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Midterm

BIOC 2580 Study Guide - Midterm Guide: Cyanogen Bromide, Catalytic Triad, Glutamine


Department
Biochemistry
Course Code
BIOC 2580
Professor
Enoka Wijekoon
Study Guide
Midterm

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Name _____________________________ Student number ____________________
University of Guelph
Department of Chemistry and Biochemistry
19-258 Introductory Biochemistry
Midterm test. October 27, 1998. Time allowed, 80 min.
Answer questions 1-20 on the computer scoring sheet provided.
Only one option is correct for each of these questions.
Use pencil to fill in the circles representing your chosen answer; and erase cleanly if you make an error. Do not use ink or
white-out on the computer scoring sheet.
You may mark your answer on the question paper for your own records, however in case of a discrepancy between question
paper and the computer scoring sheet, the choice shown on the computer sheet will be taken as final.
Answer questions 21-23 directly on the question paper. Use blue or black ink.
If you use pencil, the paper may not be eligible for appeal of grade.
Constants and other data required for numerical problems can be found on the last page.
Questions 1-20 have a weight of 1 mark each / 20 marks
Questions 21-23 are worth 5 marks each / 5 marks
/ 5 marks
/ 5 marks
=======
________ / 35 marks total
Name____________________________ Student Number______________________
Answer the following questions on the computer scoring sheet. Value 1 mark each
1. Which of the following amino acids would have the highest relative mobility Rf in normal thin layer chromatography?
Answer: Most hydrophobic, least polar
A) Arg
polar, charged B) Lys
polar,charged C) Met
nonpolar D) Thr
polar, uncharged E) Asn
polar, uncharged
2. Which of the following amino acids is most likely to be found deep in the core of a properly folded protein? Answer:
Most hydrophobic, least polar
A) Lys
charged B) Gln
polar C) Thr
polar D) Val
non-polar E) Asp
charged
3. Which of the following amino acids is a disruptor or breaker of secondary structure?
A) Ile B) Pro C) Ala D) Phe E) Glu

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Body file:///D:/Lectures/258/F98-ans.htm
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ring kinks peptide
backbone, no NH to donate
H-bond
4. Which of the following amino acids can accept or donate hydrogen bonds from its side chain?
A) Phe
hydrocarbon B) Gly
hydrocarbon C) Ala
hydrocarbon D) Val
hydrocarbon E) Ser
O-H donates, O:
accepts
5. Identify the amino acid drawn on the right:
A) Lysine
B) Asparagine
C) Aspartate
D ) Glutamine
E) Glutamate
6. Anfinsen's experiment demonstrated that a polypeptide could be denatured and then will refold, guided only by its
sequence of amino acids.
Which of the following procedures caused the unfolded polypeptide to refold correctly? (This topic was skipped or only
dealt with briefly this year.)
A) Addition of urea followed by exposure to O2.
B) Addition of urea followed by 2-mercaptoethanol.
C) Removal of urea followed by exposure to 2-mercaptoethanol.
D) Exposure to O2 followed by removal of urea.
E) Removal of urea followed by exposure to O2.
Anfinsen treated the enzyme ribonuclease A with concentrated urea, which weakens the hydrophobic effect causing proteins to unfold or
denature. The reducing agent 2-mercaptoethanol causes disulfide bonds to convert back into pairs of Cysteine -SH groups. When urea is
removed first, the protein refolds, then exposure to O2 allows properly paired up -SH groups to reoxidize to disulfides in the correct
pairings. Exposure to O2 before removal of urea causes -SH groups to pair up at random, so that the correct folding pattern can't form again.
This experiment demonstrated that folding occurs solely because of the positions of amino acids in the sequence (sequence determines
secondary structure, patterns of polar and non pola side chains, patterns of large and small side chains etc).
7. The attacking nucleophile that starts the catalytic process in chymotrypsin is
A) Aspartate B) Histidine C) Serine D) Glycine E) Tyrosine
Asp 102, His57 Ser195 make up the catalytic triad, but Ser is the nucleophile. Gly193 forms part of the oxyanion hole. Tyr is one of the
targets of chymotrypsin.
8. How many different oligopeptides will be generated when the peptide below is digested by chymotrypsin:
Ala-Ile-Leu-Phe + Val-Lys-Thr-Val-Ser-Tyr + His-Phe-Pro-Trp + Ser-Arg-Asn-Val-Leu-Val-Pro-Ser
Three cuts gives four pieces. Note that no cut is made between Phe and Pro (underlined).
A) 2 B) 3 C) 4 D) 5 E) 6
Name____________________________ Student Number______________________
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Answer the following questions on the computer scoring sheet. Value 1 mark each
9. Which of the following procedures in polypeptide analysis is cyanogen bromide used for?
A) As a color reagent to detect amino acids. = ninhydrin or fluorescamine
B) As N-terminal amino group labelling reagent.=fluorodinitrobenzene, phenylisothiocyanate or dabsyl chloride
C) To reduce disulfide bonds. = 2-mercaptoethanol or dithiothreitol
D) To cut the polypeptide chain at methionine.
E) In the cyclization step of the Edman reaction. = anhydrous trifluoroacetic acid
10. What initial reaction velocity vo is observed if substrate concentration in an enzyme reaction is 0.5 × KM and Vmax is
2.4 × 10-6 mol L-1 min-1.
A) 1.2 × 10-6 mol L-1 min-1. B) 6.0 × 10-7 mol L-1 min-1.
C) 2.4 × 10-6 mol L-1 min-1.D) 8.0 × 10-7 mol L-1 min-1.
E) 1.6 × 10-6 mol L-1 min-1.
11. What substrate concentration, expressed as a multiple of KM, must be present when an enzyme reaction is observed to
have an initial rate vo = 0.75 Vmax.?
A) [S] = 0.25 × KMB) [S] = 0.75 × KMC) [S] = 1.33 × KM
D) [S] = 3.0 × KME) [S] = 4.0 × KM
12. The plot at right represents rate of an enzyme
catalyzed reaction as a function of [S].
The curve levels off towards the right because:
A) Substrate is running out.
B) The enzyme is almost fully occupied with substrate.
C) Product is accumulating and causing the reverse reaction to occur.
D) The enzyme is running out.
E) An inhibitor must be present and is slowing down the reaction.
13. A sample of lactate dehydrogenase of mass 2.4 × 10-6 g gave a reaction rate of 1.2 × 10-4 mol L-1 min-1 in a sample
volume of 5.0 mL.
The specific activity of the enzyme is
A) 2.5 x 10-1 mol mg-1 min-1 B) 2.5 x 10-4 mol mg-1 min-1
C) 2.5 x 10-7 mol mg-1 min-1 D) 1.0 x 10-4 mol mg-1 min-1
E) 1.0 x 10-7 mol mg-1 min-1
Name____________________________ Student Number______________________
Answer the following questions on the computer scoring sheet. Value 1 mark each
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