TRANSCRIPTION

BY SHUMAILA IQBAL BS[MLT3RD YEAR] 6TH SEMISTER

INTODUCTION. The biosynthesis of RNA, called

transcription . RNA synthesis, or transcription, is the process

of transcribing DNA nucleotide sequence information into RNA sequence information

WHAT IS RNA? RNA is a polymer composed of

alternating units of ribonucleotides connected through a 3’-5’ phosphodiester bond.

It is a single stranded nucleic acid that involves in protein synthesis.

WHAT IS RNA.?In contrast with DNA,

ribonucleotides contain:

Hydroxl group on the 2’ carbon of the ribose sugar.

The base uracil in place of thymine.

TYPES OF RNA. There are three major types of RNA:

Ribosomal RNA. Transfer RNA. Messenger RNA.

TYPES OF RNA.

Minor types:

Small nuclear RNA. Small interfering RNA. Micro RNAS. Other small RNAS.

RIBOSOMAL RNA. Ribosomal RNA (rRNA)-is

the most abundant form of RNA,

nucleotides are in a globular form,

combine with proteins to make ribosomes.

Ribosomes- are organelles where proteins are made

TRANSFER RNA. Transfer RNA (tRNA)-

consist of a single chain of about 80 RNA.

nucleotides folded into a hairpin shape that binds to specific aminoacids.

Adopter molecule that carry specific amino acid to the ribosome.

MESSENGER RNA. Messenger RNA (mRNA)-

consists of RNA nucleotides in the form of a single uncoiled chain.

carries genetic information

from the DNA

in the nucleus to the cytosol of a eukaryotic cell.

DNA TRANSCRIPTIONo DNA is transcribed into RNA by DNA-

dependent RNA polymerase (usually just called RNA polymerase).

o After binding to its start site in DNA, a specific sequence of base called the promoter, RNA polymerase & its supporting accessory proteins synthesize RNA using the base sequence of one strand of double helix DNA.

Transcription requirements

Transcription requires:

1. a promoter sequence on a DNA template.

2. RNA polymerase and accessory transcription factors.

3. Nucleotide triphosphates.

promoter sequence

A region on the DNA that determines the specificity of transcription of a particular gene.

Promoters contain specific DNA sequences and response elements which provide a binding site for RNA polymerase and for proteins called transcription factors that recruit RNA polymerase.

RNA polymerase is a complex multisubunit enzyme,

responsible for the transcription .

interacts with the promoter regions of genes as well as with a variety of elements and transcription factors to determine essentially all of the parameters that govern transcription.

Classess of RNA polymerase.

1. RNA polymeraze 1: synthesizes the precursor of rRNA named pre rRNA .

2. RNA polymerase 2: synthesizes pre mRNA.

3. RNA POLYMERASE 3: synthesizes pre Trna.

All these enzymes synthesize what is called primary transcript or immature RNAs (pre form) which by some modifications occur after transcription, will give the mature rRNA, mRNA and tRNA.