Introduction to Nucleotides

Introduction to Nucleotides

Contents

• Introduction to nucleotides

• Types of nucleic acid and components

Objective

At the end of this lecture, student will be able to

• Explain the types of nucleic acid and their components

• Discuss the biological functions of nucleotides

• Describe the nomenclature of nucleotides

• Distinguish between nucleotide and nucleoside

Introduction

• Two types of nucleic acid – DNA & RNA

• It serves as transmitter of genetic information

• DNA is a chemical basis of heredity and regarded as the reserve bank of genetic information

• It is responsible for the maintaining the identity of different species of organism over millions of years

• Every aspects of cell function is under the control of DNA

• DNA is organized in to genes, fundamental unit of genetic information

Components of Nucleic acid

• Nucleic acid are the polymers of nucleotides, held by Phosphate Bridge

• Nucleotides: it composed of

Nitrogen base

Pentose sugar

Phosphate

• Nucleoside: Nitrogen base + pentose sugar

• Thus nucleotides are nucleosides + phosphate

• The atom in purine ring are numbered as 1 to 9 and for pyrimidine as 1 to 6 whereas pentose carbon 1 to 5

•       Nucleic acid are the polymers of nucleotides, held by phosphate bridge

Structure of Nucleotides

• The nitrogen bases found in nucleotides are aromatic heterocyclic compounds

• Nitrogen bases are of 2 types:

1. Purines:

a. Adenine

b. Guanine

These are numbered in anti-clock wise direction

2. Pyrimidines:

a. Cytosine

b. Thymine c. Uracil

These are numbered in clock wise direction

• DNA & RNA contain the same purine and pyrimidines

• Cytosine is found in both DNA & RNA, but differ in second pyrimidine. i.e. DNA → Thymine and RNA → Uracil

Nitrogen bases structures

Sugars of nucleic acid

• The five carbon momnosaccharides are found in nucleic acid

• RNA contains D-Ribose while DNA contains D- deoxyribose

• Ribose and deoxyribose differe in structure at C2

           

D- Ribose

D-2-Deoxyribose

Nucleic acids – Polynucleotides

•       Two types of nucleic acid – DNA & RNA- made of nucleotides

Tautomeric forms of purines and pyrimidines

• The existence of a molecule in a keto and enol for is known as tautomerism

• Purine & pyrimidines with oxo (-c-) functional group exhibits tautomerism

• The lactam and lactim forms of cytosine are represented as:

• At physiological PH the lactam tautomeric forms are present

Nucleotides

• Pentose are bonded to nitrogen bases by β-N-glycosidic bonds

• N9 of purine ring binds with C1 of pentose sugar to form a covelent bond in purine nucleotide

• In case of pyrimidines, glycosidic linkage is between N1 of pyrimidine and C1 of pentose

• The hydroxyl groupadenosine are esterified with phosphate to produce 5l or 3l monophosphate. 5l hydroxyl is most commonly esterified

• Thus AMP represents adenosine 5l monophosphate

• However, for Adenosine-3-monophosphate the abbreviation 3- AMP is used

• Pentose are bonded to nitrogen bases by β-N-glycosidic bonds

•       Nucleotides of DNA

•       Nucleotides of RNA

•       Nucleotide diphosphates and triphosphates

•       Cyclic nucleotides

Biological functions of nucleotides

• Building blocks of nucleic acids (DNA and RNA).

• Involved in energy storage, muscle contraction,

• Active transport, maintenance of ion gradients.

• Activated intermediates in biosynthesis (e.g: UDP-glucose, S- adenosyl methionine)

• Components of coenzymes (NAD+, NADP+, FAD, FMN and CoA)

• Metabolic regulators:

a. Second messengers (cAMP, cGMP)

b. Phosphate donors in signal transduction (ATP)

c. Regulation of some enzymes via adenylation and uridylylation

Summary

• 2 types of nucleic acid DNA and RNA

• Nucleotides: nucleoside + phosphate

• Nucleosides: Nitrogen base + pentose sugar

• DNA & RNA contains both purines and Pyrimidines

• Purines are Adenine and Guanine

• Pyrimidines are cytosine, thymine and uracil