BIO101: transcription

the DNA double strand is always shown and drawn with the

5' end at the top left

the _______ is the coding strand

top strand

the _____________ (starting with the 3' on the left) is the template strand

bottom strand

used to transcribe the DNA code into RNA code

template strand

identical to the nucleotide sequence in the DNA coding strand

the nucleotide sequence of the transribed RNA

Transcribes the DNA template strand into an RNA strand

RNA polymerase.

separates a short region of the DNA double strand (bubble)

RNA polymerase

the 5' end of the RNA has to be synthesized first or else it moves from 5' to 3' in an

undirectional way

prevent it from falling off the DNA

jaws of the RNA polymerase

nucleotides pass through a _________ to reach the catalytic site

NTP tunnel

catalytic site

The niche in an enzyme where the substrate is converted to the product (also active site).

transcription starts at the

transcription start site

defines the transcription start site

promoter

facilitated by the sigma-factor

binding of RNA polymerase

removed at the beginning of the elongation phase

sigma-factor

termination of transcription takes place at the

termination site

defined by conserved DNA sequences

transcription initiation and termination sites

genes in eukaryotes have different:

structure/org of coding regions in genes and promoter structure/org

transcription in eukaryotes requires

transcription factors and one of three RNA polymerases

interons

non-coding nucleotides of mRNA during transcription that are removed

transcription in eukaryotes generates a pre-RNA which is modified by

polyadenylation, capping, splicing

polyadenylation

addition of a poly-A (A-A-A-A-A-A-A) tail in the 3' end

polyadenylation stops the

cells from destroying the single stranded molecule

capping

addition of an inverted nucleotide at the 5' end

splicing

removal of introns from pre-RNA

Gene expression of eukaryotic genes

extensively regulated at multiple levels

eukaryotic genes contain

introns and exons

are spliced out (removed)

introns

may have regulatory function

introns-

contain the information for amino acid sequence of the protein

exons

do not contain introns

prokaryotic genes

bind to the promoter region of a gene

transcription factors (TF)

facilitate binding of the RNA polymerase to DNA

the transcription factors

Unidirectional from 5' to 3'

in eukaryotes, RNA synthesis is

most transcription factors remain at

the promoter and are only important for initiation of transcription

referred to as the lobster claw

RNA polymerase II

transcribed gene regions (template DNA) in genes of eukaryotes contain

exons and introns

introns are transcribed along with exons in the

primary RNA transcript (pre-mRNA)

introns are removed as the exons are spliced together in the

spliced transcript

in eukaryotes, RNA is modified before

it leaves the nucleus

modifications include

capping and polyadenylation

capping:

a GTP is added in opposite orientation to the 5' end

polyadenylation:

the poly-adenine tail is added to the 3' end of RNA

formation of a splisosome includes the following cards-

1,2,3

middle of intron:

branchpoint A

attack the phosphodiester bond linking the first exon to the first intron at GU

2' -OH group of A within intron

formed at the 5' end of the intron generating a phosphodiester bond (U-A) with the branchpoint A

a lariat

cutting the intron:

free 3' OH on exon 1 attacks the phosphodiester bond between the lariat and exon 2

exons are joined:

a phosphodiester bond is formed between the 3' end of exon 1 and the 5' end of exon 2

snRNPs (snurps)

small nuclear ribonucleoproteins