Short Notes On Types of Deoxyribonucleic Acid (DNA) (Life Science), Download PDF!

By Renuka Miglani|Updated : April 27th, 2022

Are you an Aspirant of CSIR-NET and looking for some short and reliable notes for Life Sciences to strong your base for preparations? We have got you covered!

Candidates preparing for their CSIR NET exam can really make their preparation journey easier with the help of some reliable study notes that cover the topics in the most simple way. We at BYJU'S Exam Prep have come up with the idea of providing short notes on the Deoxyribonucleic Acid (DNA), which comes under the Fundamental Processes section of the Life Science syllabus. 

The short note on Deoxyribonucleic Acid (DNA) is developed by our experienced subject-matter experts to provide you with the most standard and authentic set of study materials to be focused upon. The students need the best resources for their preparation to clear the CSIR NET examination, Here are the most reliable study Notes to make the topics easier for you and also help you to save your time for the preparations for the upcoming CSIR-NET 2022 exam.

Study Notes On Deoxyribonucleic Acid (DNA)

There are 3 forms of DNA in which A and B forms are right-handed helix while Z form is left-handed. Watson - Crick Model is of B-form. The strands run anti-parallel in nature. There are about 10 base pairs per turn of the helix. One turn of the helix is 34 Å, and the base pairs are 3.4 Å apart. Sugar phosphates are on the outside, while base pairs are on the inside. There is a minor groove and a major groove.

B-form of DNA is stable at high humidity conditions (95%), but at 75% humidity, it is converted into A form. B-DNA is the most hydrated and stable form of DNA under high humidity conditions. Since salt dehydrates DNA, thus, A-DNA converts to Z-DNA in solutions with high salt concentration. Phosphates are individually hydrated in B-form, but one water molecule forms a bridge between two phosphates in A and Z-forms, stabilizing these forms in low humidity.

In A-form, the helix axis is inclined by about 13 degrees, and there is ~10.9 bp per turn. The major groove is also very deep (~1.35 nm) and narrower (~0.27 nm) than the B form and is extensively hydrated. The minor groove is relatively wide (~1.1 nm) and shallow (~0.28nm) than B-form. It is a right-handed double helix and is short and stout compared to B-DNA. The A-form occurs only in dehydrated samples of DNA like those used in X-ray crystallographic experiments. Crystal structures of an intermediate form between A and B forms have been reported, often called the E-DNA eccentric DNA.

Z-DNA has an interesting feature; it is left-handed with the backbone following a zig-zag pattern and contains 12 bp per turn. In contrast to B-DNA, where a repeating unit is 1 bp, the repeating unit is 2 bp in Z-form. The major groove of Z-DNA is shallow, allowing it to accommodate bulky substituents at C8 of purines or C5 of pyrimidines.

Z-from is favoured in the regions rich in G-C pairs. E. coli and Halobacterium are known to contain left-handed forms of DNA. Segments of Z-DNA may occur in the enhancer region or may be formed behind RNA polymerase molecules that are moving along a gene while synthesizing mRNA. The associated negative supercoiling of the DNA could cause it to assume the Z-form. This region of Z-form can, in turn, be a site for interaction with specific proteins.

Other Rare Variants -

C-DNA - Formed at 66% relative humidity in the presence of Li+ and Mg2+ ions.

D-DNA - Scarce variant with 8 bp per helical turn found in some DNA molecules devoid of the guanine base.

Table 1. Comparison of different DNA types



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