MITOCHONDRIA III:ATP - THE ENERGY CURRENCY OF THE CELL

Karen Bame, Ph.D.Associate Professor

School of Biological SciencesUMKC

EnergyEnergy is defined as the capacity to do work, i.e. to move matter.

Cells, tissues and organisms need energy for a variety of processes• Muscle contraction• Maintaining ion gradients for nerve transmission• Biosynthesis of molecules• Removal of waste products

EnergyCells 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 mitochondriacitric acid cycle

oxidative phosphorylation• electron transport chain• ATP synthase

NADH and FADH2 donate electrons to the ETC

Electron transport chain• 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 ATPF0 subunit = H+ channel

H+ move back into matrix from IMSF1 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

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.