laboursonline – MCQs, Mock Tests | Biochemistry Biochemistry MCQS PAPER SET 11

The molecular formula for glycine is C2H5O2N. What would be the molecular formula for a linear oligomer made by linking ten glycine molecules together by condensation synthesis?

1. C20H50O20N10
2. C20H32O11N10
3. C20H40O10N10
4. C20H68O29N10

✅ Correct Answer: 2

Which of the following is an example of tertiary structure in a protein?

1. A multimeric protein
2. An a-helix
3. A P-pleated sheet
4. A globular domain

✅ Correct Answer: 4

The peptide, Val-Lys-Glu-Met-Ser-Trp-Arg-Ala, was digested with cyanogen bromide (CNBr) to produce:

1. Val-Lys + Glu-Met-Ser + Trp-Arg-Ala
2. Val-Lys-Glu-Met-Ser-Trp + Arg-Ala
3. Val-Lys-Glu-Met + Ser-Trp-Arg-Ala
4. Val-Lys-Glu + Met-Ser-Trp-Arg-Ala

✅ Correct Answer: 3

In deoxy hemoglobin (Hb), the Fe (II) is coordinated to

1. four nitrogens of heme, the proximal His, and a water molecule
2. four nitrogens of heme and to a water molecule
3. two nitrogens of heme and to three His residues in Hb
4. two nitrogens of heme and to three water molecules

✅ Correct Answer: 1

In the β-pleated sheet

1. hydrogen bonds are formed between the peptide bonds
2. adjacent polypeptide chains can either be parallel or antiparallel
3. the polypeptide chain is fully extended
4. all of the above

✅ Correct Answer: 4

The Ramachandran Plot illustrates the fact that

1. the peptide bond is planar
2. the F & Y angles can assume any value in a peptide
3. the F & Y angles can assume only a single value in a protein
4. the F & Y angles can assume approximately three different values

✅ Correct Answer: 4

The resonance structures that can be drawn for the peptide bond indicate that the peptide bond

1. is stronger than an ordinary single bond
2. has partial double bond character
3. both (a) and (b)
4. is still not completely understood

✅ Correct Answer: 3

The major element of secondary structure in myoglobin and hemoglobin is

1. the P-strand
2. the a-helix
3. the reverse turn
4. All of these

✅ Correct Answer: 2

An oil drop with a polar coat is a metaphor referring to the three dimensional structure of

1. fibrous proteins
2. collagen
3. globular proteins
4. silk protein

✅ Correct Answer: 3

What was the first protein whose complete tertiary structure was determined?

1. Lysozyme
2. Myoglobin
3. Pancreatic ribonuclease
4. Pancreatic Dnase

✅ Correct Answer: 2

The peptide bond in proteins is

1. planar, but rotates to three preferred dihedral angles
2. nonpolar, but rotates to three preferred dihedral angles
3. nonpolar, and fixed in a trans conformation
4. planar, and usually found in a trans conformation

✅ Correct Answer: 4

In β-pleated sheet structures neighbouring

1. chains lie in a flat plane
2. neighboring residues are hydrogen bonded
3. neighboring chains are connected by a-helices
4. neighboring chains are hydrogen bonded

✅ Correct Answer: 4

The same peptide, Val-Lys-Glu-Met-Ser-Trp-Arg-Ala. was digested with chymotrypsin to produce

1. Val-Lys + Glu-Met-Ser + Trp-Arg-Ala.
2. Val-Lys-Glu-Met-Ser-Trp + Arg-Ala.
3. Val-Lys-Glu-Met-Ser + Trp-Arg-Ala.
4. Val-Lys-Glu-Met + Ser-Trp-Arg-Ala.

✅ Correct Answer: 2

Disulfide bonds most often stabilize the native structure of

1. extracellular proteins
2. dimeric proteins
3. hydrophobic proteins
4. intracellular proteins

✅ Correct Answer: 1

Secondary structure in protein refers to

1. linear sequence of amino acids joined together by peptide bond
2. three dimensional arrangement of all amino acids in polypeptide chain
3. regular folding of regions of the polypeptide chain
4. protein made up of more than one polypeptide chain

✅ Correct Answer: 3

Heme is the binding pocket of myoglobin and hemoglobin and is composed of

1. negatively charged residues
2. polar residues
3. hydrophobic residues
4. positively charged residues

✅ Correct Answer: 3

What is the effect of a decrease in pH on hemoglobin oxygen affinity?

