In this post, we are providing you with the notes on DNA, RNA, Virus, and Bacteria. Questions from these topics are frequently asked in the Railways & SSC Exam.
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 sub-units called nucleotides.
- DNA is mainly found in the nucleus and in small amount it is also found in mitochondria an 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
- 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:
- Plant Virus: RNA is present as its nucleic acid
- Animal Cell: DNA and sometimes RNA is found in it.
- Bacteriophage: They kill the bacteria e.g. T-2 phage.
- Bacteria was discovered by Antonie van Leeuwenhoek and its study is known as bacteriology.
- Bacteria is of different types on the basis of shape:
- Bacillus: This is a rod-like or cylindrical.
- Round or Cocus: These are round and smallest bacteria.
- Comma shape or vibrio
- Spirillum: Spring or Screw shaped.
- Anabaena and Nostoc cyanobacteria fixed the atmospheric nitrogen into the soil.