“central dogma of molecular biology” central dogma - .central dogma - rna chapter 7 central...

central dogma - RNA

chapter 7

central dogma • “central dogma of molecular biology”

• originally coined by Francis Crick • not actually dogma • describes how DNA replicates and codes for proteins

• protein coding • DNA unwinds

• strands separate • transcription • translation

amplification • transcription

• many RNA copies can be made • translation

• many polypeptide copies can be made from each mRNA

transcription • initiation

• strands separate • promoter region

• elongation • RNA polymerase

• termination RNA

polymerase

direction of transcription

free nucleotides

template

transcription • initiation

• strands separate • promoter region

• elongation • RNA polymerase

• termination

eukaryotic transcription • more complex than prokaryotes

• 3 different polymerases • require general transcription factors • genes spread out along DNA

• large variety of regulatory sequences • more compact chromatin

eukaryotic transcription • initiation (PIC complex)

• general transcription factors 1. TFIID

• binds to TATA box (~25bp from start) or Inr 2. TFIIB 3. TFIIF / RNA polymerase II 4. TFIIE - TFIIH

TFIID

TFIIB

TFIIFTFIIH

TFIIE

• messenger RNA - • carries message

about polypeptide • contains a sequence

of codons • three base

sequence • codes for an

amino acid

RNA

• messenger RNA - • carries message

about polypeptide • contains a sequence

of codons • three base

sequence • codes for an

amino acid

RNA eukaryotic genomes • processing of mRNAs

• prokaryotes • mRNA immediately attaches

to ribosome • eukaryotes

• capping • splicing • polyadenylation

pre-mRNA splicing • splicing pre-mRNAs

• introns - intervening sequences • exons - expressed sequences • RNA splicing

• introns must be removed • introns contain splicing signals • carried out by spliceosome

• snRNPs (small nuclear ribonucleoproteins)

• splicing can affect protein produced

• same gene may produce different proteins

exporting mRNA • mRNA export

• poly-A-binding proteins • cap-binding complex • exon junction complex

• proteins bound to sites of connected exons • nuclear pore complex

• properly tagged mRNA is exported

RNA • transfer RNA

• present in the cytoplasm • carry the 20 amino acids • charged by aminoacyl-tRNA synthetases • anticodon

• ribosomes • large subunit

• 3 tRNA binding sites • 2x as big (mass)

• small subunit • mRNA binding site

E P A

assembly

G G G U U U U GC UG C

translation • three phases

• initiation • elongation

• codon recognition • peptide bond formation • translocation

• termination

• three phases • initiation • elongation

• codon recognition • peptide bond formation • translocation

• termination

translation

ribosomes • polyribosomes

• often multiple ribosomes act on mRNA • multiple copies at once

• bound ribosomes • polypeptide signals binding

ribosomes • polyribosomes

• often multiple ribosomes act on mRNA • multiple copies at once

• bound ribosomes • polypeptide signals binding

digesting proteins • controlling amounts of proteins

• proteases • proteolysis • different proteases activated at different times

• proteasomes • digest short-lived or malfolded proteins • cytosol and nucleus • protease core