Question

Identify the components of a nucleoside and a nucleotide. What distinguishes RNA from DNA? What distinguishes a pyrimidine base from a purine base ? Briefly describe the mechanism from liking nucleotides during the synthesis of a polynucletoied or nucleic acid. One strand of a double-helical DNA molecule has a fragment with the sequence.

Answer 1

Answer-

Nucleoside-(sugar+base)

Nucleoside is made up of nitrogen base which is covalently attached to sugar. Sugar is ribose in RNA and deoxy ribose in DNA

Nucleotide-(sugar+base+phosphate)

Nucleotide is made up of nitrogen base which is covalently attached to sugar along with one to three phosphate groups.

Base	nucleoside	nucleotide
Adenine	Adenosine/deoxyadenosine	Adenylate/deoxyadenylate
Thymine	Thymidine/deoxythymidine	Thymidylate

DNA	RNA
Deoxyribose nucleic acid	Ribose nucleic acid
Sugar moiety is β-D-2 deoxyribose sugar	Sugar moiety is β-D-ribose sugar
DNA is a double stranded molecule except in few viruses	RNA is a single stranded molecule except in few viruses
Nitrogenous bases present: Adenine, Guanine, Thymine and Cytosine	Nitrogenous bases present : Adenine, Guanine. Uracil and Cytosine
Only one form of DNA is present in the organisms	There are three types of RNA (tRNA, rRNA and mRNA)
DNA is resistant to alkali hydrolysis	Sensitive to alkali hydrolysis

Structure of pyrimidine-

The nitrogenous base of the nucleotide is joined covalently at N-1 of pyrimidines in an N-beta-Glycosyl bond to the 1’ carbon of the pentose and the phosphate is esterified to the 5’ carbon. Pyrimidine are cytosine, thymine.

Structure of purine-

The nitrogenous base of the nucleotide is joined covalently at N-9 of Purines in an N-beta-Glycosyl bond to the 1’ carbon of the pentose and the phosphate is esterified to the 5’ carbon. Purines are adenine and guanine