Molecules and Their Interactions -3

1)

The Solubility of NaCl is greater in water than ethanol. What physical property of the solvent governs this difference ?

(1) Surface tension
(2) Viscosity
(3) Dielectric constant
(4 ) Boiling point

2)

When a radioactive phosphorus is incorporated into DNA strand, the phosphodiester bond generally break after a short while because-

(1) The bond strength of phosphorus decreases
(2) Phosphorus on radioactive decay converts into Sulphur, which has valence of two
(3) It attacks glycosidic bond
(4) Due to nucleophilic attack of 3’OH group

3)

 Half-life of radioactive material does not depend upon
(1) Initial concentration of material
(2) Decay constant
(3) Type of radioisotope
(4) Energy emission

4)

Arrange them according to decreasing order of strength

(1) sp³>sp²>sp¹
(2) sp¹>sp²>sp³
(3) sp³>sp¹>sp²
(4) sp¹>sp³>sp²

5)

Which of the following bonds will be most difficult to break?

(1) C-O
(2) C-P
(3) C-N
(4) C-S

6)

What would be approx. energy released on breaking H- H covalent bond

(1) 4.32 x 10⁵ J/mol
(2) 1 x 10^-19 J/mol
(3) 5 x 10^-19 J/mol
(4) 8 x 10¹⁹ J/mol

7)

The interaction energy between atom A and B is 400 kJ/mol^-1. The type of interaction between them is

(1) pi – pi.
(2) covalent.
(3) ion-dipole.
(4) hydrogen bond.

8)

Covalent bond formation between two atoms takes place by
(1) Transfer of electron from one atom to other
(2) One Side sharing of electrons
(3) Electron sharing by two electronegative atoms
(4) Affinity between two atoms

9)

In crystalline NaCl, how many chloride ions surround each sodium ion?

(1) Four
(2) Six
(3) Eight
(4) Ten

10)

 Which of the following pair represents isotones?
(1) ³H, ⁴He                                           (2) ¹⁵N, ¹⁴N1
(3) ¹⁴⁰Ba, ¹⁴⁰Th                                     (4) ¹H, ³H

11)

From the following statements,
A. Hydrogen, Deuterium and Tritium differ in the number of protons
B. Hydrogen, Deuterium and Tritium differ in the number of neutrons
C. Both Deuterium and Tritium are radioactive and decay to Hydrogen and Deuterium, respectively.
D. Tritium is radioactive and decays to Helium
E. Carbon-14 decays to Nitrogen-14
F. Carbon-14 decays to Carbon-13

Pick the combination with ALL correct statements
(1) A. B and F                                           (2) B, D and E
(3) A, C and D                                           (4) C, E and F

12) Which of the following is most unstable condition in protein folding?
(1) Non-polar side chain exposed to outside
(2) Polar side chain present in core of protein
(3) Non polar side chains in core of protein
(4) Polar amino acids exposed to outside

13)

 Which one of the following is the most appropriate statement regarding folded proteins?
(1) Charged amino acid side chains are always buried.
(2) Charged amino acid side chains are seldom buried.
(3) Non-polar amino acid side chains are seldom buried.
(4) Tyrosine residues are always buried.

14)

39. The following observations are made on a 30-residue polypeptide
    (a) Unordered structure is observed in water but a helical conformation is observed in medium of low dielectric constant.
    (b)The peptide is resistant to degradation by proteases.
    (c) Red blood cells are lysed by the peptide.
    (d) β-mercaptoethanol has no effect on peptide structure.
    Which of the following statements can be correctly attributed to the above observations?
    (1)The peptide is entirely composed of D-amino acids and is amphipathic.
    (2)The peptide is entirely composed of L-amino acids and is not amphipathic.
    (3)The peptide is rich in disulphide bonds between D-cysteines.
    (4)The peptide is entirely composed of L –aromatic amino acids.

15)

Following are statements related to peptide/protein conformation.
A. The circular dichroism spectra of collagen and a protein in α-helical conformation will be identical.
B. The allowed region for the dihedral angles ϕ, Ψ in Gly, spans a large area in the
Ramachandran map. This can be drastically reduced by substituting the two hydrogens with methyl groups.
C. Proline has high frequency of occurrence in β- turns.
D. In a β-hairpin structure, the dihedral angles ϕ, Ψ of amino acids flanking the β-turn region will be 60⁰, -30⁰, respectively.

