Unit 1: Amino Acids And Proteins | From Question To Perfection| Study With Confidence!

UNIT 1: AMINO ACIDS AND PROTEINS | FROM QUESTION
TO PERFECTION| STUDY WITH CONFIDENCE!
Course Code:
Course Title:
Programme:
Academic Year: 2026/2027.
Duration: 2 Hours.
Total Marks: 100.
Candidate Instructions:
1) Write your Registration Number on every answer booklet used.
2) Answer ALL questions in Section A and ANY TWO (2) questions in Section B.
3) Read each question carefully before answering.
4) Begin each question on a new page.
5) The marks for each question are indicated in brackets.
6) This paper consists of several printed pages, including this page.
7) Ensure your copy is complete before the examination begins.
8) Unauthorized materials and communication with other candidates are not permitted.




Turn Over.




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,How does threonine's structure differ from valine's structure? Answer: Both structures are
branched at the β carbon.
However, the branches on valine are two methyl groups, whereas one of the branches on
threonine is a hydroxyl group.
What is the protonation state of the amino acid backbone under physiological conditions?
Answer: Under physiological conditions, the backbone amino group is positively charged, and
the backbone carboxyl group is negatively charged.
Overall, this means the backbone has a net charge of zero and can be described as a zwitterion.
Glutamate Answer: Note: The protonated form of this amino acid is glutamic acid.
Aspartate/aspartic acid (Asp, D) has a similar structure, but with one fewer methylene group (-
CH2-) in its side chain.
The ᴅ/ʟ convention is used to denote amino acid _______________ and is based on the
structural similarity to _____________. Answer: The ᴅ/ʟ convention is used to denote amino
acid stereochemistry and is based on the structural similarity to glyceraldehyde.
Tryptophan is the only amino acid with two aromatic rings in its side chain. (True or False)
Answer: True. Tryptophan is the only amino acid with two aromatic rings in its side chain.
The backbone of proteinogenic amino acids consists of an amino group and a _______________
group Answer: The backbone of proteinogenic amino acids consists of an amino group and a
carboxyl group.
Describe the main structural difference between α-amino acids and β-amino acids. Answer: In
α-amino acids the central carbon is directly adjacent, or alpha, to the carboxylic acid (carbon 2).
β-amino acids have the amino group on the carbon that is beta to the carboxyl group (ie, carbon
3).
In living cells, the chiral amino acids in proteins are almost exclusively ʟ-amino acids. (True or
False) Answer: True. In living cells, the chiral amino acids in proteins are almost exclusively ʟ-
amino acids.
All proteinogenic amino acids have four distinct substituents around the α-carbon and therefore
are chiral. (True or False) Answer: False. Apart from glycine, all proteinogenic amino acids
have four distinct substituents around the α-carbon and therefore are chiral.
Match each one letter symbol to the amino acid it symbolizes.
Symbol:
(1) F
(2) K



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, (3) N
(4) Q
(5) R
(6) Y
Amino acids:
(A) Arginine
(B) Asparagine
(C) Glutamine
(D) Lysine
(E) Phenylalanine
(F) Tyrosine Answer: The amino acids:
(1) F – (E) Phenylalanine
(2) K – (D) Lysine
(3) N – (B) Asparagine
(4) Q – (C) Glutamine
(5) R – (A) Arginine
(6) Y – (F) Tyrosine
What is the absolute R/Sconfiguration of the chiral ʟ-amino acids? Answer: The chiral ʟ-amino
acids are almost all S-configuration at the α‑carbon.
The only exception is ʟ-cysteine, which is R configuration because its thiomethyl side chain (C
with a bond to an S) has a higher Cahn-Ingold-Prelog priority than the carboxyl group (C with a
bond to an O).
______________'s side chain is a methyl group. Answer: Alanine's side chain is a methyl
group.
Name the two amino acids whose side chains are considered basic and predominantly charged at
physiological pH. Answer: The amino acids lysine and arginine have side chains that are basic
and predominantly positively charged at physiological pH.
Note: Histidine is basic and can be positively charged, but it is predominantly neutral at
physiological pH.
The side chains of tyrosine, cysteine, and histidine are all ionizable and are predominantly
charged at physiological pH. (True or False) Answer: False. The side chains of tyrosine,
cysteine, and histidine are all ionizable but are predominantly uncharged at physiological pH.



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