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Lecture 3

PSYD33 Lecture 3.docx

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University of Toronto Scarborough
David Nussbaum

PSYD33 Lecture 3: January 25, 2012 Film  Adaptor molecule  tRNA  basis for DNA: atcg  Acridines  Deleting or adding one base pair for viral DNA, o Induce 1 mutation in gene or virus, all amino acid will get changed; get shifted o If eliminated 2 base pairs, same result o But if eliminate/ add 3 base pairs, remaining portion of that gene will make sense (amino acid sequence will all be in register) o E.x. “old men are fun”  Genetic code made of 3 bases each  Codons: each codon representing a unique protein/ amino acid  Each codon codes for 3 base pairings in DNA  Protein = strings of amino acid  20 essential amino acids in mammals, humans  Genetic code: sequence of DNA with 3 base pairings; that through RNA – specific for an amino acid  Phenylalanine  Codon UUU = phenylalanine  Codon AAA = lysine  Codon CCC = proline  Codon GGG = glycine  Specific nucleotides pairings; when 3 together (genetic word/ codon) attracts particular amino acid in protein chain  Early days, figured out genetic code by first using same word consisting of same base pairings and see which amino acid was produced by it  Strings of protein consisting of same amino acid = UUU  Then putting in different letters in different codons in different proportions  and seeing what it looked like  Found, by experimental error – getting same portion of amino acid in protein chain in portion of the codons that went into mixture  Showed process of how DNA ultimate protein sequence was discovered  Relationship btw nucleotides and amino acids  64 possible combinations = codons and 20 amino acids  Some amino acids coded for by more than one codon  redundancy  i.e. UCU, UCC, UCA, UCG = all code for serine  with 3 positions for letters in word (UCGA) = 64 possibilities; each codes for a particular amino acid  particular codon codes for particular amino acid in eventual protein produced by that gene  each codon, each sequence of 3 basis; only codes for 1 amino acid  lack of ambiguity but redundancy  only differs by last position; same first 2 positions  3 stop codon: don’t code for a particular amino acid – serve as punctuation – that message ends here  Signaling that protein is complete  1 codon = AUG  codes for methionine + and also functions as start codon (start signal)  All mRNA begins with AUG  Serves as unambiguous marker for starting where start – beginning of set of 3 elements interpereted as codon  Know where to start defining the triplets; where to read the genetic code  Beginning of reading frame  mRNA starts with AUG  that’s the first triplet and anything after that in triplets is the genetic code  start and stop codons – where new protein is to start and stop  RNA produced attracted to amino acids btw start and stop codons  All polypeptides start with methionine  Universal; every genetic system using same triplet code  Same codon assigned to same amino acid; same start and stop codons  Genetic engineering – take gene in one organism and function in another organism  Replication, transcription and translation – differs little btw organism  Machinery recognizes same code – read same sequence  Ex. Take gene produces human insulin into e.Coli bacteria – produce human insulin quickly which we can then use  Modify organisms by inserting DNA- plants less susceptible to insects, anti- freezing – more resistant = genetically modified organisms (GMA)  Gene therapy = modifying ourselves  Take functional version of that gene into cells of individual; another source of producing gene product to substitute for diseased gene  Genetic code = universal code  Shared vocabulary of genetic code suggests all life arose from single organism long time ago  Sequence of amino acid and nucleotides – arose early in origin of life From DNA to RNA = TRANSCRIPTION (copy)  (Replication) DNA  (transcription) RNA  (translation) Protein synthesis  Transcription: DNA directed RNA synthesis (DNA  RNA)  RNA as nucleic acid – sequence of nucleotides  DNA rasncribed into RNA form  Function of RNA = act as intermediate/ messenger from DNA onto proteins through translation  DNA + RNA as nucleic acids  Key enzyme = RNA polymerase (make more RNA)  depends on complimentary base pairings of nucleotides (AUGC = A+U; C+G)  Transcription requires DNA to unwind from double helix structure by RNA polymerase  RNA polymerase adds complimentary bases  Transcription vs. Replication  Helicase to unwind double helix  RNA polymerase can open up helix itself  Only one of DNA strand is transcribed by RNA polymerase o Only need one side transcribed because other side would be same information (complimentary info)  Both strands independently replicated by DNA polymerase  Sits on strand, adding bases  Template strand = holds info that we’re interested  As RNA polymerase goes down strand, synthesizing single molecule of RN
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