Cell signalling by lipophilic molecules Flashcards
what are the different types of receptors?
Steroid receptors
Ion channels
G-protein coupled receptors
Cytokine receptors
what do steriod receptors initiate in the cell?
alter gene expression
what do ion channels initiate in the cell?
change in membrane conductance
what do G-protein couple receptors initiate in the cell?
alter protein activity
what do cytokine receptors initiate in the cell?
regulate many cellular events
what are steroids?
molecules chemically based on modifications of cholesterol
what steriods are produced in the adrenal cortex?
Cortisol
Aldosterone
when is cortisol produced?
in response to stress
what is aldosterone produced?
in response to a fall in blood pressure
what steriods are produced in the gonads?
Sex hormones with multiple roles
what is produced in the female gonads?
progesterone
estradiol
what is produced in the male gonads?
testosterone
dihydrotesterone
where are neurosteroids produced?
by neurons and glial cells
what are neurosteriods?
based on the steroid pregnenolone
what is the role of neurosteroids?
multiple actions within the brain
what is the common physiochemical property of steriods?
Insoluble in water (hydrophobic) but soluble in lipids (lipophilic)
what are the features of lipophilic hormones?
-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
what is released in the stress response?
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
what is the mechanisam of cortisol release?
- 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
what activates adrenal cortical cells?
ACTH via the MC2 receptor
what happens when adrenal cortical cells are activated?
A G-protein coupled receptor is initiated
what is the result of a G-protein coupled receptor activation?
increased cAMP levels
what happens when cAMP levels are increased?
stimulates protein kinase A (PKA)
what does PKA activate?
PKA activated transcription factors
what is the roll of transcription factors in the stress response?
increases expression of cortisol synthesizing enzymes
- more cortisol is released into the blood
how do steroids move in the blood?
they require a carrier protein
what type of hormone is physiologically active?
only the free hormone is physiologically active
how can levels of hormones be altered?
The amount of carrier protein, and therefore bound hormone, can be altered by disease or drugs
what is important is regards to hormone clinical tests?
to be able to distinguish between free and bound hormone
what are the ways that steriods can signal?
- the classical pathway
- interaction with other transcription factors
- steroid-receptor complex having non-transcriptional roles
- steriods signalling via cell surface receptors
how does steroid enter a target cell?
- 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
