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What does the response to a hormone depend on?
Both the hormone and the target cell.
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Can target cells respond differently to the same hormone?
yes
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Is the response to a hormone always the synthesis of new molecules?
No, for instance insulin.
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Name some other hormonal effects other than synthesis of new molecules.
changing the permeability of the plasma membrane, stimulating transport of a substance into or out of the target cells, altering the rate of specific metabolic reactions or causing contraction of smooth muscle or cardiac muscle.
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Where are the receptors for lipid souble hormones located?
Inside target cells
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Where are the receptors for water soluble hormones?
They are part of the plasma membrane of target cells
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What are the 4 steps of mechanism of action for a lipid soluble hormone and thyroid hormones?
1. a fee lipid soluble hormone molecule diffuses from the blood, thru interstitial fluid, and thru the lipid bilayer of the plasma membrane into a cell.
2. If the cell is a target cell, the hormone binds to and activates receptors located within the cytosol or nucleus. The activated receptor-hormone complex then alters gene expression: It turns specific genes of the nuclear DNA on or off.
3. As the DNA is transcribed, new messenger RNA (mRNA) forms, leaves the nucleus, and enters the cytosol. There, its directs synthesis of a new protein, often an enzyme, on the ribosomes.
4. The new proteins alter the cell's activity and cause the responses typical of that hormone.
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What is the action of the receptor-hormone complex?
The receptor-hormone complex alters gene expression by turning specific genes of nuclear DNA on or off.
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Why can't amine, peptide, protein and eicosanoid hormones diffuse thru the lipid bilayer of the plasma membrane and bind to receptors inside target cells?
Because they are not lipid soluble, they are water soluble.
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Where do water soluble hormones bind?
To receptors that protrude from the target cell surface.
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What type of receptors are integral transmembrane proteins in the plasms membrane?
Water soluble hormone receptors.
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When a water-soluble hormone binds to its receptor at the outer surface of the plasma membrane, it acts as the ____ ____.
first messenger
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What happens after the hormone acts as the first messenger?
It causes production of a second messenger inside the cell, where specific hormone-stimulated responses take place.
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Name a common second messenger.
cyclic AMP (cAMP)
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What is the 6 step action of a typical water-soluble hormone?
1. A water-soluble hormone (first messenger) diffuses from the blood thru interstitial fluid and then binds to its receptor at the exterior surface of a target cell's plasma membrane. The hormone-receptor complex activates a membrane protein called a G protein. The activated G protein in turn activates adenylate cyclase.
2. Adenylate cyclase converts ATP into cyclic AMP (cAMP). Because the enzyme's active site is on the inner surface of the plasma membrane, this reaction occurs in the cytosol of the cell.
3. Cyclic AMP (second messenger) activates on eor more protein kinases, which may be free in the cytosol or bound to the plasma membrane. A protein kinase is an enzyme that phosphorylates (adds a phosphate group to) other cellular proteins (such as enzymes). The door o fthe phosphate group is ATP, which is converted to ADP.
4.Activated protein kinases phosphorylate one or more cellular proteins. Phosphorylation activates some of these proteins and inactivates others, rather like turning a switch on or off.
5. Phosphorylated proteins in turn cause reactions that produce physiological responses.
6. After a brief period, an enzyme called phosphodiesterase inactivates cAMP.
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The binding of a hormone to its receptor activates many what?
G-protein molecules
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What do G-protein molecules activate?
molecules of adenylate cyclase
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Unless further stimulated by the binding of more hormone molecules to receptors, what do G-proteins do?
slowly inactivate, decreasing the activity of adenylate cyclase to help stop hormone response.
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Why do hormones that bind to plasma membrane receptors induce their effects at very low concentrations?
Because they initiate a cascade or chain reaction, each step of which multiplies or amplifies the initial effect.
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What are the 3 things the responsiveness of a target cell to a hormone depend on?
1. The hormone's concentration
2. The abundance of the target cell's hormone receptors
3. Influences exerted by other hormones
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When does a target cell respond more vigorously?
When the level of a hormone rises or when it has more receptors (up regulation)
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The actions of some hormones on target cells require a simultaneous or recent _____ to a ____ hormone.
exposure
second
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A second hormone is said to have what?
A permissive effect
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When the effect of 2 hormones acting together is greater or more extensive than the effect of each hormone acting alone, the 2 hormones are said to have a ____ ____.
synergistic effect
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When one hormone opposes the actions of another hormone, the 2 hormones are said to have ____ ____.
antagonistic effects
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