Transcription steps Initiation at 5 end of gene binding of RNA polymerase to promoter unwinding of DNA Elongation addition of nucleotides to 3 end rules of base pairing requires Mg 2+ energy from NTP substrates Termination 5 UTR coding region at 3 end of gene terminator loop (prokaryote) or processing enzyme 3 UTR Transcription steps Initiation at 5 end of gene binding of RNA polymerase to promoter unwinding of DNA Elongation addition of nucleotides to 3 end rules of base pairing requires Mg 2+ energy from NTP substrates Termination 5 UTR coding region at 3 end of gene terminator loop (prokaryote) or processing enzyme 3 UTR Eukaryote RNA processing 5 end: capping addition of 7-methylguanosine linked by three phosphates 3 end: poly(a) tail addition of up to 200 adenine nucleotides downstream of AAUAAA polyadenylation signal Intron removal by spliceosome all introns have 5 GU and 3 AG recognition sequence (GU AG rule) snrnps of spliceosome provide catalysis intron excised as lariat, destroyed Some nonproteinencoding genes have self-splicing introns.
Eukaryote RNA processing 5 end: capping addition of 7-methylguanosine linked by three phosphates 3 end: poly(a) tail addition of up to 200 adenine nucleotides downstream of AAUAAA polyadenylation signal Intron removal by spliceosome all introns have 5 GU and 3 AG recognition sequence (GU AG rule) snrnps of spliceosome provide catalysis intron excised as lariat, destroyed Some nonproteinencoding genes have self-splicing introns. Eukaryote RNA processing 5 end: capping addition of 7-methylguanosine linked by three phosphates 3 end: poly(a) tail addition of up to 200 adenine nucleotides downstream of AAUAAA polyadenylation signal Intron removal by spliceosome all introns have 5 GU and 3 AG recognition sequence (GU AG rule) snrnps of spliceosome provide catalysis intron excised as lariat, destroyed Some nonproteinencoding genes have self-splicing introns.
Protein structure Protein is polymer of amino acids (polypeptide) each amino acid has R group conferring unique properties amino acids connected by peptide bond each polypeptide has amino end and carboxyl end Structures primary: amino acid sequence secondary: hydrogen bonding, α-helix and β-sheet tertiary: folding of secondary structure quaternary: two or more tertiary structures Shape and function determined by primary structure encoded by gene Protein structure Protein is polymer of amino acids (polypeptide) each amino acid has R group conferring unique properties amino acids connected by peptide bond each polypeptide has amino end and carboxyl end Structures primary: amino acid sequence secondary: hydrogen bonding, α-helix and β-sheet tertiary: folding of secondary structure quaternary: two or more tertiary structures Shape and function determined by primary structure encoded by gene
Translation mrna is translated by trna at ribosome nucleotide sequence is read three nucleotides at a time each triplet is called a codon each amino acid has one or more codons 64 possible codons (4 4 4) = genetic code used by all organisms with few exceptions Genetic code specifies 20 different amino acids (sometimes selenocysteine) trna anticodon consists of 3 nucleotides base pairs with codon in antiparallel fashion 3 acceptor end attaches amino acid attachment catalyzed by aminoacyl-trna synthetases one for each different trna Wobble hypothesis permits third nucleotide of anticodon (5 end) to hydrogen bond with alternative nucleotide permits a trna to translate more than one codon Codon translation
Translation at the ribosome Ribosome large subunit small subunit 3 ribosomal sites A site (amino site), accepts incoming charged trna P site (polypeptide site), peptide bond E site (exit site), trna exits ribosome Amino terminus synthesized first, beginning near 5 end of mrna
Translation at the ribosome Ribosome large subunit small subunit 3 ribosomal sites A site (amino site), accepts incoming charged trna P site (polypeptide site), peptide bond E site (exit site), trna exits ribosome Amino terminus synthesized first, beginning near 5 end of mrna Stages of translation Initiation ribosome recognition prokaryotes: mrna Shine-Delgarno sequence which hydrogen bonds with rrna eukaryotes: ribosome attaches to 5 cap trna met binds to AUG codon N-formylmethionine used in prokaryotes, later removed Elongation: use of elongation factors and GTP Termination ribosome pauses at stop codon release factor binds, complex dissociates Protein function Function determined by amino acid sequence Colinearity between DNA nucleotide sequence and amino acid sequence of protein Two broad types of protein structural proteins active proteins, including enzymes Proteins often have specialized domains