Lectures 22/23: Redoxreactions and Oxidative Phosphorylation

Question 1

Glutamate dehydrogenase

Answer 1

Catalyzes the reversible conversion of ketoglutarate and glutamate
Can be cataplerotic or anaplerotic

Question 2

Pyruvate carboxylase

Answer 2

Catalyses irreversible reaction of pyruvate to oxaloacetate

Anaplerotic and gluconeogenic enzyme

Question 3

Anaplerotic carboxylation

Answer 3

Conversion of pyruvate to oxaloacetate by pyruvate carboxylase

Question 4

Acetyl-CoA

Answer 4

Oxidation of pyruvate to acetyl-CoA is irreversible
High levels inhibit pyruvate dehydrogenase
High levels activate pyruvate carboxylase: converted to citric acid cycle intermediates that are glucogenic

Question 5

Glucogenic

Answer 5

Metabolites that can be converted to glucose through gluconeogenesis

Question 6

Ketogenic

Answer 6

Metabolites that cannot be converted to glucose through gluconeogenesis

Question 7

Oxidation

Answer 7

Loss of electrons

Oxidation NADH and QH2 generate ATP

Question 8

Reduction

Answer 8

Gain of electrons

Redox through transfer of a hydride ion

Question 9

Niacin

Answer 9

Vitamin B3

Nicotinamide

Question 10

Nicotinamide adenine dinucleotide

Answer 10

NAD+
NADH carries two electrons that it can give up easily
In oxidative phosphorylation, reduces O2 to H2O to drive formation of ATP

Question 11

FAD

Answer 11

Accepts two protons and two electrons to become FADH2
No change in charge of the molecule
Riboflavin (vitamin B12)
FADH2 reduced Q to QH2: carries two electrons that it can give up easily
In oxidative phosphorylation, reduces O2 to H2O to drive formation of ATP

Question 12

Reduction potential

Answer 12

Tendency of a substance to accept electrons to become reduced
Measured in volts
Higher means that substance is more easily reduces and is a stronger oxidant
Rejects energy change that would occur if electrons were transferred
Written as a half reaction

Question 13

Standard reduction potential

Answer 13

Reduction of potential of substances under standard conditions
Standard reduction potential E*’ is a characteristic of each redox active substance and reflects its affinity for electrons

Question 14

Oxidation potential

Answer 14

Opposite in sign to standard reduction potential

Question 15

Positive reduction potential

Answer 15

Higher: greater tendency to accept electrons and therefore become reduced

Question 16

Negative reduction potential

Answer 16

Most negative: least tendency to accept electrons and become reduced
Electrons flow spontaneously from a species with a more negative E’ to a species with a more positive E’

Question 17

Nernst Equation

Answer 17

Defines actual reduction potential

Question 18

deltaE*’

Answer 18

deltaE’= E’ (e acceptor) - E*’ (e donor)

Spontaneous when positive

Question 19

Standard free energy change

Answer 19

deltaG’= -nFdeltaE’

Spontaneous when deltaE’ is positive and deltaG’ is negative

Question 20

Oxidative phosphorylation

Answer 20

Takes place in mitochondria
Occurs over the inner membrane
Proteins accumulate in inter membrane space
Series of redox reactions generates protein gradient to fuel ATP synthesis: electrons passed down electron transport chain of complexes I-IV
Protons flow back into mitochondrial matrix through complex V (ATP synthase) and fuel the synthesis of ATP

Question 21

Inner membrane

Answer 21

Proton-Rich

Impermeable to several metabolites (ATP, ADP) and ions (H, OH, K, Cl, Phosphate) and fully permeable to O2, H20, CO2

Question 22

Compartmentation of mitochondria

Answer 22

Allows pathway control through controlling the localization of metabolites
Special transport systems to transport metabolites
NADH made during glycolysis must get to the mitochondrial matrix to by reoxidizes and ATP made in mitochondrial matrix must be transported into the cytosol (ADP and P must get to matrix from cytosol)

Question 23

Malate-aspartate shuttle

Answer 23

Interaction of cytosolic malate dehydrogenase and matrix malate dehydrogenase to transport NADH to mitochondrial matrix via oxidation of malate to oxaloacetate

