RNA

Difference between DNA and RNA

DNA RNA

1- location In nucleus as chromosomes

In nucleus ,cytoplasm

and little amount in chromosomes

2- sugar Deoxyribose ribose

3- N base Thymine(T) Uracil (U)

Secondary and Tertiary Structure of RNA

RNA's are single stranded molecules, thus having no regular secondary or tertiary structures.

There are 3 different types of RNA:• Messenger \ m-RNA.• Transfer \ t-RNA.• Ribosomal \ r-RNA.

The 3 major types of RNA differ from each other in size, function, and special structural modifications.

The different types of RNA's all are transcribed from either of the DNA chain.

m-RNAformed within the nucleus ,the code element of mRNA is a linear sequence of 3 adjustment nucleotides referred as codon.Each codon corresponds to a defined amino acid.The secondary structure is a bent shape (hair pin).

Function of m-RNA: carry the message for specific protein in form of sequence of codes or nucleotides.

Typical secondary structure of m- RNA molecule

t-RNA• The secondary structure of t-RNA has the shape of a

clover leaf. This leaf like structure is produced due to the inter chain pairing of complementary nucleotides. The t-RNA segments not involved in inter chain pairing form loops.

• t-RNA has distinguished structural region1. Acceptor region. 2. Anticodon loop.3. Thymine-Pseudo-Uracil Loop.4. Dihydrouridine loop.

Typical a clover leaf diagram of t-RNA molecule

a) Acceptor regionmade of 4, 3 are CCA. The 3`-OH of A (in CCA) is free. This part functionally acts as a 'REACTION site for the addition of a.a (through its COOH group t-RNA bound to a.a., move to ribosome to help in the

lengthening of protein chains .

Function of t-RNA:

»Translator i.e. uncoding messages present in m-RNA and convert it to a.a. by anticodon.»Carrier of a.a. from cytoplasm to r-RNA

within ribosome's.

b) Anticodon loop: Consist of 7 nucleotides, consist of a nucleotide

triplet specific for each t-RNA and referred as an anticodon. The nucleotide sequence of anticodon is complementarily paired to a codon of m-RNA during translation.

c) Thymine-Pseudo-Uracil Loop: Consist of 7 nucleotides, it is involved in binding t-

RNA to ribosome's.

d) Dihydrouridine loop Composed of 8-12 nucleotides, It is essential for

binding aminoacyl t-RNA synthetase.

r-RNA Are found in association with several proteins as

components of the ribosome's-the complex structures serve as the site for proteins synthesis.

r-RNA Shows a secondary structure composed of helical regions + non helical regions in alternate fashion.

Structural Organization of DNA in Chromosomes

In higher organisms, DNA is located in chromosomes. Each chromosome contain a single giant DNA molecule of M.W. 10.

The number of chromosomes in the cell is a specific character.

Chromatin, consist of DNA, proteins and small amounts of RNA and inorganic compounds.

The major part of chromatin is “ inactive”, consisting of closely packed DNA. The active part of accounts for 2-11% of total chromatin.

Electron microscopy revealed chromosomal structure as a string of beads.

The beads, globular bulges, are called nucleosome. Each nucleosome consist of a length of double stranded DNA and eight pairs of histones. ( inactive segment – or heterochromatin ).

The thread like linkers of double strands DNA, composed of 30-60 bp, bound with histone H1, is (active segment -or euchromatin)

Functions of DNA

1. To store the complete genetic information required to specify the structure of all the proteins and RNA's.

2. To program in time the orderly biosynthesis of cell and tissue components.

3. To determine the activation of organisms through it's life cycle.

4. To determine the individuality of a given organism.