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Km of an enzyme is
- a measure of the affinity of the enzyme for the substrate
- the substrate concentration that gives half-maximal velocity
Enzymes can speed up the rate of a reaction because
enzymes lower the activation energy
The “lock and key” model and the “induced fit model” can be used to explain
the specificity of enzyme
The rate of a reaction
- a) can be expressed as the disappearance of the reactant over time
- b) can be expressed as the appearance of the product over time
- c) relate to the degree of saturation of the catalyzing enzyme
There is a reaction can catalyzed by both enzyme A and enzyme B. Kcat for enzyme A = 5, Kcat for enzyme B = 500, in general which one has the lower catalytic capacity
a) Enzyme A
Do you want a big or small Kcat and Km
Either a large value of kcat (rapid turnover) or a small value of KM (high affinity for substrate)
How does an enzyme's Km represent its affinity for substrate?
The lower the Km, the higher the affinity.
Drug A inhibitsthe target enzyme by competing with substrate S. Drug B acts by binding only to the ES complex to form ESB (inactive). Which statement is true?
Drug B is an uncompetitive inhibitor
inhibitor and substrate both compete for active site
- -does not bind at active site
- -binds to E (enzyme) not ES
- -Vmax decrease because Vmax can not become product
- -can not be overcome with more substrate
- -Km stays the same
- -only binds to ES complex
- -Vmax decrease because ESI (enzyme substrate inhibitor) complex can't become enzyme
- -can not be over come with more substrate
- -Km decrease
relationship between Km and Vmax
Km is the sustrate concentration and Vmax is the rate
Noncompetitive vs uncompetitive inhibitor
- A Noncompetitive does not compete with substrate site as it just binds to a another site on the enzyme, inactivating it (Km unchanged as those enzymes "don't count")
- An uncompetitive inhibitor undoes the effort the ES by by binding to it (Km lowers more ES is made to maintain equilbrium when ESI forms, making the substrate appear to have a higher affinity for the Enzyme)
increased Km and uneffected Vmax (as more S can over come inhibitor)
inhibitor molecule form a permanent covalent bond to inactivate the enzyme. Many "suicide inhibitors" for acetycholinesterase (nerve gas)
The Michaelis-Menton equation applies to nonallosteric enzymatic reactions.
Why do allosteric enzymes not obey Michaelis-Menten kinetics?
The reason for this is that allosteric enzymes must account for multiple active sites and multiple subunits. Thus, allosteric enzymes show the sigmodial curve shown above.
what type of curve do allosteric enzymes form?
sigmodial curve, more s shaped
The Michaelis constant is
Whatkind of enzymatic behavior followsa sigmoidal plot of reaction velocity versus substrate concentration represent?
The active site of an enzyme
- a) is frequently located in a cleft in the enzyme
- b) is the portion of the enzyme to which the substrate binds
- c) contains the reactive groups that catalyze the reaction
According to the Michaelis-Menton equation, what is the V/Vmax ratio when [S] = 0.4Km?
According to the steady-state assumption
the concentration of enzyme-substrate complex remains constant with time. It forms an equilbrium
Double displacement reactions
study all these
How to find Vmax of a substrate in a lineweaver-burk plot
homotropic effects are caused by...
R vs T state?
- R (relaxed)=high affinity
- T (tight)= low affinity
ATCase important factors
- -The R-state of ATCase is favored by asparate binding (the substrate)
- -An allosteric regulator would stabilize the T-state
- -ATP is an allosteric activator of ATCase by competing with CTP
H vs M isozyme
- H (heart)= aerobic
- M (muslce)= anaerobic
trypsin (after becoming cheymotrypsin) cleaves at what?
Which group of three amino acid residues can be phosphorylated to modulate enzyme activity?
tyrosine, threonine, and serine (the ones with alcohol groups)
Which of the following are correct about Protein Kinase A (PKA) and inhibitor
- a) Inhibitor interact with to PKA through electrostatic interactions
- b) Inhibitor interact with to PKA through hydrophobic interactions
- c) No phosphate transfer from ATP to inhibitor
practice drawing line weaver burke plots