Nucleic acids are polymers of nucleotides held together by phosphate bridges that serve as the genetic material of organisms. There are two main types: DNA and RNA. DNA is found in the nucleus and functions to store and transmit genetic information through its double helix structure. It is made of deoxyribonucleotides and follows Chargaff's rules of equal base pairing. RNA is involved in protein synthesis and certain cellular functions. Both nucleic acids maintain hereditary traits and cellular functions through their roles in gene expression and protein production.
2. Nucleic acid are the polymers of nucleotides held by 3’ & 5’ phosphate
bridges.
Reserve bank of genetic information.
Maintaining the identity of different species of organisms over millions
of year.
Two Types: DNA (Deoxy Ribonucleic Acid)
RNA (Ribonucleic Acid)
4. 4
Functions of DNA:
Responsible for the transmission of genetic information.
DNA forms the basis of Heredity.
Responsible for maintaining the identify of different species.
All cellular function are under the control of DNA.
DNA is organized into genes which is the fundamental unit of
genetic information.
DNA is also found in the mitochondria and chloroplasts,
where they perform specific function with regard to protein synthesis.
5. It was first isolated from pus cell & salmon sperm.
Polymer of deoxyribonucleotides.
Composed of monomeric units –dAMP, dGMP, dCMP & dTMP.
They are held together by 3’,5’ phosphodiester bridges constituting a
single strand.
6. CHARGAFF’S RULE:
• DNA had equal numbers of A & T residues (A=T). & equal numbers of
G &C residues (G=C).
• The molar equivalence b/w the purines & Pyrimidines in DNA structure.
Purines = Pyrimidines
• Double helical structure of DNA derives its strength from Chargaff's rule
• Single stranded DNA & RNA which are usually do not obey Chargaff's
rule
7. James Watson Francis Crick
Nobel prize in 1962
Double helical structure of DNA in 1953.
8. SALIENT FEATURES
• Right handed double helix.
• Mol wt is 660 KD
• Consists of two poly deoxyribonucleotide strands.
• Twisted around each other on a common axis.
• Two strands are antiparallal I.e. 5’ to 3’ direction,
while the other in 3’ to 5’ direction
9.
10. The width of diameter - 2nm (20 A )
Each turn of the helix -3.4nm (34 A ) with 10 BP of nucleotide
Each pair placed at a distance –about 0.34 nm (3.4 A)
Two polynucleotide chains are not identical but complementary to each
other due to base pairing.
Two strands are held together by H-bonds to formed by complementary BP.
11. Hydrogen bonds in nucleic acids
A-T pair has 2 H-bonds (A=T)
G-C pair has 3 H-bonds (GC)
12. H-bonds are formed b/w a purine & pyrimidine only.
The double helix has (wide) major grooves &narrow is minor
grooves along the phosphodiester backbone.
Proteins interact with DNA at these grooves .
13. DIFFERENT FORMS OF DNAs
B- forms (Watson & crick form)
Type of helix – right handed
Turn contains 10 BP
Distance - 3.4nm
Width – 2nm
Major groove – wide
Minor groove - Narrow
A –form of DNA:
Right handed helix.
11 BP pairs per turn.
Major groove –narrow.
Minor groove – very broad.
14. DIFFERENT FORMS OF DNAs
A –form of DNA:
Right handed helix.
11 BP pairs per turn.
Major groove –narrow.
Minor groove – very broad.
15. Z- forms of DNA:
Left handed helix with12 BP per turn
Major groove – flat
Minor groove – very narrow
Strands of DNA move in zig zag fashion
Sign role – regulating gene expression
16. Parameters of Major DNA Helices
Parameters A Form B Form Z-Form
Direction of helical rotation Right Right Left
Residues per turn of helix 11 10 12 base pairs
Rotation of helix per residue
(in degrees)
33 36 -30
Base tilt relative to helix axis
(in degrees)
20 6 7
Major groove narrow & deep wide & deep Flat
Minor groove wide & shallow narrow & narrow and
