Bio 302 Transcription

Central Dogma of Molecular Biology

DNA—>RNA—>Protein

Ribose

Contains an extra -OH group

RNA Bases

A, U, C, G

Uracil

Differs from Thymine by lacking a -CH3 group

RNA Nucleotides

Linked by phosphodiester bonds like DNA

RNA Base Pairing

Uracil pairs with Adenine. Forms 2 hydrogen bonds.

RNA Structure

-Forms single-stranded, folded, 3D structures.

-Form depends on function.

-Held together by hydrogen bonds

Template Strand

RNA strand that is complimentary to DNA strand.

Coding Strand

RNA strand that matches DNA

Result of Transcription

RNA Transcript

RNA Polymerase

-Transcribes DNA

-Catalyzes phosphodiester bonds between RNA nucleotides.

-Unwinds DNA in front and adds a few RNA nucleotides at a time.

-The incoming nucleotides provide energy to drive the reaction.

mRNA

Specifies amino acid sequences for proteins.

rRNA

Forms the core of ribosomal structure and catalyzes protein synthesis.

miRNA

Regulates gene expression

tRNA

Adaptors between mRNA and amino acids during protein synthesis.

Other Noncoding RNA

Rna splicing, gene regulation, telomere maintenance, etc.

Prokaryotic Transcription

Occurs in Cytosol

Eukaryotic Transcription

Occurs in Nucleus

Sigma Factor

Recognizes a promoter region in bacteria RNA pol

Promoter

DNA sequence that initiates transcription

Termination Sequence

Ends transcription

Prokaryotic Elongation

-Starts at +1 site

-Nascent mRNA leaves through the RNA polymerase exit channel

-Energy comes from 2nd and 3rd phosphate groups on RNA nucleotides

Bacterial Promoters

• Contain consensus sequences, which are well conserved DNA sequences that serve as important funnctional sites

• -10 element is called the pribnow box

RNA Polymerase I

Most rRNA genes

RNA Polymerase II

All protein-coding genes, mRNA genes, other noncoding RNAs

RNA Polymerase III

tRNA genes, 5S RNA gene, other small RNAs.

Initiating Eukaryotic Transcription

• Many promoters contain the DNA sequence the tata box  located at 30+.

• The tata box is organized and bound by the general transcription factor TFIID.

• TFIID has a subunit called TATA Binding Protein that specifically attaches to the TATA box.

• General transcription factors (GTFs) are proteins that are assembled on the promoters of eukaryotic genes near the start site of transcription and load RNA pol in the correct position.

Anatomy of Tata Box Containing Promoter

• Tata box element.

• Flanked by TFIIB recognition.

• Initiator element (INR)

• Motif ten element (MTE)

• Downstream core promoter element (DPE)