Choose the combination with both INCORRECT statements.
(1) B and C
(2) A and B
(3) A and D
(4) C and D

16)

Which statement is correct for globular proteins?
(1) Always contain only α helix
(2) Always contain only β sheets
(3) Contains more reverse turns
(4) Contains α helix, β sheets and reverse turns

17)

Out of the statements mentioned below

A. L-threonine and L-allo-threonine interact identically with plane polarized light.
B. van der Waals’ interactions are always attractive.
C. Poly (pro) ll-helix is not stabilized by intermolecular hydrogen bonds.
D. The folding of a protein is associated with an overall positive change in free energy and negative change in entropy.
E. Lysine acetylation on histone is associated with loosening of the histone complex from DNA.

Which of the following combinations is CORRECT?
(1) A and C
(2) B and D
(3) C and E
(4) D and E

18)

 β-α-β motif is composed of two beta strands joined by an alpha helix through connecting loops. This motif is known for
(1) ligand binding
(2) stereological hindrance in binding of ligand
(3) catalytic center
(4) transmembrane domain

19)

Following statements are made related to protein structure
A. The hydrogen bonding patterns between the CO and NH groups are n → n +3 in α-helix; n → n + 4 in 3₁₀ helix and n → n + 5 in π helix.
B. In a ß turn, there are 10 atoms between the hydrogen bond donor and acceptor.
C. In a 𝛾 tum, there are 6 atoms between the hydrogen bond donor and acceptor.
D. Parallel sheets have evenly spaced hydrogen bonds, which bridge the strands at an angle.

Which one of the following combinations of above statements is correct?
(1) A and C
(2) A and B
(3) C and D
(4) B and D

20)

Phosphorylation of ADP to ATP occurs through energy metabolism, comprising oxidative phosphorylation or substrate level phosphorylation or photo- phosphorylation (in plants). ATP can also be formed from ADP through the action of adenylate kinase. Crystal structure determination of adenylate kinase shows that the C-terminal region has the sequence – val-asp-asp-val-phe-ser-gln-val-cys-thr-his-leu-asp-thr- leu-lys. What can be a possible conformation of the sequence?

(1) A helix that is not amphipathic
(2) Amphipathic helix
(3) Leucine zipper helix
(4) Beta helix

21)

A protein has 30% alanine. If all the alanines are replaced by glycines,
(1) helical content will increase.
(2) ß-sheet content will increase.
(3) there will be no change in conformation
(4) the alanine-substituted protein will be less structured than the parent protein.

22)

Which is correct for α-helix of a protein

(1) It has H-bonding in two or more parallel running chains
(2) There is intra-chain H-bonding in single helix
(3) No H- bonding is seen
(4) is a tertiary structure

23)

The following statements describe the propensity and role of amino acids in the secondary structure of proteins

A. Alanine has a high frequency of occurrence in α- helices
B. Proline has a high frequency of occurrence in α- helices
C. The 𝛘 does not affect the helix propensity of serine, threonine and valine
D. Peptide bonds involving ‘N’ of proline may display cis-trans isomerism
Choose the correct combination.

(1) A and D
(2) B and C
(3) B and C
(4) C and D

24)

How long should it take the polypeptide backbone of a 6-residue, 10-residue, 15-residue and 20- residue folding nucleus to explore all its possible conformations? Assume that the polypeptide backbone randomly reorients every 10^-13 seconds (s).
(1) 10^-7s, 10^-3s, 10² s, 10⁷ s, respectively
(2) 10^-1Os, 10^-6s, 10³ s, 10¹⁰ s, respectively
(3) 10^-5s, 10^-2s, 10s, 10³s, respectively
(4) 1s, 10s, 100s, 10⁷s, respectively

25)

Consider a 51-residue long protein containing only 100 bonds about which rotation can occur. Assume that 3 orientations per bond are possible. Based on these assumptions, how many conformations will be possible for this protein?
(1) 3¹⁰⁰
(2) 100³
(3) 3⁵¹
(4) 51 x 100 x 3

26)

Indicate which one of the following statements about nucleic acids and protein structures is correct.
(1) Hydrogen bonding between the bases in the major and minor grooves of DNA is absent
(2) Both uracil and thymine have a methyl group but at different positions.
(3) The backbone dihedral angles of α-helices and ß- sheets are very similar. Only the hydrogen bonding pattern is different.
(4) A ß-turn is formed by four amino acids. The type of ß-turn is determined by the dihedral angles of the second and third amino acid.

