Calculate the turnover number for acetylcholinesterase
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. In an experiment completed in the biochemistry laboratory, you found that a 20mM solution of the enzyme acetylcholinesterase catalyzed the breakdown of 0.5 M acetylcholine in 1 min of reaction time. Calculate the turnover number for acetylcholinesterase.
i. 416.7 s-1
ii. 40 min-1
iii. 25000 min-1
iv. 0.025 min-1
6. While completing the experiment with acetylcholinesterase in Problem 5, you also measured the Kmvalues for the two substrates, acetylcholine and butyrylcholine.
Acetylcholine Km=1 x 10-6M
Butyrylcholine Km=1 x 10-4M
Which of the following statement(s) is (are) correct? HINT: k-1 >> k2
i. Butyrylcholine has a higher affinity for the enzyme
ii. The butyryl group does not fit/bind as well as the acetyl group at the active site.
iii. Acetylcholine has a lower affinity for the enzyme
iv. Acetylcholine is the natural substrate for this enzyme.
7. Which of the following are true of the reaction catalysed by chymotrypsin?
i. The substrate binds to the active site with relatively weak bonds.
ii. A histidine and a serine residue at the active site participate in the reaction.
iii. The side chains of amino acids at the active site are involved in the binding.
iv. The mechanism involves covalent and acid-base catalysis.
8. 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: .gif”>
proposed that Kmequals the equilibrium constant.
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.
9. Which of these statements about enzyme-catalyzed reactions is (are) correct?
i. At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration.
ii. The Michaelis-Menten constant Km equals 1/2Vmax.
iii. If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor.
iv. The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favourable in the enzyme-catalyzed reaction.
10. 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.
11. In a plot* of v against v/S for an enzyme-catalyzed reaction, the presence of a non-competitive inhibitor will alter the:
i. intercept on the v axis.
ii. Vmax.
iii. intercept on the v/S axis.
iv. slope of the plot
*equation: .gif”>
12. Which of the statements about uncompetitive inhibition is (are) true?
i. Vmaxapp decreases as inhibitor concentration increases.
ii. Vmaxapp decreases as Ki for inhibitor decreases.
iii. Km decreases as inhibitor concentration increases.
iv. Vmaxapp increases as Ki for inhibitor decreases.
13. Which units are appropriate for Km?
i. mmoles l-1 min-1
ii. mM
iii. mM min-1
iv. ?M
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.
14. The oligopeptide GARYFRSTERWILKINS
i.has a glycine residue at its C-terminus.
ii. would absorb light at 280nm.
iii. contains a total of two branched chain amino acids.
iv. has a net positive charge at pH7.
15. Collagen is a fibrous protein
i.which is composed almost entirely of ?-helices.
ii. which contains a high proportion of alanine residues.
iii. which forms weak non-elastic fibres.
iv. which contains the uncommon amino acid 5-hydroxylysine.
16. The amino acid lysine
i.can be N-acetylated in histone proteins.
ii. is an acidic amino acid.
iii. Can be N-methylated in myosin.
iv. Is represented by the single letter code L.
17. The commonb-strand
i.is unstable in isolation.
ii. is similar to a helix with two residues per repeat unit.
iii. has the amino acid R-groups on alternate side of the peptide chain.
iv. has a distance along the helical axis of 5.4Å per turn.
18. Transmembrane proteins
i.are frequently glycosylated on external (exoplasmic) regions
ii. mainly contain ?-helical secondary structures
iii. often contain clusters of 22-30 hydrophobic amino acids
iv. have clusters of acidic amino acids on the extracellular loops which link membrane-embedded secondary structures
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.
19. Protein structure is characterised as having four levels.
i. The primary structure is the sequence of amino acids linked by peptide bonds.
ii. The secondary structure is a 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 FAD.
20. When considering the relationships between energy (E), frequency (?) and wavelength (? )
i. E is inversely proportional to ?
ii. E is proportional to ?
iii. E is proportional to ?
iv. E is inversely proportional to ?
21.Absorbance
i. Is calculated after measuring the intensities of incident (Io) and transmitted (It) light
ii. Is measured in nm
iii. Is a ratio and therefore has no units
iv. Has an exponential relationship to concentration
22. Which of the following statements are true of molecular fluorescence spectroscopy?
i. The emission wavelength is always longer than the excitation wavelength
ii. It is more specific than molecular absorbance spectroscopy
iii. It can detect lower concentrations of molecules than molecular absorbance spectroscopy
iv. It is less prone to interference than molecular absorbance methods.
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.
23. The nucleotide cofactors NAD+ & NADP+ are reversibly reduced by many enzymes including malate dehydrogenase. During the reduction of oxaloacetate to malate which of the following occur?
i. NAD+ is converted to NADH
ii. NADH is converted to NAD+
iii. Absorbance at 340nm will increase
iv. Absorbance at 340nm will decrease
24. Which of the following may occur during the denaturation of a globular protein?
i. The primary structure will be altered
ii. Quenching of fluorescence may occur
iii. The UV absorbance may decrease
iv. The fluorescence may decrease
25. Which of the following can affect the validity of absorbance values?
i. Stray light
ii. Monochromating device
iii. Unstable chromophore
iv. Non specific absorption
26. Which of the following properties of a protein can be used in its purification:
i. Density.
ii. Shape.
iii. Solubility.
iv. Size.
27. Affinity chromatography can be utilised using which of the following complementary proteins bound with its specific ligand.
i. Nucleic acid binding protein with nucleic acid.
ii. Glucose oxidase with glucose.
iii. Histidine tagged recombinant protein with metal ions
iv. Insulin with insulin receptor.
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.
28. The technique of detergent disruption is performed:
i. Using a strong detergent such as sodium dodecyl sulphate (SDS).
ii. Using a mild detergent such as Triton X-100.
iii. Is used to help isolate proteins from the cytosol.
iv. Is used to help isolate proteins from cellular membranes.
29. In a crude protein extract the total amount of protein was found to be 20, 000 mg and the total enzyme activity for alcohol dehydogenase was found to be 4, 000, 000 U. Following ammonium suphate precipitation the total amount of alcohol dehydrogenase was found to be 5, 000 mg and its total enzyme activity was 3, 000, 000 U.
i. The percentage recovery of the alcohol dehydrogenase following ammonium sulphate precipitation was 25%.
ii. The fold purification of the alcohol dehydrogenase following ammonium sulphate precipitation was 1.33 fold.
iii. The ammonium suphate precipitation purified the alcohol dehydrogenase based on it size and shape.
iv. The specific activity of the alcohol dehydrogenase following ammonium sulphate precipitation was 600 U/mg.
In isoelectric focussing:
i. An ampholyte solution is incorporated into the gel.
ii. Proteins are separated related to the pore size of the gel.
iii. A stable pH gradient is established in the gel.
iv. A constant pH is established in the gel.