Chapter 7 Transcription

gene expression

__________________ is changing genetic information into RNA and then into a protein

transcription

process in which RNA polymerase uses one strand of DNA as a template to synthesize a complementary RNA sequence

single-stranded

RNA is largely ____________________; however, it can fold into a variety of shapes

-ability to fold allows RNA to carry out various functions

-RNA has structural, regulatory, and catalytic roles

-conventional and some "nonconventional" base-pair interactions (e.g., A-G)—allow an RNA molecule to fold into a three-dimensional structure

RNA polymerase

-catalyzes phosphodiester bond

-unwinds the DNA helix

-extends transcript one nucleotide at a time

-direction 5' → 3' (adds nucleotides)

-ynthesis without a primer

-error rate 1 in 104

rRNAs

________ are not translated into proteins, rather they are components of ribosomes

messenger RNAs (mRNAs)

code for proteins

-coding

ribosomal RNAs (rRNAs)

form the core of the ribosome's structure and catalyze protein synthesis

-noncoding

microRNAs (miRNAs)

regulate gene expression

-noncoding

transfer RNAs (tRNAs)

server as adaptors between mRNA and amino acids during protein synthesis

-noncoding

other noncoding RNAs

used in RNA splicing, gene regulation, telomere maintenance, and more other processes

-noncoding

noncoding

in ___________ RNAs, the final product is RNA itself

gene expression

information encoded in a DNA sequence is converted into a product (RNA or protein) that has some effect on the cell

3'→ 5'

transcription produces RNA that is complementary to one strand of DNA because...

-RNA polymerase always moves in __________ (reads the template)

-orientation of promoter determines the template

initiation of transcription in bacteria

1. RNA pol subunit sigma factor

-recognizes and binds to promoter

-RNA synthesis initiated

2. sigma factor is released(dissociates)

3. chain elongation continues until terminator sequence

4. RNA pol releases from DNA & RNA transcript

5. polymerase reassociates with sigma factor

RNA polymerase II

all protein-coding genes, miRNA genes, plus genes for other noncoding RNAs (e.g., those of the spliceosome)

RNA polymerase I

most rRNA genes

RNA polymerase III

tRNA genes, 5A rRNA gene, genes for many other small RNAs

TFIID

TBP subunit of TFIID, recognizes TATA box

-transcription factor

TFIIB

positions RNA polymerase at the start site of transcription

-transcription factor

TFIIF

attracts TFIIE and TFIIH

TFIIE

attracts TFIIH

TFIIH

unwinds DNA and phosphorylates RNA polymerase

RNA polymerase II

_______________________ requires general transcription factors to initiate transcription

-Eukaryotic promoters contain a DNA sequence called TATA box

-TATA box is recognized by a subunit of TFIID, called TATA box binding protein (TBP)

-DNA is distorted -> allowing TFIIB to bind

-TFIIB helps position RNA polymerase at the start site

TATA box

Eukaryotic promoters contain a DNA sequence called ____________

TATA box binding protein (TBP)

TATA box is recognized by a subunit of TFIID, called ______________________

TFIIB

_________ helps position RNA polymerase at the start site

-binds when DNA is distorted

TFIIH

-opens double helix using energy provided ATP hydrolysis

-phosphorylates RNA pol II releasing it from transcription factors and allowing it to begin transcription

eukaryotic promoters

___________________ contain sequences that promote the binding of the general transcription factors

TATA box

TFIID binds to _______________ (T and A nucleotides) causing a distortion in the DNA

-eukaryotic gene transcription

mRNAs

eukaryotic ___________ are processed in the nucleus

RNA processing

Steps of _________________:

1. Capping

2. Polyadenylation

3. Splicing

phosphorylated RNA pol II tail

-RNA-processing proteins assemble on the ______________________

-Modifications occur in the nucleus as RNA is being synthesized.

-mRNA are exported to the cytosol via nuclear pores

capping and polyadenylation

-mark transcript as mRNA

-facilitate export to cytoplasm

-increase stability of mRNA

bacterial

a ___________________ gene consists of a single stretch of uninterrupted nucleotide sequence that encodes the amino acid sequence of a protein

eukaryotic

the protein-coding sequences of most ________________ genes (exons) are interrupted by noncoding sequences (introns).

DMD gene (dystrophin)

-78 introns

-occupies 2,000,000 bp on Chr. X

-mRNA is 14,100 nucleotides

-largest known gene

RNA splicing

introns are removed from pre-mRNAs by ________________

splicing sequences

special nucleotide sequences in a pre-mRNA transcript signal the beginning and the end of an intron

-for intron removal

splicesomes

splicing is carried out by a collection of RNA-protein complexes called ______________

spliceosome

_________________: composed of several snRNPs (U1, U2, U6)

-snRNPs (snurps) = small nuclear ribonucleoproteins

-proteins

-small nuclear RNA (snRNA)

RNA splicing

______________ is carried out by the snRNAs of the spliceosomes

ribozymes

_____________ are RNA molecules that function as catalysts