Cellular Respiration
Cellular respiration releases chemical
energy from sugars and other carbonbased molecules to make ATP.
 It is an aerobic process.

 needs oxygen to take place.
Cellular Respiration

Cell respiration takes place in the
mitochondria.
 Foods are broken down into small molecules
like glucose.
 Glucose is broken down during glycolysis.
Glycolysis

Glycolysis
 Takes place BEFORE cell
respiration.
 Splits the glucose molecule
into two three-carbon
molecules and makes two
molecules of ATP.
 It takes place in the
cytoplasm of the cell.
 It is an anaerobic process.
○ Does NOT require oxygen
to take place.
Glycolysis
1. Two ATP molecules are used to
energize a glucose molecule.
– The glucose is then split into two
three-carbon molecules.
2. Energized electrons from the
three-carbon molecules are
transferred to molecules of NAD+.
– This makes NADH. (this is an
enzyme that helps energy
production)
– A series of reactions convert the
three-carbon molecules into
pyruvate. (used in cellular
respiration)
– 4 ATP molecules are made.
Krebs Cycle

The first part of cellular respiration.
 Sometimes called the citric-acid cycle.
Produces molecules that carry energy to
the second part of cellular respiration.
(NADH and FADH2)
 Takes place in the interior space (matrix)
of the mitochondria.

Krebs Cycle
1. Pyruvate broken down.
 Pyruvate is split into a two-
carbon molecule and
carbon dioxide (given off as
waste).
 The two-carbon molecule
donates high energy
electrons to NAD+, forming
a molecule of NADH.
○ This will move to the
electron transport chain.
2. Coenzyme A
 Bonds to the two-carbon
molecule made by the
breakdown of pyruvate.
Krebs Cycle
3. Citric acid formed.
– The two-carbon molecule
binds to a four-carbon
molecule to form citric acid.
– Coenzyme A returns to step 2.
4. Citric acid broken down.
– The citric acid molecule is
broken down by an enzyme,
and a five-carbon molecule is
formed.
– A molecule of NADH is made
and moves out of the Krebs
cycle.
– A molecule of carbon dioxide
is given off as waste.
Krebs Cycle
•
5. Five-carbon molecule
broken down.
– A four-carbon molecule, a
molecule of NADH, and a
molecule of ATP are formed.
– NADH leaves the Krebs Cycle.
– Carbon dioxide is given off as
waste.
•
6. Four-carbon molecule
rearranged.
– Enzymes rearrange the four-
carbon molecule, releasing
high-energy electrons.
– NADH and FADH2 (another
enzyme/electron carrier) are
made.
– They leave the Krebs cycle and
the four-carbon molecule
remains.
Krebs Cycle Products
•
•
The Krebs cycle will break down
TWO pyruvate molecules at the
same time.
Products:
– 6 carbon dioxide molecules.
– 2 molecules of ATP
– 4 molecules of NADH
• Will go to the electron transport chain.
– 2 molecules of FADH2
• Will go to the electron transport chain.
Electron Transport Chain
Second part of cellular respiration.
 Energy from the Krebs cycle (NADH and FADH2)
is transferred to a chain of proteins in the inner
membrane of the mitochondrion.
 A large number of ATP molecules are made.
 Oxygen is used to make water molecules.

 Water and heat are given off as a waste
Electron Transport Chain
1. Electrons removed.
 Proteins inside the mitochondrion take high-
energy electrons from NADH and FADH2.
○ Two molecules of NADH and one of FADH2 are used.
2. Hydrogen ions transported.
 Hydrogen ions are built up along the inner
mitochondrial membrane using energy from the
electrons.
Electron Transport Chain
•
3. ATP produced.
– The hydrogen pumps through a protein
channel in the mitochondrial membrane
with ATP synthase.
– ATP synthase adds phosphate groups to
ADP to make ATP molecules.
• Each pair of electrons (hydrogen) that
passes through results in an average of 3
ATP molecules made.
•
4. Water formed.
– Oxygen enters the cycle and picks up
extraneous hydrogen, forming water.
• This is given off as a waste.
Electron Transport Chain
Electron Transport Chain
Products

For EACH molecule of glucose the ETC
can make:
 Up to 34 molecules of ATP
Cellular Respiration Products
•
Up to 38 ATP are made from the
breakdown of ONE glucose molecule.
– 2 ATP from glycolysis
– 36-34 ATP from cellular respiration (Krebs
Cycle and Electron Transport Chain)
•
•
Other products include carbon dioxide
and water.
The equation for cellular respiration is:
– C6H12O6 + 6O2
6CO2 + 6H2O
Fermentation
•
Fermentation is an anaerobic process
that takes place when there is less
oxygen in the body (i.e. during
strenuous activity)
• Fermentation does NOT make ATP, but
it allows glycolysis to continue.
– Glycolysis needs NAD+ to pick up electrons
when it splits glucose into pyruvate.
– Fermentation removed electrons from
NADH molecules and recycles NAD+
molecules for glycolysis.
Lactic Acid Fermentation in
Animals
1. Pyruvate and NADH from
glycolysis enter fermentation.
 Two NADH molecules are used to
convert pyruvate into lactic acid.
○ As the NADH is used, it converts
back to NAD+.
2. TWO molecules of NAD+ are
recycled back to glycolysis.
 This allows your body to continue to
break down sugar for energy!
Alcoholic Fermentation in
Plants
1. Pyruvate and NADH from
glycolysis enter alcoholic
fermentation.
 The NADH molecules provide energy
to break pyruvate into alcohol and
carbon dioxide.
○ As the NADH are used, they are
converted to NAD+.
2. The molecules of NAD+ are
recycled back to glycolysis.
 The recycling of NAD+ allows
glycolysis to continue.
Cellular Respiration and
Photosynthesis
Cellular Respiration and
Photosynthesis are
approximately the reverse
of each other.
 Photosynthesis stores
energy.
 Cellular Respiration
releases it.

Photosynthesis and Cellular
Respiration—write this down 