transcription

Question 1

where does transcription start?

Answer 1

at the promoter of the gene

Question 2

what is required for initiation of transcription?

Answer 2

• RNA polymerase
• basal transcription factors, which is a group of proteins

Question 3

what is the promoter of a gene?

Answer 3

it is a set of sequences of nucleotides

Question 4

where is the promoter of the gene located?

Answer 4

on the DNA strand itself

Question 5

what does the promoter contain?

Answer 5

the TATA box, a short sequence of T & A nucleotides

Question 6

where is the TATA box located?

Answer 6

it is located about 30 base pairs from the transcription start site

Question 7

what are the processes involved in the formation of a transcription initiation complex?

Answer 7

• the TATA-Binding Protein, a subunit of basal transcription factors, recognizes & binds to the TATA box
• other basal transcription factors & RNA polymerase are then recruited to bind around the TATA box to form a transcription initiation complex (TIC)

Question 8

what unwinds & separates the double stranded DNA?

Answer 8

1 basal transcription factor

Question 9

are both strands of DNA used as the template for RNA polymerase for transcription?

Answer 9

no, only 1 exposed DNA strand containing the promoter is used

Question 10

when does unwinding & separation of the double helix occur?

Answer 10

when the transcription initiation complex is formed

Question 11

does the initiation of transcription require energy?

Answer 11

yes, and the energy is provided by ATP

Question 12

what is required for the formation of mRNA?

Answer 12

free ribonucleotides

Question 13

what happens once RNA polymerase starts transcribing the DNA template?

Answer 13

it would be able to continue separating the DNA helix by disrupting the hydrogen bonds between complementary base pairs

Question 14

what is the 1st step in transcription elongation?

Answer 14

• RNA polymerase separate the double stranded DNA by disrupting the hydrogen bonds between complementary base pairs
• free RNA nucleotides base pair with the template strand via complementary base pairing

Question 15

what is the 2nd step in transcription elongation?

Answer 15

• RNA polymerase synthesizes the growing mRNA by catalyzing the formation of phosphodiester bonds between RNA nucleotides
• RNA polymerase moves along the DNA template strand in the 3’ to 5’ direction, as mRNA is synthesized in the 5’to 3’ direction

Question 16

does RNA polymerase catalyze the formation of hydrogen bonds between RNA nucleotides & their complementary DNA nucleotides on the template?

Answer 16

no, RNA polymerase does not catalyze the formation of hydrogen bonds between RNA nucleotides & their complementary DNA nucleotides on the template strand, as the hydrogen bonds are synthesized automatically

Question 17

what is the 3rd step in transcription elongation?

Answer 17

as the RNA polymerase continues to move along the template strand in the 3’ to 5’ direction, the DNA strands behind it rewinds to reform the double helix

Question 18

how is transcription terminated in eukaryotes?

Answer 18

• RNA polymerase transcribes the polyadenylation signal sequence, a sequence on the DNA which codes for a polyadenylation signal (AAUAA) in the pre-mRNA
• afterwards, about 10-30 nucleotides from the polyadenylation signal, specific proteins bind to the growing pre-mRNA & cut the pre-mRNA free from the RNA polymerase, terminating transcription

Question 19

how is transcription terminated in prokaryotes?

Answer 19

the transcribed terminator sequence on the RNA serves as a termination signal to stop transcription

Question 20

what is the terminator sequence made up of?

Answer 20

it is rich in guanines & cytosines, followed by a repeating sequence of adenines

Question 21

what happens when RNA polymerase transcribes the terminator sequence?

Answer 21

• a hairpin loop forms in the guanine rich portion of the mRNA transcribed
• the formation of the hairpin causes the RNA polymerase to pause, placing it directly over the A-U pairs, straining & causing the molecule to separate from the DNA, releasing the RNA polymerase

Question 22

why do many molecules of RNA polymerase simultaneously transcribe the same gene?

Answer 22

to speed up the rate of transcription of certain genes