IB BIO I
Cellular Energy
Madden/Van Roekel
3.7 & 8.1 Cellular Respiration
Cellular Respiration: the controlled release of energy from organic compounds to form ATP in the cells.
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Use by all cells to produce ATP (Adenosine Triphosphate, energy containing molecule)
Energy is derived from potential energy stored in covalent bonds of macromolecules (i.e. glucose, fatty
acids, proteins)
Breakdown occurs via oxidation-reduction reactions, or a transfer of electrons from one molecule to the
next
o Oxidation: Loss of electrons (hydrogen molecules)
o Reduction: Gain of electrons (hydrogen molecules)
In Cellular respiration, glucose is oxidized, oxygen in reduced
Reaction:
o C6H12O6 + 6O2  6 CO2 + 6 H2O + ATP
Aerobic Cell Respiration occurs in three step:
o Glycolysis
o Krebs Cycle
o Electron Transport Chain/Chemiosmosis
Glycolysis: process of breaking down glucose into 2 pyruvate molecules, producing net gain of 2 ATPs,
and 2 NADH
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Requires the input of energy in the form of 2 ATP molecules
Glucose is phosphorylated (addition of phosphate) and becomes fructose-1,6-biphosphate
Fuctose-1,6-biphosphate splits into two 3-carbon sugars called glyceraldehyde-3-phoshphate
(lysis)
Glyceraldehyde-3-phosphate is oxidized to form NADH (reduced form of NAD+) and an enzyme
removes phosphate group and adds it to ADP, forming ATP
Substrate level phosphorylation: enzyme transfers a phosphate group from a substrate directly
to ADP, making ATP
The Link Reaction: Pyruvate molecule  Acetyl CoA
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Pyruvate loses a carbon molecule via decarboxylation and becomes an acetyl group. CO2 is
removed
Acetyl group is oxidized (forming NADH) and combines with coenzyme A, making Acetyl CoA
Krebs Cycle: 8 step cycle in the matrix of mitochondria that produces 2 ATP, 6 NADH, 2 FADH2 and 4
molecules of CO2
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Acetyl CoA combines with Oxaloacetate to form 6-carbon sugar compound Citrate
Citrate is oxidized and decarboxylated into a 5-carbon compound, releasing CO2 and forming
NADH
5-carbon compound is oxidized and decaboxylated into a 4-carbon compound, releasing CO2 and
forming NADH
IB BIO I
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Cellular Energy
Madden/Van Roekel
4-carbon sugar undergoes a variety of chemical and conformational changes, forming NADH,
FADH2 and ATP (by substrate level phosphorylation).
4-carbon compound is also changed to re-form starting compound, Oxaloacetate
For Each glucose molecule, Krebs Cycle completes two revolutions
Electron Transport Chain (ETC)/Chemiosmosis: Involves the use of the ETC and ATP synthase to
generate a large amount of ATP and water
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ETC is a collection of molecules on the inner mitochondria membrane, mainly protein, that
accept and donate electrons along an energy gradient
o FMN: Flavin mononucleotide, accepts electrons from NADH
o FE-S: Iron Sulfur protein accepts electrons from FADH2
o Coenzyme Q (ubiquinone) is a lipid
o Cytochromes (cyt) contain heme group for binding electrons
Accept electrons from NADH/FADH2, and pass them from one protein to the next
Occurs because of electronegativity; higher electronegativity=stronger electron attraction
Small amount of energy between protein carriers, less energy released, easy to harness
Oxygen is final electron acceptor; combines with two hydrogen ions and leaves as water
Does not produce ATP directly
Couples with ATP synthase to produce ATP in a process called chemiosmosis
Chemiosmosis involves the movements of protons (hydrogen ions) by ETC to provide energy for
phosphorylation
Creates a hydrogen ion (H+) gradient that results in a proton-motive force, which can be used to
power ATP synthase
H+ ions move passively through ATP synthase, and using energy gained from ions, synthase can
combine ADP and phosphate to form ATP.
Formation of ATP through this process is referred to as oxidative phosphorylation
Cell Respiration Review
Energy flow: GlucoseNADHETCChemiosmosis (proton-motive force) ATP
Theoretical production of ATP: 36
Outer Mitochondrial Membrane
Inner Mitochondrial Membrane
Cristae
Matrix
Inter-membrane Space
Actual Production of ATP: 30
Separates contents of Mitochondrion from cell
Contains proteins for ETC and ATP synthase for
chemiosmosis
Tubular regions of IMM to increase surface area
for oxidative phosphorylation
Cytosol like (liquid) area of mitochondria,
contains enzymes for Krebs Cycle
Reservoir for H+ ions (necessary for
chemiosmosis)