TRANSCRIPTION

The process of copying genetic information from one strand of the DNA into RNA is known as transcription. Only one strand is copied.

CENTRAL DOGMA ARNA

DNA gives rise to MRNA or messenger RNA by the processof transcription. This MRNA further synthesizes proteins by the process Of translation.this whole cycle of event is known as Central dogma.

TRANSCRIPTION UNIT

The segment of DNA that takes part in transcription is called Transcription unit.

It has three components :-
1. A promotor
2. The structural gene
3. A terminator

Since the two strands have opposite polarity and the DNA dependent RNA polymerase also catalyses the polymerizationi in only one direction that is 5′-3′.
The strand that has the polarity 3′-5′ act as template and is called template strand or non- coding strand.

The other strand with polarity 5′-3′ and the sequence same as RNA, except thymine at the place of uracil is displayed during transcription and this strand is called coding strand or sense strand or non template strand.

The DNA strand over which RNA replication takes place has 3 regions :-

1. Promotor– It is present at the 3` end of the template strand of DNA, o facto recognize this site and RNA polymerase starts adding nucleotide.

2. Structural gene – All along this region RNA polymerase adds the nucleotide and elongate the RNA strand.

3. Terminator – It is the region which is recognize by p factor and result in the termination of RNA polymerization and the RNA strand releases.

Transcription in prokaryotes.

There are three types major types of RNA’S in bacteria.
1. mRNA
2. tRNA
3. rRNA

All thee three RNA’s are needed to synthesise a protein in a cell.

mRNA-It provides the template for protein synthesis to occur.

tRNA – It brings aminoacid in front of mRNA and reads the genetic code.

rRNA-It plays structural and catalytic role during translation i.e, protein synthesis.

Transcription in prokaryotes or bacteria include three steps :-

1. Initiation – When RNA polymerase binds to the promotor region and initiate the transcription this is called initiation. It uses nucleoside triphosphate as substrate ad polymerises in template

2. Elongation – When RNA polymerase start and recognize the promotor region. This will elongate the template strand complementary.

3. Termination- Once the RNA polymerase reaches the terminator region the RNA falls off. So also the RNA polymerase. This results in the termination of transcription.