DNA and RNA structure - 1

Structure of Nucleic acids

DNA and RNA form the genetic material of all living organisms. They store the information in biochemical form.

What is a gene?
 
A gene is a sequence of nucleotides in DNA or RNA that encodes the synthesis of a gene product, either RNA or protein. The genes are expressed by two important process - Transcription of genes from DNA to RNA and then Translation of Genes into Proteins. While DNA makes multiple copies of itself by the process of DNA replication. We will discuss all of them in detail later.
Structure of DNA 

DNA is a double helical structure. J.D. Watson  and F.H.C. Crick proposed the three-dimensional model of physiological DNA in 1953 on the basis of X-ray diffraction studies of DNA obtained by Franklin and Wilkins. They gave the structure of B- DNA. 
The important features of Watson – Crick Model or double helix model of DNA are as follows:
1. The DNA molecule consists of two polynucleotide chains or strands that spirally twisted around each other and coiled around a common axis to form a right-handed double-helix.
2. The two strands are anti-parallel i.e. they run in opposite directions so that the 3′ end of one chain facing the 5′ end of the other.
3. The sugar- phosphate backbone is on the exterior while the nucleotide bases (ATGC) are in the interior.
4. The two strands are held together by hydrogen bonds between the purine and pyrimidine bases of the opposite strands.
5. Adenine (A) always pairs with thymine (T) by two hydrogen bonds and guanine (G) always pairs with cytosine (C) by three hydrogen bonds. This complimentarity is known as the base pairing rule.                                                                                                          Thus, the two stands are complementary to one another.
6. The base sequence along a polynucleotide chain is variable and a specific sequence of bases carries the genetic information.
7. The base composition of DNA obey's Chargaff s rules .
Chargaff's rules state that DNA from any cell of any organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine. This pattern is found in both strands of the DNA.
8. The diameter of DNA is 20nm or 20 A. Adjacent bases are separated 0.34 nm or by 3.4 A along the axis. The length of a complete turn of helix is 3.4 nm or 34 A i.e. there are 10bp per turn. (B- DNA-Watson rick DNA)
9. The DNA helix has a shallow groove called minor groove (-1,2nm) and a deep groove called major groove (- 2.2nm) across.
DNA—Watson-Crick Model and Biological Importance (With Diagram)

There are various forms of DNA , based on the structural differences. They are as follows -

DNA: Structure, Forms and Functions (With Diagram)

This are the basics about the DNA structure  and types.
We will study about the  RNA structure and types in the next article.

Thank you , I hope you all understood the topic discussed.

For any queries and suggestions please mail me.

Disclaimer - I do not claim any of the data here. I have referred various books and articles and represented here. All this is just to make concepts easy. Only important and precise data has been provided. It is not for commercial purpose. Your valuable suggestions are always welcome.


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