Term
| What are the requirements for a hormone to be effecive? (3) |
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Definition
-able to travel in blood (soluble)
-survive long enough to reach target
-be active at target site |
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Term
| What is required for specific recognition between hormones & their target cells? On what bases does this action work? |
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Definition
receptors
-based on biochemical structure of the hormone & its properties |
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Term
| Compare the production/circulation of lipophilic hormones to water soluble hormones (3 points) |
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Definition
LIPOPHILLIC
-diffuse out of producing cells
-circulate bound to carriers in blood
-diffuse into target cells via intracellular receptors
WATER SOLUBLE
-secreted (exocytosis) from producing cells
-circulate free in blood
-stay out of target cell..have a surface (extracellular) receptor |
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Term
True or False
Albumin & prealbumin are specific carriers of lipiphilic hormones |
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Definition
False - nonspecific
(globulins are specific) |
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Term
| What is the role of carrier proteins? |
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Definition
to keep the hormones in the blood vessel & prevent degradation
-hormone reservoir, buffer & protector |
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Term
| What is the active portion of the hormone-carrier complex, involved in feedback loops? |
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Definition
| the small portion of the hormone that is free and able to diffuse into tissues |
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Term
| How do carrier proteins affect levels of lipophilic hormones? |
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Definition
-binding protein increases = free hormone decreases = bound hormone increases
-absence of negative feedback = hormone secretion increases = more free AND bound hormone
-[free hormone] returns to normal = secretion stops ** total [hormone] is still elevated (some is bound) |
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Term
| Describe the process of action of lipophilic hormones |
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Definition
1. Free hormones diffuse through target plasma mmb
2. Bind to specific nuclear hormone receptor
3. Complex formed translocates to nuclear, binds to specific DNA sequence
4. Gene expression stimulated = de novo protein synthesis |
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Term
| Why are nuclear hormone receptors considered transcription factors? |
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Definition
| When lipophilic hormones bind to them, they form a complex which induces gene transcription |
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Term
True or False
NHR for Thyroid hormones are found outside nuclear |
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Definition
| False - the are already in the nucleus |
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Term
| Describe the structure of a nuclear hormone receptor |
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Definition
-ligand binding domain binds hormone
-DNA binding domain binds DNA of target gene
-activation domain stimulates transcription |
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Term
| Are lipophilic hormone fast or slow acting? |
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Definition
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Term
| What is the major circulating form of thyroid hormone? Describe the circulation/action. |
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Definition
thyroxine (T4)
-T4 enters target cell, converted to active T3
-binds to receptor after entering nucleus
-hormone partially degraded in target cells, remainder is transported to liver & degraded |
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Term
| Describe the circulation/action of steroid hormones (4) |
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Definition
-free form diffuses into target cells
-binds to specific receptor in cytoplasm
-translocates into nucleus
-dissociates from receptor after action, returns to circulation, degraded in liver |
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Term
| Describe the circulation/action of water-soluble hormones |
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Definition
-secreted by exocytosis & circulate free
-bind to specific receptors on SURFACE of target cell
-need secondary messengers to act |
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Term
| Describe the structure of a cell surface receptor |
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Definition
-hydrophobic region in mmb phospholipids
-hydrophilic region both outside & inside cell
-hormone receptor outside cell which activates secondary messengers inside cell |
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Term
| List the major types of cell surface receptors & their messengers |
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Definition
G-proteins coupled | adenylate cyclase, phospholipase C
Tyrosine kinase | auto-phosphorylation
Interleukins | JAK-STAT
TGF Beta | SMADs |
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Term
| Describe the action of G-protein coupled receptors (5 steps) |
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Definition
1. Hormone binds to a receptor coupled to G proteins
2. Change in conformation exchanges GDP with GTP on alpha subunit
3. Alpha dissociates from other subunits, activates mmb protein
4. Mmb protein stimulates a cascade of messengers
5. Biological response elicited |
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Term
| Describe the adenylate cyclase - cAMP pathway |
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Definition
-receptor is coupled to G proteins alpha-s or alpha-i
-mmb associated protein is adenylate cyclase
-alpha s stimulates AC, alpha i inhibits
-AC hydrolyzes ATP into cAMP |
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Term
| What will happen if a receptor couples to the G protein alpha-i? |
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Definition
| adenylate cyclase will be inhibited, cAMP decreases |
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Term
| Describe the phospholipase C pathway |
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Definition
-receptor coupled to G protein alpha-q
-mmb associated protein is PLC (stimulated by alpha-q)
-PLC stimulation activates release of Ca2+ (calmodulin) and a phosphorylation cascade (protein kinase C) |
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Term
| What effect does protein kinase C have? |
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Definition
| a phosphorylation cascade in the phosphplipase C pathway |
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Term
| Describe the action of tyrosine kinase receptors |
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Definition
1. hormone binds
2. receptor activated
3. autophosphorylation...becomes a kinase
4. phosphorylates tyrosines on target proteins |
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Term
| Describe the structure or a tyrosine kinase receptor |
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Definition
-transmembrane domain
-extracellular domain (ligand recognition)
-cytoplasmic domain (site of autophosphorylation) |
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Term
True or False
Tyrosine kinase receptors require secondary messengers |
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Definition
False
They directly phosphorylate the target proteins |
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Term
| What type of receptor does insulin use? |
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Definition
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Term
True or False
cytokine receptors have intrinsic kinase activity |
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Definition
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Term
| Describe cytokine receptors & their action |
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Definition
-exist as monomers
-hormone binds, causes dimerization, JAK tyrosine kinase binds, receptor is phosphorylated |
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Term
| What is the role of phosphotyrosines in cytokine receptors? |
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Definition
| act as docking site for intracellular signaling molecule (STATs) which activate various genes |
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Term
| What type of receptors do GH & prolactin use? |
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Definition
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Term
| Describe the action of serine kinase receptors |
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Definition
-hormone binds, forming a heterodimer of RI & RII
-RII is hormone specific, will recruit RI after hormone binds
-serine residues on RI are phosphorylated y RII
-SMADs proteins are phosphorylated by the active receptor, translocated into nucleus, modulate gene transcription |
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Term
| Describe the action of cell surface receptors |
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Definition
-cascade of intracellular messengers amplifies the signal
-effects on target cell vary depending on the type & amount of messenger activated
-receptor-hormone complex is internalized after signal is sent, degraded in lysosomes |
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Term
| What happens after the hormone-receptor complex of cell surface receptors is degraded in lysosomes? |
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Definition
| receptor is recycled, returns to cell surface |
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Term
| Describe the immediate effects you would see from activated cell surface receptors |
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Definition
| enzyme activation or exocyosis |
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Term
| Describe the slow effects you would see from activated cell surface receptors |
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Definition
stimulation of gene transcription
de-novo protein synthesis |
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