MCAT Biochem Questions

Amino acid catabolism releases nitrogen in the form of ammonia. In the liver, the urea cycle prepares ammonia for excretion. Which amino acid could undergo deamidation to produce ammonia for the urea cycle? a. Glutamine b. Arginine c. Glycine d. Aspartate

A

An acidic Glu residue in a protein (neutral in its protonated form) has a pKa value of 2.3 in the wild-type protein and is found near a neutral Ile residue. What will be the effect on the pKa of the Glu residue if a mutation substitutes a positively charged Lys residue for the Ile residue? a. The pKa will decrease due to favorable ionic interactions between the deprotonated Glu and Lys residues b. The pKa will decrease due to unfavorable ionic interactions between the deprotonated Glu and Lys residues c. The pKa will increase due to favorable ionic interactions between the deprotonated Glu and Lys residues d. The pKa will increase due to unfavorable ionic interactions between the deprotonated Glu and Lys residues

A

In the pentose phosphate pathway, which enzyme catalyzes the production of 6-phosphogluconolactone? a. Glucose 6-phosphate dehydrogenase b. 6-phosphogluconolactonase c. Phosphogluconate dehydrogenase d. Glycerol 3-phosphate dehydrogenase

A

The compound in the picture is the beta-derivative of the D-glucuronic acid. The alpha-D-glucuronide differs in configuration from the beta-derivative at: (IMAGE 31) a. C-1 b. C-2 c. C-3 d. C-4

A

Which of the following depicts the structure of GTP? (IMAGE 35)

A

Which statement accurately describes the properties of maltose? a. It is a reducing disaccharide in which only one anomeric carbon is involved in the glycosidic bond b. It is a reducing disaccharide in which both anomeric carbons are involved in the glycosidic bond c. It is a nonreducing disaccharide in which only one anomeric carbon is involved in the glycosidic bond d. It is a nonreducing disaccharide in which both anomeric carbons are involved in the glycosidic bond

A

Which statement best describes the structure of the avian receptor of influenza A? (IMAGE 45) a. It is a glycoprotein with the anomeric carbon of sialic acid bound to a nonreducing disaccharide b. It is a glycolipid with three reducing sugars bound to each other through their anomeric carbons c. It is a glycoprotein with sialic acid bound to the anomeric carbon of a reducing disaccharide d. It is a glycolipid with three nonreducing sugars in which only one bond contains an anomeric carbon

A

A kinetics experiment reveals that the enzyme fumarase catalyzes the dehydration of malate with a kcat of 900 s^-1. If the substrate concentration is equal to the Km of the reaction, what is the reaction velocity when the enzyme concentration is 200 nM? a. 3.6 x 10^2 µM/s b. 9.0 x 10^1 µM/s c. 4.5 x 10^-3 µM/s d. 2.2 x 10^-4 µM/s

B

Fatty acid synthesis requires all of the following EXCEPT: I) ACP, II) ADP, III) NADPH a. I only b. II only c. I and III only d. II and III only

B

Glucose transporter proteins in the liver do not require the presence of insulin to facilitate the uptake of glucose. However, insulin does stimulate the first step in the glycolytic pathway within the liver. Therefore, in liver cells, insulin most likely: a. Hinders glucose uptake by increasing the cellular concentration of glucose b. Aids glucose uptake by decreasing the cellular concentration of glucose c. Hinders glucose uptake by using the ATP needed by the glucose transporter proteins d. Aids glucose uptake by providing the ATP needed by the glucose transporter proteins

B

Relative to FADH2, at what energy state does NADH enter the electron transport chain? a. NADH enters at a lower energy state than FADH2 b. NADH enters at a higher energy state than FADH2 c. The energy state at which NADH enters cannot be predicted d. NADH enters at the same energy state as FADH2

B

Some inhibitors bind irreversibly to enzymes by covalent attachment. Would the kinetics seen under these conditions (V vs. [S] curve) be similar to those seen with a reversible noncompetitive inhibitor? a. Yes, because it would reduce the Km of the reaction b. Yes, because the net effect would be a loss of active enzyme available for the reaction c. No, because if enough substrate binds to the active site the reaction will reach Vmax d. No, because Km will increase and Vmax will stay the same similar to competitive inhibition

B

The amino acids Asp6, Asn9, Thr10, His11, and Arg27 are found near the ADP binding site of PanK3. Which two amino acids contribute to the stabilization of ADP binding? a. Asn9 and Thr10 b. His11 and Arg27 c. Asp6 and Arg27 d. Asp6 and His11

B

Under physiological conditions, peptide bond formation and degradation both require enzymes, but only formation requires coupling to GTP hydrolysis. Based on this information, peptide bonds under physiological conditions are: a. Both thermodynamically and kinetically stable b. Thermodynamically unstable but kinetically stable c. Thermodynamically stable but kinetically unstable d. Both thermodynamically and kinetically unstable

B

What is the equilibrium constant for the binding of the fourth NAD+ to GAPDH (K'4 = 1.5 x 10^5)? a. 1.5 x 10^-5 b. 6.7 x 10^-6 c. 1.5 x 10^5 d. 6.7 x 10^6

