Name: Important Sources of Vitamins
Uploaded: 2019-07-19
Duration: 2 min 57 s
Description: Vitamins are essential for several biochemical reactions and the development of the body. This video describes their sources, types based on their solubility...

Question

State the composition and functional differences between DNA and RNA. Describe the mechanism of replication of DNA.

Accepted Answer

DNA stands for deoxyribonucleic acid composed of deoxyribonucleotides and have $2$ -deoxyribose sugar. DNA occurs mainly in the nucleus of the cell and has a unique property of replication and transferring of heredity character. There are two different types of heterocyclic nitrogenous bases- the purines are adenine and guanine while pyrimidine bases are thymine and cytosine. In DNA, the complementary bases are adenine and thymine: guanine and cytosine. The two strands of DNA are said to be complementary to each other in the sense that the sequences of bases in one strand automatically determines that of the other. Adenine and thymine are joined together by two hydrogen bonds and cytosine and guanine are paired by three hydrogen bonds.

Fig- Nucleotide bases of DNA

RNA(ribonucleic acid) is a single-stranded $α$ -helix structure that mainly occurs in the cytoplasm. The size, number of loops, and helical units change in a different RNA molecules. It helps in the biosynthesis of proteins and associated with the process of learning and storage of memory. RNA contains ribose sugars. The molecules of RNA are much smaller with molecular mass ranging from $2 \times 10^{4} - 4 \times 10^{4} μ$ . RNA molecules are of three types found in cell:

messenger RNA: m-RNA( $5 %$ of RNA)- It is a complementary copy of DNA.

ribosomal RNA: r-RNA ( $80 %$ of RNA)-It is present in ribosomes.

transfer RNA: t-RNA( $5 %$ of RNA)- helps in transport of amino acids.

The structure of RNA is similar to that of DNA and they both contain two bases derived from purine: guanine and adenine and one base derived from pyrimidine cytosine but differ in fourth base; DNA contains thymine whereas RNA contains uracil. Therefore, the four bases present in RNA molecule are adenine, cytosine, uracil, and guanine.

Fig- Structure showing four bases of RNA

Replication in DNA- It is the unique property of a molecule to synthesize another molecule to form a duplicate or self duplicate or replicate itself. The nucleus of living cells contains DNA molecules. The special sequence of bases in the DNA molecules is the basis of heredity characters or genetic information. During replication, hydrogen bonds binding the two strands of the double helix to become loose, and then both the strands of the double helix separate from each other. Then during mitosis one strand of the double helix enters into one of the daughter cells and another strand enters into another daughter cell. A number of nucleotides are already present in the daughter cells. New adenine attaches with thymine and new thymine with adenine. Each strand synthesizes its appropriate complementary strand resulting in the formation of two double-stranded molecules, each of which is a replica of the present DNA. In this way, two carbon copies or two replicas are formed from one DNA molecule and heredity characters are transferred from one cell to another.

State the composition and functional differences between DNA and RNA. Describe the mechanism of replication of DNA.

Important Questions on Biomolecules

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