Intro to Endo

Question 1

How are peptide hormones synthesized?

Answer 1

Ribosomal synthesis. This can include making a huge precursor protein that is then cut into different hormones. Example: proopiomelanocortin (POMC) gives rise to ACTH, a-MSH, b-MSH, b-lipotropin and b-END

Question 2

How are steroid hormones synthesized?

Answer 2

Enzymatically. Basic process is substrate+enzyme=hormone

Question 3

How do peptide hormones exist in circulation? How does this compare to steroid hormones?

Answer 3

Peptide hormones travel freely in circulation because they are hydrophilic. Steroid hormones are hydrophobic so they need a carrier protein buddy to travel with them in circulation.

Question 4

Where are the receptors for peptide hormones located? Compared to steroid hormones?

Answer 4

Peptide: cell-surface receptor (hydrophilic so can’t just pass through the lipid bilayer)
Steroid: cytosolic and chromatin (hydrophobic so can easily pass through cell membrane, and then enter the nucleus to influence gene expression)

Question 5

One type of cell surface receptor is the G-protein-coupled receptor. Briefly describe the two cascades activated by G-proteins.

Answer 5

Activated G-protein links receptor to Adenylyl cyclase (AC) or Phospholipase C (PLC)

1. AC catalyzes the conversion of ATP to cAMP to later activate protein kinase A (PKA)
2. PLC converts PIP2 to IP3 and DAG. IP3 increases intracellular Ca2+ stores. DAG activates protein kinase C (PKC)

Question 6

Describe how steroid hormones reach their cell target

Answer 6

They dissolve through the lipid bilayer and bind to their specific receptor in the cytosol. This dimer enters the nucleus and binds to specific chromatin-promotor elements, allowing it to regulate gene expression.

Question 7

Describe how thyroid hormone works

Answer 7

It acts like a steroid (even though its a peptide) and works mainly in the nucleus. T4 (thyroxin) is its inactive form, which gets activated by deiodinase enzyme to T3 (triiodothyronine) inside the cell. T3 goes to the nucleus to effect gene expression (main job), the mitochondrial membrane and cell membrane (minor jobs)

Question 8

Comment on the speed of action of peptide vs steroid hormones

Answer 8

Peptide hormones generally work faster than steroid hormones (which are, you know, changing gene expression. That takes some time)