Miscellaneous Notes on Biology (जीव विज्ञान पर विविध नोट्स)

By Brajendra|Updated : June 26th, 2022

In this post, we are providing you with notes on DNA, RNA, viruses, and Bacteria. Questions from these topics are frequently asked in the State PCS Exams.

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 base 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, Cytosine.

Structure of DNA:

  • Watson and Crick give the structural model of DN
  • DNA molecule is consists of two polynucleotide strand, 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 is complementary to guanine.

Functions of DNA:

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

2.Ribonucleic Acid (RNA) : 

  • RNA stands for Ribonucleic acid.
  • RNA is single-stranded nucleic acid made up of phosphate, a ribose sugar and nitrogen base uracil, adenine, guanine, and cytosine.
  • It is found in the nucleus as well as 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 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

DNA & RNA

3.Virus:

  • Virus was discovered by Russian Scientist Iavanosky during the test of Mosaic disease in Tobacco.
  • Virus acts as a link between the living and non-living.
  • 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.
  • 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 was 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 a 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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