18 Questions
Which hormones are stored in secretory granules and released by exocytosis?
Catecholamines and polypeptide hormones
In which form do steroid and thyroid hormones leave the cell?
Free form within the cytoplasm
What is the role of transport proteins in hormone circulation?
To bind and transport hormones in the blood
Which hormone has a longer plasma half-life, thyroxin or aldosterone?
Thyroxin
What factor is the plasma half-life of a hormone correlated with?
% of protein binding
Which hormones circulate in a free form rather than bound to transport proteins?
Polypeptide and other amine hormones
Where are catecholamines and polypeptide hormones typically stored?
Secretory granules
Which type of hormones are readily passed into the cell due to being hydrophobic?
Steroid hormones
What is the function of the receptor site on a cell?
Location where hormone binds
How are peptide hormones primarily synthesized?
As proteins in ribosomes
Which group of cells responds to specific hormones?
Target tissues
What triggers the responses of target cells after a G protein signaling cascade?
$cAMP$
How do protein hormones initiate a response in target cells?
Bind to a receptor protein on the surface of the target cell
Which type of hormone is known to penetrate the cell and bind to intracellular receptors?
Steroid hormones
How do water-soluble hormones primarily travel in the bloodstream?
As free molecules
What is the role of a transcription factor activated by a hormone?
Synthesize specific proteins from mRNA
Which type of hormone affects the permeability of the cell membrane by opening or closing ion channels?
Peptide hormones
How do lipid hormones primarily travel in the bloodstream?
Bound to carrier proteins
Study Notes
G Protein Signaling Mechanism
- Hormone binds to receptor, activating G protein (Gs)
- G protein activates adenylate cyclase, converting ATP to cAMP (2nd messenger)
- cAMP activates protein kinases, triggering responses of target cell (activates enzymes, stimulates cellular secretion, opens ion channels, etc.)
Steroid Hormones
- Hydrophobic, readily pass into cell
- Bind receptor associated with DNA, causing gene to be transcribed
- Specific protein produced alters metabolism in various ways
Hormone Receptors and Effects
- Receptor site: location on a cell where hormone binds (lock)
- Target tissues: group of cells that respond to specific hormones
- Specificity: specific hormones bind to specific receptor sites
Synthesis and Storage of Hormones
- Amino acid and steroid hormones are synthesized through series of enzymatic reactions
- Peptide hormones are synthesized as proteins in the ribosomes
- Catecholamines and polypeptide hormones are stored in secretory granules
- Thyroxin and steroid hormones are not stored in granules and are present in the free form within the cytoplasm
Hormone Release
- Catecholamine and polypeptide hormones are released by exocytosis
- Thyroxin and steroid hormones leave the cell by simple transfer through the plasma membrane
Hormone Transport
- Released hormones enter the blood, where they may circulate in two forms: free (unbound) and bound
- Free hormones bind to receptor, while bound hormones are carried by specific albumins and globulins synthesized in the liver
- Steroid and thyroid hormones are bound to transport proteins, whereas polypeptide and other amine hormones circulate in a free form
Types of Hormones and Mechanism of Chemical Signaling
- Protein hormones: bind to receptor protein on the surface of the target cell, triggering signal transduction pathway
- Steroid hormones: penetrate the cell and bind to receptor protein inside the target cell, triggering signal transduction pathway
- Hormones can cause change by altering cell activity, changing permeability of cell membrane, and synthesizing proteins
Regulation of Hormones
- Blood levels of chemicals (e.g. blood glucose levels)
- Other hormones (e.g. TSH signals thyroid gland to release thyroid hormone)
- Nervous system
Test your knowledge on hormone synthesis, storage, and release including protein and amine hormones. Learn about the groups of hormones derived from the amino acid tyrosine and the factors determining hormone levels in the body.
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