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59 Cards in this Set
- Front
- Back
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How do lipophilic hormones travel through the blood?
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bound to transport proteins
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What are the advantages of lipophilic hormones travelling through the blood bound to a transport protein?
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it increases their solubility and increases their half-life
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Where is the hormone receptor which binds to lipophilic hormones?
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intracellular receptor
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What is the function of the hormone-receptor complex?
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typically is the signal which determines the rate of transcription of specific genes
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Describe the transport and half life of hydrophilic hormones
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They travel through the blood without being bound to a protein. As a result, they are more susceptible to clearance and have a shorter half-life
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Where are the receptors which bind hydrophilic hormones?
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bound to the plasma membrane
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What happens when a hydrophilic hormone binds to a receptor?
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it generates a signal and changes the enzyme activity (think 2nd messengers)
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Name 2 classes of lipophilic hormone receptors
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- cytosolic (subclass 1)
- nuclear (subclass 2) |
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What types of lipophilic hormones generally bind to the cytosolic receptors?
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steroids
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Describe the cytosolic lipophilic hormone receptor before the hormone binds to it
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the DNA binding domain is masked by heat shock proteins
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What happens to the lipophilic cytosolic receptor after the hormone binds to it?
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the heat shock proteins are removed
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Where does the lipophilic cytosolic hormone-receptor complex travel to after the heat shock proteins have been released?
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Into the nucleus
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What does the lipophilic cytosolic hormone-receptor bind to in the nucleus and what results?
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It binds to the hormone response element which either positively or negatively affects gene transcription
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Name three types of hormones that use nuclear lipophilic receptors
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-thyroid hormone
-retinoids -vitamin D |
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Where are lipophilic nuclear receptors found?
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in the nucleus, not bound to heat shock proteins
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What happens when the lipophilic nuclear receptor binds to horomone?
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a conformational change occurs effectively "activates" the hormone-receptor complex
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What does the activated hormone-receptor complex do (in the nuclear lipophilic model)
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binds to hormone response element and stimulates a negative or positive change in transcription
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How to hydrophilic receptors create a change in the intracellular environment?
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via second messengers
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Describe the resting state of G-protein coupled hydrophilic receptors
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alpha, beta, and gamma subunits are all bound together and also bound to the horomone receptor and GDP
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What happens to the G-protein complex when a hormone binds to the hormone receptor?
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GDP is displaced by GTP, and the g-protein complex separates from the hormone receptor and into an alpha subunit and a combined beta-gamma subunit
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What do the beta-gamma and alpha-GTP subunits do when they are dissociated from each other and the hormone receptor?
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the bind to enzymes and alter their activity
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How do G-protein subunits return to resting state?
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alpha subunit has an inherent GTPase activity which replaces GTP with GDP and allows the alpha subunit to bind to the beta-gamma subunit and the hormone receptor
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Name the 4 different g-protein subfamilies
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Gs, Gi, Gq, and G12
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What does Gs do?
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stimulates adenylyl cyclase
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What does Gi do?
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inhibits adenylyl cyclase
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What does Gq do?
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stimulates phospholipase C
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What does G12 do?
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affects various ion channels (depending on the information source)
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What happens when insulin binds to the insulin receptor?
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results in auto-phosphorylation of the receptor on specific Y residues
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What do that Y residues do in the kinase cascade once they are phosphorylated?
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They phosphorylate Insulin Receptor Substances (IRS 1-4)
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What role do the phosphorylated insulin receptor substances play in the kinase cascade?
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They directly stimulate the kinase cascades resulting in a plethora of different actions
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Name 2 hormones which interact with a tyrosine kinase receptor to stimulate a kinase cascade
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-epidermal growth factor (EGF)
- Insulin-like growth factor (IGF) |
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Name 4 hormones which utilize the Jak-STAT kinase cascade
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-prolactin
-growth hormone -erythropoietin -cytokines |
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What happens to the Jak-Stat receptor when a hormone binds to it?
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it dimerizes and the Jak proteins become phosphorylated and activated
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What role do the activated Jak proteins play in the kinase cascade?
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they activate intracellular proteins by phosphorylation
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What are "STAT's" and where do they bind?
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STAT's are signal transducer and activators of transcription, and they bind to the phosphorylated intracellular proteins on the receptor
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What effect do Jak's have on STAT's that bind to intracellular receptor proteins?
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Jak's phosphorylate STAT's
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What do STAT's do once they become phosphorylated?
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they dimerize, enter the nucleus, and activate transcription by binding to specific response elements
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What happens to the other elements which bind to phosphorylated intracellular proteins on the Jak receptor
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they become phosphorylated by Jak's and are activated
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Name 3 of the major intracellular second messengers
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-cAMP
-cGMP -Ca, IP3, DAG (all grouped together) |
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How is cAMP formed?
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from ATP by adenylyl cyclase
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What activates/inhibits adenylyl cyclase?
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-Gs stimulates
-Gi inhibits |
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What does cAMP do?
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stimulates the activity of protein kinase A by binding to the regulatory domains and releasing the catalytic domains
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How many cAMP molecules are required to release 1 catalytic subunit of protein kinase A?
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2
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How is active protein kinase A reverted back to inactive protein kinase A?
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cAMP is hydrolyzed by phosphodiesterase and the regulatory and catalytic subunits recombine
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What affect does protein kinase A have on other proteins?
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phosphorylates them and as a result alters their activity
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How does cAMP affect gene transcription?
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it phosphorylates cAMP-response element binding protein (CREB) which binds to CREB-binding protein to act as a co-activator which increases gene expression
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What happens when there is an increase in intracellular cGMP?
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increased vascular tone
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Name the two different forms of guanylyl cyclase that act in cGMP
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membrane bound and soluble forms
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What factor stimulates the membrane bound guanylyl cyclase?
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atrial natriuretic factor
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What factor stimulates the soluble form of guanylyl cyclase?
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nitric oxide
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How does cGMP affect the vascular tone?
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cGMP stimulates protein kinase G which phosphorylates smooth muscle proteins
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What initiates the Ca/IP3/DAG kinase cascade?
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Hormone binds to receptor stimulating the activity of Gq
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What does the alpha-GTP subunit do in the Ca/IP3/DAG kinase cascade?
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it activates phospholipase C
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What does the newly activated phospholipase C do in the Ca/IP3/DAG kinase cascade?
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stimulates the division of PIP2 into IP3 and DAG
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What does IP3 do in the Ca/IP3/DAG kinase cascade?
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binds to a receptor on the endoplasmic reticulum and stimulates the release of Calcium
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Describe the role of the newly released calicium and DAG in the Ca/IP3/DAG kinase cascade
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Ca and DAG can stimulate protein kinase C
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What protein does Ca usually bind to in order to become cellularly active?
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calmodulin
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How many calcium binding sites are located on a calmodulin molecule?
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4
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How does the Ca/DAG/IP3 kinase cascade relate to CREB?
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Ca-calmodulin complex stimulates a kinase (CaMK II) which stimulates the activity of CREB
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