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Biology 30 MCQ questions
DIRECTIONS:ONE or MORE of the options numbered (i-iv) are correct
Select
A
if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
1. Which of the following is correct regarding enzyme names and the reactions they catalyse?
i. The name “malate dehydrogenase” implies removal of hydrogen from malate.
ii. A “phosphatase” catalyses the removal of phosphate from the substrate.
iii. The name “ornithine decarboxylase” implies a highly specific enzyme that removes carbon dioxide from ornithine.
iv. Glucose oxidase can catalyse the oxidation of any six carbon sugar.
2. Enzymes are important to cells because :
i. They increase the rates of chemical reactions.
ii. They can be regulated.
iii. They channel intermediates to useful pathways.
iv. They are not affected by temperature changes.
3. In enzymes that have a non-protein part:
i. The complete structure of the active enzyme is called “holoenzyme”.
ii. The non-protein part is called “cofactor” and if this is an organic molecule it is called “coenzyme”.
iii. The protein structure alone is an “apoenzyme”.
iv. Various metal ions act as cofactors.
4. Which of the following is/are TRUE of the binding of substrate to the active site of the enzyme?
i. Relatively weak bonds are involved.
ii. The transition state is bound less tightly than the substrate.
iii. Most frequently the three-dimensional structure of the active site changes to fit the substrate.
iv. The side chains of amino acids at the active site are not involved in the binding.
Continued …
DIRECTIONS: ONE or MORE of the options numbered (i-iv) are correct
Select
A if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
5. An enzyme catalysing a reversible reaction:
i. Shifts the equilibrium to the right.
ii. Increases the rate of the forward reaction only.
iii. Increases the equilibrium constant (K).
iv. Increases the rate constants (k1 and k2) of both the forward and reverse reactions.
6. Which of the following is/are TRUE regarding the activation energy of a reaction?
i. Activation energy is the energy required to form the transition state.
ii. Enzymes lower the activation energy by providing a lower-energy reaction path and by binding the transition state with high affinity.
iii. The lower the activation energy the higher the rate constant of the reaction, at constant temperature.
iv. Activation energy is the energy difference between substrate and product.
7. In trying to explain the effect of
[S]
on initial rate (v), Michaelis and Menten:
i. Assumed that the conversion of product to substrate is insignificant.
ii. Assumed that the concentration of enzyme-substrate complex is decreased during the time of the experiment.
iii. Derived the following equation:
v=Vmax.[S]/Km+[S]
iv. Proposed that Km equals the equilibrium constant.
8. In the plot of v against [S]:
i. Km is calculated as ½Vmax.
ii. The Km and Vmax can be calculated accurately.
iii. A competitive inhibitor will lower the plateau.
iv. The plateau will be higher if the experiment is carried out using a higher enzyme concentration.
A if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
9. A 0.02 μM solution of the enzyme catalase catalyses the breakdown of hydrogen peroxide at a maximum rate of 0.4 M H2O2 in 1 sec. Calculate the turnover number (kcat).
i. 20 s-1
ii. 0.2 x 108 s-1
iii. 1200 min-1
iv. 20000000 s-1
10. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:
|
[S]
(M) |
Initial rate (v) (M/min)
|
|
2.5 |
28 |
|
4.0 |
40 |
|
10.0 |
70 |
|
20.0 |
95 |
|
40.0 |
112 |
|
100.0 |
128 |
|
2000.0 |
139 |
|
10000.0 |
140 |
Without plotting the data, the Vmax for this enzyme is approximately:
i. 10000.0 M
ii. 140 moles l-1 min-1
iii. 10000.0 moles l-1
iv. 140 M min-1
11. Using the data from problem 10, Km for this enzyme is approximately:
i. 10 M
ii. 70 moles l-1 min-1
iii. 10 moles l-1
iv. 70 M min-1
Continued …
DIRECTIONS: ONE or MORE of the options numbered (i-iv) are correct
Select
A if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
12. Enzyme inhibition:
i. Is always reversible.
ii. Can always be overcome by addition of substrate.
iii. Occurs to the same extent at all concentrations of inhibitor.
iv. Is characterised by when and where the inhibitor binds.
13. To calculate the turnover number of an enzyme you need to know the:
i. Enzyme concentration.
ii. Initial velocity of the catalyzed reaction at low [S].
iii. Initial velocity of the catalyzed reaction at [S]>>Km (i.e.Vmax).
iv. Km for the substrate.
14. The aromatic amino acids:
i. Are represented by the one letter codes T, Y and F.
ii. Are classified as nonpolar, amino acids.
iii. All absorb light strongly at 280nm.
iv. Are all zwitterionic at pH 7.0.
15. The amino acid glutamine:
i. Is represented by the one letter code Q.
ii. Has an uncharged nitrogen in its side chain.
iii. Has a side chain that acts as both a hydrogen bond donor and acceptor.
iv. Is a polar amino acid.
