We all are familiar about Evolution and mutation we also know that these terms depends directly on DNA structure. We all know that our ancestors are apes. But have you tried to find out what is that thing which control all of this?
Here is the answer!!
DNA and RNA are considered as genetic material. They are two types of nucleic acids and are polymer of nucleotides. Study of DNA structure is most important for Biochemists, Biologist and Chemist because the main controlling system of our body is DNA. Each cell of our body carries about 2.2 metres of DNA. Our body have around 37.2 trillion cells and if one cell contain 2.2 metres long DNA then can you calculate what is the total length of DNA which our body carries? Isn’t it interesting?
1. Discovery of DNA
- DNA was discovered by Friedrich Meischer in 1869. He named it as “NUCLEIN“. He also added that DNA is acidic in nature.
- In 1953 James Watson and Francis Crick proposed Double Helix model of DNA Structure. It was only possible due to X-Ray diffraction technique which was discovered by Rosalind Franklin and Maurice Wilkins
2. Structure of Polypeptide chain
DNA structure is made up of Nucleotides. Each nucleotide is made up of one nucleoside and a phosphate group.
What are Nucleotides and Nucleosides??
Nucleotides are the smallest unit of DNA chain. It has three components- a nitrogenous base, Five carbon sugar (Ribose in RNA and De-oxyribose in DNA) and a phosphate group. Nucleoside include pentose sugar with a nitrogenous base. It do not have phosphate group.
Types of Nitrogenous bases
There are two types of Nitrogenous bases:
- Purines: Purines belongs to heterocyclic compound’s family under and contains two rings. Adenine and Guanine are two purine bases.
2. Pyrimidines: They contains only one ring. Cytosine, Thymine (In the case of DNA) and Uracil (In the case of RNA) are pyrimidine bases.
3. DNA structure
When a nitrogenous base get linked with pentose sugar through N-glycoside linkage Form a nucleoside for example deoxyadenosine in DNA and adenosine in RNA, Guanosine in RNA and de-oxyguanosine in DNA, cytidine in RNA and Deoxycytidine, Uridine and Deoxythymidine. Now this nucleoside is linked with phosphate group at 5′-OH through phosphoester bond and ultimately form Corresponding Nucleotide.
Two nucleotides linked through 3′-5′ phosphodiester linkage and so on thus a polymer of nucleotides is formed and ultimately known as a strand of DNA. A free phosphate moiety at 5′- end of polymer is present which is known as 5′- end of polypeptide chain. Similarly a 3′-end is also present in DNA structure.
4. What is “Double helix Model”?
According to Double helical DNA structure it contains following features:
- DNA consist of two polynucleotide chains, made up of sugar-phosphate backbone and the nucleotide bases are projected inside.
- The two chains are anti–parallel and also have opposite polarity i.e. one chain has polarity of 3′—>5′ and another one has 5′—–>3′ polarity.
- The two bases are bonded with Hydrogen bonds. Adenine is bonded to thymine with 2 Hydrogen-bond and Guanine is bonded to cytosine with 3 Hydrogen- bond. Two chains are coiled in a right-handed fashion.
- Two double helical strands of DNA are right handed fashion. The pitch of helix is 3.4nm. And the distance between two base pairs is 0.34nm.
- The plane of base pairs are connected with Hydrogen bonds and stacked over one another into the helix.
5. Types of DNA
There are three types of DNA:
- A-DNA– It is a right-handed coiled DNA containing approximately 11 base pairs per turn.
- B-DNA- It is also a right-handed coiled DNA containing approximately 10 base pairs per turn.
- Z-DNA- Z-DNA is the type of DNA where two chains are coiled in a left-handed fashion.
6. Central Dogma of life
“Central dogma of Life” was proposed by Francis Crick. It states that the genetic information of life flows from DNA to RNA and then RNA to proteins ultimately. (DNA —>RNA—>Proteins)
7. What is Chargaff’s Rule of DNA replication?
Erwin Chargaff’s rule was proposed after the discovery of Double Helix DNA structure. This rule states that for a double stranded DNA, the number of purine and pyrimidine nucleotides remains same or in other words the number of adenine always equals to thymine and that of cytosine is equal to guanine and vice versa.
Also Read: http://www.genome.gov