Science Study Notes on Important facts about DNA, RNA, Virus, and Bacteria

By Neha Joshi|Updated : April 24th, 2020

In this post, we are providing you with notes on DNA, RNA, viruses, and Bacteria. Questions on this topic are generally asked in the paper-2 science section of REETUPTETCTET and other teaching examinations. Let's check out all the exam-related important study notes on the topic and get ourselves prepared for the upcoming examination.

Deoxyribonucleic Acid (DNA) :

  • DNA stands for Deoxyribonucleic Acid, it was discovered by Frederic Mischer.
  • DNA is a double-stranded molecule made up of an elongated chain of subunits called nucleotides.
  • DNA is mainly found in the nucleus and in small amounts it is also found in mitochondria and chloroplast.
  • Chemically a nucleotide has three components.

(1) Nitrogenous base

(2) Pentose Sugar

(3) Phosphate group.

  • The nitrogenous base is of two types i.e.Purine & Pyrimidines. 
  • Purines contain two nitrogen bases i.e. Adenine and Guanine.
  • Pyrimidine nitrogen bases are Thymine and Cytosine, thus there are four kinds of nucleotide present in DNA i.e. Adenine, Guanine, Thymine, and Cytosine.

Structure of DNA:

  • Watson and Crick give the structural model of DN
  • DNA molecule is consists of two polynucleotide strands, forming a double helix structure.
  • Each strand has a backbone of sugar and phosphate, nitrogen base is attached to the sugar.
  • Two strands are joined together by hydrogen bonds between the bases.
  • Adenine pairs with thymine whereas guanine pairs with cytosine.
  • Adenine and thymine are complementary to each other and cytosine are complementary to guanine.

Functions of DNA:

  • DNA is the genetic material and contains genetic information in coded form.
  • DNA has two main functions replication and expression.

2. Ribonucleic Acid (RNA) : 

  • RNA stands for Ribonucleic acid.
  • RNA is a single-stranded nucleic acid made up of phosphate, ribose sugar and nitrogen base uracil, adenine, guanine, and cytosine.
  • It is found in the nucleus as well as the cytoplasm.
  • Its main function is to synthesise the protein.
  • RNA is of three kinds.

    1. Messenger RNA (mRNA): It brings the message from DNA found in the nucleus to the 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 acid and transfers it to the ribosome.

Difference between RNA and DNA



  • The virus was discovered by Russian Scientist Iavanosky during the test of Mosaic disease in Tobacco.
  • The virus acts as a link between the living and non-living.
  • A virus is dead but when it comes in contact with the living cell it gets activated.
  • The virus in which RNA  is found as the genetic material is called Retrovirus.
  • A virus is of three types:
  1. Plant Virus: RNA is present as its nucleic acid
  2. Animal Cell: DNA and sometimes RNA is found in it.
  3. Bacteriophage: They kill the bacteria e.g. T-2 phage.

4. Bacteria:

  • Bacteria were discovered by Antonie van Leeuwenhoek and its study is known as bacteriology.
  •  Bacteria is of different types on the basis of shape:
  1. Bacillus: This is rod-like or cylindrical.
  2. Round or Cocus: These are round and smallest bacteria.
  3. Comma shape or vibrio
  4. Spirillum: Spring or Screw shaped.
  • Anabaena and Nostoc cyanobacteria fixed the atmospheric nitrogen into the soil.




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