I
3
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1. Many enzymesareregulatedby bothallostericfactorsandby phosphorylation.Please
explainbriefly:
o whatpbospborylation
is
. why it is an effectivemethodof controlling enzymaticactivity from a structural
standpoint
. why it is an effectivemethodof contrclling enzymaticactivity from a biological
perspectlve
. key similarities anddifferencesbetweenthe threemain regulatorymechanismsthat
we havestudied:allostericeffectors,selectiveproteolysis,andphosphorylation.
(15points)
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2. In class,you receivedtwo handoutson theregulationof glycogenphosphorylase
activity. Oneof thesedetailstheeffectson theenzyme'sactivityof bothallosteric
regulatorsandcovalentregulationby phosphorylation,
andtheotheroutlinestheweb of
kinaseandphosphatase
reactionsthat ultimately determinesthe phosphorylationstateof
the enzyme.Pleasereferto thesefiguresandthenanswerthefollowingquestionsabout
glycogenphosphorylase.
a) Figure10.20on page230of your text bookshowstherelativeactivityof glycogen
phosphorylase
undervariousconditions.Pleaseexpiain
o whatthe curvesindicate(e.g.,Whatis changingalongeachaxis? Whatdo the
differentlinesrepresent?How shouldtheuninitiatedinterpreta high valueversusa
Iow value?)
r how this figuredemonstrates
theresponse
of the glycogenphosphorylase
enzymeto
both intracellular and extracellular stimuli
r the biochemicallogic thatunderliestheseresponses
(i.e.,why is it in thebest
biochemicalinterestof a cell or organismfor this enzymeto respondin this manner).
Put simply,pleaseexplainwhatis shownby this figureandthenexplainwhy it makes
goodsensefrom a biologicalperspective.In your answer,you may wish to referto other
diagramsor otherinformation,andyou shouldbe sureto explainthelogic of both the
intracellularresponsiveness
( 10points)
andtheextracellular
responsiveness.
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Question#2, continued...
b) Thecomplementof the glycogenolysis
processcatalyzedby glycogenphosphorylase
is glycogensynthesis.This processis facilitatedby glycogensynthase.As shownon one
of your handoutsandagainon page312in your text,glycogensynthase
is alsoregulated
bothby allostericeffectorsandby phosphorylation.
Pleaseexplainwhy it is logicalthat
bothinsulinandglucose-6-phospfhate
stimularetheactivityof this enzyme.(5 points)
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