6.3 continued: transcription in depth

Question 1

What are the three steps in transcription (DNA to RNA)?

Answer 1

1. Initiation
2. Elongation
3. Termination

Question 2

What occurs in initiation? (2)

Answer 2

• transcription begins when RNA polymerase ( enzyme that builds RNA molecules) molecules attached to a promoter region of DNA
• do not need a primer to attach

Question 3

In initiation, which direction are promoter regions facing?

Answer 3

Promoter regions are upstream of the desired gene to transcribe

Question 4

In eukaryotes, what is the promoter region called?

Answer 4

TATA box for eukaryotes

Question 5

In initiation, what helps RNA polymerase bind to the promoter region of DNA for eukaryotes?

Answer 5

• transcription factors

- transcription activators (also proteins) allow RNA polymerase to speed up its process

Question 6

In initiation in prokaryotes, does RNA polymerase need transcription factors or activators to help bind the the promoter?

Answer 6

• no they can bind directly to the promoter

Question 7

What occurs in elongation? (3)

Answer 7

• RNA polymerase opens the DNA and reads the triplet code the template strand
• moves in the 3’ to 5’ direction
  — The mRNA transcript elongates 5’ to 3’

Question 8

In elongation, which direction does RNA polymerase move? how often does it open DNA? (2)

Answer 8

• downstream

- only opens small section of DNA at a time

Question 9

What other things occur in elongation? (3)

Answer 9

1. Pairs complementary RNA nucleotides
2. The growing mRNA strand peels away from the DNA template strand
3. DNA double helix then reforms

Question 10

Elongation: can a single gene be transcribed by many RNA polymerase molecules? (3)

Answer 10

• yes
• this helps increase the amount of mRNA synthesized
• increases protein production

Question 11

What occurs in termination for PROKARYOTES? (4)

Answer 11

1. transcription proceeds through a termination sequence
2. Causes a termination signal
3. RNA polymerase detaches
4. mRNA transcript is released and proceeds to translation (mRNA does NOT need modifications)

Question 12

What occurs in termination for EUKARYOTES? (4)

Answer 12

1. RNA polymerase transcribes a sequence of DNA called the polyadenylation signal sequence
2. Codes for a polyadenylation signal (AAUAAA)
3. Releases the pre-mRNA from the DNA
   —Must undergo modifications before translation