This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Amino Acids, DNA and RNA”.
1. In double helix of DNA, the two DNA strands show which type of characteristics?
a) coiled around a common axis
b) coiled around each other
c) coiled differently
d) coiled over protein sheath
View Answer
Explanation: The DNA molecule consists of two long, parallel chains which are joined together by short crossbars at regular intervals. The two chains are spirally coiled around a common axis in a regular manner to form a right handed double helix.
2. A nucleotide 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
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Explanation: Nucleotide is an organic compound consisting of a nitrogen-containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.
3. Which of the following nitrogenous base is not present in RNA?
a) adenine
b) thymine
c) cytosine
d) guanine
View Answer
Explanation: Though both RNA and DNA contain the nitrogenous bases adenine, guanine and cytosine, RNA contains the nitrogenous base uracil instead of thymine. Uracil pairs with adenine in RNA, just as thymine pairs with adenine in DNA.
4. To which of the following does thymine form hydrogen bonds in DNA?
a) adenine
b) thymine
c) cytosine
d) guanine
View Answer
Explanation: In molecular biology, two nucleotides on opposite complementary DNA strands that are connected via hydrogen bonds are called a base. In the Watson-Crick DNA base pairing, Adenine (A) forms a base pair with Thymine (T) and Guanine (G) forms a base pair with Cytosine (C).
5. What term is used to describe the process by which DNA is copied to produce two daughter DNA molecules?
a) reproduction
b) replication
c) translation
d) transcription
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Explanation: Replication is the copying of DNA into two daughter DNA molecules. Translation is the process by which the genetic code for a specific protein (carried in messenger RNA) is used for the synthesis of a new protein.
6. What term is used to describe the process by which a segment of DNA is copied to produce a molecule of messenger RNA?
a) reproduction
b) replication
c) translation
d) transcription
View Answer
Explanation: Transcription is the term used to describe how the genetic code relevant for the synthesis of one protein (a gene) is copied from DNA to form messenger RNA.
7. What amino acid is coded by the triplet of bases UAU?
a) phenylalanine
b) serine
c) tyrosine
d) cysteine
View Answer
Explanation: The triplet code for phenylalanine can be UUU or UUC. For serine it can be UCU, UCC, AGU or AGC. For tyrosine, it is UAU or UAC. For cysteine it can be UGU or UGC.
8. To which of the following does guanine form hydrogen bonds in DNA?
a) adenine
b) thymine
c) cytosine
d) guanine
View Answer
Explanation: In molecular biology, two nucleotides on opposite complementary DNA strands that are connected via hydrogen bonds are called a base. In the Watson-Crick DNA base pairing, Adenine (A) forms a base pair with Thymine (T) and Guanine (G) forms a base pair with Cytosine (C).
9. 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
View Answer
Explanation: A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (either ribose or deoxyribose).
10. DNA is composed of repeating units of ___________
a) ribonucleosides
b) deoxyribonucleosides
c) ribonucleotides
d) deoxyribonucleotides
View Answer
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.
11. Glycine and proline are the most abundant amino acids in which of the following structure?
a) Hemoglobin
b) Myoglobin
c) Insulin
d) Collagen
View Answer
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.
12. 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
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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.
13. Which of the following amino acids is mostly likely to disrupt an alpha helix?
a) Proline
b) Leucine
c) Glycine
d) Valine
View Answer
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.
14. Which amino acid can form disulphide bonds?
a) Proline
b) Leucine
c) Cysteine
d) Valine
View Answer
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.
15. Which of the following amino acid is a limiting amino acid in pulses?
a) Leucine
b) Lysine
c) Methionine
d) Glutamine
View Answer
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.
16. 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
View Answer
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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