16. Collagen is a fibrous protein:
i. Which contains exclusively left-handed helices associated in bundles of three.
ii. Which has a high content of Glycine residues.
iii. Which contains the unusual amino acid Hydroxy-lysine.
iv. Which forms weak non-elastic fibres.
Continued …
DIRECTIONS: ONE or MORE of the options numbered (i-iv) are correct
Select
A if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
17. Within secondary structures:
i. The R groups of residues separated by four places are in close proximity.
ii. There are many intra-peptide chain hydrogen bonds.
iii. Proline is a rare amino acid.
iv. The R-groups alternate on either side of the peptide chain.
18. Which is/are TRUE regarding the levels of protein structure?
i. The primary structure is the sequence of amino acids linked by peptide bonds.
ii. The secondary structure is a wide range of localised folds due to the flexibility of the peptide chain.
iii. The tertiary structure is the overall three-dimensional shape of the polypeptide.
iv. The quaternary structure is the association of the polypeptide with accessory groups such as haem.
19. In the investigation of protein primary structure:
i. 1-fluoro-2,4-dinitrobenzene (FDNB) can be used to determine the C terminal residue.
ii. Phenylisothiocyanate is used in the Edman degradation process.
iii. Trypsin can be used to fragment the protein at aromatic residues to generate peptides that can be more easily sequenced.
iv. Cyanogen bromide can be used to fragment the protein at methionine residues to generate peptides that can be more easily sequenced.
20. Which of the following statements are true of molecular fluorescence spectroscopy?
i. The emission wavelength is always longer than the excitation wavelength.
ii. It can detect lower concentrations of molecules than molecular absorbance.
iii. It is more prone to interference than molecular absorbance methods.
iv. The excitation wavelength is always longer than the emission wavelength.
Continued …
DIRECTIONS: ONE or MORE of the options numbered (i-iv) are correct
Select
A if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
21. The enzyme “X” dehydrogenase requires NAD+/NADH as a co-factor. Which of the following observations is true regarding the oxidation of XH2 → X + 2H by this enzyme?
i. Absorbance at 280nm will increase.
ii. NADH is converted to NAD+.
iii. Absorbance at 260nm will decrease.
iv. Absorbance at 340nm will increase.
22. For which of the following are the stated % transmittance and absorbance values equivalent?
i. 10% transmittance and an absorbance of 1.
ii. 1% transmittance and an absorbance of 1.
iii. 0.1% transmittance and an absorbance of 3.
iv. 0.1% transmittance and an absorbance of 4.
23. When light is said to be ‘red shifted’:
i. It has more energy.
ii. It has less energy.
iii. It‘s wavelength becomes shorter.
iv. It‘s wavelength becomes longer.
24. When quantifying an analyte by absorption spectroscopy, it is important to prepare a blank because :
i. It accounts for the non-specific absorbance.
ii. The sample contains impurities.
iii. It is identical to the standard or sample except for the presence of the analyte.
iv. It allows the least transmission of radiation.
25. Which of the following may give inaccurate data when measuring UV absorption?
i. A glass cuvette.
ii. A scratched cuvette.
iii. Fluorescence of the sample.
iv. A quartz cuvette.
Continued …
DIRECTIONS: ONE or MORE of the options numbered (i-iv) are correct
Select
A if only i, ii, and iii are correct.
B if only i and iii are correct.
C if only ii and iv are correct.
D if only iv is correct.
E if all are correct.
26. Which of the properties given below can be used to purify a protein?
i. Density.
ii. Shape.
iii. Hydrophobicity.
iv. Solubility.
27. In the technique of gel filtration chromatography:
i. Molecules are separated on the basis of their size and shape.
ii. Molecular mass can be calculated by plotting the relative elution volume of a protein (Ve/Vo) against the logarithm of its molecular mass.
iii. Larger proteins are eluted before smaller proteins.
iv. The pore size of the beads in the column can be changed.
28. In the technique of affinity chromatography:
i. Enzymes can be eluted following binding to their free substrate.
ii. Proteins are separated on the basis of their hydrophobic interactions.
iii. Complete purification may be achieved in a single step.
iv. Affinity depends on the charge of the protein.
29. Subcellular Fractionation is often used as the initial step of a protein purification procedure because:
i. Most proteins are purified from mitochondria.
ii. It is the only way of obtaining proteins from the cytosol.
iii. It is a good substitute for ammonium sulphate precipitation.
iv. It simplifies the subsequent purification procedure.
30. Dialysis is an important stage in some purification procedures because:
i. It allows proteins to be separated from nucleic acids.
ii. It allows amino acids to be separated from large proteins.
iii. It concentrates solutions of proteins.
iv. It separates proteins from ammonium sulphate.
END OF EXAMINATION PAPER
