concept 17.2: transcription is the DNA directed synthesis of RNA: a closer look

what is the first stage of gene expression

transcription

what occurs during transcription

one of the two DNA strands, called the template strand, provides a template for the production of an RNA transcript and the nucleotides of the RNA transcript are complementary base pairs with the template DNA strand

template strand

always the same strand for any given gene, one of the two DNA strand that is providing the template for the transcript

the coding strand

the complementary strand for the template strand

what catalyzes RNA synthesis

RNA polymerase

what does RNA polymerase do

pries the DNA strands apart and attaches together the RNA nucleotides to form an RNA strand

does RNA polymerase need primer

no

what are the base pairing rules for RNA synthesis

same as DNA except sub uracil for thymine

what direction does synthesis occur for RNA

5’ to 3’

the promoter

the DNA sequence where the RNA polymerase attaches

the terminator (ONLY IN BACTERIA)

the sequence signaling the end of transcription (ONLY IN BACTERIA)

transcription unit

the stretch of DNA that is transcribed

describe the similarities between the RNA strand produced by the template strand and coding strand of DNA

nearly identical except T is now U in RNA

what are the three stages of transcription

initiation,

elongation,

termination

where does initiation occur - IN PROKARYOTES

occurs in the nucleoid region because prokaryotes do not have any membrane bound organelles

what happens during initiation- IN PROKARYOTES

the enzyme polymerase binds to the promoter region of the DNA and the binding of the polymerase spreads apart the two strands

how many types of RNA polymerase do bacteria have and what do they do

only one type of RNA polymerase that works to produce mRNA and other types of RNA

where does elongation occur- IN PROKARYOTES

the RNA polymerase moves along one strand of DNA- the template strand

what occurs during elongation - IN PROKARYOTES

the mRNA assembles by adding nucleotides to the 3’ end of the elongating mRNA molecule in the 5’ to 3’ direction and nucleoside triphosphates are added initially

where does termination occur- IN PROKARYOTES

the end of transcription, the end of the terminator region

what occurs in termination- IN PROKARYOTES

the mRNA molecule is complete and the RNA polymerase dissociates from the DNA template and the two strands- the coding and template strand- are able to reform their bonds again

where does transcription occur in eukaryotes

the nucelus

promoters in eukaryotes

signal the transcriptional start point and can extend several dozen nucleotide pairs above the start point

TATA box

a promoter that is used to form the initiation complex in eukaryotes

describe how transcription occurs - IN EUKARYTOES

the TATA box forms the initiation complex, as RNA polymerase moves along the DNA, it untwists the double helix 10-20 nucleotides at a time, and nucleotides are added to the 3’ end of the growing RNA, and RNA polymerase II transcribed the polyadenlation signal sequence, terminating it

transcription factors in eukaryotes

they mediate the binding of RNA polymerase II and the initation of the transcription, they are proteins that enhance RNA polymerase binding to increase the rate of transcription

transcription initiation complex

the completed assembly of transcription factors and RNA polymerase II bound to a promoter

how many RNA polymerases do eukaryotes have

at least three

what is RNA polymerase II used for

mRNA synthesis

how is transcription terminated- IN EUKARYOTES

RNA polymerase II transcribed the polyadenylations signal sequence and the pre-RNA continues to elongate past this signal, and then the proteins bound to the polyadenylations signal sequence cuts the pre-RNA free from the RNA polymerase