Introduction
DNA (deoxyribonucleotide acid) is the genetic material that stores all of the genetic information in its nucleotide sequence.
Composition
DNA is made up of building units called nucleotides. A nucleotide contains a nitrogenous base, phosphate group and deoxyribose. An organic molecule containing a nitrogenous base called purine or pyrimidine is present in nucleotide. Purines are adenine or guanine and pyrimidines are cytosine, thymine or Uracil. Depending on the number of phosphate groups present in nucleotides, they are known as nucleotide monophosphates, diphosphates or triphosphates.
Structure
DNA is a very long thread like molecule made up of a very large number of deoxyribonucleotides joined together. DNA is a linear double stranded polymer made up of deoxyribonucleotides. Deoxyribonucleotide is made up of a sugar called deoxyribose, a nitrogenous base and a phosphate group. DNA is located in the nucleus. Nucleotides are joined together by a phosphodiester bond in a condensation reaction. Double helix is formed when two strands are joined together by hydrogen bonds. Double helix is anti parallel. Both the stands run in opposite direction and are parallel to each other.
Gene and RNA
Genes are functional unit of DNA, usually a segment of DNA in chromosome. RNA is a linear polymer in which nucleotides are linked together by means of phosphodiester bridges. It does not form a double helix like DNA. The genetic information is copied from DNA to mRNA in cells by base complementation mechanisms, therefore DNA molecule can be hybridized to RNA to detect its own expression.
DNA replication
DNA molecules are replicated precisely before cells divide. The replication is semi-conservative, with double strand open to form a replication fork. Then one strand (the leading strand) is synthesized continuously, while the other strand (the lagging strand) is synthesized as Okazaki fragments and then ligated together to form continuous molecule. At both ends of the DNA molecules, there is a special structure called telomeres which contain many tandem repeats to protect the DNA molecules from shortening.
