Chapter 14.3.2 (Exam 3) Transcription

Question 1

What are the three steps of transcription?

Answer 1

Initiation

Elongation

Termination

Question 2

What is initiation of transcription?

Answer 2

RNA polymerase binds to a DNA promoter sequence

Question 3

What is the role of promoters in initiation?

Answer 3

Promoters tell the enzyme where to start (initiation site) and which strand of DNA to transcribe

Question 4

What is the role of sigma factors and transcription factors in initiaition?

Answer 4

RNA polymerase uses sigma factors (prok.) and transcription factors (euk.)

They help direct the polymerase onto the promoter and determine which genes are expressed at particular times

Question 5

What is the substrate for RNA polymerase during elongation during transcription?

Answer 5

RNA polymerase uses nucleoside triphosphates (NTPs) — ATP, UTP, GTP, CTP — as building blocks for RNA

Question 6

Where does the energy to form phosphodiester bonds in RNA come from?

Answer 6

When RNA polymerase adds one NTP to the RNA chain, it breaks off two phosphates, releasing the energy that drives the reaction

Question 7

Describe some characteristics of elongation during transcription.

Answer 7

RNA polymerase unwinds and rewinds DNA to expose the template strand that is being copied

The new RNA strand is antiparallel to the template strand

RNA polymerase does not proofread, meaning mistakes can occur

Question 8

What is termination in transcription?

Answer 8

Termination occurs after reaching a termination sequence

For some genes, the transcript forms a loop and falls away from the DNA

For others, a protein binds to the transcript and causes it to detach from the DNA