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Biochemistry Exam II


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Differentiate berween endocrine autocrine and paracrine
Endocrine - hormone acts on cells in distance
Paracrine - hormone acts on cells nearby
Autocrine - hormone acts on cell from which its secreted
2 types of membrane receptors
Metabotropic-changes activity of metabolic enzymes
Ionotropic- let ions into or out of cell, associated with depolarization, classical synaptic transmission
How does cocaine act on cell
Blocks dopamine reuptake and leads to overexcitability of cells
Describe steps of synapse
1.Depolarization opens voltage gated Ca channel
2.Ca leads to vesicle fusion and release of NT
3. NT diffuses over synaptic cleft and binds to ligand gated channel
4.NT also acts on G protein linked receptor
5.NT is reuptaken
How is Ach degraded
by enzyme Ach esterase
How do cells become polarized
Na/K pump gets 3 Na out, 2 K in, this creates high Na outside, high K inside
-creates NEGATIVE charge inside
How does nicotine act on cell
Overstimulates N1 and N2 receptors
How does tetrodotoxin act on cell
Block voltage gated sodium channels
How does boulinum toxin act on cell
Botulinum toxin blocks Ach release, leads to paralysis
Describe myasthenia gravis
Autoimmune disorder where nicotinic type I (N1) Ach receptors are attacked and destroyed
Number of N1 receptors is decreased and this causes decrease in muscle response to Ach
How is myasthenia gravis treated
With drugs that inactivate Ach esterase, which will prevent degrading of Ach and increase its half life
Explain cascade of events involving trimeric g proteins
1. Hormone or NT binds serpentine receptor (heptahelical receptor)
2.Allosteric changes in serpentine proteins induce G protein to dissociate into alpha subunit and dimeric beta gamma subunit, alpha subunit kicks out GDP and binds GTP
3. Activated alpha subunit is free to drift until it encounters target enzyme, so alpha subunit stays active for limited time and then dissociates
What does cAMP activate
protein kinase A
What does cAMP do
cAMP activates PKA which is a Ser/Thr kinase that phosphorylates numerour target enzymes. One of the many targets is CREB, which is a transcription activator
Which amino acids get phosphorylates
Describe action of cholera toxin
Prevents G alpha s from hydrolyzing ATP
Adenylated g protein sabotages ability of g protein to turn GTP into GDP, so GTP cant turn off
Result - INCREASED cAMP (mostly in intestinal cells)
Desribe action of pertussis toxin
Prevents G alpha i from binding GTP, results in increased cAMP
Describe action of beta blockers
Prevents activation of G alpha s , results in decreased cAMP
What activates PLC
G alpha q
PIP2 cleavage by phospholypase C yields ...
DAG and IP3
PIP 2 phosphorylation leads to
PIP3 which activated PKB
Which toxin is agonist for PKC
Phorbol ester
What is the effect of NO
How does nitroglycerine work
Slowly breaks to NO which causes vasodilation and turned off when oxidized to nitrate
How does Viagra work
Specific to isoform of cyclic nucleotide found in penis
Inhibits cyclic GMP phosphodiesterase
What does caffeine do
Inhibits phosphodiesterase, thus increasing cAMP in cells
Phospholipase C associates with what subunit
Beta gamma subunit
What does DAG do
Stays with membrane
Stimulates PKC to phosphorylate Ca dependent targets
Phorbol ester
Mimicks DAG, activates PKC, can lead to cancer
What does IP3 do
Goes to ER, stimulates release of Ca, which activates PKC, which in turn activates Ca calmodulin kinase
Amplification of signaling
Very low concentration of hormone has large intracellular effect

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