1 - Intro Flashcards
What are the precursors of steroid hormones?
cholesterol
Give an example of a hormones that would fit into the miscellaneous category of hormone?
thyroid hormones
What are peptide hormones synthesised from?
prohormones - they are cleaved to generate the hormones
Give an example of a protein/peptide hormones and its inactive precursor?
ACTH (adrenocorticotropic hormone)
prohormone= POMC
Where is ACTH produced?
by the anterior pituitary
All of the anterior pituitary hormones are _____
polypeptides
Where do the amino acids come from that are used to synthesis protein/peptide hormones?
the blood supply
Describe the synthesis of protein/polypeptide hormones
- the pro-hormone is transcribed from the DNA and the mRNA bind to the rER (where it is translated)
- the prohormone is endocytose by the Golgi, which adds enzymes to the vesicles containing the pro-hormone. These cleave the prohormone
- the Golgi ‘liberates’ the active hormone
- vesicles filled with the active hormones accumulate near the cell surface
- when a signal arrives—–> exocytosis and the hormones is released into the blood
Give an example of a steroid hormone
cortisol
steroid producing cells have lots of _____
fatty droplets
Describe the synthesis of steroid hormones
- cholesterol is delivered to the cell (e.g. adrenal) by LDLs and is stored as Fatty Acid Esters
- esterase enzymes break down the fatty acids esters to liberate the cholesterol
- StAR proteins drove cholesterol into the mitochondria
- in the mitochondria, many enzymes convert the cholesterol into the steroid hormone of choice
- is is secreted into the cytoplasm and then the bloodstream
NOTE: the enzymes present in the cells determine the final steroid hormone product
Where are most steroid hormones produced?
adrenal glands or gonads
Why are steroid hormones not stored in cells (like protein hormones are)?
because they are very lipid soluble —–> ‘constitutive’ secretion
Would an RNA synthesis inhibitor cause a greater reception in protein or steroid hormone production?
NOTE: it would reduce the rate of synthesis of both
BUT it would greatly reduce protein hormones production because it is preventing mRNA production, which is key in the production of proteins
in the steroid hormones, it would interfere with the cholesterol pathway, but would reduce the production of esterase and StAR proteins
How are proteins/polypeptide hormones transported?
- secreted into the blood and travel unbound to the site of action
- stored in the tissues that produce them (in vesicles)
- they aren’t bound to any plasma protein, so are sensitive to enzymatic breakdown
What are some features of polypeptide/protein hormones?
- very short half life (minutes)
- short acting effect
How are steroid hormones transported?
(they are stored in the blood)
- majority bind to plasma proteins
- —-> ALBUMIN is the most common plasma protein - it can mop up a large amount of steroid hormones, but the interaction isn’t very specific
- —-> for each individual steroid hormone, there is a more specific plasma protein, which forms a much stronger binding
- small amount is free in the blood - ONLY FREE STEROID HORMONES CAN LEAVE THE BLOOD, if it bound to plasma protein, it is not leaving the bloodstream
What hormones does ACTH stimulate the production of in cells?
cortisol
What is the mechanism of action of ACTH (protein/polypeptide hormones)?
- hormone binds to protein (ACTH) receptor (usually G-coupled protein receptors)
- this activates adenylate cyclase
- increase cAMP production from ATP
- cAMP activates protein kinase A
- this phosphorylates esterase, which liberate cholesterol
- also phosphorylates StAR proteins (becoming activated) and allows cholesterol to move into the mitochondria
(steroid hormone production)
What is the mechanism of action of steroid hormones?
- free steroid hormones enter cells (diffusion) and bound to intracellular receptors
- translocate to the nucleus, and impact the rate of transcription
The steroid hormone mechanism of action on the cell has an effect that is _____
slow, but powerful
