Block 2 Practice Questions 2023 PDF

**[Macromolecules]{.smallcaps}** 1\. Which one of the four classes of biologically important molecules does **insulin** belong to? \(A) Carbohydrates \(B) Proteins \(C) Nucleic acids \(D) Lipids \(E) Terpenes **[Amino acids]{.smallcaps}** 2\. The following titration curve is identified for o...

**[Macromolecules]{.smallcaps}** 1\. Which one of the four classes of biologically important molecules does **insulin** belong to? \(A) Carbohydrates \(B) Proteins \(C) Nucleic acids \(D) Lipids \(E) Terpenes **[Amino acids]{.smallcaps}** 2\. The following titration curve is identified for one of the proteinogenic amino acids (used to make proteins). Which of the following is **[TRUE]**? \(A) The amino acid may be any of the nonpolar, aliphatic amino acids \(B) The first pKa represents protonation/deprotonation of the amine \(C) The amino acid cannot be a member of the sulfur-containing classification \(D) The side chain contains a carboxylate functional group \(E) The side chain contains an amine functional group 3\. Of the 20 standard amino acids, only \_\_\_\_\_\_\_\_ is not optically active. The reason is that its side chain \_\_\_\_\_\_\_\_\_. \(A) Ala; is a simple methyl group \(B) Gly; is a hydrogen atom \(C) Ile; is unbranched \(D) Lys; contains a nitrogen \(E) Pro; forms a covalent bond with the side chain 4\. Two amino acids of the standard 20 contain sulfur atoms. They are: A. Cys and Ser B. Cys and Thr C. Met and Cys D. Met and Ser E. Ser and Thr 5\. All of the amino acids described in class, except for Pro, contain a: A. Primary amino group B. Carbonyl group C. Carboxyl group D. Ester group E. Thiol group 6\. The chirality of an amino acid results from the fact that its alpha carbon (Cα) A. Has no net charge B. Is a carboxylic acid C. Is bonded to four different chemical groups D. Is in the [D]{.smallcaps} configuration for those incorporated into proteins E. Is symmetric 7\. The amino acid Glu has an R group that makes Glu: A. A zwitterion with no net charge at pH = 7. B. Found in proteins in the [d]{.smallcaps}-configuration. C. Never found in proteins D. Nonionic E. Function in acid/base catalysis 8\. Titration of valine by a strong base, for example NaOH, reveals two pK's. The titration reaction occurring at pK~2~ (pK~2~ = 9.62) is: A. --COOH + OH^-^ \--COO^-^ + H~2~O B. --COOH + \--NH~2~ \--COO^-^ + \--NH~2~^+^ C. --COO^-^ + \--NH~2~^+^ \--COOH + \--NH~2~ D. --NH~3~^+^ + OH^-^ \--NH~2~ + H~2~O E. --NH~2~ + OH^-^ \--NH^-^ + H~2~O 9\. In a highly basic solution, pH = 13, the dominant form of Gly is: A. NH~2~---CH~2~---COOH B. NH~2~---CH~2~---COO^-^ C. NH~2~---CH3^+^---COO^-^ D. NH~3~^+^---CH~2~---COOH E. NH~3~^+^---CH~2~---COO^-^ 10\. For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have: A. A net negative charge B. A net positive charge C. No charged groups D. No net charge E. Positive and negative charges in equal concentration 11\. Arg has the following properties of significance in protein chemistry? \(A) Often found in β-turns because of the low steric constraints of the R group \(B) Involved in π−π stacking interactions \(C) Found in hydrophobic regions of proteins \(D) Can function as an acid/base \(E) Capable of forming a covalent bond as a catalytic strategy **Protein Structure** **12. Amino acids** are joined during a(n) \_\_\_\_\_\_\_\_\_\_ reaction and a(n) \_\_\_\_\_\_\_\_\_\_bond/linkage is formed. \(A) hydrolysis; amide \(B) condensation; peptide \(C) neutralization; ether \(D) oxidation; ester \(E) reduction; thioester 13\. The total number of proteinogenic amino acids (used to make proteins; does not include posttranslational modifications) in humans is: A. 19 B. 20 C. 21 D. 22 E. 23 14\. The [acetyl]ation posttranslational modification occurs on what amino acid? A. His B. Cys C. Lys D. Val E. Ala 15\. Some proteins contain amino acids that are modified following the incorporation into a protein. Examples include: A. Oxidation (hydroxylation) of Pro B. Decarboxylation (removal of CO~2~^-^) of Glu C. Glycosylation of Ala, Val, or Leu D. Palmitoylation (lipid addition) to Met E. Epinephrine (adrenaline) 16\. Which