1. Decrease in oxygen affinity
2. Increase in oxygen affinity
3. No effect on oxygen affinity
4. Increase affinity in muscle cell otherwise decrease

✅ Correct Answer: 1

What is the proportion of glycine residues in collagenous regions?

1. One-fourth
2. One-third
3. Half
4. One-tenth

✅ Correct Answer: 2

Which of the following statements is incorrect?

1. Protein G contains both a-helix and P-sheet
2. Protein G contains only a-helix
3. Fatty acid binding protein contains largely P-sheet
4. Hemoglobin contains four sub-units

✅ Correct Answer: 2

The oxygen binding curves of hemoglobin and myoglobin

1. allow maximum transfer of oxygen to the tissues
2. are a consequence of the quaternary structure of hemoglobin
3. Hydrogen bond
4. are identical

✅ Correct Answer: 3

The nature of peptide bond can be best explained as

1. partial double bond
2. truly double bond
3. Hydrogen bond
4. Van der waals force

✅ Correct Answer: 1

Which of the following statement is incorrect?

1. Hemoglobin and myoglobin are the two oxygen binding proteins
2. Hemoglobin transports O2 in the blood
3. Myoglobin stores O2 in muscles
4. None of the above

✅ Correct Answer: 4

Which hemoglobin chain replaces the beta chain in embryonic hemoglobulin?

1. Delta
2. Epsilon
3. Gamma
4. Alfa

✅ Correct Answer: 2

Hemoglobin has quaternary structure and is made up of

1. six polypeptide chains, two α-chains and four β-chains
2. two polypeptide chains, one α-chains and one β-chains
3. four polypeptide chains, two α-chains and two β-chains
4. five polypeptide chains, two α-chains and three β-chains

✅ Correct Answer: 3

Peptides in the fully extended chain conformation

1. have Y = F = 180°
2. do not occur in nature
3. also have a cis geometry in their peptide bonds
4. are equivalent to the (3-sheet structure

✅ Correct Answer: 1

The oxygen in hemoglobin and myoglobin is bound to

1. the iron atom in the heme group
2. the nitrogen atoms on the heme
3. histidine residues in the protein
4. lysine residues in the protein

✅ Correct Answer: 1

Which of the three subunits of the G proteins binds GDP and GTP?

1. Alpha
2. Beta
3. Gamma
4. Delta

✅ Correct Answer: 1

If the F and Y angles of each peptide unit in a protein are known, which of the following may also be determined?

1. Complete secondary structure
2. Complete tertiary structure
3. Complete quaternary structure
4. Thermodynamic stability

✅ Correct Answer: 1

The different orders of protein structure are determined by all of the following bond types except

1. peptide bonds
2. phospho-diester bonds
3. disulfide bridges
4. hydrogen bonds

✅ Correct Answer: 2

The heme is held in place by a bond between

1. the Fe2+ and cysteine
2. the Fe3+ and histidine
3. the Fe3+ and cysteine
4. the Fe2+ and histidine

✅ Correct Answer: 4

Unpaired H-bond donors and acceptors are found in the hydrophobic core of a protein

1. only at the ends of a-helices
2. only at the turns connecting p-strands
3. only on Pro residues
4. rarely

✅ Correct Answer: 4

For the unfolding reaction of Protein G, ΔH° =210.6 kJ/mol, this means that

1. unfolding is favored enthalpically
2. folding is favored enthalpically
3. the entropy is positive at all temperatures
4. the entropy is negative at all temperatures

✅ Correct Answer: 2

Attractive Vander Waals forces occur between

1. apolar molecules in the liquid state
2. any pair of nearby atoms
3. polar molecules in the solid state
4. only if other forces are less favorable

✅ Correct Answer: 2

Which of the following forces is the most favorable for protein folding?

1. Conformational entropy
2. Hydrophobic Interactions
3. Vander Waals interactions
4. Hydrogen bonds

✅ Correct Answer: 2

At the midpoint of a temperature transition curve,

1. half of the protein is denatured
2. Keq = 1.0 and ΔG = 0
3. [Native] = [Unfolded]
4. All of these

✅ Correct Answer: 4

Which of the following is the most correct?

