Lecture 7.docx

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University of California - Irvine
Biological Sciences
Alexander Mc Pherson

Lecture 7 02/05/2014 Protein Structure & Protein Folding Amphensen's dogma - 3D structure of protein = function Disulfide bonds on ribonuclease Though this is not always true, not all proteins can be denatured and refolded Looking at all the hemoglobin, the 3D structure for all of them look very similar The backbone is very similar in size & shape But the variation of amino acid sequence also matters This tells us that different sequence of amino acids can produce a similar structure The high identity among protein tells us that they produce a similar structure Thus there is a tremendous redundancy across proteins, as long as the structure is okay and key amino acids in the important location, the backbone sequence may not have to be exactly the same Conserved Residues are regions where His (the active site) and the Cysteine (S-S) We can determine the phylogenetic relationship by looking at the redundancy of amino acid sequence across species Divergent Evolution Start with a precursor (primordial Dehydroenase) Then Diverges, creates similar but different Dehydrogenases with similar function Lecture 7 Convergent Evolution Trypsin: digests meat Looking at Trypsin, there are 3 conserved residues that perform the catalytic activity Looking at E. Sutlus: the 3 key residues are in the same place, but the rest of the sequence is much different We know that Humans are not from E. Sutulus, but this tells us that there is an ideal constellation (specific residues) that gives the best conditions for a catalytic reaction Gene Duplication An organism has 2 genes that are similar One of the genes mutates The mutation allows for a new biochemical activity Gene Fusion A transposition of 1 gene, close to another one During transcription, both genes are transcribed together forming 1 peptide This allows for new Biochemical Function Margoliask Sequenced Cytochrome C Present in all organism 104 residues in animals, 112 plant, 108 yeast From 50 different species, 27aa are invariant (the same) Lecture 7 This tells us these 27aa are necessary This does not tell us that we can any aa in the rest of the structure Residue differences between species is proportional to phylogenetic differences Protein Folding Problem Not all proteins will fold without Chaperone proteins These produce a special container, and a special environment for folding We don't actually know how protein structure is determined by AA sequence How it came about? Heat shocked flies, and these flies produced Chaperones Anthensen's experiment is not always true Membrane proteins also do not fold by themselves They only fold properly if they fold in a lipid environment This is what the rough ER does Hemoglobin will not fold properly unless in the presence of the heme What do proteins look like? Ribbon structure? Beads on a string?
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