BRIEFLY J answer 5 of the following questions (2 pts each):

1. Identify three effects that contribute to the thermodynamic driving force for hydrolysis of the phosphoanhydride in ATP. If hydrolysis of ATP is so exergonic, why doesn’t it hydrolyze more readily in the absence of enzymes?

(1/2 pt each)

• electrostatic repulsion between negative phosphoryl groups.
• Resonance stabilization
• Less solvation energy for ATP than hydrolyzed product
• Hydrolysis of ATP is thermodynamically favored, but not kinetically favored. Enzymes are required to decrease the free energy of activation.

1. Why are NADH and NADPH not metabolically interchangeable?

Different enzyme specificities determine divergent methabolic paths of NADH and NADPH

2. Describe the role of coupled reactions in metabolism, give an example of a coupled reaction in one of the biochemical pathways we have covered AND identify the high energy compound in the reaction.

• In coupled reactions, one exergonic reaction drives an endergonic reaction (1/2 pt).
• An example is provided by the two half reactions below (1 pt):

Reaction 1: F6P + Pi -> FBP D G >0

Reaction 2: ATP + H2O -> ADP + Pi D G <0

Sum D G <0

• ATP is the high energy compound in the above coupled reaction (1/2 pt).

1. What enzymes catalyze the 3 irreversible (far from equilibrium) reactions in glycolysis? What is the significance of a large negative D G in general, and which of the 3 irreversible reactions in glycolysis is the most important regulatory site?

• Enzymes that catalyze the 3 irreversible reactions in glycolysis (1 pt)

• Significance of D G <<< 0: A large negative D G means the reaction is irreversible and thus a potentially important regulatory site (1/2 pt).
• Phosphofructokinase catalyzes phosphorylation of F6P to F1,6P and is the most important regulatory site in glycolysis (rate limiting reaction; committed step) (1/2 pt).

1. List 4 means to regulate metabolic flux. Identify which modes of regulation are most important for the rate limiting enzyme in glycolysis AND the rate limiting enzyme in glycogenolysis.

• Substrate Cycling (1/4 pt)
• Allosteric Effectors (1/4 pt)
• Covalent Modification (eg phosphorylation) (1/4 pt)
• Genetic Control (enzyme induction) (1/4 pt)

1. Identify each of the following pathways or processes and indicate if the process occurs in the cytoplasm or mitochondrion.

Process	Name of Process/ Cellular Compartment
Converts 1 mole of glucose to 2 moles of pyruvate	Name: Glycolysis Compartment: Cytoplasm
Transfers electrons in a series of redox reactions that produces a separation of charge across the inner mitochondrial membrane. Ultimately transfers electrons to O2 which is then reduced to H2O.	Name: Electron transport chain (ETC) Compartment: Mitochondria
Accepts 2 carbons from acetyl CoA which combine with oxaloacetic acid to form citric acid. Generates reduced coenzymes (NADH and FADH2) that carry electrons to the electron transport chain. Regenerates oxaloacetic acid.	Name: TCA, Krebs or citric acid cycle Compartment: Mitochondria
Synthesizes ATP from ADP. Is driven by the separation of charge across the inner mitochondrial membrane.	Name: Oxidative Phosphorylation Compartment: Mitochondria

1. Refer to the diagram showing oxidation of glycogen or glucose to pyruvate and complete the following table: (minus 1 for each wrong or missing answer, down to –5 pts)

8. Draw a graph to illustrate the following: (5 pts)

1. Activity of phosphofructokinase as a function of fructose 6 phosphate concentration in the absence of ATP.
2. Add a curve to the same graph showing the effects of a drug that is a competitive inhibitor of phosphofructokinase.
3. Add a third curve showing the allosteric effects of AMP.

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