of the following is a force stabilizing protein structure? \(A) Hydrogen bonding \(B) Hydrophobic effects \(C) Electrostatic interactions \(D) Disulfide bonds \(E) All of the above 17\. In the dipeptide shown, what position denotes a pivot point? \(A) 1 \(B) 2 \(C) 3 \(D) 4 \(E) 5 18\. Which is the best description of parallel β-sheets? \(A) One amino acid makes two hydrogen bonds with two different amino acids of the adjacent strand \(B) Adjacent, interacting peptides are oriented such that the N-terminus of one aligns with the C-terminus of the other \(C) Consists of R groups in *trans* with hydrophobic side chains on one side of the sheet and hydrophilic side chains on the other \(D) Tend to twist toward the left \(E) A carbonyl oxygen makes a hydrogen bond to every n+4 amide hydrogen 19\. Phosphorylation of a protein is a posttranslational modification that usually serves which purpose? \(A) Targets the protein for degradation in the lysozome \(B) Often found on the extracellular surface to protect the cell from proteolysis or immune attack \(C) Regulates the function of this protein \(D) To increase the affinity for calcium, aiding in blood clotting \(E) Anchors protein to lipid membrane 20\. Which of the following is a description or terminology used to denote quaternary structure? \(A) Ordered sequence of amino acids \(B) Subunits of oligomers \(C) Loops and coils \(D) Transmembrane domain \(E) α-Helix or β-pleated sheet 21\. Of the levels of protein structure, which are formed and maintained predominantly by noncovalent bonds? \(A) Primary structure \(B) Secondary structure \(C) Tertiary structure \(D) B and C \(E) All of the above 22\. Which of the following statements does **[NOT]** accurately describe protein structure? \(A) Folds and domains are terms used to describe quaternary structure \(B) Every molecule of the same protein folds into the same tertiary structure in the native state \(C) Proteins fold into the correct structure because of the primary structure or with help from heat shock proteins \(D) Temperature and pH can cause proteins to unfold (denature) \(E) The shape of protein is typically globular, fibrous, or membrane-spanning **[Protein-Ligand Binding]{.smallcaps}** 23\. Myoglobin is an oxygen-carrying molecule in muscle. It consists of just one polypeptide chain. Myoglobin **lacks**: \(A) Primary structure \(C) Tertiary structure \(B) Secondary structure \(D) Quaternary structure \(E) Class 24\. A mutation in hemoglobin that changes an Asp to a Met alters the binding affinity for oxygen and carbon monoxide so that binding constants are changed as follows: Which of the following is **[TRUE]**? \(A) The mutant hemoglobin (with Met) binds carbon monoxide with a lower binding affinity than oxygen \(B) The Asp to a Met is a conservative substitution \(C) The wild-type hemoglobin (with Asp) has a higher binding affinity for oxygen than carbon monoxide \(D) The mutation has a greater effect on oxygen binding than carbon monoxide \(E) B and D 25\. A protein was recently discovered that binds arsenic (As) with a *K~D~* = 3 mM. Biochemical studies revealed this protein consists entirely of α-helices, purifies as a homotetramer, and displays the following binding curve:  Which of the following is **[TRUE]**? \(A) Arsenic binding to the protein can be described as positive cooperativity \(B) The binding of arsenic to one subunit does not appear to affect the binding to other subunits \(C) The protein is essentially saturated with arsenic when the concentration of arsenic is 2 mM \(D) The binding curve has an identical sigmoidal shape when compared to oxygen binding to hemoglobin \(E) A and D 26\. Which of the following is **[TRUE]** regarding heme? \(A) It does not bind molecular oxygen without myoglobin or hemoglobin \(B) Binding to the protein is mediated by covalent bonds \(C) Binds ferrous iron (Fe^2+^) through four interactions with the pyrrole groups \(D) Functions in covalent catalysis during group transfer reactions \(E) Functions as an oxidation-reduction cofactor during oxygen transport 27\. During the change of hemoglobin from the T to the R state, \(A) The