Structure and Properties of Peptides

Q1: The major element of secondary structure in myoglobin and hemoglobin is

A the P-strand

B the a-helix

C the reverse turn

D All of these

ANS:B - the a-helix

No answer description is available.

Q2: The Ramachandran Plot illustrates the fact that

A the peptide bond is planar

B the F & Y angles can assume any value in a peptide

C the F & Y angles can assume only a single value in a protein

D the F & Y angles can assume approximately three different values

ANS:D - the F & Y angles can assume approximately three different values

No answer description is available.

Q3: In β-pleated sheet structures neighbouring

A chains lie in a flat plane

B neighboring residues are hydrogen bonded

C neighboring chains are connected by a-helices

D neighboring chains are hydrogen bonded

ANS:D - neighboring chains are hydrogen bonded

No answer description is available.

Q4: 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?

A C20H50O20N10

B C20H32O11N10

C C20H40O10N10

D C20H68O29N10

ANS:B - C20H32O11N10

Condensation means loss of water. For linking two glycine molecules one water molecule is lost so for 10 glycines, 9 water molecules are lost so answer B is correct.

Q5: The oxygen in hemoglobin and myoglobin is bound to

A the iron atom in the heme group

B the nitrogen atoms on the heme

C histidine residues in the protein

D lysine residues in the protein

ANS:A - the iron atom in the heme group

No answer description is available.

Q6: The peptide bond in proteins is

A planar, but rotates to three preferred dihedral angles

B nonpolar, but rotates to three preferred dihedral angles

C nonpolar, and fixed in a trans conformation

D planar, and usually found in a trans conformation

ANS:D - planar, and usually found in a trans conformation

No answer description is available.

Q7: What is the proportion of glycine residues in collagenous regions?

A One-fourth

B One-third

C Half

D One-tenth

ANS:B - One-third

No answer description is available.

Q8: Secondary structure in protein refers to

A linear sequence of amino acids joined together by peptide bond

B three dimensional arrangement of all amino acids in polypeptide chain

C regular folding of regions of the polypeptide chain

D protein made up of more than one polypeptide chain

ANS:C - regular folding of regions of the polypeptide chain

No answer description is available.

Q9: Heme is the binding pocket of myoglobin and hemoglobin and is composed of

A negatively charged residues

B polar residues

C hydrophobic residues

D positively charged residues

ANS:C - hydrophobic residues

No answer description is available.

Q10: Which of the following statements is incorrect?

A Protein G contains both a-helix and P-sheet

B Protein G contains only a-helix

C Fatty acid binding protein contains largely P-sheet

D Hemoglobin contains four sub-units

ANS:B - Protein G contains only a-helix

What is a Psheet?

Q11: When pO2 = Kd of myoglobin, the fractional saturation (YO2) is about

A 0.1

B 0.5

C 0.9

D 1.7

ANS:B - 0.5

No answer description is available.

Q12: The oxygen binding curves of hemoglobin and myoglobin

A allow maximum transfer of oxygen to the tissues

B are a consequence of the quaternary structure of hemoglobin

C both (a) and (b)

D are identical

ANS:C - both (a) and (b)

No answer description is available.

Q13: The same peptide, Val-Lys-Glu-Met-Ser-Trp-Arg-Ala. was digested with chymotrypsin to produce

A Val-Lys + Glu-Met-Ser + Trp-Arg-Ala.

B Val-Lys-Glu-Met-Ser-Trp + Arg-Ala.

C Val-Lys-Glu-Met-Ser + Trp-Arg-Ala.

D Val-Lys-Glu-Met + Ser-Trp-Arg-Ala.

ANS:B - Val-Lys-Glu-Met-Ser-Trp + Arg-Ala.

Chymotrypsin generally cleaves at carboxyl side of aromatic amino acids residues (Tryptophan, Tyrosine & Phenylalanine) and proline residue's must absent just after aromatic amino acids residues.

Q14: The peptide bond in proteins is

A only found between proline residues

B usually cis unless proline is the next amino acid

C usually trans unless proline is the next amino acid

D is planar because of steric hinderance

ANS:C - usually trans unless proline is the next amino acid

Yes, the peptide bond is a planner but not of a stearic hindrance. And peptide bond is also a non-polar btw alfa amino group of amino acid and alpha-carbonyl group of another amino acid.

Q15: The peptide, Val-Lys-Glu-Met-Ser-Trp-Arg-Ala, was digested with cyanogen bromide (CNBr) to produce:

A Val-Lys + Glu-Met-Ser + Trp-Arg-Ala

B Val-Lys-Glu-Met-Ser-Trp + Arg-Ala

C Val-Lys-Glu-Met + Ser-Trp-Arg-Ala

D Val-Lys-Glu + Met-Ser-Trp-Arg-Ala

ANS:C - Val-Lys-Glu-Met + Ser-Trp-Arg-Ala

Cyanogen bromide cleave at carboxyl terminal of metheionine.

Q16: Disulfide bonds most often stabilize the native structure of

A extracellular proteins

B dimeric proteins

C hydrophobic proteins

D intracellular proteins

ANS:A - extracellular proteins

No answer description is available.

Q17: In deoxy hemoglobin (Hb), the Fe (II) is coordinated to

A four nitrogens of heme, the proximal His, and a water molecule

B four nitrogens of heme and to a water molecule

C two nitrogens of heme and to three His residues in Hb

D two nitrogens of heme and to three water molecules

ANS:A - four nitrogens of heme, the proximal His, and a water molecule

No answer description is available.

