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Sample Exam III
Terms in this set (70)
What is the Michaelis-Menten expression under uncompettive inhibition?
What is the Line-weaver Burke expression under competitive inhibition?
How many sugar molecules does a ketotetrose represent?
What kind of functional group does an aldose contain?
How many carbon atoms does a fructose contain?
The cyclic six-membered ring form of a sugar is called:
Which closed-ring form of D-glucose is most energetically stable?
In what conformation does lysozyme cause the D-ring sugar to adopt in its substrate in order to facilitate catalysis?
What is the identity of the catalytic triad in serine proteases?
What is the most suitable substrate for lysozyme?
What are the catalytic residues of lysozyme?
what is the highest energy phosphate containing compound that we have discussed?
What gets put into the oxyanion hole in the active site of serine proteases?
The O- generated during attack of the substrate peptide backbone C=O
The Michaelis constant, Km, is
The concentration at which the Vo is half maximal
A measure of the catlytic effeciency of an enzyme reaction is
Some enzymes have attained perfection. Enzymes that fall into this category have
kcat/Km which is between 10^8-10^9 M-1 s-1
The lines on a Lineweaver-Burk plot for an noncompetitive inhibitor, with the variation or alpha (=1.0, 1.5, 20.0) are characteristically
What downstream product of ATCase acts as a feedback inhibitor?
What is true about a metabolic pathway?
1. they are irreversible
2. they are regulated
3. there is a committed step
4. they are made up of, largely, reversible steps
What is the equation for alpha under competitive inhibition?
(1 + [I]/KI)
What is the half-life of a first order reaction with a rate constant of 1.1
555 x 10^-4 sec-1
which is the most stable form of a pyranose sugar?
The rate determining step in a sequence of reactions in a metabolic pathway is ____________.
a step with a large negative free energy
Through what major pathway or mechanism are NAD+ and FAD regenerated from NADH and FADH2, respectively
What is the name of the enzyme target for the nerve poison sarin?
What is the half-life of a second order reaction with a rate constant of 1.155 x 10^-3 and an initial substrate concetration of 1.2 x 10^-1?
oxidation occurs with the:
loss of electrons
what is the reduced form
of nicotinamide adenine dinucleotide
what is the oxidized form of nicotinamide adenine dinucleotide
What is the oxidized form of flavin adenine dinucleotide
What is the reduced form of flavin adenine dinucleotide
What role does glutamic acid 35 in lysozyme play in the first catlytic step (note: GluH is the neutral form of glumamic acid)
GluH(35) protonates O1 of the D-ring sugar
what is the name of the proenzyme form of an enzyme
At what concentration of S will vo=0.80 Vmax?
A competitive inhibitor (pyrrole-2-carboxylate) or prolyl isomerase was added in a concentration of 1.88x10^-3 M to a solution containing prolylisomerase and L-proline. The Vmax, and Km for the uninhibited enzyme at 25degreeC are 20M/s and 1.53x10^-2 M, respectively, and the initial substrate concentration was 2.456x10^-2 M. The Ki of this inhibitor is 7.23x10^-4 M. What was the initial velocity of the uninhibited enzyme?
For the Michaelis-Menten reaction, k1= 2x10^2 M-1s-1, k-1= 3x10^2 s-1 and k2= 5x10^2 s-1. Calculate the Km.`
KM= (k-1 +k2)/k1
Calculate the change of G for the following reaction at 44degC: ATP--> AMP + PPi with the following concentrations:
[ATP]= 10 mM
[AMP]= 1.25 mM
[PPi]= 2.5 mM
Compute the free energy for the overall reaction below using the half reactions that you were asked to remember:
phosphenolpyruvate + ADP --> pyruvate + ATP
What is the equilibrium constant for the hydrolysis of glucose-1-P at 25 degC
Compute the catalytic constant, kcat, from an eznymatic raection with a Vmax and [E}T of 15 mM/s, and 2.4x10^-2 M, respectivley
what is the role of the aspartic acid in the catalytic triad in serine proteases?
stabilize the charged state of the catalytic histidine residue
copmute the free energy for the overall reaction below using the half reactions near the end of the exam:
creatine + ATP --> phsophocreatine + ADP
In what part of the cell does the metabolic oxidative phosphorylation occur?
With what catalytic residue does diisopropylphosphofuridate (DIPF) react with in preoteases?
An enzyme is considered to have evolved to its most efficient form if
Kcat/Km is near the diffusion-controlled limit
The constiutent of the petiodglycan from bacterial cell walls that hleps them resist the action of proteases is:
In general, enzymes increase the rates of chemical reactions by
preferentially stabilizing the transition state
a linear polymer of glucose with beta(1-4) linkages
In the lysozyme reaction the subsite D NAM is in the _______ conformation.
What is the role of His119 in the first step of the RNAse A mechanism?
it donates a proton to the phosphoester bond being broken
If the protein environment surrounding Glu35 in lysozyme, which is non-polar in the wild-type, what impact would you expect it to have on the catalytic rate?
it would be reduced
The formation of a Schiff's base in the enzymatically catalyzed decarboxylation of acetoacetate that we discussed in class is an example of:
In a line-weaver burke plot of 1/vo vs 1/[s] for an enzyme catalyzed reaction the presence of a competitive inhibitor will alter the
- intercept o the 1/[s] axis
- slope of the lines
What is the half-life of a first order reaction with a rate constant of 7.22x10^-4 sec-1?
protein kinases are involved in
the phosphorylation of a wide variety of proteins
ATP is a high energy compound because hydrolysis of ATP:
-relieves electrostatic repulsion
- produces products that are more favorable hydrated than ATP itself
Cells control or regulate the flux through metabolic pathways by:
1. allosteric control
2. covalent modification of enzymes
3/ genetic control of the concentrations of enzymes
4. non-equilibration concetrations of metabolites
alpha amylose is a linear polymer of several thousand glucose residues connected via
alpha(1-4) glycosidic bonds
Which of the molecules below has a carbon in its highest oxidation sate?
In the following reaction, which molecule is the oxidizing agent?
CH3-CH2-OH + NAD+ ---> CH3-CHO- + NADH + H+
The ubiquitous chemistry of acetyl-CoA is centered on its high-energy ____ bond.
Which closed form of D-glucose is the most energetically stable?
What is the primary mechanism that serine proteases emply in order to increase the reate of peptide hydrolysis?
it provides the oxyanion hole
A pH/rate curve with a inflection point at pH~4 suggests the involvement of a(n) _____ in the catalytic step.
acidic amino acid
A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic terminal is termed a
how may steroisomers are possible for an aldohexose?
How many carbon atoms does an aldopentose contain?
The lines of a line weaver burke plot for a COMPETITIVE INHIBITOR, with the variation of alpha (=1, 1.5, 2.0) are characterisitcally
coincident on the y-axis at 1/vmax
An inhibitor would be most promising as a drug canditate if it had a k1 or:
In order for an enzymatic reaction obeying Michaelis-Menten kinetics to reach 90% of its max velocity,
[S] would need be be 9 Km
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