The genetic information of a cellis stored within its DNA(Deoxyribonucleic acid)macromolecules.The segment of DNA carry thisgenetic information called “Genes”.
In 1869Johann Friedrich miescher had isolated from the pus cells obtained from the discarded bandages.Frederick Griffith (1928) demonstrated the transformation fromheat killed S-type to live R-typestreptococcus.
Rosalind Franklin (1952) X ray diffraction image of DNA. Watson and Crick (1953) concluded DNA is the helical form.
DNA is a polymer DNA is a long polymeric molecule . A polymer is a long chain like molecule comprisingnumerous individual units called “monomers”Nucleotides- the monomers in DNA DNA which contains four kinds of smaller buildingblocks (monomers)called deoxyribotides ordeoxyribonucleotides .
The nucleotide itself a complex molecule being madeup of three components. Nitrogenou s base sugar Phosphoric acid Nucleotide
The sugar component The sugar component of the nucleotide is a pentose(containing five carbon atom) called 2’-deoxyribose. Pentose sugar can exist in two forms , 1.straight chain (or) Fischer structure 2.ring (or) Haworth structureThe 2’-deoxyribose that occurs in nucleotide.
PURINES 1. Adenine (A) 2. Guanine (G) A or G PYRIMIDINES 3. Thymine (T) 4. Cytosine (C) T or C
A pairs with T by twohydrogen bonds C pairs with G by threehydrogen bonds
It is a right-handed doublehelix fairly similar to the morecommon and well-known B-DNAform, but with a shorter morecompact helical structure. It contains 11 base pairs perturn. Its is right handed but lessthan the B-form DNA.
It appears likely that it occursonly in dehydrated samples ofDNA, such as those used incrystallographic experiments, andpossibly is also assumed byDNA-RNA hybrid helices and byregions of double-stranded RNA.
B-DNA is the form commonlyobserved in chromosomes. B-DNA is aright-handed helix with 10 base pairsper turn. This structure was described byWatson and crick is the mostpredominant turn of physiological Each under the B-formconditions. base pair spanning has 10 a distance of 3.4nm.
Z-DNA is a left handed helix generatedbecause of different conformation betweenone of its bases and the deoxyribose sugar. This bond is called a The syn conformation is found in Z-DNA .
The alteration of a purine(G) and a pyrimidine (C)along a Z-DNA double strandproduces the anti-synalteration that gives thebackbone of Z-DNA aappearance.
Feature B-DNA A-DNA Z-DNAHelix type Right handed Right handed Left handedHelical diameter 2.37 2.55 1.84(nm)Distance per eachturn (nm) 3.4 3.2 4.5Number of basepair per turn 10 11 12Helix axis rotation Major groove Through base pairs Minor groove (variable)
During the cell division, thedaughter cells receive anidentical copy of geneticinformation from the parentcell.Replication is a process inwhich DNA copies itself toproduce identical daughtermolecules of DNA .
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