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

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

• 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) • 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’

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

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

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

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

• initiation • elongation • termination

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

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

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

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

crucial promoter DNA sequence

• Includes a TATA box which is 25 nucleotides upstream from the start point • Once the TATA box has been recognized, multiple transcription factors bind before RNA polymerase 2 does • 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

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

• 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