Question 24

Complex I

Answer 24

Transfers electrons from NADH to H and transports 4H into inter membrane space
Energy release by oxidation of NADH used to transport H using proton pump
H transport is against concentration and charge gradient: requires energy
NADH - FMN - Fe-S - Q

Question 25

Coenzyme Q

Answer 25

Hydrophobic and remains inside lipid bilayer

Question 26

FMN

Answer 26

Redox active cofactor Transport electrons Related to FAD

Question 27

Complex II

Answer 27

Succinate dehydrogenase from citric acid cycle Oxidation of succinate to fumarate and reduction of FAD to FADH2 Oxidation of FADH2 to FAD and reduction of Q to QH2

Question 28

Fatty acid oxidation

Answer 28

Produces QH2

Question 29

Glycerol-3-phosphate shuttle

Answer 29

Two redox reactions catalyzed by glycerol-3-phosphate dehydrogenase 1. Reduction of 1,3-bisphosphoglycerate to glycerol-3P 2. Deoxidation of DHAP to transfer electron Q

Question 30

Complex III

Answer 30

Two electrons from QH2 reduce two molecules of cytochrome C Reduced cytochrome c moves to Complex IV Q returns to complex I and complex II Four protons are pumped to intermembrane space

Question 31

Cytochrome

Answer 31

Contains heme prosthetic group Undergoes reversible one-electron transfers Oxidized to Fe3+ or reduced to Fe2+ Membrane soluble Transfers one electron at a time from Complex III to Complex IV

Question 32

Complex IV

Answer 32

Cytochrome C oxidase Oxidizes cytochrome C and reduces O2 For every 2 electrons donated by cytochrome C, two protons are translocated into the intermembrane space Sometimes oxygen escapes after receiving only one electrons: free radicals

Question 33

Free radicals

Answer 33

When oxygen takes up only 1 electron Forms superoxide radical anion Highly reactive, can damage nucleic acid, proteins and lipids Cumulative damage from free radicals is thought to contribute to many diseases and aging

Question 34

Proton gradient

Answer 34

Source of free energy through proton motive force Potential free energy due to chemical and charge imbalance ATP synthase taps into the electrochemical proton gradient to phosphorylate ADP

Question 35

Complex V

Answer 35

ATP synthase (F1F0-ATPase) Uses electrochemical gradient to provide free energy for phosphorylation Needs ADP and P in mitochondrial matrix

Question 36

ATP translocase

Answer 36

Imports ADP into matrix and exports ATP

Question 37

Phosphate transporter

Answer 37

Brings P and H into matrix

Question 38

F0

Answer 38

Transmembrane portion of ATP synthase Blocked by antibiotic oligomycin H binds to C subunit C subunit moves away from A subunit, when a new C reaches A subunit H is released One rotation of ring translocates 8 protons

Question 39

F1

Answer 39

Water soluble peripheral portion that extends into matrix Catalyzes the phosphorylation of ADP and ATP 3 alternating alpha and beta form a hexameter around the end of the gamma subunit

Question 40

F1 beta subunit

Answer 40

Binds to ADP/ATP Forms Open, Tight and Loose with alpha subunit as the gamma subunit rotates At any given time, there is one alpha-beta in each conformation

Question 41

P:O ratio

Answer 41

``` # of phosphorylations of ADP per # of oxygen atoms reduced Not a whole number: conversion of energy ```

Question 42

Rate of oxidative phosphorylation

Answer 42

Depends on rate of fuel catabolism Regulated by the availability of reduced cofactor produced by other metabolic processes Efficiency of coupling between electron transport chain and ATP synthesis If proton gradient is used to fuel other processes or if H are transported back over membrane, less ATP synthesized per oxygen

Question 43

Uncoupling

Answer 43

Protons flowing into matrix without powering ATP synthase Proton motive force is dissipated NADH is oxidized, electrons are transported and oxygen is reduced to water but ATP is not made Mediated by uncoupling proteins or chemicals Some is always ongoing: protective by reducing oxygen species production Generates heat

Question 44

Uncoupling proteins

Answer 44

Mediates uncoupling

Question 45

Dinitrophenol

Answer 45

Causes uncoupling

Question 46

FCCP

Answer 46

Causes uncoupling

Question 47

Non-shivering thermogenesis

Answer 47

Heat caused by uncoupling | In brown adipose tissue