Question

How is the structure of DNA organized? what is the biological significance of DNA ?

Answer 1

Answer:

Structure of DNA:-

The most widely accepted model of DNA is the double helical structure of James Watson and Francis Crick.

Chemical Composition of DNA molecule:-

DNA is a large molecule consisting of millions of nucleotides. Hence, it is also called a polynucleotide. Each nucleotide consists of three components.

• A sugar molecules - Deoxyribose sugar
• A nitrogenous base.

There are two types of nitrogenous bases in DNA. They are,

1. Purines ( Adenine and Guanine )
2. Pyrimidines ( Cytosine and Thymine )

• A phosphate group

Nucleoside and Nucleotide:-

Nucleoside = Nitrogen base + Sugar

Nucleotide = Nucleoside + Phosphate

The Nucleotides are formed according to the purines and pyrimidines present in them.

Watson and Crick model of DNA:-

• DNA molecule consists of two polynucleotide chains.
• These chains form a double helix structure with two stands which run anti-parallel to one another.
• Nitrogenous bases in the centre are linked to sugar-phosphate units which form the backbone of the DNA.
• Pairing between the nitrogenous bases is very specific and is always between purine and pyrimidine linked by hydrogen bonds.

1. Adenine (A) links Thymine (T) with two hydrogen bonds (A=T)
2. Cytosine (C) links Guanine (G) with three hydrogen bonds ( C = G)

This is called complementary base pairing.

• Hydrogen bonds between the nitrogenous bases make the DNA molecule stable.
• Each turn of the double helix is 34 A° (3.4nm). There are ten base pairs in a complete turn.
• The Nucleotides in a helix are joined together by phosphodiester bonds.

Significance of DNA:-

• It is responsible for the transmission of hereditary information from one generation to next generation.
• It contains information required for the formation of proteins.
• It controls the developmental process and life activities of an organism.

Answer 2

Structure and organisation of DNA:

Deoxyribonucelic acid is a molecule which stores information about the gene, which an organism got from the both parents (sexual reproduction) or from single parent (asexual reproduction).

It's structure can be explained as, it is present inside nucleus of every cell of an organism and distributed into 46 long chromosomes. DNA helps mainly in reproduction to copy the behaviour of the organisms and transfer to their young ones.

Biological significance of DNA:

The most important thing is DNA plays a vital role in reproduction of every organism. The acidity comes from the phosphate groups used in forming DNA and RNA molecules. It is composed of two polynucleotide.

It is a eucaryotic cell because it is a complex cells in which the genetic material is organised into membrane-bound nuclei. The information contained in it is called as "biological instructions". It is arranged in three dimensional space.

Note:

In the attached image it is given that real structure of DNA and types of forms by which dna exists.

Hope it helps you...