lecture 20: gene expression

CH 9

transcription happens:

DNA to RNA

translation happens:

Rna to protein

does both strands of the DNA double helix serve as a template for a single-stranded RNA transcript

No, just ONE strand

The RNA strand is formed through

complementary base pairing

both strands of DNA can be used for transcription

TRUE

the template strand varies from gene to gene, depending of the promotor orientation (the transcript elongates in the 5’-to-3’ direction)

if top strand is used : right to left

if bottom strand is used: left to right

major differences in RNA:

-sugar-phosphate backbone hs the sugar ribose, not deoxyribose

-uracil replaces thymine, and pairs with adenine

hydrogen bonding is transient, and the RNA transcript is displaced soon after nucleotides are added

3 major steps of transcription (prokaryotes as model)

-promotors (initiation)

-RNA polymerase (elongation)

-terminators (termination)

promotors (initiation)

DNA sequences that provide the signal to RNA polymerase for starting transcription

RNA polymerase (elongation)

adds nucleotides in 5’-to-3’ direction

-same direction (synthesize dna)

terminators (terminaton)

RNA sequences that provide the signal to RNA polymerase for stopping transcription

what happens in initiation

RNA polymerase binds to promoter sequence located near beginning of gene

•Region of DNA is unwound to form open promoter complex

•Phosphodiester bonds formed between first two nucleotides

what happens in elongation

Core RNA polymerase loses affinity for promoter, moves in 3’-to-5’ direction on template strand

-Within transcription bubble, NTPs added to 3’end of nascent mRNA

what happens is termination

Terminators are RNA sequences that signal the end of transcription

•Usually form hairpin loops (intramolecular H-bonding)

the product of transcription is a…

single-stranded primary transcript

In prokaryotes, the primary transcript is

the mRNA

In eukaryotes, the primary transcript is processes to make an

mRNA