Molecular Biology Multiple Choice Questions on “Nucleotides are the Precursors for DNA Synthesis”.
1. Which of the following is not true about nucleotides?
A. Monomeric units
B. Ubiquitous substances
C. Energy rich molecules
D. Non enzymatic molecules
Answer: D
Explanation: The nucleotides are known to be enzymatic molecules. For example, ribozymes are catalytic molecules. Also certain derivatives of nucleotides such as ATP, coenzyme A, nicotinamide adenine dinucleotide, etc., are important catalytic molecules that participate in various enzymatic processes.
2. The nitrogenous base is covalently linked to the _________ carbon of the pentose sugar.
A. C1
B. C2
C. C3
D. C4
Answer: A
Explanation: Nucleotides are phosphate esters of a five carbon sugar, either ribose of 2’-deoxyribose. The nitrogenous base is covalently linked to the C1 carbon of this pentose sugar to form the nucleotide.
3. In which carbon do the deoxyribonucleotides lack an –OH molecule?
A. C1
B. C2
C. C3
D. C4
Answer: B
Explanation: A deoxyribonucleotides lack an –OH molecule at the C2 position of the ribose sugar ring. This is the substrate for DNA synthesis and is known as the 2’-deoxyribonucleotide.
4. Which of the following is not a part of a nucleotide?
A. Ester linkage
B. Phosphate group
C. Base
D. Hydrogen bond
Answer: D
Explanation: Nucleotides are phosphate esters of a five carbon sugar, either ribose of 2’-deoxyribose. The nitrogenous base is covalently linked to the C1 carbon of this pentose sugar to form the nucleotide. Hydrogen bond is made by the bases to hold the two strands of DNA together and is not a part of the nucleotide.
5. Which of the following is not a part of a nucleoside?
A. Deoxyribose sugar
B. Glycosidic linkage
C. Phosphate
D. Base
Answer: C
Explanation: A nucleoside is the deoxyribose sugar linked to the base with a glycosidic linkage. Addition of phosphate at the 5’-carbone leads to the formation of the nucleotide.
6. The linkage between the sugar and the base is a covalent linkage.
A. True
B. False
Answer: A
Explanation: A glycosidic bond is one which links a type of covalent linkage which forms between a sugar molecule and another molecule which may or may not be a sugar. In case of nucleotide/nucleoside the sugar and the base is a glycosidic linkage.
7. Which of the following is not a nucleotide?
A. AMP
B. TMP
C. GMP
D. CMP
Answer: B
Explanation: TMP is not a nucleotide. Thymine is not present in form of Thymidine monophosphate as it is not used in RNAs. Thymine is present in the form of dTMP deoxythymidine monophosphate as it is used in the synthesis of DNA only.
8. Purines and pyrimidines form glycosidic linkage with the purines and pyrimidines at the N6 position.
A. True
B. False
Answer: B