L3 Transcription

Question 1

How is DNA lost at the telomeres

Answer 1

DNA is lost from telomeres hen joining of adjacent Okazaki fragments, polymerase enzyme at last bit of lagging strand is unable to work.

Question 2

What Processionals is RN polymerase involved in and what are its functions

Answer 2

catalyses formation of mRNA- transcription, moves in 5-3 direction, no thymine now replaced with uracil, it also induced renaturation- DNA anneals

Question 3

3 stages of transcription

Answer 3

o Initiation- small region of DNA (gene) is unwound by RNA polymerase
o Elongation- one strand acts as a template for mRNA production by complementary base pairing with ribonucleotides
o Termination- as mRNA forms it is displaced from the DNA and the DNA double helix reforms.o Initiation- small region of DNA (gene) is unwound by RNA polymerase

Question 4

what is the function of the promoter?

Answer 4

initiation of transcription. is controlled by the promoter

Question 5

enhancer and silencer?

Answer 5

enchanter-proteins bind to enhance expression of gene

Question 6

silencer?

Answer 6

repressor proteins bind to prevent gene expression

Question 7

what are the 5’UTR and 3UTR’

Answer 7

the last section before the OFR and the first thing after the OFR
copied into RNA but are not translated into the protein

Question 8

special function of 3’UTRe

Answer 8

localisation sequence- can direct the mRNA to certain locations in the cytosol. synthesis of protein takes place near to location that protein is being used.

Question 9

what are the 3 main post-transcriptional modification that occur even before mRNA has left the nucleus

Answer 9

5’ capping
RNA splicing
Polyadenylation (poly A tail)

Question 10

describe 5’capping

Answer 10

• Regulated nuclear export
• Prevents degradation of mRNA by exonucleases
• Promotes translation
• Helps to distinguish from other types of RNA

Question 11

describe RNA splicing and alternative splicing

Answer 11

• Removes introns leaving only exons- introns are present so tat some of the exons can be removed as well to make different versions of the same gene protein. - alternative splicing

Question 12

describer epoxy adenylation

Answer 12

• Poly A-tail of 200 adenine nucleotides is added to the 3’ end of the mRNA
• Makes the mRNA more stable and prevent degradation
• Allows export to form the nucleus

Question 13

what are the 6 steps at which gene. expression can be controlled?

Answer 13

1. transcription regulators, epigenetic regulation
2. RNa processing- RNA cleavage, Alternative splicing (Ab)
3. RNa transport from nucleus to cytosol
4. translation repressors- bind to 5’ or 3’ UTR
5. mRNa degradation - poly A tail over time acts as a timer
6. Protein activity- post translational modification- will active or inactive a protein- phosphorylation