Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
History of RNA biology wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Non-coding RNA wikipedia , lookup
Messenger RNA wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Frameshift mutation wikipedia , lookup
Point mutation wikipedia , lookup
Epitranscriptome wikipedia , lookup
Transfer RNA wikipedia , lookup
Chapter 15 – The Genetic Code and Translation Beadle and Tatum • Neurospora crassa – Haploid orange bread mold – Haploid? • Prototrophs – grow on minimal media; auxotrophs can only grow on media that has been supplemented with substance that it can’t synthesize • Irradiated spores to induce mutations Beadle and Tatum • Irradiated spores first grown on complete media, then transferred to minimal media – Showed strains that had acquired mutations • Series of tubes with minimal media PLUS one additional ingredient – If strain grew, indicated mutation affected production of that substance Sib and Horowitz • Biochemical pathway for arginine production • I – grew in presence of ornithine, citrulline, arginine • II – grew in presence of citrulline and arginine • III – grew in presence of arginine • Which type codes for which enzyme? One gene/One enzyme • Each gene codes for one enzyme • Many proteins are composed of multiple polypeptides, each coded for by a different gene – One gene/one polypeptide Protein Structure • Polymer of 20 amino acids • Amino acid structure – – – – – Central carbon atom Hydrogen atom Amino group Carboxyl group R/radical group • What defines one amino acid • Each R group has different sizes/properties Amino acid linkage • Two amino acids covalently linked together by process of dehydration synthesis – Formed bond = peptide bond • Long chain called a polypeptide Levels of Protein Structure • Primary structure – Amino acid sequence • Secondary structure – Hydrogen bonds form alpha helices or beta sheets Levels of Protein Structure • Tertiary structure – Interactions between R groups • Quaternary structure – Only present in proteins composed of multiple polypeptide chains – How polypeptide subunits are associated to make a complete protein Genetic code • Nucleotide sequence must code for specific amino acids • Francis Crick – 3 nucleotides code for one amino acid – codon • 64 codons – 61 code for an amino acid – “degenerate” • More than one codon can code for the same amino acid Genetic code • tRNA – 30-50 tRNA for 20 amino acids – Isoaccepting tRNA have different anticodons but still carry the same amino acid • Wobble – 1st nucleotide in anticodon pairs with the 3rd codon of mRNA – Flexibility in bonding allows one tRNA to recognize more than one codon • Still codes for same amino acid Reading frame • Determined by the START/initiation codon – AUG – also codes for methionine • No overlapping or skipping of bases • Termination/stop codons – Also called nonsense codons • Universality – With rare exception, genetic code is read the same by all organisms tRNA charging • Attachment of appropriate amino acid • Aminoacyl-tRNA synthetase (20 different) – Recognize specific sequences in certain regions of tRNA, and binds the appropriate amino acid to 3′ acceptor arm of tRNA – Forms aminoacyl-tRNA Translation • Occurs at ribosomes – Attaches to 5′ end of mRNA and moves toward 3′ end – Binding determined by Shine-Dalgarno sequence in prokaryotic cells/ modifications in eukaryotic cells Initiation of translation • Ribosome has two subunits – small (30S) and large (50S) – Complete ribosome (70S) • Initiation factors bind to small unit, prohibiting small unit from binding with large subunit – Now free to bind to mRNA • Aminoacyl-tRNAmet attaches to initiation/ start codon • Large ribosomal subunit attaches Ribosome • Has three sites for tRNA – A (aminoacyl) site – P (peptidyl) site – E (exit) site • Initiator tRNAmet enters P site; all other tRNA first enter the A site – A→P→E Elongation • Next codon is exposed in the A site – Charged tRNA enters A • Peptide bond forms between the P site amino acid and A site amino acid – Peptidyl transferase • Translocation – – – – – ribosome moves down mRNA molecule P site tRNA enters E site A site tRNA with growing polypeptide enters P site A site now has next codon exposed; ready for next tRNA During next shift, E site tRNA is released into cytoplasm to be recharged with another specific amino acid Termination • A STOP codon enters A site – No appropriate tRNA • Release factors enter A site – Ribosome subunits dissociate – Polypeptide is released from last tRNA Post-translation modifications • Methionine cleaved off; chain possibly cleaved • Carbohydrates attached (forms glycoproteins) • Folding into proper 3D shape – Aided by chaperone proteins