Biology notes for Competitive Exam

Biology

Deoxyribo nucleic Acid (DNA) :

• DNA stands for Deoxyribo nucleic Acid , it was discovered by Frederic Maischer.
• DNA is a double stranded molecule made up of elongated chain of sub-units called nucleotides.
• DNA is mainly found in 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.

• Nitrogenous  base are of two type i.e.Purine & Pyrimidines. 
• Purines contain two nitrogen base i.e. Adinine and Guanine.
• Pyrimidine nitrogen base are Thymine and Cytosine, thus there are four kinds of nucleotide present in DNA i.e. Adinine, 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.

Function 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, ribose sugar and nitrogen base uracil, adinine, guanine and cytosine.
• It is found in nucleus as well as cytoplasm.
• Its main function is to synthesis the protein.
• RNA is of three kind.

    1.Messenger RNA (mRNA): It brings the massage 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

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 are 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 Antony von Lecuwenhoek 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. Sprillum: Spring or Screw shaped.

• Anabaena and Nostoc cyanobacteria fixed the atmospheric nitrogen into soil.