web_L23_10BIO311C - BIO 311C Spring 2010 Lecture 23 Friday...

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Unformatted text preview: BIO 311C Spring 2010 Lecture 23 Friday 26 Mar. I (JB) made two errors on the answer key for Exam 2. Multiple Questions 2 and 5 were incorrectly keyed. To compensate, we have added 4 points (= 4 percentage points) to all scores. Thus your recorded grade is 4 percent higher than the grade written on your exam. The correct key is now posted on the course web site and on Blackboard. Consider two reactions: one exergonic, the other endergonic ATP + H 2 O ADP + P i G = - 30 kJ/mol glucose + P i glu-6- P + H 2 O G = + 14 kJ/mol energy release as heat energy required ATPase glucose-6- phosphatase Generally energy cannot be transferred from one reaction to another unless the two reactions are coupled together in some way. Thus, the energy released in the reaction catalyzed by ATPase cannot be directed to the reaction catalyzed by glucose-6-phosphatase in order to produce glucose-6-phosphate unless the reactions occur in a very confined space such that the ATPase-catalyzed reaction substantially increases the concentration of P i , thereby increasing the G value of glu-6-phosphate-catalyzed reaction. note: The names of many enzymes end in ase". * 5 glu-6- + H 2 O * pushing effect ATP + H 2 O ADP + P i Glu + P i P ATPase-catalyzed reaction (exergonic) Glu-6-Phosphatase-catalyzed reaction (endergonic) Loose coupling of two reactions together In order for a pushing reaction to produce this effect on a second reaction: (1) both reactions must occur in the same compartment, (2) a product of the pushing must be a reactant of the reaction to be pushed, (3) the pushing reaction must be more exergonic than the is the reaction that is loosely coupled to it. 6 pushing reaction Reaction that is being pushed Some enzymes are capable of coupling an exergonic reaction to an endergonic reaction as a single coupled reaction, in order to drive the endergonic reaction in the forward direction. ATP + H 2 O ADP + P i G = - 30 kJ/mol glucose + P i glu-6- P + H 2 O G = + 14 kJ/mol ATPase glucose-6- phosphatase * loosly coupled reactions } ATP + glucose ADP + glu-6- P sum G = - 16 kJ/mol ATP + glucose ADP + glu-6- P A single tightly coupled reaction G = - 16 kJ/mol hexokinase Hexokinase is the name of an enzyme that activates glucose so that...
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web_L23_10BIO311C - BIO 311C Spring 2010 Lecture 23 Friday...

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