Transcription

Question 1

What do both eukaryotes and prokaryotes require in transcription?

Answer 1

Control factors - promoters, activators and repressors

Question 2

Where does prokaryotic transcription occur?

Answer 2

Prokaryotes = cytoplasm

Question 3

Where does eukaryotic transcription occur?

Answer 3

Eukaryotes = nucleus

Question 4

What is the role of catalytic RNA?

Answer 4

Involved in reactions in the cell cytoplasm

Question 5

What is the function of mRNA?

Answer 5

Carries genetic information out the nucleus to

Question 6

What is the role of rRNA?

Answer 6

rRNA makes up 50% of the ribosome where proteins are assembled

Question 7

What is the role of tRNA?

Answer 7

tRNA carries the anticodon and specific amino acid

Question 8

What is the role of RNA Pol I and where is it found?

Answer 8

RNA Pol I transcribes genes coding for rRNAs

Found in the nucleolus

Question 9

What is the role of RNA Pol II and where is it found?

Answer 9

RNA Pol II transcribes all protein coding genes (mRNA)

Found in nucleoplasm

Question 10

What is the role of RNA Pol III?

Answer 10

RNA Pol III transcribes genes synthesizing tRNA, 5s RNA and small RNA’s

Question 11

What is needed for RNA transcription?

Answer 11

DNA
RNA Polymerase
Triphosphate ribonucleotides
Transcription complex - formed of RNA Pol and cofactors which binds to TATA box
Topoisomerase and helicase - unwinds DNA helix
Splicesomes - removes introns from pre-mRNA

Question 12

What is meant by the promoter region?

Answer 12

Area containing the TATA box - transcription complex bind to the TATA box in the promoter region.
The promoter region in CLOSE to the initiation site
Unwinding of the DNA begins from the promoter region

Question 13

What is meant by a regulatory element? List some regulatory elements

Answer 13

Regions of DNA which control gene expression - ensure that every gene is not replicated. e.g. enhancers, repressors, activators, promoters.

Question 14

What DNA strand acts as the template for mRNA?

Answer 14

The antisense strand acts as a template for mRNA. Thus mRNA is complementary to the antisense strand

Question 15

Which strand of DNA is mRNA and exact copy of?

Answer 15

mRNA is an exact copy of the sense (coding strand)

Question 16

What are the 3 steps in eukaryotic transcription?

Answer 16

1. Initiation
2. Elongation
3. Termination

Question 17

Describe initiation in transcription

Answer 17

Transcription complex binds to the TATA box in the promoter region just before the 5’ end of the antisense strand.
Topoisomerase and Helicase move along the chain, causing local unwinding of the double helix.
RNA polymerase moves behind the transcription complex, beginning to synthesis RNA at the initiation site.

Question 18

Where are regulatory elements found in location to the promoter region?

Answer 18

Regulatory elements are found further upstream than the promoter region

Question 19

In what direction does the DNA chain grow?

Answer 19

DNA grows from 5’ to 3’ (even though nucleotides are added from 3’ to 5’)

Question 20

Describe elongation in transcription

Answer 20

Triphosphate ribonucleotides base pair to complementy bases on the antisense strand (template) - RNA polymerases facilitates binding of new ribonulceotides to the 3’ end of the growing RNA chain.
DNA is recoiled (with the help of topoisomerase) after RNA polymerase moves over it, causing RNA to be released

Question 21

What is meant by the terminator?

Answer 21

Terminator = hairpin loop of DNA on the antisense strand which is self complementry. Many C-G bonds (3H) makes the terminator strong, preventu RNA polymerase from moving along the strand

Question 22

Describe termination in transcription

Answer 22

RNA polymerase reaches the terminator which can alone stop transcription.

Question 23

List the methods of mRNA processing

Answer 23

Splicing of pre-mRNA by splicesomes
Addition of a 7-methylguanosine cap
Addition of a poly-adenylic tail
Methylation of nucleotides

Question 24

Describe the role of splicesomes

Answer 24

Splicesomes remove introns from pre-mRNA - cratea continuous coding strand

Question 25

Describe the role of capping

Answer 25

An 7-methylguanosine cap containing no free phosphates is added to the end of mRNA. It prevents mRNA being attacked by phosphates

Question 26

Describe the role of a poly-a tail

Answer 26

A poly adenylic tail is a sequence of 100-200 nucleotides added to the end of mRNA by poly a synthase and ATP

Question 27

Where does RNA polymerase bind during transcription for eukaryotes and prokaryotes?

Answer 27

Eukaryotes - RNA polymerase binds to TATA box

Prokaryotes - RNA polymerase binds directly to the promoter region

Question 28

Does prokaryotic transcription create pre-mRNA?

Answer 28

Prokaryotes have no introns - mRNA does not need to be processsed

Question 29

In prokaryotes do transcription and translation occur at different time?

Answer 29

In prokaryotes, transcription and translation occur at the same time

Question 30

Describe methylation

Answer 30

A methyl group is added to nucelotides

Question 31

What is the size of prokaryotic ribosomes/rRNA?

Answer 31

Prokaryotic Ribosomes = 70s

Question 32

What is the size of eukaryotic ribosomes/rRNA?

Answer 32

Eukaryotic Ribosomes = 80s

Question 33

What does each RNA gene produce during rRNA transcription?

Answer 33

45s rRNA - pre-rRNA. This is cleaved to produce smaller rRNA’s which are packaged into ribosomes

Question 34

Where does 5s rRNA synthesis occur and what does it require?

Answer 34

5s rRNA synthesis occurs at a different section of DNA and require RNA Pol III