1. Charged amino acids are never buried in the interior of a protein
2. Charged amino acids are seldom buried in the interior of a protein
3. All hydrophobic amino acids are buried when a protein folds
4. Tyrosine is only found in the interior of proteins

✅ Correct Answer: 2

Which of the following forces is the most unfavorable for protein folding?

1. Conformational entropy
2. Hydrophobic interactions
3. Vander Waals interactions
4. Electrostatic interactions

✅ Correct Answer: 1

Since ΔG° = -RTlnK

1. a 10-fold increase in K decreases ΔG° by about 10-fold
2. a 10-fold decrease in K decreases ΔG° by about 2.3*RT
3. a 10-fold increase in K decreases ΔG° by about 2.3*RT
4. a 10-fold decrease in K increases ΔG° by about 10-fold

✅ Correct Answer: 3

The correlation between free energy ΔG transfer between the aqueous/organic phases and the surface area of amino acid residues

1. reflects the reduction in solvent-accessible area during protein folding
2. is only meaningful for the polar amino acids
3. ignores the important contribution of the peptide bond
4. is similar to effects seen with SDS denaturation

✅ Correct Answer: 1

If the egg white protein, ovalbumin, is denatured in a hard-boiled egg, then which of the following is least affected?

1. The primary structure of ovalbumin
2. The secondary structure of ovalbumin
3. The tertiary structure of ovalbumin
4. The quaternary structure of ovalbumin

✅ Correct Answer: 1

Buried hydrophobic side chains in a globular protein fit into a hole formed by the side chains of

1. 1-3 other amino acids
2. 5-7 other amino acids
3. 9-12 other amino acids
4. 13-15 other amino acids

✅ Correct Answer: 2

In an SDS-PAGE

1. proteins are denatured by the SDS
2. proteins have the same charge-to-mass ratio
3. smaller proteins migrate more rapidly through the gel
4. all of the above

✅ Correct Answer: 4

Proteins can be visualized directly in gels by

1. staining them with the dye
2. using electron microscope only
3. measuring their molecular weight
4. none of these

✅ Correct Answer: 1

In SDS-PAGE, the protein sample is first

1. treated with a reducing agent and then with anionic detergent followed by fractionation by electrophoresis
2. fractionated by electrophoresis then treated with an oxidizing agent followed by anionic detergent.
3. treated with a oxidizing agent and then with anionic detergent followed by fractionation by electrophoresis
4. none of the above

✅ Correct Answer: 1

Electrophoresis of histones and myoglobin under non-denaturing conditions (pH = 7.0) results in

1. both proteins migrate to the anode
2. histones migrate to the anode and myoglobin migrates to the cathode
3. histones migrate to the cathode and myoglobin migrates to the anode
4. both proteins migrate to the cathode

✅ Correct Answer: 3

In isoelectric focusing, proteins are separated on the basis of their

1. relative content of positively charged residue only
2. relative content of negatively charged residue only
3. size
4. relative content of positively and negatively charged residue

✅ Correct Answer: 4

In a gel filtration column

1. smaller proteins enter the beads more readily
2. large proteins elute first
3. both (a) and (b)
4. large proteins enter the beads more readily

✅ Correct Answer: 3

In a native PAGE, proteins are separated on the basis of

1. net negative charge
2. net charge and size
3. net positive charges size
4. net positive charge

✅ Correct Answer: 2

The subunit molecular weight as well as the number of subunits in the quaternary structure can be determined by

1. SDS-PAGE electrophoresis
2. gel filtration chromatography
3. combining information from (a)and (b)
4. isoelectric focusing

✅ Correct Answer: 3

Proteins are separated in an SDS-PAGE experiment on the basis of their

1. positively charged side chains
2. molecular weight
3. negatively charged side chains
4. different isoelectric points

✅ Correct Answer: 2

Enzyme-driven metabolic pathways can be made more efficient by

1. concentrating enzymes within specific cellular compartments
2. grouping enzymes into free-floating, multienzyme complexes
3. fixing enzymes into membranes so that they are adjacent to each other
4. All of the above

✅ Correct Answer: 4

Which of the following (s) is/are serine proteases?

1. Chymotrypsin
2. Trypsin
3. Elastase
4. all of these

✅ Correct Answer: 4

Which of the following statements about enzymes or their function is true?

