Transcription in eukaryotes

Question 1

What is DNA combined with to be packaged and what does it form?

Answer 1

DNA + histone proteins = chromatin

Question 2

How long is DNA in a cell usually?

Answer 2

2 metres

Question 3

How many histone proteins are there and which one reacts with DNA?

Answer 3

There are 5 histone proteins:
H1 - interacts with negatively charged DNA
H2A - small, basic +ve
H2B - small basic +ve
H3 - highly conserved
H4 - highly conserved

Question 4

What is the subunit of chromatin in eukaryotes?

Answer 4

The nucleosome - 2 copies of each 4 histones (8 in total)

Question 5

What is the structure of subunit of chromatin?

Answer 5

Squashed cylindrical structure. DNA is wrapped around the outside (2 trust on each histone)

Question 6

What stages are introns and exons removed from the RNA?

Answer 6

Introns are removed from the final RNA product

Exons are present in the final mRNA

Question 7

Which RNA polymerase transcripts DNA to make an RNA copy?

Answer 7

RNA polymerase 2 - interacts with a promoter and stops at the polyadenylation site

Question 8

On a eukaryotic gene, what are the 2 start and end points?

Answer 8

There is the first start - RNA
There is a second start just further on - protein

The first stop - protein
The second stop - RNA

Question 9

Where are the locations of transcription and translation in a eukaryotic cell?

Answer 9

Transcription - Nucleus

Translation - cytoplasm

Question 10

What is RNA polymerase 1’s role in transcription?

Answer 10

rRNA - ribosomal DNA

Question 11

What is RNA polymerase 2’s role in transcription?

Answer 11

mRNA - transcribes protein coding genes

Question 12

What is RNA polymerase 3’s role in transcription?

Answer 12

tRNA, snRNA (small nuclear - removes introns), 5SRNA (ribosomes)

Question 13

What is the order of promoters in DNA coding?

Answer 13

Enhancer 100bp, then proximal promoter, then core promoter with TATA, mRNA starts

Question 14

Which promoter do general transcription factors interact with?

Answer 14

Core promoter - present in all cells and combines with RNA polymerase

Question 15

Which promoter does a specific transcription factor interact with?

Answer 15

Proximal promoter and enhancer - regulates level and timing of transcription

Question 16

What is the model for a transcription complex at the core promoter (general)

Answer 16

Transcription factors with RNA polymerase and A, B, D, E, F assemble in order to allow RNA polymerase to associate and creates the stepwise assembly model - produce the structure

Question 17

How are introns removed from the mRNA?

Answer 17

Splicing - exons are joined together

Question 18

How does capping work?

Answer 18

Capping is when a modified gene at the 5’ end is added to stop transcription (GTP + methylation + 5’-p-p-p-5’ bond)

Question 19

Where does polyadenylation occur?

Answer 19

Polyadenylation occurs at the 3’ end

Question 20

What is the role of the mRNA cap? (5)

Answer 20

Protects the 5’ end from degradation
Provides stability
Cap interacts with translation factors to recruit ribosomes
Cap interacts with cap binding complex in exporting mRNA
Cap is important in the splicing of introns near the 5’ end

Question 21

What happens ate the 3’ end of RNA?

Answer 21

Transcription goes past the position of the end to make a longer RNA
This is then cut and polyadenyl tail is added on
Provides stability