RNA and Transcription

DR. MD.MAHBUBUR RAHMAN MBBS, MPhil. MSc in Biotechnology

Assistant Professor

Dept. of Biochemistry

RAJSHAHI MEDICAL COLLEGE

At the end of session student will be able to

• Structure of RNA and its type

• Function of different type of RNA

• Special types of RNA (Si RNA and mi RNA)

• Definition of Transcription

• Stages of transcription

• Post transcriptional modification

The general steps of initiation, elongation,

and termination with 5′–3′ polarity; large,

multicomponent initiation complexes

Adherence to Watson–Crick base-pairing

rules

DNA and RNA synthesis are similar

1) ribonucleotides are used in RNA synthesis

rather than deoxyribonucleotides;

2) U replaces T as the complementary base for

A in RNA;

3) a primer is not involved in RNA synthesis as

RNA polymerases have the ability to initiate

synthesis de novo

DNA and RNA synthesis differ

(4) in a given cell only portions of the genome

are vigorously transcribed or copied into RNA,

whereas the entire genome must be copied,

once and only once during DNA replication;

(5) there is no highly active efficient

proofreading function during RNA transcription

DNA and RNA synthesis differ

Types of RNA

• Ribosomal RNA (rRNA)-80%

• Transfer RNA (tRNA)-15%

• Messenger RNA (mRNA)-5%

Function of rRNA

These RNAs interact with each other and with

proteins, to form a ribosome that provide the basic

machinery on which protein synthesis takes place.

Function of tRNA

They function as adapter molecules that translate

the information stored in the mRNA nucleotide

sequence to the amino acid sequence to the

amino acid sequence of protein.

Function of mRNA

They carry the genetic information defining

the sequence of all protein in the cell.

Transcription

Synthesis of RNA using the DNA as a template is

called transcription

Concept of coding and template strand

A series of complicated enzymatic process that

result in the transfer of genetic information

stored in the double stranded DNA to Single

stranded RNA molecule that will be used by

the cell to direct the synthesis of its protein.

Transcription

RNA polymerase

RNA polymerase differ from DNA polymerases

in that they can initiate the synthesis of new

strand in the absence of a primer and has no

known endo or exonuclease activity.

Process of Transcription

• Initiation

• Elongation

• Termination

Initiation

• Promoters are characteristic sequence of DNA

usually located in front of the gene that is to be

transcribed.

• In prokaryotic transcription

– Pribnow box -10 base pair

– -35 sequence

• In Eukaryotic transcription

– TATA Box—25 bases

– CAAT Box- 40 bases

Elongation

RNA polymerase utilize ribonucleotide triphosphate

and releases pyrophosphate each time nucleotide is

added to the growing chain

Post Transcriptional modification

• Eukaryotic messenger RNA

• –5’ Capping by 7-methylguanosine

• –Poly- A tail ( adenine nucleotide attached to

3’ end)

• –Removal of introns--splicing.

Termination

• rho independent termination

• rho dependent termination

A primary transcript is a linear copy of a

transcriptional unit, the segment of DNA

between specific initiation and termination

sequence.

Thank You