4- Transcription

Parts of the operon in prokaryotes

Promoter, operator, and structural genes

Where does RNA polymerase bind to initiate transcription in prokaryotes?

The promoter region. More specifically, the -10 and -35 promoter regions. Sigma factors help RNApol recognize the promoter region on the DNA strand.

What happens after RNA polymerase bind to the promoter region in prokaryotes?

RNApol opens up the DNA

Why is the promoter region in prokaryotes the -10 and -35 region?

This region contains a lot of As and Ts, which are easy to break since they only have 2 hydrogen bonds

What happens after RNApol unwinds the DNA in prokaryotes?

RNApol “walks” along one strand of DNA, known as the template strand, in the 5’ to 3’ direction. For each nucleotide in the template, RNApol adds a complementary nucleotide to the 3’ end of the mRNA strand

What is formed during elongation?

Phosphodiester bond, which are the covalent bond that links nucleotides together in a strand of nucleic acid (DNA or RNA).

What happens as RNApol reached the end of the DNA being transcribed in prokaryotes?

RNApol hits a region rich in C and G nucleotides, causing the mRNA to base pair and fold back on itself, forming a hairpin structure

What does the hairpin structure in prokaryotes result in?

The hairpin structure leaves the mRNA unstable, causing it to be released

Is the promoter transcribed?

No

Is the terminator (stop codon) transcribed?

Yes

Where does transcription take place in prokaryotes?

Cytoplasm

How does transcription begin in eukaryotes?

Basal transcription factors recognize the TATAA box, which is in the promoter region, and bind to it. This allows RNApol to bind to the promoter region.

What happens after the transcription factors and RNApol bind to promoter region?

Helicase unwinds the DNA at the transcription start site, creating an open complex or transcription bubble

What happens after helicase unwinds the DNA?

RNA polymerase II begins RNA synthesis, using one DNA strand (the template strand) to synthesize pre-mRNA in the 5’ to 3‘ direction

What stops transcription in eukaryotes?

RNApol will transcribe a terminator sequence, which disrupts the interaction of RNApol with mRNA, causing mRNA to be released

What is made from transcription in eukaryotes?

pre-mRNA

How is pre-mRNA turned into mRNA

Slicing! Splicing is done by splicosomes- it removed introns and leaves exons

What is done before splicing in eukaryotes?

A 5’ cap and Poly-A tail is added to 3’ end of pre-mRNA to pre-mRNAWhe

Where does transcription occur in eukaryotes?

Nucleus