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1.
What is amino acid ?
Ans:
An organic compound containing an amino group (NH2), a carboxylic
acid group (COOH), and any of various side groups, especially
any of the 20 compounds that have the basic formula NH2CHRCOOH,
and that link together by peptide bonds to form proteins or
that function as chemical messengers and as intermediates
in metabolism.
2. Why learn these structures and properties?
Ans:
It is critical that all students of the life sciences know
well the structure and chemistry of the amino acids and other
building blocks of biological molecules. Otherwise, it is
impossible to think or talk sensibly about proteins and enzymes,
or the nucleic acids.
3. Which is the smallest amino acid?
Ans:
Glycine is the smallest amino acid as it has no side chain.
4. What is special about proline?
Ans:
Due to the cyclic binding of the three-carbon side chain to
the nitrogen of the backbone, proline lacks a primary amine
group (-NH2). The nitrogen in proline is properly referred
to as a secondary amine. Proline is sometimes called an imino
acid, although the IUPAC definition of an imine requires a
carbon-nitrogen double bond.
5. What is special about glycine?
Ans: There is a second hydrogen atom at the a carbon,
glycine is not optically active. Since glycine has such a
small side chain, it can fit into many places where no other
amino acid can.
6. What is special about cysteine?
Ans:
Cysteine is unique amongst the twenty natural amino acids
as it contains a thiol group. When cysteine is oxidised it
can form cystine, which is two cysteine residues joined by
a disulfide bond which are crucial to defining the structures
of many proteins.
7. Which amino acids have highest codons?
Ans:
Arginine, Leucine and Serine have highest codons i.e 6.
8. Which, if any, amino acids are achiral?
Ans:
Glycine.
9. Which, if any, amino acids have an R configuration?
Ans:
Cysteine.
10. Which, if any, amino acids have no 1º-amine functions?
Ans:
Proline.
11. Which, if any, amino acids have more than one stereogenic
center?
Ans:
Isoleucine and Threonine.
12. Which amino acid has the highest pI?
Ans:
Arginine
13. Which amino acid has the lowest pI?
Ans:
Aspartic acid.
14. Which is the largest standard amino acid?
Ans:
Tryptophan.
15. Which is the most acidic standard amino acid?
Ans: Aspartic acid.
16. Which standard amino acid contains an unusual carbon nitrogen
bond making it an imino acid?
Ans:
Proline.
17. Which standard amino acid is the best buffer under physiological
conditions where pH = 7.0?
Ans:
Histidine.
18. Which standard amino acid has the longest aliphatic side
chain branched at the beta carbon?
Ans: Isoleucine.
19. Which standard amino acid can covalently dimerize spontaneously?
Ans:
Cysteine.
20. What is the C-terminal amino acid of the following peptide
- Met-Ile-Val-Glu-Gln-Tyr-Phe-Trp-Asp?
Ans:
Asp.
21. Which amino acid in the following peptide sequence --
Met-Ile-Leu-Glu-Gly-Gln-Tyr-Phe-Trp-Asp -- is the most flexible
in terms of sterically allowed conformations?
Ans:
Glycine.
22. Which amino acid is the least flexible in terms of sterically
allowed conformations?
Ans:
Proline.
23. In the following peptide sequence -- C-D-V-N-Q-P-F-W-E
-- the R-group of which amino acid is likely to be the most
chemically reactive at physiological pH = 7.0?
Ans:
Cysteine
24. Which two amino acids have the same Isoelectric point?
Ans:
Leucine and Isoleucine.
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