Presented by

Nishanth S

Nucleic acids

• Nucleic acid consists of ---------

Sugar (5 Carbon)

Nitrogenous base

Phosphate group

Nitrogenous bases includes ---

Adenine

Guanine

Cytosine

Thymine (DNA)

Uracil (RNA)

NUCLEOSIDE = Sugar + Nitrogenous base

NUCLEOTIDE = Sugar + Nitrogenous base + Phosphate group

C

C

C

C

N

N

O

O

C

C

C

C

C

N

N

O

N

C

C

C

C

N

N

N

N

N

C

C

C

C

C

N

N

O

N

N

N

C

C

C

C

C

N

N

O

O

CC

C

C

C

N

N

O

N

C

C

C

C

NN

O

N

N

N

C

Structure of Nucleic acids

• Primary structure --- A, G, C, T, U

• Secondary structure --- A=T, …

• Tertiary structure --- Helix of DNA/RNA

• Quaternary structure --- relation of nucleic

acids with other mols

Nucleus Chromosome Gene DNA

Difference between RNA and DNA

RNA

(Ribonucleic acid)

DNA

(Deoxyribo nucleic acid)

RNA is more primitive than DNA. DNA is originated from RNA.

RNA is the genetic material of some plants,

animals and bacterial viruses.

DNA is the genetic material of almost all

living organisms.

Pentose sugar is ribose. Pentose sugar is deoxyribose.

The bases are adenine, guanine, cytosine

and uracil.

The bases are adenine, guanine, cytosine

and thymine.

Base pairing occurs between adenine,

uracil (A-U) and guanine, cytosine (G-C).

Base pairing occurs between adenine,

thymine (A-T) and guanine, cytosine (G-C).

RNA DNA

The RNA molecules are of three types viz.,

mRNA, tRNA, and rRNA.DNA is of only one type.

The mRNA is found in nucleus, tRNA and

rRNA are found on cytoplasm.

DNA is found in chromosomes,

mitochondria, and chloroplast.

RNAs translate the transcripts DNA into

proteins.

DNA encodes the genetic messages in the

form of mRNA.

Base pairing is seen only in hairpin

structure and helical region.

Base pairing occurs throughout the length

of the DNA molecule.

RNA contains a few nucleotides. DNA contains millions of nucleotides.

Difference between mRNA and tRNA

mRNA tRNA

Transcribed from DNA in the nucleus and

posted out to the ribosomes for translation.

Used to translate mRNA by the ribosome,

making a new polypeptide.

Codons are complementary to DNA

triplets.

Anticodons are complementary to mRNA

codons and correspond to specific amino

acids.

mRNA is a simple strand. tRNA has a clover-shaped loop structure.

Broken down after translation.Reactivated with a new amino acid after

translation.

DNA double helix structure is

stable – why ?

1) Both internal and external hydrogen bonds stabilizes the double helix.

2) The negatively charges phosphate groups are all situated on the exterior surface of the helix.

3) The base pairs are bonded together with hydrophobic interactions and Vanderwallforces besides hydrogen bonding.

Difference between A-, B- & Z-forms of DNA

CHARACTERS A form B form Z form

Helical sense Right handed Right handed Left handed

Size Short and broad Longer and thinner Elongated and slim

Diameter 2.8 nm 2.0 nm 1.8 nm

Base pairs per helical 11 10 12

Major groove Narrow / deep Wide / deep Flat

Minor groove Wide / shallow Narrow / deep Narrow / deep

Stability More stable Less stable Less stable