oxygen ligand is moved from one subunit to another \(B) Iron moves into the heme plane causing a movement of the α-helix containing the proximal His \(C) The heme group becomes covalently bonded to the enzyme \(D) Additional hydrogen-bonding is formed between subunits \(E) The affinity for oxygen binding stays the same **[Enzyme Structure/Function]{.smallcaps}** 28\. In the **induced-fit model** of enzyme action, a \_\_\_\_\_\_\_ must bind to the enzyme\'s\_\_\_\_\_\_ for the enzyme to perform its function. \(A) Catalyst; activation energy \(B) Product; catalytic site \(C) Product; active site \(D) Water molecule; allosteric site \(E) Substrate; active site 29\. **Enzymes**: \(A) Increase the rate of a chemical reaction \(B) Do not have specificity \(C) Are consumed in chemical reactions \(D) Raise activation energy \(E) All of the above 30\. Consider the first step in the mechanism for RNase shown below. What type of strategy is NOT used by this enzyme? A. Acid-base catalysis B. Proximity and orientation C. Covalent catalysis D. Metal ion catalysis E. C and D 31\. The mechanistic step for chymotrypsin depicted below corresponds to what place in the shown energy diagram. The binding energy associated with substrate binding is **[NOT]** shown in the energy diagram. (Substrate is shown in bold; R denotes the rest of the substrate).  32\. Which of the following cofactors is used in **[acyl]** group transfer? \(A) Flavin adenine dinucleotide \(B) Coenzyme A \(C) Biotin \(D) Thiamine pyrophosphate \(E) Nicotinamide adenine dinucleotide 33\. During the characterization of a new enzyme, it is revealed that Zn^2+^ is essential for catalysis. What role might the Zn^2+^ play? \(A) Stabilize negative charges in the substrate to aid in binding \(B) Transient formation of an enzyme-substrate covalent bond \(C) Transfer of a proton to stabilize the transition state \(D) Stabilize negative charge developed during the transition state \(E) A and D **[Inhibitors and Enzyme kinetics]{.smallcaps}** 34\. The interaction of organophosphorus compounds such as sarin with the enzyme acetylcholinesterase is an example of what type of inhibition? \(A) Competitive \(B) Noncompetitive \(C) Covalent irreversible \(D) Transition-state analogs \(E) Allosteric 35\. When \[S\] is much **[HIGHER]** than *K~M~* (\> 10-fold), what would you expect when you double \[S\]? \(A) The v~i~ will be approximately the same \(B) The v~i~ will approximately double \(C) The *V~max~* will approximately double \(D) The *V~max~* will decrease buy half \(E) The *k~cat~* will approximately double 36\. If a single-substrate reaction follows Michaelis-Menten kinetics, what is observed in the presence of the respective inhibitors? \(A) A competitive inhibitor decreases the apparent *K~M~* and a noncompetitive inhibitor increases the apparent *V~max~* \(B) A competitive inhibitor decreases the apparent *K~M~* and a noncompetitive inhibitor decreases the apparent *V~max~* \(C) A competitive inhibitor increases the apparent *K~M~* and a noncompetitive inhibitor decreases the apparent *V~max~* \(D) A competitive inhibitor increases the apparent *K~M~* and a noncompetitive inhibitor increases the apparent *V~max~* \(E) An irreversible inhibitor increases the apparent *K~M~* and the apparent *V~max~* 37\. Which of the following is **[TRUE]** for the depiction shown wherein an inhibitor SI binds the same region of the active site as substrate B B? \(A) Under saturating levels of B (very high concentration), the true *V~max~* can be reached \(B) The apparent *K~M~* with respect to substrate A is increased by the presence of the inhibitor \(C) The inhibitor SI is a competitive inhibitor with respect to substrate A \(D) The velocity plot versus the concentration of substrate B is sigmoidal \(E) The inhibitor SI is an allosteric inhibition 38\. Which of the following does **[NOT]** describe β-lactams? \(A) They inhibit bacterial transpeptidases \(B) They are covalent, irreversible inhibitors \(C) They are competitive inhibitors and increase the apparent K~m~ \(D) They are transition state analogs \(E) They are mechanism-based inhibitors