Transcription: From DNA to RNA in Cells

Transcription

The first step in the transfer of genetic information from DNA to RNA to make proteins.

RNA

An intermediate in information transfer, first demonstrated in the early 1960s.

Central Dogma

Proposed by Francis Crick in 1957, outlining the flow of genetic information from DNA to RNA to proteins.

Reverse Transcriptase

An enzyme that allows information flow from RNA to DNA in some viruses.

mRNA

Encodes information for proteins.

rRNA

A functional component of a ribosome involved in translation.

tRNA

Brings amino acids to the ribosome during translation.

Pre-mRNAs

Processed to mature mRNA before translation.

Long Non-coding RNAs (lncRNAs)

Tens of thousands found only in eukaryotes, with mostly unknown functions; some control gene expression.

Transcription Unit

A stretch of DNA encoding an RNA molecule with necessary transcription sequences.

Promoter

A DNA sequence recognized by RNA polymerase to start transcription.

Terminator

Part of the RNA coding region that marks the end of transcription.

Ribonucleotide Triphosphates

Basic building blocks of RNA and substrate for RNA polymerase.

Template Strand

The DNA strand transcribed into RNA.

Non-template Strand

The DNA strand not transcribed during RNA synthesis.

Bacterial RNA Polymerase

Exists in core and holoenzyme forms, with the holoenzyme required for transcription initiation.

Initiation (Transcription)

Recognition of the promoter, binding of RNA polymerase, and initiation of RNA synthesis.

Elongation (Transcription)

Extension of RNA by adding new nucleotides to the growing strand.

Termination (Transcription)

Recognition of the end of the transcription unit and separation of RNA polymerase from the DNA template.

Conserved Sequences

Sequences shared across promoters with vital functions

Consensus Sequences

Non-identical matches to a common sequence for recognition

Pribnow Box

Recognized by RNA polymerase at the -10 sequence

Transcription Start Site

Location marked by +1 where RNA synthesis begins

Promoters

Regulate transcription efficiency and initiation frequency

Down Mutation

Reduces transcription frequency due to promoter recognition issues

Up Mutation

Enhances transcription frequency by improving promoter recognition

Transcription Direction

Determines the orientation of RNA polymerase on the template strand

Transcription Bubble

Region where RNA polymerase unwinds DNA for transcription

Transcription Elongation

RNA polymerase moves downstream, adding nucleotides at ~40/sec

Proofreading Ability

RNA polymerase corrects errors by removing misincorporated nucleotides

Termination Signals

Sequences in RNA indicating the end of transcription

Gyrase

Relieves supercoiling ahead of the transcription bubble

Transcription Termination

RNA polymerase detaches after RNA release and DNA template detachment

Consensus Sequences Orientation

Shown on the non-template DNA strand for promoter recognition

Transcription Initiation Efficiency

Governed by promoters, affecting initiation frequency

Transcription Bubble Opening

Initially opens from -12 to +2 during transcription initiation

Transcription Directional Arrows

Indicate the 5' to 3' direction of mRNA synthesis

RNA Polymerase Holoenzyme

Recognizes and binds to promoter sequences for transcription initiation

Transcription Initiation Location

RNA polymerase binds DNA from -50 to +20 during initiation

Rho-independent termination

Termination process not requiring a protein, also known as intrinsic termination.

Rho-dependent termination

Termination process requiring the Rho protein.

Transcription in Eukaryotes

Process involving initiation, elongation, and termination stages, with five forms of RNA polymerase.

RNA polymerases I, II, and III

RNA polymerases present in all eukaryotes, each recognizing a different promoter type.

RNA polymerases IV and V

RNA polymerases exclusive to plants, involved in regulating chromatin structure.

Initiation of Transcription in Eukaryotes

Process involving over 70 proteins, focusing on genes transcribed by RNA polymerase II to produce mRNA.

Eukaryotic Promoter Structure

Comprising a core promoter adjacent to +1 and a regulatory promoter, with RNA polymerase binding to the core promoter.

Elongation of the Transcript

Process where RNA polymerase II leaves the promoter after ~30 nucleotides, with multiple polymerases transcribing a gene simultaneously.

Evidence of Transcription

Indicated by the disappearance of central fiber with DNase treatment (DNA template) and granular strings with RNase treatment (RNA).

Major Concepts in Transcription

Involving RNA polymerase, different classes of RNA, DNA template for RNA synthesis, transcription unit components, and stages of transcription.