Lectures 22/23: Redoxreactions and Oxidative Phosphorylation Flashcards Preview

Biochemistry 2300 > Lectures 22/23: Redoxreactions and Oxidative Phosphorylation > Flashcards

Flashcards in Lectures 22/23: Redoxreactions and Oxidative Phosphorylation Deck (47):
1

Glutamate dehydrogenase

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

2

Pyruvate carboxylase

Catalyses irreversible reaction of pyruvate to oxaloacetate
Anaplerotic and gluconeogenic enzyme

3

Anaplerotic carboxylation

Conversion of pyruvate to oxaloacetate by pyruvate carboxylase

4

Acetyl-CoA

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

5

Glucogenic

Metabolites that can be converted to glucose through gluconeogenesis

6

Ketogenic

Metabolites that cannot be converted to glucose through gluconeogenesis

7

Oxidation

Loss of electrons
Oxidation NADH and QH2 generate ATP

8

Reduction

Gain of electrons
Redox through transfer of a hydride ion

9

Niacin

Vitamin B3
Nicotinamide

10

Nicotinamide adenine dinucleotide

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

11

FAD

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

12

Reduction potential

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

13

Standard reduction potential

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

14

Oxidation potential

Opposite in sign to standard reduction potential

15

Positive reduction potential

Higher: greater tendency to accept electrons and therefore become reduced

16

Negative reduction potential

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*'

17

Nernst Equation

Defines actual reduction potential

18

deltaE*'

deltaE*'= E*' (e acceptor) - E*' (e donor)
Spontaneous when positive

19

Standard free energy change

deltaG*'= -nFdeltaE*'
Spontaneous when deltaE*' is positive and deltaG*' is negative

20

Oxidative phosphorylation

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

21

Inner membrane

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

22

Compartmentation of mitochondria

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)

23

Malate-aspartate shuttle

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

24

Complex I

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

25

Coenzyme Q

Hydrophobic and remains inside lipid bilayer

26

FMN

Redox active cofactor
Transport electrons
Related to FAD

27

Complex II

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

28

Fatty acid oxidation

Produces QH2

29

Glycerol-3-phosphate shuttle

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

30

Complex III

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

31

Cytochrome

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

32

Complex IV

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

33

Free radicals

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

34

Proton gradient

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

35

Complex V

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

36

ATP translocase

Imports ADP into matrix and exports ATP

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Phosphate transporter

Brings P and H into matrix

38

F0

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

39

F1

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

40

F1 beta subunit

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

41

P:O ratio

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

42

Rate of oxidative phosphorylation

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

43

Uncoupling

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

44

Uncoupling proteins

Mediates uncoupling

45

Dinitrophenol

Causes uncoupling

46

FCCP

Causes uncoupling

47

Non-shivering thermogenesis

Heat caused by uncoupling
In brown adipose tissue