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
transcription• initiation
• strands separate• promoter region
• elongation• RNA polymerase
• termination
incoming nucleoside triphosphates
pre-mRNA transcript
RNA POLYMERASE
5’ 5’
3’
5’ 3’
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 factors1. TFIID
• binds to TATA box (~25bp from start) or Inr
2. TFIIB 3. TFIIF / RNA polymerase II4. TFIIE - TFIIH
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
• messenger RNA - • carries message
about polypeptide• contains a sequence
of codons• three base
sequence • codes for an
amino acid
RNA 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
