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10 Cards in this Set
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ATP hydrolysis can be COUPLED toan endergonic reaction to make that reaction happen. For example, an unfavorable reaction with a DG of _____ could be driven (or fueled) by a mole ofATP. a) +5.5 kcal/mole b) +8.0kcal/mole c) −14.6kcal/mole d) −7.3kcal/mole e) 0kcal/mole |
A The DG of ATP hydrolysis—an exergonic reaction—is −7.3 kcal/mole. ATP hydrolysis can be used to fuel anendergonic reaction—one with a positive DG—that requires LESS THAN 7.3 kcal/mole. |
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During coupling, HOW is ATPactually USED to make a reaction happen (see Figure 8.9)? A phosphate istransferred from ATP to a reactant. It catalyzes the reaction. Italters the rate of the reaction. Itprovides heat energy. Itis dehydrated. |
A phosphate is transferred from ATP to a reactant Phosphorylation is the basic mechanism by which ATP is used to dowork. Either a REACTANT (as seenin Figure 8.9) or a PROTEIN (as seen in Figure 7.18) may be phosphorylated. In steps 1 and 3 of glycolysis, phosphorylation is used to boost the energy ofmetabolic intermediates. |
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How exactly does ATP drive thesodium-potassium pump (see Figure 7.18)? Aphosphate is transferred from ATP to the pump. It travels across the membrane through the pump. It becomes covalently attached to the pump. It attracts sodium so that it crosses the membrane andenters the cell. |
A phosphate is transferred from ATP to the pump |
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Does ALLOSTERIC regulationSTIMULATE or INHIBIT an enzyme’s activity?stimulates inhibits either stimulates orinhibits neither stimulates nor inhibits |
Either stimulates or inhibits |
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Isoleucine biosynthesis isregulated by FEEDBACK INHIBITION; an early step of its metabolic pathway isblocked at high concentrations of _____. threonine isoleucine intermediateA intermediate D all ofthese answers are correct |
Isoleucine As the concentration of the final product increases it binds moreoften to this enzyme, effectively shutting off the pathway from that pointonward. The pathway will remainoff until the product’s concentration drops again. Note that it is not always the first step of the pathwaythat is regulated, but merely an earlystep. For example, cellularrespiration is regulated through the enzyme _____ which catalyzes the _____step of _____. |
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During feedback inhibition ofisoleucine synthesis, which of the following molecule(s) stops being made? threonine isoleucine intermediateA morethan one of these answers are correct all ofthese answers are correct |
More than one of the answers are correct First, the product of the reaction that is catalyzed by thedeactivated enzyme (in this case, intermediate A) stops being made. The remaining ‘A’ will be converted to‘B’, ‘B’ will be converted to ‘C’, and so on until all of these intermediatesrun out and isoleucine stops being made. As mentioned above, the pathway remains off untilisoleucine becomes scarce again. |
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Regulation occurs through the enzyme threoninedeaminase, whose activity is curtailed through _____. competitive inhibition noncompetitiveinhibition normal binding threonine inhibition |
Noncompetitive inhibition Notice that it has an allostericsite in addition to its active site! |
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If the activity of threoninedeaminase is completely inhibited, would you expect greater concentrations ofthreonine to increase activity? YES, greater concentrations of threonine would out-competethe inhibitor and increase activity. NO, greaterconcentrations of threonine would not be able to out-compete the inhibitor, soinhibition would continue. |
No Competition between the substrate and the regulatory molecule occurswhen both molecules are capable of binding to the active site; this is known ascompetitive inhibition. |
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Threonine deaminase binds threoninethrough _____ interactions. weak covalent disulfide bond glycosidic permanent |
Weak Binding ofthreonine occurs at the active siteof the enzyme. |
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How are lysosomal hydrolases localized in a cell? they are confinedtogether within an organelle they are embedded within a membrane they are bound together into complexes of enzymes |
They are confined together within an organelle Confining the hydrolytic enzymes to thelysosome both protects the cell from the enzymes as well as insures that theenzymes are only active within thelysosome (and not for example in the ER, where they are constructed). This is accomplished by controlling pH;the enzymes are most active at a pH of 5, and only the interior of lysosomes havea pH this low! (pH control isdescribed in the textbook.) |
