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Nucleic acids are the polymers of nucleotide made up of carbon, hydrogen, oxygen, nitrogen and phosphorus and which controls the basic functions of the cell. These were first reported by Friedrich Miescher (1871) from the nucleus of pus cell. Altmann called it first time as nucleic acid. Nuclein was renamed nucleic acid by Altman in (1889). They are found in nucleus. They help in transfer of genetic information.

Types of nucleic acids : On the basis of nucleotides i.e., sugars, phosphates and nitrogenous bases, nucleic acids are of two types which are further subdivided. These are DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).

(1) DNA (Deoxyribonucleic acids) : Term DNA was given by Zacharis. 

(i) Types of DNA : It may be linear or circular in eukaryotes and prokaryotes respectively.

Palindromic DNA : The DNA helix bears nucleotide in a serial arrangement but opposite in two strands.

\[-T-T-A-A-C-G-T-T-A-A.......\]

\[-A-A-T-T-G-C-A-A-T-T......\]

Repetitive DNA : This type of arrangement is found near centromere of chromosome and is inert in RNA synthesis. The sequence of nitrogenous bases is repeated several times.

Satellite DNA : It may have base pairs up to \[160\,\,bp\]and are repetitive in nature. Microsatellite has \[16\,\,bp\]and minisatellite has \[1160\,\,bp.\] They are used in DNA matching or finger printing (Jefferey). In eukaryotes, DNA is deutrorotatory and sugars have pyranose configuration.

(ii) Chargaff’s rule : Quantitatively the ratio of adenine (A) to thymine (T) and guanine (G) to cytosine (C) is equal. i.e., “Purines are always equal to pyrimidine”.

(iii) C value : It is the total amount of DNA in a genome or haploid set of chromosomes.

(iv) Sense and Antisense strand : Out of two DNA strand one which carries genetic information in its cistrons is called sense strand while the other strand does not carry genetic information, therefore, doesn’t produce mRNA. The non-functional DNA strand is called antisense strand.

(v) Heteroduplex DNA : Hybrid DNA formed as a result of recombination is called heteroduplex DNA. It contains mismatched base pair of heterologous base sequence.

X-Ray crystallography study of DNA : It was done by Wilkins. It shows that the two polynucleotide chains of DNA show helical configuration.

Single stranded DNA (ssDNA) : It is single helixed circular. And isolated from bacteriophage \[\phi \times 174\] by Sinsheimer (1959). It does not follow chargaff’s rule. The replicative form (RF) has plus – minus DNA helix. e.g., parvovirus.

Double helical model of DNA: It is also known as Watson and Crick model.

(2) RNA or Ribonucleic acid : RNA is second type of nucleic acid which is found in nucleus as well as in cytoplasm i.e., mitochondria, plastids, ribosomes etc. They carry the genetic information in some viruses. They are widely distributed in the cell. Genomic RNA was discovered by Franklin and Conrat (1957).