1. Enzymes do not alter the overall change in free energy for a reaction
2. Enzymes are proteins whose three-dimensional form is key to their function
3. Enzymes speed up reactions by lowering activation energy
4. All of the above

✅ Correct Answer: 4

Tryprotophan synthetase of E.coli, a typical bifunctional oligomeric enzyme consist of

1. a protein designated A
2. two proteins designated A and B
3. a protein A and one-subunit a
4. a protein designated B

✅ Correct Answer: 2

What is the specificity of the Clostripain protease?

1. It cleave after Arg residues
2. It cleave after His residues
3. It cleave after Lys residues
4. None of the above

✅ Correct Answer: 1

The proteolysis rate enhancement by chymotrypsin (~1010 folds) corresponds to a reduction in activation energy of about

1. 40 kJ/mol
2. 49 kJ/mol
3. 58 kJ/mol
4. 88 kJ/mol

✅ Correct Answer: 3

Which of the following is false statement with regard to comparison between Serine and HIV proteases?

1. Both use nucleophilic attack to hydrolyze the peptide bond
2. Both require water to complete the catalytic cycle
3. Both forms an acyl-enzyme intermediate
4. Both show specificity for certain amino acid sequences

✅ Correct Answer: 3

In the enzyme-catalyzed reaction shown below, what will be the effect on substances A, B, C, and D of inactivating the enzyme labeled E2? A ---(E1)---> B ---(E2)---> C ---(E3)--->

1. A, B, C, and D will all still be produced
2. A, B, and C will still be produced, but not D
3. A and B will still be produced, but not C or D
4. A will still be produced, but not B, C, or D

✅ Correct Answer: 3

The nucleophile in serine proteases is

1. Serine
2. water
3. both (a) and (b)
4. Asparagine

✅ Correct Answer: 3

The role of Asp 102 and His 57 during trypsin catalysis is to

1. neutralize the charge on the other's side chain
2. keep the specificity pocket open
3. function as a proton shuttle
4. clamp the substrate into the active site

✅ Correct Answer: 3

The cleavage specificity of trypsin and chymotrypsin depend in part on the

1. proximity of Ser 195 to the active site or specificity pocket
2. size, shape, and charge of the active site or specificity pocket
3. presence of a low-barrier hydrogen bond in the active site or specificity pocket
4. absence of water in the active site

✅ Correct Answer: 2

The E.coli pyruvic acid dehydrogenase complex is reported to

1. decatalyze the oxidation of pyruvic acid to acetyl Co A and CO2
2. Catalyze the oxidation of pyruvic acid to acetyl Co A and CO2
3. retard the reduction of pyruvic acid to acetyl Co A and CO2
4. Catalyze the reduction of pyruvic acid to acetyl Co A and CO

✅ Correct Answer: 2

Which of the common features are shared between serine and aspartate proteases?

1. Both require water to complete the catalytic cycle
2. Both use a base to activate the nucleophile
3. Both show specificity for certain amino acid sequences
4. All of the above

✅ Correct Answer: 4

Before they can react, many molecules need to be destabilized. This state is typically achieved through

1. changing the three-dimensional shape of the molecule
2. oxidizing the molecules by removing electrons
3. changing the reaction from a biosynthetic to a catabolic pathway
4. the input of a small amount of activation energy

✅ Correct Answer: 4

Common feature in all serine proteases is a

1. hydrophobic specificity pocket
2. hydrophilic specificity pocket
3. cluster of reactive serine residues
4. single reactive serine residue

✅ Correct Answer: 4

How is the enzyme COX-1 important in human health?

1. It helps to transport carbon dioxide in the blood
2. It is critical for the biosynthesis of DNA
3. It is a chemical derivative of aspirin
4. It catalyzes the production of hormones that maintain the stomach lining

✅ Correct Answer: 4

For specific antigen recognition by T cells,

1. antigen is bound by a T cell membrane antibody
2. denaturation of antigen does not reduce epitope recognition
3. MHC molecules are not required
4. antigen exposure during T cell maturation is required

✅ Correct Answer: 2

Antigen, when injected in the body activates its specific lymphocytes in the

1. blood circulation
2. draining lymph nodes
3. MALT (mucosa associated
4. spleen lymphoid tissue

✅ Correct Answer: 2

A molecule that can be covalently linked to a non-immunogenic antigen to make it an immunogen is called a (n)

1. adjuvant
2. carrier
3. hapten
4. mitogen

✅ Correct Answer: 2