Lecture 4 - EXAM II Fall term 2011 PROTEIN STRUCTURE AND...

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EXAM II Fall term 2011 PROTEIN STRUCTURE AND FUNCTION Lecture Goals 4. How is enzyme activity controlled? Be able to define and identify feedback control, allosteric control, reversible and irreversible inhibition, inhibition by covalent modification, and genetic control of enzymes. 5. What are vitamins? Be able to describe the two major classes of vitamins, the reasons vitamins are necessary in our diets, and the general results of excesses or deficiencies. Exam II Lecture #4, M, Oct 24, 2011 Enzymes and Vitamins Reading material, Chapter 19, pp. 606-621 Problem Set 5 (posted on CTools); due Tues, Nov 1st at the beginning of Discussion
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Application: Enzymes in Medical Diagnosis Measurement of blood enzymes is a valuable diagnostic tool in heart attacks (myocardial infarct) , and bone and liver damage. Information is gained about heart attacks by measuring LDH isozymes , structural variants of the same enzyme that catalyze the same reaction but in different tissues . LDH1 is present in heart; an elevated level compared to LDH2 is characteristic of a heart attack. When tissue is injured large quantities of enzymes are released; an example is release into the blood as a result of cell death. The levels of three enzymes vary over several days in response to a heart attack; CPK rises immediately, then decreases, AST triples over 40 hrs, the level of LDH doubles after ~ 4 days.
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19.7 Enzyme Regulation: Feedback and Allosteric Control Enzyme 1 Enzyme 2 Enzyme 3 A B C D Feedback Control The pathway in which A is converted to D undergoes feedback control if D inhibits Enzyme 1. Lecture Goal # 4. How is enzyme activity controlled? Biochemical reaction pathways are dependent on a series of consecutive reactions in which a product of one reaction is the reactant of the next reaction, and so on. Such pathways are dependent on feedback control, which occurs when the result feeds information back to affect the beginning of the process Why does D inhibit Enzyme 1? The overall goal of the reaction is to produce D; by inhibiting Enzyme 1 no energy is wasted in producing the intermediates B and C.
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Allosteric control Allosteric control involves the binding of a molecule (an allosteric regulator or effector) at a site (NOT the active site) on the enzyme which affects the binding of another molecule at a different site. The word allosteric means other space . Allosterically regulated proteins may be composed of more than one subunit (chain) and two kinds of binding sites, one for the substrate (reactant) and one for the regulator.
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– negative or positive Allosteric control can be negative or positive; binding a negative effector changes the active site so the enzyme is a less effective catalyst and the rate slows down. An advantage of allosteric control is the effector does not need to be structurally similar to the
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Lecture 4 - EXAM II Fall term 2011 PROTEIN STRUCTURE AND...

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