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29 Cards in this Set
- Front
- Back
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What happens when light hits the cis-retinal and to rhodopsin?
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- cis-retinal turns to trans-retinal
- rhodopsin is activated |
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What is transducin (T)?
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- protein that interacts with rhodopsin when excited by light
- binds either GDP or GTP * in dark, GDP is bound |
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What happens to transducin when rhodopsin is activated?
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- GDP turns to GTP on transducin
- transducin dissociates into Talpha-GTP and Tbetagama |
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What happens to phophodiesterase (PDE) when Talpha-GTP is dissociated?
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- Talpha-GTP activates PDE by binding and removing its inhibitory subunit (I)
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What happens after PDE is activated?
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- reduces [cGMP]
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What happens when [cGMP] is very low?
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- it closes cation channels
- preventing influx of Na+ and Ca2+ |
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What happens to the membrane when cation channels close?
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- prevent influx of Na+ and Ca2+
- membrane is hyperpolarized signaling to the brain |
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What happens to cystolic [Ca2+] when cation channels close?
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- it is reduced when it effluxes through the Na+-Ca2+ exchanger
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What is the guanylyl cyclase (GC)?
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- converts GTP to cGMP
- increase lvls of cGMP to dark lvls - reopens cation channels and returning to prestimulus state |
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How is guanylyl cyclase activated?
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- when Ca2+ is reduced
* also PDE is inhibited stopping cGMP to GMP |
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What happens when Ca2+ is too high?
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- it inhibits guanylyl cyclase inhibitin cGMP synthesis
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What happens to Ca2+ levels when there is light?
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- it declines activating guanylyl cyclase making cGMP, opening cation channels
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How is rhodopsin desensitized?
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- phosphorylation by rhodopsin kinase
- rhodopsin kinase is activated by low Ca2+ and recoverin |
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What is recoverin?
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- the Ca2+ binding protein that inhibits rhodopsin kinase at high Ca2+, but the inhibition is relieved when Ca2+ drops after illumination
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What is arrestin?
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- binds phosphorylated carboxyl terminus, inactivating rhodopsin
- trans to cis - it dissociates - rhodopsin is dephosphorylated ready for another phototransduction cycle |
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What happens when the photosensory system is shut off?
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- GTP is hydrolyzed and Talpha reassociates with Tbetagama
- PDE is bound to inhibitory subunit |
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The four stages of the cell cycle
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1.) S phase
2.) G2 phase 3.) M phase 4.) G1 phase |
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S phase
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- DNA synthesis doubles the amount of DNA in the cell
- RNA and protein also made - 6 to 8 hours |
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G2 phase
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- gap 2
- no DNA synthesis - RNA and protein synthesis continues doubling cell size - 3-4 hours |
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M phase
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- mitosis (nuclear division) and cytokinesis (cell division) yield 2 daughter cells
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G2 phase
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- RNA and protein synthesis
- No DNA synthesis |
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G0 phase
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- terminally differentiated cells withdraw from cell cycle indefinitely
- reenters at early G1 phase |
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Restriction point
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- a cell that passes this point is committed to pass into S phase
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cyclin-dependent protein kinases (CDKs)
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- regulates progression through the cell cycle
- act at specific points in the cycle by phosphorylating key proteins - the catalytic subunit of CDKs is inactive unless associated with the regulatory cyclin subunit |
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When does cyclin E-CDK2 peak?
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- near the G1-S phase boundary
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When does cyclin A-CDK2 peak?
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- during the S and G2 phases, then drops sharply in the M phase
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When does cyclin B-CDK1 peak?
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- it peaks at M phase
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ErbB oncogene
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- truncated normal receptor for epidermal growth factor (EGF)
- lacks extracellular binding site for EGF - tyrosine kinase always active and signals cell division - cancers of breast, stomach, and ovary |
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Apoptosis
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- cell death
- receptors in plasma membrane receives signals from outside cell - activates proteases that degrade protein leading to cell death |
