Nucleotide

A nucleotide consists of an organic molecule composed of a nitrogenous base, pentose sugar, and phosphate.

DNA and RNA are polynucleotides, which contain a chain of nucleotides monomers with different nitrogenous bases. Nucleotides are essential for carrying out metabolic and physiological activities.

ATP (Adenosine triphosphate) acts as the energy currency of cells, while nucleotides are essential for many metabolic processes and form various coenzymes and cofactors, such as NAD, NADP, FAD, and coenzyme A.

Table of Contents

Nucleotide Structure

Nucleotides vs Nucleosides

Nitrogenous Bases

Nucleotide Function

Nucleotide Structure: What does a nucleotide look like?

A nucleotide consists of three units, which are covalently linked:

  • a 5-carbon sugar
  • a phosphate group
  • a nitrogenous base
  1. Nitrogenous Bases:
  • Purine
  • Pyrimidine

2. Pentose Sugars:

  • Ribose
  • Deoxyribose
  1. Phosphate
  2. Monophosphate
  3. Diphosphate
  4. Triphosphate

Nucleotide

1. Nitrogenous Base: DNA contains adenine (A), guanine (G), cytosine (C) and thymine (T), whereas RNA contains adenine, guanine, cytosine and uracil (U). Both DNA and RNA comprise pyrimidine or purine bases.

Nitrogenous bases

2. Sugar: A nucleotide consists of a pentose sugar. DNA (Deoxyribonucleic acid) contains a deoxyribose sugar and RNA (Ribonucleic acid) contains a ribose sugar.

A Nitrogenous base attached to a sugar is called a “Nucleoside”.

3. Phosphate: Phosphate is associated with the sugar of nucleoside through an ester bond with the 5th Carbon hydroxyl group. Nucleotides typically contain at least one phosphate group.

The phosphate of the first nucleotide attaches to the third C-OH group of the sugar of the second nucleotide, thereby forming a 5’ → 3’ linkage.

In DNA (double helix), two antiparallel strands of polynucleotides are linked together by hydrogen bonds between nitrogenous bases. Purine pairs with pyrimidine base, A pairs with T and G pairs with C by two and three hydrogen bonds, respectively.

In RNA, A pairs with U instead of thymine (T).

The sugar-phosphate backbone of a polynucleotide chain is formed by the interlinking of phosphate groups to the sugar molecules of two nucleotides. DNA and RNA are examples of polynucleotides.

When the phosphate group attaches to the hydroxyl group of the same sugar, it forms a cyclic nucleotide. These cyclic nucleotides are present as a single monomer, such as cAMP and cGMP, and are used in intracellular signal transduction processes.

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