Question 1

What is hormone binding specificity?

Answer 1

Measure of the ability of a receptor to distinguish between closely related substances

Question 2

What are the 2 main functions of receptors?

Answer 2

Binding the hormone with high affinity

Invoking signal inside the cell to initiate biological response

Question 3

What kind of proteins are receptors usually?

Answer 3

High affinity binding proteins

Question 4

What happens to receptor when it is bound by hormone?

Answer 4

Conformational changes in the receptor take place and those changes are detected by intracellular molecules

Question 5

How does the filter assay for reecptor binding work?

Answer 5

Equilibrium binding takes place between labeled ligand and the receptor

Bound complex is radioactive and free receptor is not.

Free ligand can pass through filter but complex cannot pass

Question 6

What are the steps to conduct a filter assay?

Answer 6

Membrane is isolated

Ligand added to membrane

Solution is passed through a filter and unbound ligand is washed off

Bound radioactivity is then measured which is proportional to amount of complex

Question 7

What is a limitation to the filter assay?

Answer 7

Hydrophobic ligands are non-specifically incorporated into the membrane

Question 8

How is the issue of nonspecific binding accounted for?

Answer 8

Total binding is measured

Nonspecific binding is measured after taking receptors out of the membrane

Total binding - NSB = specific binding

Specific binding data is then analyzed

Question 9

What does Kd refer to?

Answer 9

The concentration of hormone at which half the maximal binding takes place

Question 10

What is the slope of the [RL]/[L] vs [RL] graph?

Answer 10

-1/Kd

Question 11

What are the methods of signalling through the cell membrane?

Answer 11

G protein coupled receptor activation

Receptor tyrosine kinase which activates transcription factor altering gene expression

Receptor guanylyl cyclase: Ligand binding to extracellular domain stimulates formation of cyclic GMP

Gated ion channels

Adhesion receptor (integrin) which binds molecules in extracellular matrix changes conformation thus altering interaction with cytoskeleton

Nuclear receptor allows receptor to regulate expression of specific genes

Question 12

Which hormones bind to intracellular receptors?

Answer 12

Steroid hormones and thyroid hormones

Question 13

What molecules are steroid hormones produced from?

Answer 13

Cholesterol via stepwise removal of carbon atoms and hydroxylation

Question 14

Where are steroid hormones synthesized?

Answer 14

In the adrenal cortex (glucocorticoids and mineralocorticoids) and the gonads (estrogens, progesterone, and androgens)

Question 15

What type of molecules are thyroid hormones? What does this allow them to do?

Answer 15

Small and hydrophobic, lipid soluble

Can diffuse through membrane of target cells

Question 16

What happens after thyroid hormones bind to their target receptors?

Answer 16

Affects the ability to transcribe specific genes by interacting directly with the transcription factors they control

Question 17

What hormone stimulates androgen production?

Answer 17

Luteinizing hormone

Question 18

Which cells produce androgen hormones?

Answer 18

Leydig cells

Question 19

What are the target cells of androgens?

Answer 19

Prostate

Bone

Muscle

The function is to maintain functional male reproductive system as well as male secondary characteristics and increasing muscle and skeletal size.

Question 20

What are the main functional regions of a nuclear receptor?

Answer 20

Central DNA-binding domain which contacts the DNA

Ligand binding domain which binds specifically to hormone

Variable N terminal regions which contain one or more activation domains.

Question 21

What happens to receptor that is unbound?

Answer 21

Inhibitory proteins bind to it and prevent transcription from taking place.

Question 22

What happens to nuclear receptor when bound by ligand?

Answer 22

Conformational change releases inhibitory protein and a co-activator protein binds to it to induce gene transcription

Question 23

Where are intracellular receptors located?

Answer 23

They can be in the cytosol and then travel to nucleus when ligand is bound.

Or they can be located in the nucleus.

Question 24

What are nuclear receptor response elements?

Answer 24

Nucleotide binding sequence that interacts with nuclear receptors.

Question 25

What do nuclear receptor response elements look like?

Answer 25

They lie adjacent to genes that the hormone regulates and consist of 6 base pair repeat sequences separated by 3 - 5 base pairs.

Question 26

What do steroid hormones do to gene expression?

Answer 26

When they bind to their receptors the complexes promote activation of response element and in turn increase transcription and then translation.

Question 27

Are there any intermediate molecules involved with nuclear receptors?

Answer 27

No, the receptor is the transcription factor which means there is less opportunity for regulation by other factors and pathways and thus there is limited amplification of signal

Question 28

What domain structure is shared among all nuclear receptors?

Answer 28

Variable region DBD and LBD

Question 29

Learning outcomes:

Answer 29

Understand that receptor/ligand interaction is very
specific
2. Understand how receptor ligand studies are
performed and be able to describe Kd and Bmax
represent
3. Understand the properties of small hydrophobic
signalling molecules
4. To describe the steroid hormone signal transduction
mechanism with particular reference to regulation of
gene TRANSCRIPTION

Question 30

What is Kd?

Answer 30

The concentration of hormone at which half the maximal binding occurs

Question 31

What does Bmax refer to?

Answer 31

The maximal binding which also means the total number of receptors available for binding