1. DEOXYRIBONUCLEIC ACID
SUBMITTED BY : AMIT KUMAR SUBMITTED TO :Ms. SHEETAL SAINI
B.Sc. BIOTECHNOLOGY DEPARTMENT OF BIOTECHNOLOGY
V SEMESTER
2. Deoxyribonucleic Acid
• DNA is a double stranded molecule that is twisted into a Helix
• DNA is Polymer of Deoxyribonucleotides
• DNA has Deoxyribose sugar
• Found in chromosomes, mitochondria and chloroplasts
• Carries the genetic information
• DNA is stable in alkaline condition
3.
4. HISTOY OF DNA
• WILLAM ASTBURY (1938) detected a periodicity of 3.4 Angstroms
• ROSALIND FRANKLIN (1952) Performed X-ray diffraction analysis of DNA
crystal
• FRANKLIN AND WILKINS (1950-1953) Confirmed 3.4 periodicity and noted
uniform diameter 20A (2nm)
• WATSON AND CRICK (1953) Proposed the DNA double helical model based
on franklin’s X-ray crystallography analysis and other evidences
7. STRUCTURE OF DNA
• The double helical structure of DNA was proposed by JAMES WATSON AND
FRANCIC CRICK in 1953
• The structure of DNA double helix is comparable to a twisted ladder . The
salient feature of WATSON-CRICK models of DNA (knows as B-DNA)
• The DNA is a right handed double helix. It consists of two polydeoxyribo
nucleotide chains (stands) twisted around each other on a common axis.
• The two stand are antiparallel i.e one stand runs in 5’ to 3’ direction while
the other 3’ to 5’ direction
8. • This is comparable to two parallel adjacent roads carry traffic in
opposite direction
• The diameter of a double helix is 20A (2nm)
• Each turn of the helix is 34A (3.4nm) with 10 pairs of nucleotides, each
pair placed at a distance of about 3.4A
• Each stand of DNA has a hydrophilic deoxyribose phosphate backbone
(3’ – 5’) phosphodiester bonds on the outside of the molecules while
the hydrophobic bases are stacked inside
9.
10. • The two polynucleotide chain are not identical but complimentary to
each other due to base pairing
• The two chain are held together by hydrogen bonds formed by
complementary base pair .The adenine(A)-thymine(T) pair has 2
hydrogen bonds while guanine(G)- pair has 3 hydrogen bonds
• The hydrogen bonds are formed between a purine and a pyrimidine only
.If two purines face each other. They would not fit into the allowable
space.
• The DNAmolecules is a polymer consisting of several thousand pairs of
nucleotide monomers.
11. COMPONENTS OF A NUCLEOTIDE
DEOXYRIBOSE
• Deoxyribose is a pentose with five carbon atoms. Four of the five carbon
atoms plus a single atom of oxygen form a five membered ring
• The fifth carbon atom is outside the ring and forms a part of a –CH2
group.
• All the sugar in one stand are directed to one end.
• The sugar of the two stands are directed in opposite direction
12.
13. NITROGENOUS BASES
• There are two types of nitrogenous bases, pyrimidines and purines.
• The pyrimidine are ring compounds , with nitrogen in positions 1 and
3 of a 6-membered benzene ring.
• The two most common pyrimidines of DNA are cytosine (C) and
thymine(T)
• The purines are double ring compounds.
• A purine molecules consists of a 5-membered imidazole ring joined to
a pyrimidine ring a position 4 and 5
• The two most common purine of DNA are adenine(A) and guanine(G)
14.
15. BASE PAIRING
• Each step of the DNA ladder is made up of a purine and a pyrimidine
pair of a double ring and a single ring compound
• Two purines would occupy too much space, while two pyrimidines
would occupy too little
• Because of the purine -pyrimidine pairing the total number of purines
in a double standed DNA molecules is equal to the total number of
pyrimidines
16.
17. TYPE OF DNA
• DNAs are of various types A, B, C, D, E, and Z, the most important DNA A, B, and
Z, DNA .
B DNA
• Described by JAMES WATSON and CRICK
• Commonly found in DNA
• DNA molecule consists of 2 helical polynucleotide chain coiled around common
axis
• Right handed helix
• Turn every 3.4 nm
• Contain two grooves
18. • Major groove (wide)
• Minor groove (narrow)
A DNA
• Right handed helix
• Each turn contain 11 b.p/turn
• Contain two different grooves
• Major groove very deep and narrow
• Minor groove very shallow and wide
19. Z DNA
• Lift handed helix, very extended
• Discovered by RICH,NORDHEIM and WANG in 1984
• The sugar base backbone form Zig-Zag shape
• It is antiparallel strands as B-DNA
• It is long and thin as compared to B-DNA
• Only one deep helical grooves
• There are 12 bases pair per turn with axial rise 3.8A and angle of twist
60 degri
