Different Types of DNA

Different types of DNA

• There are 6 types of DNA-
• A, B, C, D, E- is right handed
• Z is left handed

1.  A – DNA-

• Right handed double- helix.
• 11 base pairs per turn.
• Found in low humidity and high salt concentration.

2. B- DNA-

• Most common form.
• Right handed double helix.
• Highly flexible.
• Watson and Crick model describes the B- form of DNA. 
• B- DNA is found in high humidity and low salt concentration.       

3. Z-DNA-

• 12 base pairs per turn.
• Left handed helix.
• Phosphodiester bond.
• Z- form is favoured by alternating G-C sequences.
• Zig- zag fashion.
• Longer and thinner.
• Seen in 5′ end of chromosomes
• Also seen in alternating purine and pyrimidine.
• Z- DNA influences gene expression and regulation

Others Types of DNA-

1. Bent DNA

2. Triple- stranded DNA- forms hydrogen bonds with another surface of the double helix through called Hoogsteenpairs. 

Poly (dA) + Poly(dT) strands= triple stranded DNA

3. Four- stranded DNA- formed in DNA high in guanine content.

• A base pairing scheme for parallel four- stranded DNA referred as G- quartet DNA.
• Hoogsteenpairs are seen in four stranded DNA also.
• Antiparallel four- stranded DNA structures, called as G- tetraplexes.

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