Important MCQs on Nucleotide | Nucleoside


Nucleotides are the building blocks of nucleic acids; they are composed of three sub unit molecules: a nitrogenous base (also known as nucleobase), a five-carbon sugar (ribose or deoxyribose), and a phosphate group consisting of one to three phosphates.

The nitrogen-containing bases of nearly all nucleotides are derivatives of three heterocyclic compounds: pyrimidine, purine, and pyridine. The most common nitrogen bases are the pyrimidines (cytosine, thymine, and uracil), the purines (adenine and guanine), and the pyridine nicotinamide.

Nucleotides join together through phosphodiester linkages between the 5' and 3' carbon atoms to form nucleic acids. The 3' -OH of the sugar group forms a bond with one of the negatively charged oxygens of the phosphate group attached to the 5' carbon of another sugar. When many of these nucleotide subunits combine, the result is the large single-stranded polynucleotide or nucleic acid.


Important MCQs/ quiz on Nucleotide

1. Which of the following statements is true?
a) Sugar component of a nucleotide is ribose
b) Sugar component of a nucleotide is deoxyribose
c) The bases in nucleotides are attached to a pentose sugar moiety by a glycosidic linkage
d) The sugar molecule of the nucleotide is in L-configuration
Answer : C

2. What is the composition of nucleotide?
a) a sugar + a phosphate
b) a base + a sugar
c) a base + a phosphate
d) a base + a sugar + phosphate
Answer : d

3. A phosphodiester bond is present in
a) Nucleic acids in a nucleotide

b) Monosaccharides in a polysaccharide

c) Amino acids in a polypeptide

d) Fatty acids in a diglyceride
Answer : a

4. What is the composition of nucleoside?
a) a sugar + a phosphate
b) a base + a sugar
c) a base + a phosphate
d) a base + a sugar + phosphate
Answer : b

5. Group of adjacent nucleotides are joined by____
a) Phosphodiester bond
b) Peptide bond
c) Ionic bond
d) Covalent bond
Answer : a

6. Uridine present in RNA is____
a) nucleotides
b) pyrimidine
c) purine
d) nucleoside
Answer : b

7. The sugar molecule in a nucleotide is__
a) Pentose
b) Hexose
c) Tetrose
d) Triose
Answer : a

8. Which of the following is true about phosphodiester linkage?

a) 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide

b) 3’-phosphate group of one nucleotide unit is joined to the 5’-hydroxyl group of the next nucleotide

c) 5’-phosphate group of one nucleotide unit is joined to the 5’-hydroxyl group of the next nucleotide

d) 3’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide
Answer : a

9. Nucleic acids are a polymer of nucleotide monomeric units. Each nucleotide consists of____
a) base­-sugar-­OH
b) sugar-­phosphate
c) base­-sugar-­phosphate
d) none
Answer : c

10. Which of the following is false about purine and pyrimidine bases?

a) They are hydrophobic and relatively insoluble in water at the near-neutral pH of the cell

b) At acidic or alkaline pH the bases become charged and their solubility in water increases

c) Purines have two rings in their structure, but pyrimidine bases have only one ring

d) At acidic or alkaline pH the bases become charged and their solubility in water decreases
Answer : a

11. A DNA segment contains 100 Adenine and 100 cytosines, how many nucleotides are present in the segment?
a) 100
b) 200
c) 400
d) 50
Answer : c

12. Building blocks of nucleic acids are__
a) Nucleotides
b) Nucleosides
c) Amino acids
d) Histones
Answer : a

13. Nucleoside contains___
a) base-sugar
b) base-phosphate
c) base-sugar-phosphate
d) sugar-phosphate
Answer : a

14. The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is:
a) a deoxyribonucleoside.
b) a purine nucleotide.
c) a pyrimidine nucleotide.
d) adenosine
Answer : D

15. A major component of RNA but not of DNA is:
a) adenine.
b) cytosine.
c) guanine.
d) uracil
Answer : d

16. ATP is a___
a) nucleoside
b) nucleotide
c) vitamin
d) nucleic acid
Answer : b

17. Find the correct statement about phosphodiester linkage between adjacent nucleotides in nucleic acids

a) 3’-phosphate of one nucleotide joins the 3’-hydroxyl of the next nucleotide

b) 3’-phosphate of one nucleotide joins the 5’-hydroxyl of the next nucleotide

c) 5’-phosphate of one nucleotide joins the 5’-hydroxyl of the next nucleotide

d) 5’-phosphate of one nucleotide joins the 3’-hydroxyl of the next nucleotide
Answer : d

18. The sugar molecule present in nucleotide is_____
a) triose
b) tetrose
c) pentose
d) hexose
Answer : c

19. Which of the following nucleotide contains only ribose sugar and not deoxyribose____
a) Thymine – pentose sugar-phosphate
b) Uracil – pentose sugar-phosphate
c) Thymine – pentose sugar-phosphate
d) Cytosine – pentose sugar-phosphate
Answer : b

20. Purine base found in RNA is____
a) Cytosine
b) Thymine
c) Guanine
d) Uracil
Answer : c

21. Identify the purine base of nucleic acids in the following___
a) Cytosine
b) Thymine
c) Uracil
d) Adenine
Answer : d


22. The difference between a ribonucleotide and a deoxyribonucleotide is:

a) a deoxyribonucleotide has an —H instead of an —OH at C-2.

b) a deoxyribonucleotide has α configuration; ribonucleotide has the β configuration at C-1.

c) a ribonucleotide has an extra —OH at C-4.

d) a ribonucleotide has more structural flexibility than deoxyribonucleotide.

Answer : a


23. Which one of the following is true of the pentoses found in nucleic acids?

a) C-5 andC-1 of the pentose are joined to phosphate groups.

b) C-5 of the pentose is joined to a nitrogenous base, and C-1 to a phosphate group.

c) The bond that joins nitrogenous bases to pentoses is an O-glycosidic bond.

d) The pentoses are always in the β-furanose forms.
Answer : d


24. The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA:
a) always link A with T and G with C.
b) are susceptible to alkaline hydrolysis.
c) are uncharged at neutral pH.
d) None
Answer : d


25. The alkaline hydrolysis of RNA does not produce:
a) 2'- AMP.
b) 2',3'-cGMP.
c) 2'-CMP.
d) 3',5'-cAMP.
Answer : d

26. In a double-stranded nucleic acid, cytosine typically base-pairs with:
a) adenosine.
b) guanine.
c) inosine.
d) thymine.
Answer : b

27. Chargaff's rules state that in typical DNA:
a) A=G.
b) A=C.
c) A=U.
d) A+G=T+C.
Answer : d

28. In nucleotides and nucleic acids, syn and anti conformations relate to:
a) base stereoisomers.
b) rotation around the phosphodiester bond.
c) rotation around the sugar-base bond.
d) sugar pucker.
Answer : c

29. In living cells, nucleotides and their derivatives can serve as:
a) carriers of metabolic energy.
b) enzyme cofactors.
c) intracellular signals.
d) precursors for nucleic acid synthesis.
e) all of the above.
Answer :e

30. The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is:
a) a deoxyribonucleoside.
b) a purine nucleotide.
c) both a & b
d) None
Answer : d


31. The "energy carrier" ATP is an example of a(n):
a) deoxyribonucleoside triphosphate
b) di-nucleotide
c) peptide
d) ribonucleoside triphosphate
Answer : d