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From Gene to Protein

17. From Gene to Protein. Science as a process. 1909: Archibald Garrod : genes  enzymes  proteins 1930: Beadle and Ephruss : Drosophila eye color can be mutated by preventing the production of enzymes that catalyze pigment synthesis. Beadle and Tatum: Bread mold neurospora crassa

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From Gene to Protein

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  1. 17 From Gene to Protein

  2. Science as a process • 1909: Archibald Garrod: genes enzymes  proteins • 1930: Beadle and Ephruss: Drosophila eye color can be mutated by preventing the production of enzymes that catalyze pigment synthesis. • Beadle and Tatum: Bread mold neurosporacrassa • Wild type: needed only minimal media to grow • Mutant type: auxotrophs: needed complete media (all 20 amino acids) to grow • Separated vials with minimal media and single additional nutrient, wanted to isolate the metabolic defect • Precursorornithine(class I mutant)citrulline (class II mutant)arginie (class III mutant) • Led to one gene one enzyme hypotheis • Revised now: one gene one PROTEIN or one gene one polypeptide

  3. Pathway • DNA mRNA polypeptide/protein

  4. THE CODE • Triplet code: 3 nucleotides for each amino acid, called a _____________ • DNA template strand mRNA • Complementary base pairing, but RNA has __ instead of ___. A to __, C to G, T to A, G to C • Cracking the code: • 1961: 1st amino acid; Marshall Nirenberg synthesized artificial UUU and always got the amino acid phenylalanine. All 64 codons were decifered in the 1960’s.

  5. Code Continued • AUG: Methione and _________ signal go ahead for translation. • 3 stop codons • Redundancy: more than one codon per amino acid, but no ambiguity (codon only codes for one amino acid); codes are read from left to right, nonoverlapping • Genetic code is nearly universal

  6. Closer look at Transcription • RNA polymerase: Separates DNA strands and adds RNA nucleotides; elongates in the 5’ to 3’ direction. • 1. Initiation: ____________: where DNA and RNA polymerase initiate transcription • In Eukaryotes: Transcription factors proteins that bind promoter to help RNA polymerase bind (Transcription Initiation Complex) • ____________: Transcription factor that binds TATA sequence, then RNA polymerase binds

  7. Transcription Continued • 2. Elongation: RNA polymerase adds nucleotides to the 3’ end, may be many mRNA’s following each other • 3. Termination: DNA “terminator” codes for RNA terminator. Eukaryotes: enzyme cleaves mRNA 10-35 nucleotides after terminator.

  8. Modification after Transcription (Eukaryotes) • mRNA ends: adds a _____(guanine nucleotide) to protect against degradation from enzymes and is the attachment site for ribosomes, on other end adds 30-200 adenines called a ______________ to protect and facilitate export from the nucleus. • RNA splicing: ________ are noncoding segments dispersed within the coding segments called _______. snRNP’s (aka __________) recognize splice sequences at the ends of introns, join with a protein to form a ____________ which cuts and releases introns and reseals the exons.

  9. Closer look at Translation • tRNA: _______ RNA: transfers amino acids from cytoplasm to ribosome. • tRNA joins amino acid by the enzyme ________________________.

  10. Side note • Relaxed base pairing rules: ___________: sometimes U in 3rd position can bind A or G. May also have I (Inosine) in the third position that can bind A, U or C. • Don’t worry about this for the test!

  11. Ribosomes • Large and small subunit; made up of proteins and rRNA (ribosomal); made in the _____________ of eukaryotes. • Subunits don’t attach until mRNA is present. • Application: tetracycline and streptomycin antibiotics paralyze prokaryotic ribosomes without hurting eukaryotic ribosomes.

  12. 3 Phases • 1. Initiation: Small subunit binds with ______ of mRNA and an initiator tRNA (binds to start codonAUG); large subunit binds to form a ____________________________. Proteins with GTP (energy) are required, tRNA with amino acid moves to P site, A is vacant for next tRNA • 2. Elongation: mRNA codon binds tRNAanticodon in A site, ribozyme (side note: RNA enzyme) in large subunit catalyzes binding of polypeptide in P to new amino acid in A, tRNA in A site moves to P site (tRNA in P moves to E and exits) • 3. Termination: Stop codons ____, ____, or ____ signal release of protein that binds the codon in the A site, adds water instead of amino acid to ______________ polypeptide from the ribosome

  13. Eukarotesvs Prokaryotes • Prokaryotes: can have __________ and __________ at the same time. • Eukaryotes: ____________ in the nucleus, _______________ in the cytoplasm.

  14. Mutations: changes in genetic material • Point mutations: 1 or few base pairs ex. Sickle cell-mutation of 1 base pair in the gene that codes for hemoglobin • 1. Base pair substitution: replacement of one nucleotide; could be ________ (no effect on protein) or ________ disrupts protein. (missense-change to another amino acid, nonsense-change to a ________ signal). • 2. Insertions and deletions: adding or losing a base pair. Frameshift mutation: alters reading frame, often disastrous effect.

  15. Mutagens: Interact with DNA to cause mutations • _______light, X rays • Base analogues: similar to DNA bases but pair incorrectly during DNA replication • AMES test: EX. bacteria with a point mutation –can’t make histidine. Amount of bacteria that grows on histidine lacking medium = strength of mutation

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