Lecture 8- Intracellular Receptors 2

Question 1

What two hormones use intracellular receptors? and why?

Answer 1

Steroids and thyroid hormones (an amine)

As both can cross over cell membrane and nucleus membrane freely

Question 2

Describe the general process that a steroid hormone undergoes to have an effect in a cell…

Answer 2

• Diffuses freely across the cell membrane here if there is a cytoplasmic receptor a steroid hormone-receptor complex will form.
• This crosses into the nucleus where it activates primary response genes. This causes synthesis of a few different protein types in what is known as the primary response.
• Sometimes this is not where the process ends and the primary response protein shuts off primary-response genes to allow for the turning on of secondary response genes which produce secondary-response hormones.

Question 3

What is the main function of steroid hormones?

Answer 3

To form proteins

Question 4

What are the two thyroid hormones called?

Answer 4

Tri-iodothyronine (T3) means 3 iodine’s

Thyroxine (T4) means 4 iodine’s

Question 5

Do all thyroid hormones simply diffuse through the cell membrane?

Answer 5

They can at a base level but there are also channels

Question 6

What happens once T3 or T4 is inside the nucleus?

Answer 6

They form a complex with a receptor. This combines with a retinoid x receptor and a thyroid Response element. This is the final product of thyroid hormone release and results in gene transcription to form a variety of products.

Question 7

What is a ligand?

Answer 7

Anything that binds to a receptor e.g. ligand gated ion channel

Question 8

How do ligand gated ion channels work?

Answer 8

Start closed, signaling molecule binds and changing the shape of the receptor so the channel becomes open. Ions can they flow down concentration gradient from high to low.

Question 9

Assertion question:-
Steroid hormone receptors are only found in the nucleus BECAUSE
steroid hormone-receptor complex binds to DNA.
Answer:-
A. if both statements are true, and the second causes the first.
B. if both statements are true but the second does not cause the first.
C. if the first statement is true and the second is false.
D. if the first statement is false and the second is true.
E. if both statements are false.

Answer 9

D.

Question 10

What two G protein- coupled receptors work in the same way?

Answer 10

G stimulatory

G inhibitory

Question 11

What subunits are the G protein made of?

Answer 11

Alpha
Beta
Gamma

Question 12

What is the alpha subunit bound to in its inactive state?

Answer 12

GDP

Question 13

What are the steps for G protein coupled receptors (Gs and Gi) to work?

Answer 13

• Amine/ peptide (signal molecule) binds to receptor
• Receptor associates with subunits
• Alpha subunit releases GDP
• GTP binds to alpha subunit (now in active form)
• Alpha subunit dissociates with beta and gamma
• All subunits are now activated and can go on to activate other things

Question 14

What’s the pathway if an activated alpha subunit interacts with adenylyl cyclase?

Answer 14

• ATP is converted to cyclic AMP (cAMP)
• A cascade of other things are activated including protein kinase A
• This phosphorylates a lot of other things in turn activating them

Question 15

How does a Gq receptor differ from Gs and Gi?

Answer 15

• First receptor attaches to receptor on membrane, this means the GDP connected to the alpha subunit is swapped for GTP and alpha subunit disassociates. (same as before)
• Then phospholipid C converts PIP to IP3 and DAG (secondary messengers)
• IP3 binds to receptors found on the endoplasmic reticulum causing calcium to be released and a subsequent cellular response
• DAG alongside the calcium released above helps an inactive protein kinase C be converted to its active form
• This results in protein +ATP being converted to Dissociate with beta and phosphorylated protein and ADP. This leads to a cell response.

Question 16

How do receptor tyrosine kinases work?

Answer 16

You don’t have a G protein then down steps instead the tyrosine kinase is part of the receptor itself and thus has direct effects on a docking protein (phosphorylating using ATP). Multiple steps ensue from this and a cellular response.

Question 17

How do enzyme linked receptors work?

Answer 17

A signaling molecule exists as a dimer. They bind to an inactive catalytic domain causing it to become active. From here a physical change in the structure results in the activation of enzyme that can then go on and have an effect in the cell.

Question 18

How does a tyrosine kinase-associated receptor (type of enzyme- linked receptor work)?

Answer 18

• Janus kinase is not actually part of the receptor just associated with it.
• It acts to phosphorylate proteins and cause a subsequent cellular response

Question 19

How do eicosanoid receptors work?

Answer 19

They are a very specific system.

• A messenger binds to a receptor which activates phospholipase A this acts on the phospholipid membrane (taking parts of it) to form arachidonic acid.
• The cyclooxygenase pathway is then initiated.
• This ends in the production of prostaglandins, thromboxane and leukotrienes

Question 20

What’s the effect of prostaglandins?

Answer 20

Vascular actions, inflammation, uterine birth contractions

Question 21

What does thromboxane’s do?

Answer 21

Blood clotting and other vascular actions

Question 22

What does leukotrienes do?

Answer 22

Mediate allergic and inflammatory actions