Nucleic Acid & Chromosome

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Nucleic Acid

Nucleic acid is complex organic compound found in cell. It contains special genetic instruction in coded form.
Nucleic acids are of two kinds —
1. Deoxyribo Nucleic Acid (DNA)
2. Ribonucleic Acid (RNA)

Deoxyribo Nucleic Acid (DNA)

Frederic Meischer was the first who isolated DNA from the nucleus of pus cells. DNA is a macro molecule in which large number of nucleotides are present. Chemically a nucleotide has three components :
1. Nitrogen base
2. Sugar
3. Phosphate group
» Nitrogen base are of two types—Purines & Pyrimidines. Purines contain two types of nitrogen base—Adinine and Guanine.
» Pyrimidine nitrogen base are Thymine and Cytosine.
» DNA molecule is consist of two polynucleotide strand, forming a double helix. Each strand has a backbone of sugar and phosphate. Nitrogen base is attached to the sugar.
» Phosphorous is an essential constituent of nucleic acid.

Ribonucleic Acid (RNA)

RNA is single stranded nucleic acid made up of phosphate, ribose sugar and nitrogen base uracil, adenine, guanine and cytosine. It is found in nucleus as well as cytoplasm.
RNA is of three kind —
1. Messenger RNA (mRNA): It brings the message from DNA found in the nucleus to cytoplasm in the coded form.
2. Ribosomal RNA (rRNA): Present in ribosome which is the site of protein synthesis.
3. Transfer RNA (t RNA): It is the carrier of amino add and transfer it to the ribosome.

Difference between RNA and DNA

Sugar is deoxyribose type Sugar is ribose type
It contains the base adenine, thymine and cytosine and guanine It contains uracil at the place of thymine
It is double stranded structure It is single stranded structure
It is mainly found in nucleus It is found in both nucleus and cytoplasm


»   Chromosome is thread like structure found in the nucleus. It becomes visible during cell division. Each chromosome is made up of two chromatids joined together at a point centromere. Bead like structure found on chromosome is called gene. Genes are made up of DNA (deoxyribo nucleic add) which is the carrier of genetic information from generation to generation. In some viruses RNA is the genetic material called retrovirus. In prokaryotes there is only one chromosome, like bacteria and virus.
»   Chromosome was named by Waldeyer in 1888 capable of self replication, which transmit coded information from one generation to other.
»   Eukaryotic cell possess many chromosome. A particular kind of species have definite number of chromosome in their cell, which are in pair known as diploid. The set of unpaired chromosome is called haploid. Gametes have haploid set of chromosome.

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