L4 enz activ: kinetics and inhib

Question 1

LO2: how reac rate vary as func of E and S conc. V vs [S] graphs. enz kinetics.

Answer 1

• enz optim temps and ph. Vo init rate. max velocity, rectang hyperbola.

Question 2

LO3: define activity, internat unit of enz activ, Km and Vmax. MM mod enz ctal.

Answer 2

• MM proposes specif complex btw E and S necess intermed in catal. V0=Vmax[S]/Km+[S]. Km=michaelis const. Vmax= max velocity mol/min. predicts hyperbol V0 vs [S], not all enzs obey eg if show coop.
  Vmax= max rate when all enz AS sat, very dep on [enz].
  Km= [S] that gives half max velocity.

Question 3

LO4: anal and interp kinetic data for enz catal reac. work out rates. apply Km and Vmax.

Answer 3

• Km meas affin of E for S. low Km=high affin. high Km=low. eg HK higher affin for gluc than GK.
• linewaver burk plot- recip of MM=straight line. y intercept=1/Vmax so higher= low Vmax. x intercept=-1/Km so lower=lower Km= higher affin.
• Vmax is meas of amnt per unit time. 1 unit= amnt of enz that convs 1umol of prod per min stand conds. often exp as stand rate- per L serum or g tiss. rate propor to [enz].

Question 4

LO5: desc effs of enz inhibs on enz kinetics and disting by graphs. how alt shape of V vs [S] or linewaver, and determ type inhib from these.

Answer 4

• inhibs prev/slow enz reac eg drugs.
  irrev bind v tight, gen cov eg nerve gas sarin.
  rev non cov, freely dissoc. comp bind AS aff Km NOT Vmax as overcome by incr [S], decr propor E bound to S, eg tamiflu. non comp bind other site but not allost, decr turnover so aff Vmax NOT Km.

Question 5

LO1: effs of enzs on chem reacs. key feats and role of AS.

Answer 5

• S to P. TS= high energ intermed btw. Ea=min energ S req to allow reac.
• incr rate reac: incr temp= more molecs with Ea. incr conc= more chance collis. but these not in biol sys. enzs- decr Ea, facil form of TS.
• imp feats: v specif to S and type reac. unchanged after eac even if charge change dur. dont aff eq. most are prots. some req inorg ion cofacs or coenzs organ comps act as temp carriers of grps in reac. if tight cov linked to enz=prosthet.
• enzs inv in genet disords, metab dis, mut destr func/slows/overactive eg CA RAS mut. meas enz for diag. inhib by drugs.
• AS- where S bind and chem reac occ. few aa. from diff parts prim seq. clefts or crevices to excl water. complem shape to S lock key OR induced fit S bind chnages conf to complem. S bound by multip weak bonds.