BIOL2020 - Chapter 26 - RNA Transcription and Processing

What strand does mRNA resemble?

The Non-template/coding strand.

What enzyme is the template DNA strand read by?

Polymerase.

True/False; Genes can overlap each other.

True

What is the main difference of enzymes in transcription between Prokaryotes and Eukaryotes?

• One RNA polymerase in Prokaryotes

• Three RNA polymerase in Eukaryotes

What does the σ subunit in RNA polymerase in E. coli do?

Binds to the DNA strand and helps recruit RNA polymerase to promoters.

What is the 70σ subunit in RNA polymerase in E. coli and what does it do?

• Specific type of σ subunit that helps recruit RNA polymerase to “normal” promoters.

Does RNA transcription require primers?

No.

What do different σ subunits of RNA polymerase exist for?

To bind to different promoters.

What are the 3 main sites on the promoter that bound polymerase includes?

-35, -10, +1

In RNA transcription, what protein replaces the σ subunit when it detaches?

Nus A.

What are the 2 ways that transcription terminates called?

Intrinsic and Rho (p) dependent.

What happens during Intrinsic termination of transcription?

RNA polymerase encounters a terminator sequence, forming a hairpin at the palindromic sequences, and forcing the mRNA to be released.

What happens during Rho (p) dependent termination of transcription?

p helicase binds to a rut site on the RNA strand, travels up the strand until it reaches the Polymerase (uses ATP) and separates it from the DNA template.

Where does transcription and translation occur in Prokaryotes vs Eukaryotes?

Prokaryotes: Both in Cytoplasm

Eukaryotes: Transcription in the nucleus, translation in the cytoplasm

In what type of cells does mRNA processing occcur?

Eukaryotic.

What shape is Prokaryotic DNA?

Circular.

“Inr” are common sequences found where?

At the promoter.

Core promoter elements recruit what to help recruit RNA polymerase?

RNA polymerase II general transcription factors.

What are the 3 main steps in transcription initiation by RNA Polymerase II?

• TATA box is recognized by TATA-binding protein (TBP), initiating assembly of general transcription factors and RNA Polymerase II

• DNA is unwound

• Nucleotides are transcribed and CTD of Polymerase II is phosphorylated

What impact does Rifampicin have on transcription?

Inhibits Initiation of RNA synthesis.

What impact does Actinomycin D have on trancription?

Inhibits elongation.

How were the 3 Polymerases in Eukaryotes identified with α-Amanitin?

RNA synthesis was measured at different levels of α-Amanitin to determine the impact it had on different parts of transcription.

Where does Eukaryotic mRNA processing occur?

In the nucleus.

What are the 3 main types of processing that mRNA undergoes?

5’ capping, Poly (A) tail addition, and splicing.

Only mRNA transcribed by what polymerase are processed?

Polymerase II.

What is the 5’ cap composed of?

A N7-methyl G cap (7-Methylguanosine) linked to the +1 nucleotide (first nucleotide added).

What type of linkage is a 5’ cap held to the mRNA by?

A special 5’-5’ triphosphate linkage.

What are the base and sugar of a 5’ cap held together by?

a N9-Glycosidic bond.

What is the purpose of a 5’ cap?

Acts as a signal, and protects mRNA from exonucleases.

What happens to the first 2 nucleotides of mRNA in 5’ capping?

Methylated at the 2’ OH position.

What is Splicing?

The removal of sequences called introns.

What are the 2 ways that introns can be spliced out?

• Splice themselves out (called “self-splicing” introns)

• Use enzymes called spliceosomes

What are the subunits of spliceosomes called and what are they made of?

snRNPs (small nuclear ribonucleoproteins); made of both RNA and protein.

How do splicosomes work?

use their subunits (snRNPs) to base pair with RNA to bind to the ends of an intron, join the ends of the exons together, cut out the intron, and release it.

What is the Poly (A) tail?

A stretch of A residues at the 3’ end of an mRNA

What is termination and Poly (A) machinery recruited by?

Recognition of the AAUAAA sequence.

What is the purpose of the Poly (A) tail?

To enhance gene expression and protect mRNA from degradation.

What are the components of a mature RNA?

• only exons

• Poly (A) tail

• 5’ Cap

What is the energy input of adding a Poly(A) tail?

1 ATP.