B

Which amino acids are most likely present at the dimerization interface of proteins? a. Polar amino acids b. Hydrophobic amino acids c. Positively charged amino acids d. Negatively charged amino acids

B

Which methods separate proteins based on their charge? I) SDS-PAGE, II) isoelectric focusing, III) ion-exchange chromatography, IV) affinity chromatography a. I and II only b. II and III only c. I, II, and III only d. II, III, and IV only

B

With respect to their relative pH, how do the cytosol, intermembrane space of the mitochondria, and the mitochondrial matrix compare? a. pH of mitochondrial matrix < pH of cytosol = pH of intermembrane space b. pH of mitochondrial matrix > pH of cytosol > pH of intermembrane space c. pH of cytosol > pH of intermembrane space = pH of mitochondrial matrix d. pH of intermembrane space < pH of mitochondrial matrix < pH of cytosol

B

A description of the structures of four proteins is shown in the table. Which protein has the highest electrophoretic mobility in SDS_PAGE under non-reducing conditions? (Note: there are no disulfide interactions unless stated in the table) (IMAGE 37) a. Protein 1 b. Protein 2 c. Protein 3 d. Protein 4

C

Acetylation of lysine residues in histones increases gene expression because: a. DNA is tightly bound to negatively charged amino acids on histones b. The carboxyl oxygen atoms in acetyl groups form hydrogen bonds with nitrogenous bases c. The salt bridges between charged amino acids and phosphate groups are disrupted d. Lysine residues in histones associate with positively charged phosphate groups in DNA

C

In designing an experiment to measure the amount of radioactivity incorporated into sT-loop, the researchers should use which type of 32-P labeled ATP? a. Alpha-32-P ATP b. Beta-32-P ATP c. Gamma-32-P ATP d. Delta-32-P ATP

C

Rate experiments were performed to determine the effect of an inhibitor on the kinetics of a reaction catalyzed by an enzyme. The results were plotted, as shown. Based on the data, which statement best describes the interaction between the inhibitor and the enzyme? The inhibitor: (IMAGE 36) a. Irreversibly binds the enzyme b. Can only bind the enzyme after the enzyme has already bound substrate c. Binds the enzyme and the enzyme-substrate complex with the same affinity d. Prevents the binding of the enzyme to its substrate by occupying the enzyme's active site

C

Specific activity is a measure of: a. The total units of an enzyme in solution b. The amount of substrate converted to product in one minute c. The enzyme units per milligram of total product in solution d. The concentration of enzyme that results in a particular rate of catalysis

C

The enzyme responsible for the conversion of L-hydroxyacyl-CoA to ketoacyl-CoA is a: a. Hydratase b. Reductase c. Dehydrogenase d. Transacylase

C

To confirm that beta-oxidation is NOT impaired in healthy controls, researchers most likely measured which metabolic step in PBMCs? a. The exportation of citrate to the cytoplasm to produce acetyl-CoA b. The release of CO2 from malonyl-CoA c. The translocation of acylcarnitine to the mitochondrial matrix d. The depletion of reduced electron carriers

C

Which of the following could affect any of the dissociation constants for hemoglobin? I) decreasing the temperature, II) adding NH3, III) increasing the [O2] a. I only b. III only c. I and II only d. I, II, and III

C

An enzyme is most effectively inhibited by uncompetitive inhibitors when: I) the substrate concentration is decreased, II) the substrate concentration is increased, III) the inhibitor concentration is increased a. I only b. III only c. I and III only d. II and III only

D

Compared to normal glycogen, the amount of what type of bond is decreased in Lafora bodies, which characteristically lack branching? a. Phosphomonoester b. Phosphodiester c. Alpha-1,4-glycosidic bond d. Alpha-1,6-glycosidic bond

D

In all fermentation processes the final acceptor of electrons from NADH is: a. O2 b. NAD+ c. An alcohol d. An organic compound

D

Lipolysis is followed by beta-oxidation, in order to ensure the cell can harvest ATP from lipid molecules. Which of the following is true of this process? a. An isomerase and a reductase are required for complete oxidation of a monounsaturated fatty acid b. Lipolysis of a DAG will generate twice the amount of fatty acids and glycerol, compared to the lipolysis of a MAG c. Unlike cell respiration, fatty acid catabolism starts in the mitochondria and finishes in the cytosol d. The cell requires more than twice the number of NAD+ electron carriers compared to FAD electron carriers, in order to harvest ATP from fatty acids

D

Which experimental procedure(s) must scientists use to determine Vmax and Km of an enzymatic reaction using the Michaelis-Menten model? They must ensure that: I) they only measure the initial reaction rate for each substrate concentration, II) total enzyme concentration is much greater than the Km of the reaction, III) each initial substrate concentration tested is much greater than the enzyme concentration a. I only b. III only c. I and II only d. I and III only

D

Which of the following compounds is NOT a gluconeogenic precursor or substrate? a. Lactate b. Glycerol c. Oxaloacetate d. Phosphogluconate

D