TEST 2 2018 - BCHE 5180/6180 Spring 2018 Test 2 Dr E C Duin...

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1 10 points List and describe the posttranslational modifications that take place at the N-terminus. If this information is available, describe the function of these modifications. - Removal of Met: The initiating amino acid in all proteins is Met, which is formylated in prokaryotes (N-formylmethionine). In many proteins (pro-/eukaryotic) the formyl group and the Met residue is cleaved off. This creates a wider variety of amino acids at this position which affect the half-life of the protein. - Acetylation: The N-terminus is acetylated. 50% of eukaryotic proteins are modified in this way, 90% of human cytosolic proteins - Fatty acyl groups: Fatty-acid-associated proteins can be attached to the lipid bilayer of the membrane and are usually membrane proteins 2 10 points How does a change to low (or high) pH unfold a protein? Low pH, for example, causes protonation of the side chains of Asp, Glu, and His. For Asp and Glu that will be a change to a neutral species. If any of these charge residues were involved in electrostatic interactions, the loss of these causes the enzyme to become unstable and local structural changes will take place resulting in partial unfolding and exposing more of underlying hydrophobic amino acids to water and the harsh pH. For the His the side group changes from uncharged to positively charged. Having this charged in an area that was previously completely uncharged can cause structural changes too. The cascade of structural changes causes the whole protein to unfold. BCHE 5180/6180 Name: Spring 2018 Test 2 Dr. E. C. Duin AU Username:
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2 3 10 points Describe in detail the mechanism of protein folding by the chaperones DnaJ/DnaK.
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