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

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