Cellular Respiration
Breakdown of glucose to carbon dioxide
and water
Redox reaction




Hydrogen atoms consist of a hydrogen ion and an
electron (H+ and e-)
Glucose is oxidized when the hydrogen is removed
Oxygen is reduced when it gains hydrogen and
becomes water
Exergonic reaction – glucose is a high energy
molecule  water and carbon dioxide are low
energy molecules
ATP




Build up of ATP = endergonic
Glucose is broken down slowly, ATP
produced gradually
Maximum production of ATP = 36 – 38
39% efficiency from glucose to ATP
Coenzymes

NAD+ (nicotinamide adenine dinucleotide)


Accepts 2 electrons and 1 hydrogen = NADH
FAD (flavin adenine dinucleotide)

Accepts 2 electrons and 2 hydrogens = FADH2
Phases of cellular respiration




Glycolysis – outside mitochondria, anaerobic,
splitting of glucose – 2 pyruvate, yield 2 ATP
Preparatory reaction – in mitochondria, pyruvate
oxidized to 2 – C acetyl group, preps for citric acid
cycle
Citric acid cycle – (Krebs) in matrix of
mitochondria, yield 2 ATP
Electron transport chain – cristae, oxygen is final
electron acceptor and forms water, result in 32 – 34
ATP
Glycolysis



Outside of mitochondria in cytoplasm
Glucose  2 pyruvate
Does not require oxygen, anaerobic
Energy investment

2 ATP are used to activate glucose and break
down into 2 C3 molecules of G3P.
Energy harvesting




Electrons removed (oxidation) with hydrogen ions.
NAD picks up Hydrogen and electrons = NADH
Substrate level phosphorylation – production of ATP
via an enzyme passing a high energy phosphate to
ADP = 4 ATP
Investment of 2 ATP minus 4 ATP = 2 net ATP
Prep Reaction




Pyruvate (2 C3 molecules) is converted to an acetyl
group (C2) that is attached to coenzyme A (CoA)
CO2 is a product
Oxidation occurs, electrons from pyruvate are
removed, NAD  NADH
Reaction occurs twice since there are 2 pyruvate per
glucose molecule
Prep reaction
Inputs: 2 pyruvate, 2 NAD+, 2 CoA
 Outputs: 2 CO2 (Product), 2 NADH,
2 acetyl CoA

Citric Acid Cycle




Matrix of mitochondria
C2 (acetyl CoA) joins with C4 molecule = C6
citrate molecule.
Each acetyl group is oxidized to 2 CO2
molecules = 4 CO2 total released
Cycle goes around 2 times
Citric Acid Cycle



Substrate Level phosphorylation - An
enzyme passes a high energy phosphate to
ADP = ATP
Inputs: 2 acetyl CoA, 6 NAD, 2 ADP/P, 2
FAD
Outputs: 4 CO2 (product), 6 NADH, 2
FADH2, 2 ATP
Prep reaction  Citric acid cycle

Cycle goes around 2 times
Electron Transport Chain



Electrons are carried by NADH and FADH2
Oxidation-reduction reaction starts the ETC. High
energy electrons enter the chain, low energy
electrons leave.
There is a series of carriers that transport the
electrons, first reduced when it accepts the
electrons, then oxidized when it releases them.
Carriers



3 protein complexes (NADH-Q reductase,
cytochrome reductase and cytochrome
oxidase)
2 carriers that transport electrons on ETC–
coenzyme Q and cytochrome c
Cytochrome – protein that has a tightly
bound heme group with a central atom of
iron.
Oxidative phosphorylation

Hydrogen ions are pumped out of the matrix into the
intermembrane space, H+ flow back through membrane due to
H+ gradient = chemiosmosis

Production of ATP as a result of energy released by the ETC =
32 – 34 ATP

Production of ATP via substrate phosphorylation is 4 ATP
Total ATP = 36 – 38 ATP 39% efficiency of cellular resp.

ETC


For each NADH that is oxidized, 3 ATP
molecules are produced
For each FADH2 that is oxidized, 2 ATP are
produced, (due to the fact that they follow
NADH and electrons are at a lower energy
level).
Electron transport chain


Oxygen is the final electron acceptor in the
ETC
Receives last electrons and combines with
the hydrogen ions to form water (product)