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Cellular Respiration
Glycolysis, Kreb’s, and ETC
Cellular Respiration
 How our body turns food and oxygen into ENERGY called
ATP
 Glycolysis
 Kreb’s Cycle
 ETC (Electron Transport Chain)
Redox Reactions
 Chemistry review:
 Oxidation = losing an electron
 Reduction = gaining an electron
 A redox reaction is a chemical reaction in which one
molecule gains electrons and one loses them
 Example of cellular respiration: glucose is oxidized into
carbon dioxide, oxygen is reduced to water
Glycolysis
 Glycolysis is the first step of cellular respiration
 It means “splitting sugar”
 One molecule of glucose is split in half into 2 molecules of
pyruvic acid (pyruvate)
 C6H12O6  2 C3H6O3
Glycolysis
 Occurs in the cytoplasm of
cells
 It is a 10 step process that
occurs in 2 phases
 It can occur whether or not
oxygen is present
Glycolysis
 Input: glucose
 Output: 2 molecules of
pyruvate, 2 ATP, and 2
NADH
 NADH is a molecule that
carries electrons from
glycolysis and the Kreb’s
Cycle to the ETS (it gains
electrons = reduced)
 Once there, it releases the
electrons to make ATP (it
is oxidized to NAD+)
Kreb’s Cycle
 Step 2 of Cellular Respiration is called the Kreb’s Cycle, and
is also known as the Citric Acid Cycle
 It ONLY occurs in the presence of oxygen
 It takes place in the mitochondrial matrix, the space between
the inner folded membranes of the mitochondria
Kreb’s Cycle
 The 2 pyruvates from glycolysis are converted to 2 molecules
of acetyl coenzyme A (acetyl coA)
 This enters the Kreb’s Cycle one at a time.
 For each original glucose molecule, the Kreb’s Cycle will
spin twice, one for each acetyl coA
Kreb’s Cycle
Kreb’s Cycle
 Acetyl coA undergoes a series of redox reactions in the
Kreb’s cycle, rearranging its formula and transferring
electrons
 The net output for 2 TURNS of Kreb’s is: 6 NADH, 2
FADH2 (another electron carrier), and 2 ATP
 A byproduct, carbon dioxide, is released
Electron Transport Chain
 The last step is called the electron transport chain (ETC) or
system (ETS), or oxidative phosphorylation (means losing
electrons and adding a phosphate group to ADP to make
ATP)
 It occurs in the cristae of the mitochondria, on the
membranes on the inside
ETC
 The NADH and FADH2 molecules made in glycolysis and
Kreb’s are what are used by the ETC to make ATP
ETC
 The ETC is a series of proteins
embedded in the cristae like a
waterfall
 NADH and FADH2 enter the
highest protein, and as they
“fall” down the waterfall, they
pass their electrons down to
more electronegative carriers
 As this occurs, hydrogen ions
(H+), which have lost their
electrons, are pumped to the
outside of the membrane
ETC
 At the end of the chain, there is a
big protein enzyme called ATP
Synthase
 The H+ ions flow down their
concentration gradient through
ATP synthase
 ATP synthase spins around each
time and generates enough energy
to add a P to ADP, making ATP
ETC
 As ADP is getting phosphorylized (called chemiosmosis), the electrons have
reached the bottom of the waterfall
 The electrons are attracted to a super electronegative atom, oxygen
 Oxygen is the final electron acceptor. It gains electrons (is reduced) and joins
with the H+ ions coming through ATP synthase to make water
 We breathe out the water (along with the CO2 from Kreb’s)
ETC
 At the end of the ETC, approximately 34 ATP are generated
through the processes of Oxidative Phosphorylation (the
electrons moving down the waterfall) and chemiosmosis (the
diffusion of H+ ions through ATP synthase)
Summary
 Oxygen we breathe in becomes water
 Glucose we eat is used to make ATP and CO2 (waste)
 A total of approximately 38 ATP are made per glucose
molecule