Chapter 17

The Central Dogma

Transcription & TranslationThree main steps for each:

InitiationElongationTermination

Transcription: Initiation Promoters (TATAA) & transcription factors RNA Polymerase II & transcription initiation

complex DNA unwinds, transcription begins

Transcription: Elongation

RNA nucleotides added in 5’ to 3’ direction

Transcription: Termination

Prokaryotes: terminator signal

Transcription: Termination

Eukaryotes: polyadenylation signal sequence

RNA Processing in Eukaryotes5’ guanine cap & 3’ poly-A tail added

Facilitate export from nucleusPrevent degradation

RNA Processing in EukaryotesSpliceosome of

snRNP removes introns, leaves exons

RNA Processing in Eukaryotes

Translation – Basic InfoIn cytoplasmCodonsWobble

Translation – Basic InfoAnticodons & tRNA

Translation – Basic InfoAminoacyl tRNA synthetase

Translation – Basic InforRNA (ribosome) – two

subunits

Translation - InitiationInitiator tRNA hydrogen bonds at start codon (AUG)Requires GTPInitiation factors attach ribosomal subunits

Translation - ElongationA new tRNA with complementary anticodon

bonds at the A site.Requires GTP

Translation - ElongationPeptide bond forms between amino acids at P

& A sites

Translation - ElongationTranslocationRequires GTPEmpty tRNA is released

Translation - Elongation

Process repeats

Translation - TerminationRelease factor bonds at stop codon (UAG,

UAA, UGA)Hydrolyzes bond between peptide chain &

last tRNAAssembly separates

Translation

Polyribosomes

Free vs. Bound RibosomesAll start freeSignal peptide sequence on those bound for

ERSignal-recognition particle (SRP) attaches

Prokaryotes vs. EukaryotesDifferent RNA polymerasesDifferent transcription terminationDifferent sized ribosomal subunits

Prokaryotes vs. Eukaryotes

Coupled T & T in prokaryotes