Which are the 3 components of DNA nucleotide? Types of bonds in a DNA nucleotide.

 DNA (deoxy ribo nucleic acid)is made up of two strands that are twisted around each other to form a right-handed helix, called a double helix. DNA stores genetic information in all organisms.

Russian biochemist Phoebus Levene discovered the order of the three major components of a single nucleotide (phosphate-sugar-base)

Each strand is made up of deoxyribonucleotides joined by phosphodiester bond. The two strands are held together by hydrogen bonds between nitrogenous bases. Sugar and phosphate forms the backbone of DNA

The 3 components of DNA nucleotide

1. Phosphate group

2.  Pentose Sugar molecule (deoxyribose in DNA)

3. Nitrogen-containing base 

1. Phosphate group

A free, unincorporated nucleotide contains a chain of three phosphates (triphosphosphates). During formation of DNA strand, it loses two of these phosphate groups, so that only one phosphate is incorporated into a strand of DNA.

The negative charge of DNA is due to the phosphate group that contains one negatively charged oxygen atom (see the figure).

2.  Pentose Sugar molecule (deoxyribose in DNA)

• The sugar in DNA contains deoxyribose. 
• In deoxyribose, the 2^nd C position of deoxyribose sugar has H atom only. That is why it is called 2-deoxy ribose.

3. Nitrogen-containing base.

• The 4 bases used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T).
• Adenine and Guanine are two ringed (nine-member double ring) and forms the purines
• Cytosine (C) and thymine (T) are single ringed (six-member single ring) and forms the pyrimidines

Bonds within DNA nucleotide or deoxyribonucleotide

1. Glycosidic bond

• Pentose Sugar and nitrogenous base joined by glycosidic bond forms nucleoside
• Glycosidic bond (nitrogen-carbon linkage) between C1 of sugar-N9 of purine bases (C1-N9 glycosidic bond) (Adenine and Guanine)
• Carbon 1 of sugar and nitrogen 1 of pyrimidine bases (C1-N1 glycosidic  bond)(Cytosine and thymine)

2. Ester bond in a Nucleotide

Ester bond formed within nucleotide between 5^th Carbon of sugar and phosphate.

Sugar reacts with phosphate forming an ester –C-O-bond with release of H₂O

These are the bonds within a nucleotide

Now Between adjacent nucleotides in a DNA strand; phosphate is the connecting link.

-C-O bond is called the ester bond.

Two Ester bonds connect the adjacent nucleotide via phosphate. Therefore called as phosphodiester bond.

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