L4: Bioenergetics and Biological Oxidations

Question 1

LO1: define free energy change and the equation used to represent it

How is deltaG related to the pathway by which the reaction occurs?

Answer 1

-the free energy of a system that is available for useful work (portion of total energy)
deltaG= deltaH - T(deltaS)

deltaG is independent of the pathway by which the reaction occurs (value is the same regardless of the method used)

Question 2

LO1: how do you use deltaG to predict the direction of a reaction?

Answer 2

Exergonic: -deltaG (reaction proceeds spontaneously in the direction written)

Equilibrium: deltaG=0 (reaction is in equilibrium)

Endergonic: +deltaG (reaction will not proceed in the direction written unless energy is supplied)

Question 3

LO2: what do coupled enzymatic reactions require?

Answer 3

• the product of the first reaction must be a substrate in the second reaction
• endergonic reaction coupled with an exergonic reaction
• overall deltaG must be negative

Question 4

LO3: what are the function(s) of adenine nucleotides in enzymatic reactions?

Answer 4

major roles: storage of chemical energy in the cell; energy is released by hydrolysis of the terminal phosphate bonds to drive endergonic reactions
-allosteric regulation of regulatory enzymes

Question 5

LO3: list the major metabolic pathways that result in synthesis of high energy phosphate bonds, NADH, or FADH2

Answer 5

glycolysis: conversion of glucose–>pyruvate to synthesize net 2 molecules of ATP and 2 molecules of NADH

TCA cycle: oxidation of acetyl-CoA–>CO2 to synthesize net 1 molecule of GTP (eq. in energy to ATP), 3 molecules of NADH, and 1 molecule of FADH2

fatty acid oxidation: for each cycle of oxidation, 1 molecule of NADH and 1 molecule of FADH2 are produced

oxidative phosphorylation: oxidation of NADH and FADH2 by ETC results in synthesis of 3 or 2 molecules of ATP

Question 6

LO4: define energy charge and its role in cell metabolism regulation

Answer 6

• an index of the metabolically available energy in the cell, defined as the ratio of (ATP+1/2 ADP)::(ATP+ADP+AMP)
• can range from 0 to 1
• catabolic pathways activated when EC decreases (anabolic inhibited)
• anabolic pathways activated when EC increases (catabolic inhibited)
• ultimately involved in regulation because many regulatory enzymes are allosterically regulated by the adenylate nucleotides

Question 7

LO5: Define oxidation and reduction reactions

list the three types of enzymes that catalyze them

Answer 7

LEO GER
-dehydrogenases catalyze transfer of H from substrate to a conenzyme acceptor (some require NAD+ and NADP+, some require FAD and FMN)

• oxidases catalyze transfer of electrons from an organic substrate to molecular oxygen via an intermediate carrier which is tightly bound to the enzyme (carriers either metal ions or FMN or FAD)
• oxygenases catalyze the incorporation of molecular oxygen into organic substrates

Question 8

LO6: Define redox potential

Answer 8

• measure of the tendency for a compound to lose electrons
• the half reaction with the more negative redox potential will be the reducing agent (gets oxidized)
• the half reaction with the more positive redox potential will be the oxidizing agent (gets reduced)

Question 9

LO5: Define oxidizing agent and reducing agent and give examples

Answer 9

-oxidizing agent accepts electrons (gets reduced)
O2 in reaction that produces water

-reducing agent loses/donates electrons (gets oxidized)
NAD+ in recreation that produces NADH

Question 10

LO6: Role of free energy in ox-redox reactions

Answer 10

• the change in standard redox potential for a reaction can be used to calculate the standard free energy for a reaction
• a positive value for the standard redox potential generates a -deltaG and indicates an exergonic reaction

Question 11

LO7: Compare/contrast the major electron carriers

Answer 11

NADH vs FADH2

• NAD/NADH pair participates in transfer of hydride ion (redox potential: -0.32)
• FAD/FADH2 pair participates in transfer of two hydrogen ions (redox potential: -0.06)

Question 12

LO8: Describe the two major enzymes involved in detoxing ROS and how hydrogen peroxide is typically formed

Answer 12

Peroxidases: reduce hydrogen peroxide to H2O

Catalases: catalyze the dismutation of hydrogen peroxide to H2O and O2

Hydrogen peroxide: formed during detox of superoxide and oxidase-catalyzed reactions