Nucleic Acids and Nucleotides: Structure and Functions and MCQs with Answer for NEET, GATE, GPAT, NET

Nucleic Acids and Nucleotides: Structure and Functions and MCQs with Answer for NEET, GATE, GPAT, NET

Nucleic acids are the macromolecules in the living cells. When these nucleic acids combine with proteins, they form nucleoproteins. The protein components are protamine and histones. Nucleic acids are polymers of nucleotides which are linked by phosphor-di-ester bond and are known as polynucleotides.

Structure of Nucleotides

Nucleotides are building blocks of nucleic acids. Nucleotides have 3 components

  • Nitrogen containing base
  • Pentose sugar
  • One or more phosphate

The molecule without phosphate group is known as nucleosides. The nitrogenous bases are derived from two parent compounds known as pyrimidine and purine. Purine bases: The two basic purine found in DNA as well as RNA are

  • Adenine (A)
  • Guanine (G)

Pyrimidine bases: The major pyrimidine bases are

  • Cytosine (C)
  • Uracil (U)
  • Thymine (T)

Cytosine and uracil are found in RNA while cytosine and thymine are found in DNA. Pentose sugar:- Nucleic acids have two types of pentose sugar, the DNA contain beta-2-deoxy-D-ribose and RNA contains beta-D-ribose. In nucleotides, both type of pentoses are in their isomeric form. The nitrogenous base of nucleotides is linked covalently to pentose sugar by glycosidic bond. The glycosidic bond is formed by removal of a molecule of water. Attachment of phosphate to pentose sugar The phosphate group is esterified to 5- carbon of pentose sugar. Some nucleotides have phosphate group attached to carbon atom other that 5- carbon, like cyclic-AMP, cyclic-GMP etc. Different ribonucleotides are:

  • AMP- adenosine mono-phosphate
  • GMP- guanine mono-phosphate
  • UMP- uridine mono-phosphate
  • CMP-cytidine mono-phosphate

Different types of deoxy ribonucleotides are:

  • d-AMP- deoxy adenosine mono-phosphate
  • d-CMP- deoxy cytidine mono-phosphate
  • d-UMP- deoxy uridine mono-phosphate
  • d-TMP- deoxy thymine mono-phosphate
  • d-GMP- deoxy guanine mono-phosphate

 

Functions of Nucleotides:

  1. They are precursors of DNA and RNA
  2. They work as energy carriers in cells
  3. They are component of enzyme co-factor
  4. They also work as chemical messengers

Multiple Choice Questions MCQs

1. Nucleic acids combine with which biomolecule?

A. Fats

B. Carbohydrates

C. Lipids

D. Proteins

2. Nucleotides are linked together to form nucleic acid through which type of bond?

A. Glycosidic bond

B. Phosphor-di-ester bond

C. Both

D. None

3. nucleotides have how many components?

A. 2

B. 3

C. 4

D. 5

4. If the compound does not contain the phosphate group, it is known as?

A. Nucleotide

B. Nucleoside

C. Both

D. None

5. Which of the following is purine nucleotide?

A. Adenine

B. Uracil

C. Thymine

D. All of the above

6. Which of the following is pyrimidine nucleotide?

A. Uracil

B. Cytosine

C. Thymine

D. All of the above

7. Which of the following is not present in RNA?

A. uracil

B. adenine

C. thymine

D. guanine

8. Match the following- 9. Where is DNA present?

A. Mitochondria

B. Nucleus

C. Cytoplasm

D. Both A and B

10. Where is RNA present?

A. Mitochondria

B. Nucleolus

C. Cytoplasm

D. Both B and C

11. In most of the nucleotides, the phosphate group is attached to which carbon of pentose sugar?

A. C-1

B. C-2

C. C-4

D. C-5

12. Which of the following statement is NOT true? 13. Which of the following is NOT the function of nucleotides?

A. Works as chemical messenger

B. Co-enzymes

C. Co-factors

D. Energy carries

14. What is the full form of AMP?

A. Adenine mini-phosphate

B. Aldehyde mono-phosphate

C. Alcohol mono-phosphate

D. None of the above

15. Which of the following protein is the component of nucleoprotein?

A. Proline

B. Arginine

C. Histones

D. All of the above

ANSWERS:-

1. Proteins

2. Phosphor-di-ester bond

3. 3

4. Nucleoside

5. Adenine

6. All of the above

7. Thymine

8.

9. Both A and b

10. Both B and C

11. C-5

12.

13. Co-enzymes

14. None of the above

15. Histones

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REFERENCE:- Pankaja Naik- Biochemistry; 4th edition; page no:- 124-127

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