27)

The following statements were made to describe a typical collagen structure.
A. Collagen has a triple-helical domain structure which consists of three distinct α-chains.
B. The collagen triple helix is stabilized by isoprenyl bonds.
C. Each α-chain has a left-handed polyproline ll-type helix.
D. Each α-chain is composed of multiple triplet sequences of Gly-Y-Z in which Y is commonly proline and Z is usually hydroxyproline.
Which one of the following options has all correct statements?
(1) A, C and D
(2) A, B and C
(3) A and B only
(4) B and D only

28)

In a 30-residue peptide, the dihedral angles φ/Ψ have been determined by one or more methods. When their values are examined in the Ramachandran plot, it is
(1) not possible for φ/ Ψ values to be distributed in the helical as well as beta sheet region.
(2) possible that the φ/ Ψ values are all in the helical region although circular dichroism spectral studies indicate beta sheet conformation.
(3) possible to conclude that the peptide is composed of entirely D-amino acids.
(4) not possible to conclude if the peptide is entirely helical or entirely in beta sheet conformation.

29)

The exact backbone dihedral angles in a folded protein can be obtained by

(1) deconvolution of its circular dichroism spectra obtained at different pH and temperature
(2) estimating the number of protons that exchange with deuterium on treating the protein with D₂O
(3) forming fibres of the protein and analyzing the fibre diffraction pattern
(4) analysis of the crystal structure of the protein obtained by X-ray diffraction at high resolutions

30)

Given below are statements related to protein structures:
A. The dihedral angles of an amino acid X in Acetyl-x- N-Methyl amide in the Ramachandran plot, occur in very small but equal areas in the left and right quadrants. It can be concluded that X is not one of the 20-coded amino acids.
B. The dihedral angles of a 20-residue peptide are represented in the Ramachandran plot. It is possible to conclude that the peptide does not have a proline.
C. Two proteins can have a similar fold even if they do not share significant similarity in their primary structure.
D. On denaturation of a protein by urea, the interactions that would be disrupted are ionic bonds and van der Waal’s interaction but not disulfide bonds.
Choose the combination with ALL CORRECT answers:

(1) A, B, C
(2) A, C, D
(3) B, C, D
(4) A, B, D

31)

An α-helix in a peptide or protein is characterized by hydrogen bonds and characteristic dihedral angles. Choose the right combination.
(1) Hydrogen bonding between the amide CO of residue i and amide NH of residue i + 4. Dihedral angles in the region φ = -50⁰, Ψ = -60⁰

(2) Hydrogen bonding between the amide NH of residue i and amide CO of residue i + 4. Dihedral angles in the region of φ = -50⁰, Ψ = -60.

(3) Hydrogen bonding between the amide CO of residue i and amide NH of residue i + 4. Dihedral angles in the region of φ = -50⁰, Ψ = +60.

(4) Hydrogen bonding between the amide CO of residue i and amide NH of residue 1 + 3. Dihedral angles in the region of φ = -50⁰, Ψ = -60

32)

The regions of phi, psi space occupied by well characterized protein secondary structures are marked on a Ramachandran plot as shown above. Which of the following statements is CORRECT?

(1) A- right handed α helix, B- ß strand, C- left handed α helix, D- collagen,
(2) A- ß strand, B- right handed α helix, C- left handed α helix, D- collagen,
(3) A- collagen, B- right handed α helix, C- left handed α helix, D- ß strand,
(4) A- left handed α helix, B- ß strand, C-collagen, D- right handed α helix

33)

The Ramachandran plot graphically shows which combination of torsional angles phi (φ) and psi (Ψ) of amino acid residues contained in a peptide are possible. Examination of the plot below shows that only certain regions of the conformational space are permissible. Why are all the theoretical combinations of φ and Ψ not possible?

(1) Two atoms cannot occupy the same space
(2) The geometry of the peptide bond that links two amino acid residues restricts φ and Ψ and angles
(3) Beta sheets and alpha helices determine the allowed regions of conformational space.
(4) The tertiary fold of polypeptides restricts conformational space

34)

In the diagram for peptide shown below, angle ϕ represents bonds between

(1) N – C’

(2) C’ – C
(3) C – O

(4) N – H