Transcription

Lecture 10

Transcription

The process of copying DNA into RNA

Genetic Information Storage

DNA stores genetic instructions for an organism.

Genetic Information Transfer

DNA passes genetic information through RNA to proteins.

RNA

nucleic acid with ribose sugar, phosphate, and nitrogenous bases

Uracil (U)

The nitrogenous base in RNA that replaces thymine (T) in DNA.

Messenger RNA (mRNA)

Carries genetic information from DNA to ribosomes

Transfer RNA (tRNA)

Transfers amino acids to ribosomes during protein synthesis.

Ribosomal RNA (rRNA)

A structural component of ribosomes, aiding in protein synthesis

Gene

segment of DNA that encodes a protein.

Promoter Region

directs RNA polymerase where to start transcribing,
which strand to use, and which direction to move

Transcription Start Site (+1)

The first nucleotide transcribed into RNA

Open Reading Frame (ORF)

region of an mRNA that is translated into a protein.

Untranslated Region (UTR)

sequences in mRNA transcript that do not code for protein

RNA Polymerase

enzymes that carry out the process of transcription

5′ to 3′

RNA Polymerase Synthesizes RNA in the ____ direction.

Template Strand

The DNA strand used by RNA polymerase to make complementary RNA.

Coding Strand

The DNA strand with the same sequence as the RNA (except U replaces T).

Transcription Initiation

RNA polymerase binds to the promoter and starts RNA synthesis.

Transcription Elongation

RNA polymerase moves along DNA, synthesizing RNA and the RNA chain is extended in the 5′–3′ direction

Transcription Termination

RNA polymerase stops transcription and releases the RNA transcript.

Prokaryotic Transcription

Occurs in the cytoplasm and is coupled with translation

Eukaryotic Transcription

Occurs in the nucleus; mRNA is processed before export to the cytoplasm.

Sigma Factor

directs core RNA polymerase to the promoter region at the start of the gene

Consensus Sequence

The common nucleotide sequence found in promoters (-10 and -35 sites in bacteria).

Poly-A Tail

A string of adenines added to the 3′ end of eukaryotic mRNA for stability.

5′ Cap (m7G Cap)

A modified guanine nucleotide added to the 5′ end of eukaryotic mRNA.

Intrinsic Termination

RNA forms a hairpin loop, causing RNA polymerase to dissociate

Rho-Dependent Termination

a protein that binds to a specific site on the newly made RNA, then moves along the RNA until it gets to RNA polymerase which causes RNA polymerase to fall of the DNA and release the RNA transcript

Pre-mRNA

The initial RNA transcript before processing.

Splicing

Removal of introns and joining of exons in eukaryotic mRNA.

Introns

Non-coding sequences removed during splicing.

Exons

Coding sequences retained in the mature mRNA

Spliceosome

A complex of proteins and small RNAs that carries out splicing

General Transcription Factors (GTFs)

TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH

bind to the promoter region first and recruit
RNA polymerase to the correct site

TATA Box

A common promoter sequence in eukaryotic genes.

Alternative Splicing

Process where different exons are combined to produce different proteins.

RNA polymerase

requires a template strand, NTPs and ATP for RNA synthesis

RNA polymerase

can start transcription without a primer

holoenzyme

core RNA polymerase plus sigma factor

-10 site

consensus sequence = TATAAT

-35 site

consensus sequence = TTGACA

Closed complex

Sigma binds to the -10 and -35 regions of the promoter, brings RNA polymerase to the start of a gene, pointing the right direction

open complex

Local unwinding of the DNA strands occurs, exposing the template strand

+1 base (start site of transcription) is in the
active site of the enzyme

Intrinsic termination

a sequence in the newly made RNA
is able to base pair with itself

forms an RNA ‘hairpin’ structure

Intrinsic termination

Formation of this structure in the
newly made RNA causes RNA
polymerase to fall off the DNA
template and terminate transcription

RNA polymerase I

synthesizes ribosomal RNA (rRNA) in the nucleolus

RNA polymerase II

synthesizes protein-coding messenger RNA (mRNA)

RNA polymerase III

synthesizes transfer RNA (tRNA) and other small
RNAs in the nucleoplasm

polycistronic mRNA

bacterial genes coding for proteins that function in the same pathway may be located next to one another in the genome and transcribed as a single transcript

preinitiation complex

final complex, ready to initiate transcription

Topoisomerase

prevents the DNA double helix ahead of the replication fork from getting too tightly wound as the DNA is unwound at the replication fork