Kinetics and Regulation Flashcards
What is meant by reaction velocity?
it measures the how much reactant disappears as function of time or how much product appears.
V= -dt [A]/dt= dt [P]/dt a= substrate P= product. d=decrease or increase of substrate [ ].
What is enzyme kinetics?
studying the rate of enzyme-catalyzed reactions.
What does the Michaelis-Menten equation describe? Write the equation.
the initial reaction velocity as a function of substrate concentration.
(also determines variation of enzyme activity). V0= Vmax [S}/[S] + KM
Define what vmax and km are. What do they mean?
Vmax- maximum velocity possible, only achieved when all of the enzyme (ET) is bound to substrate. V= k2[E]T
Km- Michaelis constant that is the substrate concentration that yields 1/2 vmax.
Km is also total of constants: kM= k-1 + k2/k1; Km values for enzymes vary widely and is approximately substrate [ ] in vivo (living things).
What components make up Lineweaver- Burk plot? What are the variables for graph?
it is a double reciprocal plot that yields straight line equation:
composed of inverse of Vo as a function of inverse of substrate concentration
1/Vo= kM/Vmax times 1/S + 1/Vmax.
Slope= KM/Vmax; Y- intercept: 1/vmax ; x intercept: -1/Km
What is catalytic efficiency? What are the variables involved? What are the conditions for this to occur. How is the michaelis-menten equation adjusted for catalytic efficiency?
the efficiency of an enzyme in catalyzing a reaction.
Kcat/Km is a measure of catalytic efficiency, as it takes into account, both rate of catalysis (kcat) and nature of enzyme substrate interaction (Km)
stems from [S} being less than Km, since a lot of active sites are unoccupied and the free enzyme, [E}= E{T}
Michaelis equation will yield Vo= kcat/Km [S}{E]T
What are allosteric enzymes? How do they work?
enzymes that control the flux of biochemical reactions in metabolic pathways.
Due to their regulatory properties, they allow for generation of complex metabolic pathways.
Mechanism: activator or inhibitor molecule will bind to specific regulatory site on enzyme (not active site), which induces conformational or electrostatic changes to either enhance or reduce activity.
Distinguish between concerted model and sequential model of allosteric enzymes. Which molecule is a good example of this?
Concerted model - A conformational change in one subunit will be conferred to ALL other subunits (one r state, lead to all 4 being in r state)
Sequential model-subunits undergo sequential changes in structure.
when measuring the disappearance of A (substrate), what is the velocity of reaction? Write the equation and describe relationship between variables.
V= k [A], k is a proportionality constant.
The velocity of reaction is proportional to the reactant concentration.
What’s the difference between first order reaction? vs Second- order reaction? Unit difference?
First order reaction- The velocity is proportional to reactant concentration (as V increases, concentration of reactant gets higher) V=k [A ]. measured in s-1 units.
Second order reaction: bimolecular rxns where two reactants are involved. The rate of reaction is proportional to the product of the two reactants.
V= k [A}^2 AND V= k [A] [B}
proportionality constant k has M-1 s-1 units.
How is initial velocity (Vo) measured?
by measuring the product formation as a function of time, at beginning of reaction, and then determining velocity soon after reaction has started.
How should you evaluate enzyme kinetics? Why?
measure velocity as a function of substrate concentration with fixed amount of enzyme concentration. This is b/c enzyme [ ] is constant, while substrate concentration may vary depending on environmental conditions. this is when t= 0 and [P] = 0
E+S > ES > E + P ; there are rate constants on arrows in equation. k1 is for first step E and S form ES complex (k-1 is the reverse reaction of this) k2 is the second step ES to E + P(k-2 is reverse rxn, but it is ignored by keeping [P] 0. )
When viewing velocity vs substrate concentration graph, why does the curve eventually level off?
it levels off since the enzyme is saturated and V max has been reached.
What are the two fates of the ES complex?
ES can proceed to form Product P with rate constant k2, or go backwards and dissociate into E + S, k-1.
What is Vmax directly dependent on? independent? what happens at high substrate concentrations, when [S] is higher than Km?
depends on enzyme concentration.
Vmax independent of substrate concentration
if [S} is higher than Km, Vo= Vmax
What occurs when vmax is reached?
When vmax is reached, the total amount of enzyme is bound to substrate, enzyme is saturated. Also adding more substrate will not affect velocity, since it’s already at its max.
When does Km approximate dissociation constant of ES complex?
When k-1 (reverse step) is greater than k2 (forward, form product)
what does a high Km indicate in terms of binding? Low Km?
High Km- weak binding
low Km- strong binding
What is the steady state?
the assumption that concentration of reaction intermediates remain constant throughout reactions (they’re being produced as being consumed).
Which two enzymes play a key role in metabolism of alcohol? What are the reactants and products in the equation.
Alcohol dehydrogenase and Aldehyde dehydrogenase.
Ch3ch2OH (ethanol) + NAD+ using alcohol dehy. forms CH3CHO + NADH and H+
CH3CHO + NAD+ + H20 using aldehyde dehy. forms CH3COO- (acetate) + NADH + 2H+
Explain what high km and lowe km mean in terms of catalysis and substrate concentration.
With low km, their is a high affinity, and more catalysis occurs at lower substrate concentrations
High km- lower affinity; less catalysis at lower substrate concentration.
How does Km levels affect how people respond to alcohol consumption?
After drinking alcohol, some people may have symptoms of facial flushing, rapid heart beat due to excessive amounts of acetaldehyde in the blood. 2 different forms of acetaldehyde dehydrogenases in people.
Those individuals susceptible to symptoms have inactivated low km. They instead have HIGH km, and cannot process all of acetaldehyde (weak binding) , some acetaldehyde appears in blood, causing symptoms.
What is one enzyme/Substrate pair that has high affinity of binding? Low affinity?
High affinity (due to low km value)- E: Lysozyme and S: Hexa-N-acetlyglucosamine Low affinity (high km)- E: carbonic anhydrase and S: CO2.
Write an equation for when the total enzyme concentration, [E] T is known.
Vmax= k2[E] T or k2= Vmax/[E}T