DNA Transcription

CENTRAL DOGMA

DNA → RNA → PROTEIN

DNA REPLICATION

DNA is copied to make more DNA

DNA TRANSCRIPTION

DNA is copied to RNA

TRANSLATION

RNA is ready to make more proteins

REVERSE TRANSCRIPTION

enzyme makes a copy of DNA from RNA

DNA TRANSCRIPTION

the process by which RNA is synthesized from its template DNA by the enzyme RNA polymerase

DNA TRANSCRIPTION

base sequence of a dsDNA to form base sequence of a sRNA

DNA REPLICATION

Both strand, Whole genome

DNA REPLICATION

Primer

DNA POLYMERASE

Enzyme in DNA Replication

dsDNA

Product in DNA Replication

A-T, G-C

Base Pair in DNA Replication

DNA REPLICATION

Proof Reading

DNA TRANSCRIPTION

Single strand, Small portion of genome

DNA TRANSCRIPTION

No Primer

RNA POLYMERASE

Enzyme in DNA TRANSCRIPTION

ssRNA

Product in DNA TRANSCRIPTION

A-U, T-A, G-C

Base Pair in DNA TRANSCRIPTION

DNA TRANSCRIPTION

No Proofreading

FEATURES OF TRANSCRIPTION

• It is highly selective

• Many of the RNA transcripts are synthesized as precursors known as primary transcripts

• Which on modifications & trimming converted into functional RNA

SPECIFIC SEQUENCE

mark the beginning and end of the DNA segment which is to be transcribed

PRIMARY TRANSCRIPTS

Many of the RNA transcripts are synthesized as precursors known as

FUNCTIONAL RNA

Which on modifications & trimming converted into

DNA REPLICATION

entire DNA molecule is normally copied

DNA TRANSCRIPTION

only a particular gene is copied at any time and some portions of DNA are never transcribed

RNA POLYMERASE

main transcription enzyme

DNA TRANSCRIPTION

begins when RNA polymerase binds to a promoter sequence near the beginning of a gene

TERMINATION

Transcription ends in a process called

CODING STRAND

strand that contains the gene

TEMPLATE STRAND

3’ - 5’

CODING STRAND

5’ - 3’

TEMPLATE STRAND

the complementary strand that is transcribed

ATP, GTP, CTP, UTP

Ribonucleotide required

MULTIMERIC ENZYME

consisting of six subunits

RNA POLYMERASE

• Search and binds to promoter site

• Unwinds a short stretch of double helical DNA

• Selects correct ribonucleotide and catalyze the formation of phosphodiester bond (polymerization)

• Detects termination signals

• Interacts with activator and repressor proteins that regulates the rate of transcription

α,α

Determine the DNA to be transcribed

β

Catalyze polymerization

β’

Bind & open DNA template (unwinding)

ω

Function is not known

σ

Recognize the initiation sites called promoter

RNA POLYMERASE I

synthesizes the precursor of the larger ribosomal RNAs

RNA POLYMERASE II

synthesizes the precursor of the mRNA synthesizes certain small nuclear RNA

RNA POLYMERASE III

produces the small RNAs including tRNA

STAGES OF TRANSCRIPTION

• Initiation

• Elongation

• Termination

INITIATION

• RNA polymerase recognizes the promoter

• Unwinding of DNA

ELONGATION

• RNA polymerase reads the unwound DNA

• Addition of nucleotides to the mRNA strand

TERMINATION

• RNA polymerase crosses a stop sequence

• mRNA is complete and detaches from DNA

INITIATION

Involves the interaction of RNAP with DNA at a specific site or sequences of DNA

PROMOTER

characteristic sequences of DNA that directs the RNA polymerases to initiate the transcription

TRANSCRIPTION FACTORS

mediate binding of RNAP

RNAP CAN START TRANSCRIBING

Once transcription bubble has formed,

ELONGATION

RNA strand gets longer due to the addition of new nucleotides

σ FACTOR

released from the transcriptional complex to leave the core enzyme (α2 ββω) which continues elongation of the RNA transcript

pppG or pppA

The first nucleotide in the RNA transcript is usually

TERNARY COMPLEX

The complex of RNA polymerase, DNA template and new RNA transcript is called

TRANSCRIPTION BUBBLE

region of unwound DNA that is undergoing transcription

3’-5’ PHOSPHODIESTER BOND

A 3'-OH group of one nucleotide reacts with the 5'- triphosphate of a second nucleotide to form

TERMINATION

process of ending transcription and happens once the RNAP transcribes a sequence of DNA known as terminator

RHO-DEPENDENT TERMINATION

Signaled by a sequence in the template strand of the DNA molecule

RHO-DEPENDENT TERMINATION

Which are 40bp in length & are inverted repeat or hyphenated

RHO

These signals recognized by a termination protein

RHO

an ATP-dependent RNA-stimulated helicase which binds to the signal

RHO-INDEPENDENT TERMINATION

1. One is palindromic G-C rich region which is followed by an A-T rich region. Thus, RNA transcript of this palindrome is self complementary sequences, permitting the formation of a hairpin structure.

2. The second feature is a highly conserved string of A residues in the template strand that are transcribed into U residues. The RNA transcript ends within or just after them

PALINDROMIC SEQUENCE

referred to as the sequence of nucleotides in the RNA

PALINDROMIC SEQUENCE

sequence in one strand is the same as the complementary sequence of the other strand when read from the same direction on both the strands, either 5' to 3' or 3' to 5'

HETEROGENEOUS NUCLEAR RNA

Mature mRNA is formed by extensively modifying the primary transcript

THREE MAJOR MODIFICATION BEFORE MATURING INTO MRNA

• 5’ Capping

• 3’ Polyadenylation

• Pre-mRNA Splicing

5’ CAPPING

A 7-methylguanosine attached to the 5'- terminal end of the mRNA

3’ POLYADENYLATION

Addition of a chain of adenylate residues, known as a poly A tail to the 3’ terminus of mRNA

EXONS

protein-coding sequences

INTRONS

do not encode functional proteins