Cell signalling by lipophilic molecules

Question 1

what are the different types of receptors?

Answer 1

Steroid receptors
Ion channels
G-protein coupled receptors
Cytokine receptors

Question 2

what do steriod receptors initiate in the cell?

Answer 2

alter gene expression

Question 3

what do ion channels initiate in the cell?

Answer 3

change in membrane conductance

Question 4

what do G-protein couple receptors initiate in the cell?

Answer 4

alter protein activity

Question 5

what do cytokine receptors initiate in the cell?

Answer 5

regulate many cellular events

Question 6

what are steroids?

Answer 6

molecules chemically based on modifications of cholesterol

Question 7

what steriods are produced in the adrenal cortex?

Answer 7

Cortisol
Aldosterone

Question 8

when is cortisol produced?

Answer 8

in response to stress

Question 9

what is aldosterone produced?

Answer 9

in response to a fall in blood pressure

Question 10

what steriods are produced in the gonads?

Answer 10

Sex hormones with multiple roles

Question 11

what is produced in the female gonads?

Answer 11

progesterone
estradiol

Question 12

what is produced in the male gonads?

Answer 12

testosterone
dihydrotesterone

Question 13

where are neurosteroids produced?

Answer 13

by neurons and glial cells

Question 14

what are neurosteriods?

Answer 14

based on the steroid pregnenolone

Question 15

what is the role of neurosteroids?

Answer 15

multiple actions within the brain

Question 16

what is the common physiochemical property of steriods?

Answer 16

Insoluble in water (hydrophobic) but soluble in lipids (lipophilic)

Question 17

what are the features of lipophilic hormones?

Answer 17

-cannot be stored therefore synthesized when needed
- require a carrier protein after being released into the blood
- cross the membrane of the target cell and act on intracellular receptors

Question 18

what is released in the stress response?

Answer 18

Stress causes the release of both adrenaline and cortisol from the adrenal gland

-the increase in cortisol concentration in the blood is slower than that of adrenaline
- but it remains elevated for longer
- and its effects on target tissues are more prolonged

Question 19

what is the mechanisam of cortisol release?

Answer 19

• adrenal cortical cells activated by ACTH via MC2 receptor
• activates a G-protein coupled receptor
• increases in cAMP
• stimulates protein kinase A (PKA)
• PKA activates transcription factors
• increases expression of cortisol synthesizing enzymes
• more cortisol released into the blood

Question 20

what activates adrenal cortical cells?

Answer 20

ACTH via the MC2 receptor

Question 21

what happens when adrenal cortical cells are activated?

Answer 21

A G-protein coupled receptor is initiated

Question 22

what is the result of a G-protein coupled receptor activation?

Answer 22

increased cAMP levels

Question 23

what happens when cAMP levels are increased?

Answer 23

stimulates protein kinase A (PKA)

Question 24

what does PKA activate?

Answer 24

PKA activated transcription factors

Question 25

what is the roll of transcription factors in the stress response?

Answer 25

increases expression of cortisol synthesizing enzymes
- more cortisol is released into the blood

Question 26

how do steroids move in the blood?

Answer 26

they require a carrier protein

Question 27

what type of hormone is physiologically active?

Answer 27

only the free hormone is physiologically active

Question 28

how can levels of hormones be altered?

Answer 28

The amount of carrier protein, and therefore bound hormone, can be altered by disease or drugs

Question 29

what is important is regards to hormone clinical tests?

Answer 29

to be able to distinguish between free and bound hormone

Question 30

what are the ways that steriods can signal?

Answer 30

1. the classical pathway
2. interaction with other transcription factors
3. steroid-receptor complex having non-transcriptional roles
4. steriods signalling via cell surface receptors

Question 31

how does steroid enter a target cell?

Answer 31

• free steroid crosses into the target cell
• Binds to its intracellular receptor
• an inhibitory regulator dissociates
• S-GR complex enters cell nucleus via nuclear pores
• binds to glucocorticoid response element on specific genes
• regulates mRNA transcription from those genes