Transcription The Details

Question 1

Transcription step 2. Elongation

Answer 1

• RNA polymerase starts to build single stranded mRNA in 5’ to 3’ direction
• no primer is needed
• promotors does not get transcribed
• only one DNA strand is used called template strand
• unused strand is called the coding strand

Question 2

Transcription step 3. Termination

Answer 2

• RNA polymerase will come to end of gene and recognize the terminator sequence (string UUUUUUU)
• primary transcript of mRNA disassociates from DNA template strand
• RNA polymerase can then bind to another promoter and transcribe another gene

Question 3

Post transcription Modifications (cap, tail, introns)

Answer 3

-Primary transcript mRNA not ready to leave nucleus
-5’ cap is added made of a modified 7 guanine nucleotide triphosphate –> protects mRNA from digestion by other enzymes and initiates translation
-3’ poly-A tail is added a poly A polymerase = 200 (adenine) nucleotides long to protect from degradation
-

Question 4

Exons

Introns

Answer 4

Genes have coding regions

Non coding regions (introns cannot be translated or protein will fold incorrectly, introns are removed b4 primary transcript mRNA leaves nucleus

Question 5

Splicesomes

Answer 5

Made of RNA and protein
Cut out introns and join exons

Now called mRNA transcript

Question 6

What would happen if the nucleotide sequence of the gene were changed? Consequences for the person with the different DNA sequence?

Answer 6

You would change primary protein structure therefore you change the function

Question 7

Transcription step 1. Initiation

Answer 7

• RNA polymerase binds to DNA and opens double helix
• RNA polymerase bonds upstream to the gene being transcribed
• region upstream is called the promoter high in A and T bases (TATA box)
• because T-A pair only has 2 H bonds, it is easier for RNA polymerase to break helix here