Week 7, Lecture 1, Proteins and Protein Structure

Week 7, Lecture 1, Proteins and Protein Structure - FROM...

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1 You are responsible for Section F-27 and F-28 Proteins and Protein Structure 17-Oct-09 Gardiner 1 B I O L O G Y FROM GENE 0 2 3 O PROTEIN Genes and Proteins • Archibald Garrod – 1909 – Suggested genes dictate phenotypes via enzymes 17-Oct-09 Gardiner 3 • Beadle and Tatum - Neurospora mutants to show one gene one enzyme hypothesis 17-Oct-09 Gardiner 4 Fig. 14.2 Genes and Proteins • Not all proteins are enzymes so the hypothesis became one gene one protein However some proteins such as 17-Oct-09 Gardiner 6 • However some proteins such as haemoglobin are made up of two kinds of polypeptides and so coded for by two genes One Gene One Polypeptide
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2 Fig. 14.3 During transcription, one DNA strand, the template strand , provides a template for ordering the sequence of nucleotides in an RNA transcript. The complementary RNA molecule is synthesized according to base-pairing rules except that uracil is rules, except that uracil is the complementary base to adenine. During translation, blocks of three nucleotides, codons , are decoded into a sequence of amino acids. Fig. 14.4 B I O L O G Y Codons • If each base translated to an amino acid there could be only 4 and not 20 • A 2 base code could give 16, still not enough 0 2 3 17-Oct-09 Gardiner 9 • Triplets are the smallest number that can code for all possible amino acids The Code • There is redundancy but not ambiguity • Two codons may specify the same amino acid but no others rd 17-Oct-09 Gardiner 10 – Sometimes these only differ in 3 base • Reading frame – mRNA read in 5’ 3’ direction Breaking The Code • Marshall Nirenberg in 1961 • Made poly-uracil RNA sequence – UUUUUUUUUUUUU………. 17-Oct-09 Gardiner 11 • Used a cell free translation system and found they only got a polypeptide that consisted of phenylalanines • Extending the work they determined the other codons By the mid-1960s the entire code was deciphered. 61 of 64 triplets code for amino acids. The codon AUG not only codes for the amino acid methionine amino acid methionine but also indicates the start of translation. Three codons do not indicate amino acids but signal the termination of translation. Fig. 14.5
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3 B I O L O G Y Specific sequences of nucleotides along the DNA mark where gene transcription begins and ends. RNA polymerase attaches and initiates
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Week 7, Lecture 1, Proteins and Protein Structure - FROM...

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