8 Flashcards
(30 cards)
How do we measure the velocity/rate of reaction?
The amount of substrate that has disappeared
or
The amount of product that has appeared
Both over time
How is Vo measured?
by measuring product formation as a function of time, and then determining the velocity soon after the reaction has started.
You make the measurment in the first mins/secs of the reaction
What is the difference between continous and discontinous enzyme assays?
Continous: Measure product formation continously over time
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Discontinous: Measure product formation over a set period of time
What substrate is often used in enzyme kinetics experiments to make it easier to measure?
A chromogen is used to allow the use of colorimeter or a spectrophotometer.
What is the difference in the graphs of measuring Vo and measuring Vmax?
Vo: It is a graph of product Concentration/time
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Vmax: Graph of Vo/substrate concentration
What is Vmax?
When the enzyme is fully saturated and working at max speed
What is Km?
It is the amount of substrate at 1/2 Vmax
What is the relation between Km and affintiy?
They are inversely proportional (More Km = less affintiy and vice versa)
What is michalis-menten equation for intial velocity
What is the reciprocal (1/X) of the Michaelis-Menten equation
What is the slope of the reciprocal (1/X) of the Michaelis-Menten equation
Km/Vmax
What is the x and y intercepts in the reciprocal (1/X) of the Michaelis-Menten equation
Y= 1/vmax
X= -1/Km
Do Isoenzymes have different kinetics and give me an example?
Yes
Glucokinase and hexokinase
G: Higher Km, lower affinity
H: Lower Km, higher affinity
What do allosteric enzymes usually regulate?
The commited step in a pathway
What type of curve does the allosteric enzyme show?
A sigmoidal curve
What regulates the allosteric enzymes?
Feedback inhibtion by the product of the pathway
What are the two states that allosteric enzymes can be in?
They are:
Tense state: low affinity for substrate
Relaxed state high affinity for substrate
When are allosteric enzymes in the tense state and when are they in the relaxed state?
Tense: When no substrate is available
Relaxed: When substrate is available On substrate binding all subunits go into the ‘R’ state
A mutation in which allosteric enzyme causes gout?
A mutation in Phosphorybosylpyrophosphate synsthatase (PRS)
in the purine nucleotide synthesis pathway
What are the two main enzyme inhibtor types and what are the main differences between them?
Irreversible: Covalently bound
Progresses over time.
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Reversible:
Bound by weak bonds
What are the three types of reversible enzyme inhibtors?
a) Competitive (many have therapeutic applications)
(b) Non-competitive (simple and mixed)
(c) Uncompetitive
What is an example of an irreversible enzyme inhibtor?
Nerve gases, and pestcides
Contain: Organophosphrus
Organophosphrus combines with serine residues in the enzyme actylcoline estrase causing its inactivation
What are competitive inhibitors and how do they work?
inhibitors that are analogus with the substrate and therefore compete with it for the active site
How can inhibition caused by competitve inhibtors be reversed?
By adding excess substrate
