watson and crick model of DNA

Watson and crick model of DNA replication

Watson and Crick describe structure of DNA in 1953 in the late nineteenth century.A German biochemist found the nucleic acids, long-chain polymers of nucleotides, were made up of sugar, phosphoric acid, and  nitrogen-containing bases. It was found that the sugar in nucleic acid can be ribose or deoxyribose, giving  RNA and DNA. 
 In the start of their work Watson and Crick made a failed model. It caused the head of their unit to tell them to stop DNA research. But the subject just kept coming up.
Watson and Crick took a crucial  step, suggesting the molecule was made of two chains of nucleotides, each in a helix  but one going up and the other going down. Crick had just learned  about base pairs in the  1952. He added  so that matching base pairs interlocked in the middle of the double helix to keep the distance between the chains constant.
Watson and Crick told that each strand of the DNA molecule was a template for the other. During cell division the two strands separate and on each strand a new "other half" is built. This way DNA can reproduce itself without changing its structure.
 By 1962,  Watsonand Crick won the Nobel Prize for their model

Significance of base sequence in DNA molecule.

First basic thing in their model was base pairing in DNA molecule.The base pairing in the DNA molecule is highly specific because adenine always pairs up with thymine and gunine with cytosine. So it means the two strands of DNA double helix are complementary to each other. If the sequence of base in one strand is known, the other strand will be obviously known due to specific base pairing. The base sequence of DNA in a linear order forms genetic information. 

The specificity of base pairing of DNA makes it unique molecule to store, copy and transmit genetic information from generation to generation. Mutated gene The change in base sequence is called point mutation. It results in a mutated gene, which is different in behaviour from its parental gene. 
For example, if the base sequence CTT is changed to CAT, it would be point mutation. Replication of DNA Duplication of the DNA molecule is called replication of DNA. The human genome contains about 6 x 109 nucleotide pairs of DNA. All the genetic information is stored in DNA in the sequence of its bases in order. 
This information must be duplicated before each cell division, so that each daughter ceil must have identical information like the parent cell. DNA is the heredity material only because it is capable of self­ replication. 

Watson and Crick model

 Watson and crick proposed semi-conservative mechanism of DNA replication. According to which each daughter DNA molecule contains one old parental strand and a new strand. 
 

watson and crick model

This mechanism is based on the principal of complementary base pairing. The semi-conservative replication of DNA molecule is completed in following eight steps. 

Steps Involved in DNA Replication: 

 1- The double helix of DNA molecule begins to uncoil at one end. It unzips like a zipper! 
2-The hydrogen bonds between base pairs are broken and the two complementary strands of DNA double helix separate as the two halves of the open zipper. 'A' separates from T and 'G' from 'C. 
3- The bases along each parental strand are exposed free. Replication in progress, parental DNA is unzipped and new nucleotides are pairing with those in parental strands Replication is complete. Two identical double helix molecules (Daughter DNA) are formed Each strand of the parental DNA now serves as template. 
The exposed bases of the templates strands attract the fresh complimentary bases. These fresh bases move freely in the nucleoplasm. Their bases are attracted by complementary bases of each exposed strand. Hydrogen bonds Hydrogen bonds are established between the older bases of template and new bases of nucleoplams. 
A complete complementary new strand is formed opposite to old parental strand. The new strand is exactly like the one that had been separated. Thus the identical double helix molecules are formed from parental DNA. 

Messanger RNA 

The messenger RNA's message is for the protein synthesis. Its base sequence is .translated into a sequence of amino acids of  a particular protein. Translation is decoding of mRNA information into a sequence of amino acids in a protein. e.g., proteins. These proteins are made in the cells under the instructions of genes. 
Genes sit like a 'Boss' seated comfortably on chromosomes in their office - the nucleus. They get their job done in the cytoplasm through their managers- RNAs. In addition to the genetic make up of an individual.

Expression of gene 

 A gene expresses itself in two steps: 
1. Transcription 
2. Translation 

Transcription: 

The coded information in DNA,which is there in the form of base sequence, is copied into the base sequence of messenger RNA. Copying of DNA-encoded information into RNA- encoded information is called transcription.