Transcribtion

Question 1

What are the 3 stages of transcription?

Answer 1

Initiation
Elongation
Termination

Question 2

Initiation

Answer 2

RNA polymerase binds to DNA and opens double helix

RNA POLYMERASE BINDS UPSTREAM to the gene being transcribed

Upstream region = promoter (high in A and T bases - TATA box
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Because T-A pair only has 2 hydrogen bonds, it’s easier for RNA polymerase to break helix here

Question 3

Elongation

Answer 3

RNA polymerase starts to build single stranded mRNA in 5’-3’ direction

RNA primer is not needed to start the process

Promoter is not transcribes
Only 1 DNA strand is used, which is called the template strand

Template strand reforms as helix as soon as the enzyme passes through

Unused strand is called coding strand

Question 4

What does RNA polymerase do in transcription?

Answer 4

Binds to DNA and opens double helix, binds UPSTREAM TO gene being transcribed

Question 5

What is the upstream region called? What are its. Characteristics?

Answer 5

The promoter

It’s high in T and A bases (TATA BOX)

Question 6

What is the overall goal of transcription ?

Answer 6

To copy information in DNA into mRNA

Question 7

What is the template strand?

Answer 7

The single DNA strand that is used, it’s reformed as a helix as soon as the enzyme passes through

Question 8

Termination

Answer 8

RNA polymerase goes to end of gene and recognizes the terminator sequence (strings of Adenines in DNA, string of uracil in RNA)

The primary transcript (first draft) of mRNA disassociates from DNA template strand

RNA polymerase can then bind to another promoter and transcribe another gene

Question 9

What is the terminator sequence in DNA and RNA

Answer 9

DNA - string of Adenines

RNA- string of uracil

Question 10

What happens when primary transcript mRNA is not ready to leave the nucleus?

Answer 10

5’ cap is added, it’s made of a modified guanines nucleoside triphosphate- protects mRNA from digestion by other enzymes and initiates translation

Then 3’ polyA tail is added by poly-A polymerase (200 adenine nucleotides long to protect from degration)

Question 11

What are genes coding and non coding regions?

Answer 11

Coding regions: EXONS

non coding: INTRONS

Question 12

Introns

Answer 12

Can not be translated or protein will fold incorrectly

So introns are removed before primary transcript mRNA leaders nucleus

Question 13

Splicesomes and extons

Answer 13

Splicesomes are made of RNA and protein, and they cut out introns and join extons =mRNA transcript

Question 14

Is there proofreading in transcription?

Answer 14

No because lots of copies of mRNA are made and because of the redundancy of the genetic code