14.2: Transcription is the DNA directed synthesis of RNA: A Closer Look

Question 1

Overall purpose

Answer 1

to copy the DNA message for the protein needed to be produced to a messenger that will take it to production.

Question 2

2 major concepts of transcription

Answer 2

1. Only the DNA of selected genes will be transcribed according to what the cell needs to produce. (just the part needed not the entire chromosome)
2. The DNA helix was made by semi-conservative replication. That means it has a template side and a complementary side. The template is the side that codes for the mRNA.Could be either side (only one side for a gene) mRNA is said to be complementary (also called the coding strand). Written 5’ to 3’

Question 3

RNA polymerase

Answer 3

pries the 2 strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, assemble a polynucleotide in the 5’ to 3’ direction, and requires no primer

In eukaryotes, there are at least 3 types of RNA polymerase, the one involved with the synthesis of pre-RNA is RNA polymerase 2

Question 4

promoter

Answer 4

the DNA sequence where RNA polymerase attaches and initiates transcription, upstream

Question 5

terminator

Answer 5

the sequence that signals the end of transcription, bacteria only, downstream

Question 6

transcription unit

Answer 6

the stretch of DNA downstream from the promoter that is transcribed into an RNA molecule

Question 7

3 stages of transcription

Answer 7

1. initiation
2. elongation
3. termination

Question 8

start point

Answer 8

within the promoter, the nucleotide where RNA polymerase begins synthesizing the mRNA, extends many nucleotide pairs upstream from the start point

Question 9

How does the RNA polymerase know where to bind?

Answer 9

RNA polymerase binds in a precise location and orientation on the promoter, this determines which of the 2 strands of the DNA helix is used as the template

In bacteria, some of the RNA polymerases recognizes and binds to the promoter

Question 10

transcription factors

Answer 10

in eukaryotes, mediates the binding of RNA polymerase and the initiation of transcription, only after this attaches to the promoter does the RNA polymerase 2 bind(since it is dumb), additional ones soon bind

Question 11

transcription initiation complex

Answer 11

the whole complex of transcription factors and RNA polymerase 2 bound to the promoter

Question 12

TATA box

Answer 12

crucial promoter DNA sequence

Question 13

Steps of Initiation

Answer 13

1. Includes a TATA box which is 25 nucleotides upstream from the start point
2. Once the TATA box has been recognized, multiple transcription factors bind before RNA polymerase 2 does
3. Once RNA polymerase 2 binds, the transcription initiation complex has been formed and RNA synthesis can be started

After everything is attached, the enzyme unwinds the 2 DNA strands and begins transcribing the template strand at the start point

Question 14

Elongation

Answer 14

cAs RNA polymerase moves along the DNA, the double helix untwists, the enzyme adds nucleotides to the 3’ end of the growing RNA molecule as it continues along the double helix as this happens, RNA nucleotides start to peel off and the DNA winds back up

Multiple RNA polymerases can do this on one DNA molecule, produces multiple RNA strands for various uses

Question 15

Termination

Answer 15

• In Bacteria, when the RNA polymerase goes through the terminator, it detaches from the DNA and releases the transcript which requires no further modification before transcription
• In Eukaryotes, RNA polymerase 2 transcribes a sequence on the DNA called the polyadenylation signal sequence, specifies a polyadenylation signal(AAUAAA) in the pre-mRNA called a signal. Then proteins 10-35 nucleotides downstream from the signal cut the RNA transcript free and release the pre-mRNA