Q18: What is the effect of a decrease in pH on hemoglobin oxygen affinity?

A Decrease in oxygen affinity

B Increase in oxygen affinity

C No effect on oxygen affinity

D Increase affinity in muscle cell otherwise decrease

ANS:A - Decrease in oxygen affinity

No answer description is available.

Q19: Which hemoglobin chain replaces the beta chain in embryonic hemoglobulin?

A Delta

B Epsilon

C Gamma

D Alfa

ANS:B - Epsilon

Right option would be B because embryonic (<8 weeks) hemoglobin contains epsilon and zeta and it also called Grower I type of hemoglobin.

But fetal (3-9 months) hemoglobin contains of alpha and gamma (it's a HbF type of hemoglobin).

Q20: If the F and Y angles of each peptide unit in a protein are known, which of the following may also be determined?

A Complete secondary structure

B Complete tertiary structure

C Complete quaternary structure

D Thermodynamic stability

ANS:A - Complete secondary structure

No answer description is available.

Q21: Which of the three subunits of the G proteins binds GDP and GTP?

A Alpha

B Beta

C Gamma

D Delta

ANS:A - Alpha

No answer description is available.

Q22: Peptides in the fully extended chain conformation

A have Y = F = 180°

B do not occur in nature

C also have a cis geometry in their peptide bonds

D are equivalent to the (3-sheet structure

ANS:A - have Y = F = 180°

No answer description is available.

Q23: Which of the following is an example of tertiary structure in a protein?

A A multimeric protein

B An a-helix

C A P-pleated sheet

D A globular domain

ANS:D - A globular domain

Why is it that globular domain is an example of tertiary structure in a protein? Please explain.

Q24: The heme is held in place by a bond between

A the Fe2+ and cysteine

B the Fe3+ and histidine

C the Fe3+ and cysteine

D the Fe2+ and histidine

ANS:D - the Fe2+ and histidine

No answer description is available.

Q25: Which of the following statement is incorrect?

A Hemoglobin and myoglobin are the two oxygen binding proteins

B Hemoglobin transports O2 in the blood

C Myoglobin stores O2 in muscles

D None of the above

ANS:D - None of the above

No answer description is available.

Q26: The resonance structures that can be drawn for the peptide bond indicate that the peptide bond

A is stronger than an ordinary single bond

B has partial double bond character

C both (a) and (b)

D is still not completely understood

ANS:C - both (a) and (b)

Because double bond is strong due to resonance' movement of electrons.

Q27: An oil drop with a polar coat is a metaphor referring to the three dimensional structure of

A fibrous proteins

B collagen

C globular proteins

D silk protein

ANS:C - globular proteins

No answer description is available.

Q28: Hemoglobin has quaternary structure and is made up of

A six polypeptide chains, two α-chains and four β-chains

B two polypeptide chains, one α-chains and one β-chains

C four polypeptide chains, two α-chains and two β-chains

D five polypeptide chains, two α-chains and three β-chains

ANS:C - four polypeptide chains, two α-chains and two β-chains

No answer description is available.

Q29: Hydrogen bonds in a-helices are

A more numerous than Vander Waals interactions

B not present at Phe residues

C analogous to the steps in a spiral staircase

D roughly parallel to the helix axis

ANS:D - roughly parallel to the helix axis

He secondary structure of DNA is actually very similar to the secondary structure of proteins. The protein single alpha helix structure held together by hydrogen bonds was discovered with the aid of X-ray diffraction studies. The X-ray diffraction patterns for DNA show somewhat similar patterns.

In addition, chemical studies by E. Chargaff indicate several important clues about the structure of DNA. In the DNA of all organisms:

A) The concentration of adenine equals that of thymine.
B) The concentration of guanine equals that of cytosine.

Chargaff's findings clearly indicate that some type of heterocyclic amine base pairing exists in the DNA structure. X-ray diffraction data shows that a repeating helical pattern occurs every 34 Angstrom units with 10 subunits per turn. Each subunit occupies 3.4 Angstrom units which is the same amount of space occupied by a single nucleotide unit. Using Chargaff's information and the X-ray data in conjunction with building actual molecular models, Watson and Crick developed the double helix as a model for DNA.

The double helix in DNA consists of two right-handed polynucleotide chains that are coiled about the same axis. The heterocyclic amine bases project inward toward the center so that the base of one strand interacts or pairs with a base of the other strand. According to the chemical and X-ray data and model building exercises, only specific heterocyclic amine bases may be paired.

Q30: In the β-pleated sheet

A hydrogen bonds are formed between the peptide bonds

B adjacent polypeptide chains can either be parallel or antiparallel

C the polypeptide chain is fully extended

D all of the above

ANS:D - all of the above

No answer description is available.

Q31: The different orders of protein structure are determined by all of the following bond types except

A peptide bonds

B phospho-diester bonds

C disulfide bridges

D hydrogen bonds

ANS:B - phospho-diester bonds

No answer description is available.

Q32: The nature of peptide bond can be best explained as

A partial double bond

B truly double bond

C Hydrogen bond

D Van der waals force

ANS:A - partial double bond

No answer description is available.

Q33: What was the first protein whose complete tertiary structure was determined?

A Lysozyme

B Myoglobin

C Pancreatic ribonuclease

D Pancreatic DNase

ANS:B - Myoglobin

No answer description is available.



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