Biology Lecture 35 - Transcription Termination

Questions and Answers

What are the two ways in which prokaryotes terminate transcription?

Rho Dependent (correct)

Rho Efficient

Rho Independent (correct)

Rho Recessive

What is Rho Independent transcription termination?

It occurs when an RNA polymerase transcribes a series of Gs and Cs followed by U, causing the polymerase to fall off due to the formation of a stem/loop.

What is Rho Dependent transcription termination?

It involves a protein hexamer called Rho that follows RNA polymerase, catches up to it, and knocks it off while unwinding the DNA/RNA hybrid.

Rho dependent termination is an imprecise, messy mechanism.

False Signup and view all the answers

What effect does Rho protein have on the DNA/RNA hybrid?

Rho protein unwinds the DNA/RNA hybrid, allowing the DNA to return to its double-stranded form. Signup and view all the answers

Rho dependent termination does not require ATP; however, Rho independent termination does.

False Signup and view all the answers

In eukaryotic transcription, how does RNA polymerase 1 transcription termination occur?

A termination factor binds to the end of the rRNA gene, causing RNA polymerase 1 to fall off. Signup and view all the answers

In eukaryotic transcription, how does RNA polymerase 2 transcription termination occur?

We do not know the exact mechanism but it transcribes past the end of the mRNA before stopping. Signup and view all the answers

In eukaryotic transcription, how does RNA polymerase 3 transcription termination occur?

RNA polymerase 3 stops after a series of U's, essentially stuttering and falling off. Signup and view all the answers

How does HIV trick the cell into transcribing its RNA?

HIV uses a sequence that forms a stem loop to prevent termination, and employs a protein called Tat to stabilize RNA polymerase. Signup and view all the answers

What is the function of Tat in HIV RNA transcription?

Tat increases the level of transcription of HIV DNA and acts as the first protein in the HIV genome. Signup and view all the answers

Study Notes

Transcription Termination in Prokaryotes

Prokaryotes terminate transcription primarily through two mechanisms: Rho Independent and Rho Dependent.

Rho Independent Termination

Occurs when RNA polymerase transcribes consecutive G and C nucleotides, followed by a series of U's.
The preceding G and C sequences form a stem/loop structure, forcing RNA polymerase off the DNA strand.

Rho Dependent Termination

Involves a protein hexamer called Rho that follows RNA polymerase along the mRNA strand.
Rho catches up to RNA polymerase, knocks it off the DNA, and unwinds the DNA/RNA hybrid.
ATP is required for this process, making it energy-dependent.

Precision of Rho Dependent Termination

Contrary to some beliefs, Rho dependent termination is extremely precise, occurring predictably at specific locations and times.

Role of Rho Protein

Rho protein unwinds the DNA/RNA hybrid, allowing the DNA to revert to its double-stranded form and enabling the transcription bubble to close.

ATP Requirement

Rho dependent termination necessitates ATP, while Rho independent termination operates without it.

Eukaryotic Transcription Termination

RNA Polymerase 1: Terminates transcription when a termination factor binds to the end of the rRNA gene, prompting RNA polymerase 1 to detach.
RNA Polymerase 2: Mechanism remains largely unknown; transcription appears to continue past the mRNA end before halting.
RNA Polymerase 3: Stops transcription after encountering a series of U's; similar to Rho Independent termination in prokaryotes but lacks the GCGCG stem/loop structure.

HIV Transcription Mechanism

HIV's RNA contains a sequence that forms a stem loop, typically causing transcription termination.
To circumvent this, HIV utilizes a protein called Tat that binds to the stem loop, recruits cellular factors, and stabilizes RNA polymerase, allowing continued transcription.
Tat functions as the first protein from the HIV genome, significantly increasing HIV DNA transcription levels.

Description

This quiz covers the mechanisms of transcription termination in prokaryotes, focusing on Rho Independent and Rho Dependent methods. Understand how RNA polymerase functions during these processes and the key features that distinguish the two pathways.