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Kevin

You have a monosubstrate enzyme with 4 ground states in the energy diagram. So you need a mechanism that incorporates both of these facts. E+S to ES to EP to E+P is the most straight forward, but any mechanism that incorporates these two facts and doesn't violate any other enzyme truths would work. Whatever your mechanism is, the last step has to be rate limiting because it's Ea is the biggest. 15 May 2008

Kevin |

Christine, Done. Megan, #5: You have 1 mol of the buffering molecule and a pH less than the pKa. While you can certainly buffer something, you can't buffer 0.5 mol or more because of the relative position of the pH value (which means there's more HA than A to start). This leaves 0.25 as the only valid answer. #10: It's a basic amino acid, which means that the ionizable side chain is an amine and pos charged below its pKa value. So you need to average the pK2 and the pKR to have a neutral species. The AA would be +1 at pH 5.6. 15 May 2008

Megan |

A couple questions from the first exam. For # 5 MC how did you arrive at .25 moles as the answer? For # 10 MC, why wouldn't it be 5.6 Thanks! 15 May 2008

Christine |

could you please post another practice buffer problem? Thanks! 15 May 2008

Kevin |

You do not need to know structures of metabolites by name. Just the AAs/peptides, FAs (by numerical nomenclature), GPL head groups, generic GPLs, sterol ring structure, aldoses/ketoses, pyranoses/furanoses, etc. In other words, no structural responsibilities beyond what you've had already. However, regarding the metabolite structure: while you won't have to recognize or draw them by name, I should be able to give you metabolite structures and ask you whether redox chemistry or hydration or isomerization, etc. has taken place. 15 May 2008

Kelsey |

what structures, other than AA, FA, and th basic structures, should we know? for example, I'm assuming we need to know choline- and other headgroups in that table? do we also need to know, for example, structures of pyruvate and succinate? 15 May 2008

Kevin |

Yvo, Lipoic acid is one of the cofactors in pyruvate decarboxylase. It works via a disulfide / dithiol exchange (a redox process). AdoMet is S-adenosyl methionine which is a cofactor that deals with single carbon transfer reactions. Cheers, K 14 May 2008

Yvonne |

Hola! Can you explain number 4 on the practice final? What's lipoic acid, why would it be involved in redox chemistry, what's AdoMet, and why wouldn't it be involved in redox chemistry? Thanks! 14 May 2008

Kevin |

You don't need to go in depth on that at all. Just know what it is. No enzymes or steps. Just know that it exists to get the reducing equivalents from glycolysis into the mitochondria to make ATP. The glycerol-3-phosphate shuttle is just an alternative pathway that does the same thing. They just exist in different tissues. 14 May 2008

Rosie |

Hi Kevin, How in depth do you want us to go in regards to the malate/asp shuttle? should we know specific steps/enzymes/what not? Also, I don't understand where exactly the shuttle contributes (I know it's to do with e- transport) compared to the glycerol 3-P shuttle that sends e- to Q. Thanks! 14 May 2008

Kevin |

Hi Student Feldman (you can call me Kevin already!!), Your interpretation is correct. You will not be expected to recreate a derivation. However, you will need to know what the steady assumption means, what the Km refers to, the reasoning behind the Hill plot, the origin of the theta plot, etc. Cheers, Kevin 14 May 2008