Exam (elaborations)

ACS BIOCHEMISTRY EXAM 2023 WITH LATEST QUESTIONS AND ANSWERS 9June 2023

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Module
CHM 360

Institution
The University Of Bradford (UoB)

Explanation – Utilize the one-letter codes for all amino acids and know their charge and polarity. Globular proteins are usually seen in aqueous environments and will fold to have nonpolar amino acids on its interior. Based on that information, the polypeptide needs to have outside amino acids...

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ACS Biochemistry 360 Review

1. Which of the following statements about collagen is correct?
a) Collagen contains a high proportion of hydroxylated proline residues.
b) Collagen is a globular, intracellular protein.
c) Post-translational modification of collagen involves vitamin A.
d) The structure of collagen consists of a superhelix of three α helices twisted together

Explanation – collagen has α chains, NOT helices. Each of the polypeptides in the triple
superhelix of procollagen is an unusual left-handed helix not the right-handed α helix seen in
globular proteins. However, the three polypeptides are twisted around each other in a right-
handed manner to form the triple helix. All α helices are right-handed and get broken from high
amounts of proline, hydroxylated proline, and glycine; but, these triplets of amino acids strength
collagen. Glycine-X-Y.

2. Which of the following polypeptides is expected to be a globular protein?

a) KFSCCKDVVDG
b) IPVDSEDKHWY
c) AFSCKHEDGML
d) RDGLIVFYWSC
e) DEHRKICLRRG

Explanation – Utilize the one letter codes for all amino acids and know their charge and polarity.
Globular proteins are usually seen in aqueous environments and will fold to have nonpolar amino
acids on its interior. Based on that information, the polypeptide needs to have outside amino
acids that are charged or polar while the interior will have nonpolar/hydrophobic amino acids. D
is correct because (RDGLIVFYWSC) arginine, aspartate, serine, and cysteine are
polar/charged.

3. Select answers that match with the amino acid. Some answers will have more than one
answer.
1. acidic side chain ____________leucine 11
2. non-chiral amino acid ____________aspartate 1
3. basic side chain ____________serine 4, 12
4. side chain can be modified by adding ____________lysine 3, 8, 9
phosphates ____________phenylalanine 7, 13
5. involved in disulfide cross links ____________asparagine 9, 12
6. often found in the turns of proteins ____________glycine 2, 6
7. is converted to tyrosine by hydroxylation ____________tyrosine 4, 12, 13

, 8. important in the structure in collagen ____________proline 6, 8
9. has more than one amino group ____________cysteine 5, 12
10. has overall net charge of -2 at pH 7.4
11. only straight or branched hydrocarbons in
side chain
12. polar, non-charged side chain
13. aromatic side chain

Explanation – 6: Follow-up question: Where are Pro & Glycine seen in proteins? Ans: Beta
sheets (for turns) and collagen. Can these AA be used for α-helices? Ans: No. Due to Proline’s N
involved in the ring, it is too rigid for a N-Cα bond (makes kink) & N doesn’t have hydrogen
bond. For Glycine, too much flexibility; more likely to be seen in a coiled-coil structure
(collagen) 8: Lys increases tensile strength by cross-linking between α chains. This may not be
common knowledge about Lys. During the ACS Review, I did not go over this. 10. There are
amino acids that have a -2 charge at physiological pH. If it said -1, then the acidic amino acids
would be correct. 12. Technically tyrosine is a polar, non-charged side chain, but through GCU
we are taught that it is aromatic. During ACS Review, this was not added to the list.

4. The amino acid most likely to yield the above titration curve above would be:
a) Arginine
b) Glutamic acid
c) Glycine
d) Methionine
e) Tyrosine

Explanation – Based on the location where pI is, the amino acid is basic (due to it having a basic
pH). The only possible answer that is a basic amino acid is arginine. Know the properties of all
amino acids and how to calculate pI from a titration curve. From pI, you should be able figure
out the amino acid the titration curve corresponds with.

5. An enzyme has Vmax of 50 mol product formed (minute x mg protein)-1 and a Km of
10for the substrate. When a reaction mixture contains the enzyme and 5 substrate,
which of the following percentages of the maximum velocity will be closest to the initial
reaction rate?
a) 5%
b) 15%
c) 33%

, d) 50%
e) 66%

Explanation
Km = 10
Vmax = 50
1/2Vmax = 25 
S

Option 1: Rearrange Michaelis-Menten equation to find the ratio between the new
𝑉 [𝑆]
velocity (Vo) and Vmax. The original equation was 𝑉𝑜 = 𝐾𝑚𝑎𝑥
𝑚+[𝑆]


Find ratio of Vo and Vmax based from the given substrate concentration. Plug it into the
equation with Km.
5
= 0.33 ∗ 100 = 33%
5 + 10

If the question had asked for the actual value, you would not need to manipulate the
𝑉 [𝑆]
question at all and would be able to just plug in the values to find Vo from 𝑉𝑜 = 𝐾𝑚𝑎𝑥 .
𝑚+[𝑆]
Option 2: Visualize the concept via graph. This might be easier to due to estimating the
percentage. At 50% Vmax, Vo = 25. At 25% Vmax, Vo = 12.5. Label these points on the y-
axis. After drawing the Km and Vmax, draw a vertical line from 5 until it hits the
graph. Then draw a horizontal line to connection that point from the graph to the y-axis.
Based on where 25 and 12.5 are. The Vo of 5 lies between 25% and 50%. Since there
is one answer between that range, the answer is 33%, and the other possible answers can
be eliminated.

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Exam (elaborations)

ACS BIOCHEMISTRY EXAM 2023 WITH LATEST QUESTIONS AND ANSWERS 9June 2023

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