MITOCHONDRIA III:
ATP - THE ENERGY CURRENCY
OF THE CELL
Karen Bame, Ph.D.
Associate Professor
School of Biological Sciences
UMKC
Energy
Energy is defined as the capacity to do work, i.e. to move matter.
Cells, tissues and organisms need energy for a variety of processes
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Muscle contraction
Maintaining ion gradients for nerve transmission
Biosynthesis of molecules
Removal of waste products
Energy
Cells generate energy by oxidation-reduction (redox) reactions
• redox reactions move electrons (and H) between molecules
Energy is generated when reduced molecules are oxidized
• more reduced a molecule is, the more energy it contains
metabolism
• catabolic pathways are a series of chemical reactions that oxidize
molecules into CO2, H2O and NH3
• some of the energy released in the pathway can be used to make
ATP and NADH
• the ATP and NADH can then be used in anabolic processes that
require energy
NADH and FADH2
Coenzymes derived from B vitamins
• niacin
• riboflavin
Accept electrons and become
reduced in catabolic reactions
Donate electrons to the electron
transport chain (ETC), which
generates energy to make ATP
ATP
Called the energy
currency of the cell, since
hydrolysis of ATP releases
energy
ATP + H2O  ADP + Pi
ATP is generated in the mitochondria
citric acid cycle
oxidative phosphorylation
• electron transport chain
• ATP synthase
NADH and FADH2 donate electrons to the ETC
Electron transport chain
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Complexes I, II, III, IV
Coenzyme Q (CoQ)
Cytochrome c
Movement of electrons through ETC sets
up a proton (H+) gradient across the inner
mitochondrial membrane
ATP synthase uses the proton gradient to make ATP
F0 subunit = H+ channel
H+ move back into matrix from IMS
F1 subunit = catalytic activity
ADP + Pi  ATP
• movement of H+ through F0 causes the c-ring
of the F0 subunit and the ge-shaft of F1 to
rotate.
• rotation of the ge-shaft causes conformational
changes in the ab-subunits of F1
• these conformational changes drives the
chemical reaction: ADP + Pi  ATP
Youtube video:
http://www.youtube.com/watch?v=PjdPTY1wHdQ
Summary
• Cells require energy to perform a variety of functions.
• Energy is generated in catabolic processes, when molecules
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are oxidized to CO2 and H2O.
Some of the energy released in catabolic processes is used to
make ATP.
ATP is mostly synthesized in the mitochondria, via the electron
transport chain (ETC) and ATP synthase.
Oxidation-reduction reactions of the ETC sets up a proton
gradient; energy “stored” in the proton gradient is converted to
mechanical energy (rotation), which drives the synthesis of
chemical energy (ATP).
ATP is used to power cellular processes that require energy to
occur.