Organic Chemistry Mcqs


Which of the characteristics below apply to amino acid Glycine?

A) Optically inactive B) Hydrophilic, basic and charged
C) Hydrophobic D) Hydrophilic, acidic and charged
Answer & Explanation Answer: A) Optically inactive

Explanation: The entire class of amino acids has a common backbone of an organic carboxylic acid group and an amino group attached to a saturated carbon atom. The simplest member of this group is glycine, where the saturated carbon atom is unsubstituted, rendering it optically inactive.

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Which of the following amino acid is a limiting amino acid in pulses?

A) Leucine B) Lysine
C) Methionine D) Glutamine
Answer & Explanation Answer: C) Methionine

Explanation: Amino acids that are present in low proportion limit the functioning of the proteins, and are so called limiting amino acids of those particular proteins. Generally proteins in pulses like beans are limited in methionine.

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Which amino acid can form disulphide bonds?

A) Proline B) Leucine
C) Cysteine D) Valine
Answer & Explanation Answer: C) Cysteine

Explanation: Cysteine aminoacid can form disulphide bond(bond which joins two atoms of sulphur atom) because this is the only amino acid with a sulphydryl group in its side chain is cysteine.

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Which of the following amino acids is mostly likely to disrupt an alpha helix?

A) Proline B) Leucine
C) Glycine D) Valine
Answer & Explanation Answer: A) Proline

Explanation: Certain amino acids with simple side chains, such as alanine, are very favorable for formation of alpha helices, whereas cyclic amino acids like proline tend to disrupt alpha helices.

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Which of the following statements about amino acids is correct?

A) Amino acids are uncharged at neutral pH B) Amino acids are classified according to the structures and properties of their side chains
C) Amino acids in proteins are mainly in the D-configuration D) Twenty four amino acids are commonly used in protein synthesis
Answer & Explanation Answer: B) Amino acids are classified according to the structures and properties of their side chains

Explanation: Amino acids are usually classified by the properties of their side chain into four groups. The side chain can make an amino acid a weak acid or a weak base, and a hydrophile if the side chain is polar or a hydrophobe if it is nonpolar.

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Glycine and proline are the most abundant amino acids in which of the following structure?

A) Hemoglobin B) Myoglobin
C) Insulin D) Collagen
Answer & Explanation Answer: D) Collagen

Explanation: Glycine and proline are the most abundant amino acids in collagen. The most common motifs in the amino acid sequence of collagen are glycine-proline-X and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline or hydroxyproline.

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DNA is composed of repeating units of ___________

A) ribonucleosides B) deoxyribonucleosides
C) ribonucleotides D) deoxyribonucleotides
Answer & Explanation Answer: D) deoxyribonucleotides

Explanation: It is a long, double” chain of deoxyribonucleotide, or deoxyribotide, units. The two deoxyribonucleotide chains are twisted around a common axis to form a right-handed double helix (spiral) that encloses a cylindrical space in it. Each deoxyribonucleotide unit, in turn, consists of three different molecules: phosphate molecule, a 5-carbon deoxyribose sugar and a nitrogenous base.

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A nucleoside is formed of which of the following units?

A) nitrogen base and phosphate B) nitrogen base, sugar and phosphate
C) nitrogen base and sugar D) sugar and phosphate
Answer & Explanation Answer: C) nitrogen base and sugar

Explanation: A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (either ribose or deoxyribose).

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