Cellular Respiration
Chemical Energy and Food
• A Calorie (with a capital C) is the amount of
energy required to raise the temperature of 1
gram of water by 1 degree Celsius.
– Note: The calorie you see on a cereal box is
actually a kilocalorie or 1,000 Calories.
• 1 Calorie = 4,184 joules
Cellular Respiration
• Cellular Respiration is the process that
releases energy by breaking down glucose and
other food molecules in the presence of
oxygen.
• Cellular Respiration Equation:
• 6O2 + C6H12O6  6CO2 + 6H2O + Energy
Glycolysis
• First part of cellular respiration: Glycolysis.
• Glycolysis is the process in which one
molecule of glucose is broken in half,
producing two molecules of pyruvic acid (a 3carbon compound)
• 2 ATP molecules are needed go into glycolysis
• The cell uses those two ATP and makes 4 ATP
molecules and 2 NADH molecules
• Therefore, a net gain of 2 ATP and 2 NADH
No oxygen? No problem… sort of
• When oxygen is not
present, glycolysis is
followed by fermentation.
• Fermentation releases
energy from food
molecules by producing
ATP in the absence of
oxygen
• Fermentation is anaerobic
– does not require oxygen.
• Two main types:
– Lactic acid fermentation
– Alcoholic fermentation
Alcoholic Fermentation
• Yeast uses alcoholic fermentation, forming
ethyl alcohol and carbon dioxide as wastes
• Pyruvic acid + NADH  alcohol + CO2 + NAD+
• This process makes bread rise and of course
alcohol
Lactic Acid Fermentation
• Lactic acid can be made from pyruvic acid in
the absence of oxygen
• This occurs in your muscles during rapid
exercise when you’re not getting enough
oxygen to your cells
• Pyruvic acid + NADH  Lactic acid + NAD+
• Lactic acid build up is painful = pain in muscles
while working out
Lactic Acid Fermentation
• Unicellular organisms going through lactic acid
fermentation are used to make cheese,
yogurt, buttermilk, and sour cream.
The Krebs Cycle
• In the presence of oxygen (aerobic), after
glycolysis, pyruvic acid goes to the Krebs Cycle
(also called the Citric Acid Cycle).
• During the Krebs Cycle, pyruvic acid is broken
down into carbon dioxide and energy is extracted
• Step 1: Pyruvic acid enters mitochondria. One
carbon is wasted as carbon dioxide. Two carbons
become acetyl-CoA and forms citric acid.
The Krebs Cycle
• Step 2: The citric acid is broken down, more carbon
dioxide is released, and electrons are transferred
to electron carriers.
– This carbon dioxide that is released is what you
breathe out.
– NAD+ and FAD (flavine adenine dinucleotide)
are the electron carriers. They are converted
into NADH and FADH2.
Electron Transport
• Electrons from the Krebs Cycle are passed from
NADH and FADH2 to the electron transport chain
(ETC).
• The ETC uses these electrons from the Krebs cycle
to convert ADP into ATP.
• Step 1: Electrons passed through carrier proteins
located on membrane of mitochondria
(eukaryotes) or cell membrane (prokaryotes).
– Oxygen is the final electron acceptor and combines
with H+ to form water.
Electron Transport
• Step 2: Every time 2 electrons move down the
chain, H + is moved across the membrane.
– These H + ions make the membrane positive
• Step 3: As the H + ions move across the
membrane, ATP synthase attaches a
phosphate group to ADP making ATP.
Electron Transport Chain
Totals of Cellular Respiration
• 36 total ATP produced in presence of oxygen
Energy and Exercise
• Exercise that is intense and ends quickly will
utilize fermentation.
– Example: 200 m dash
– Body only has enough ATP for a few minutes of
intense activity
• Exercise that is long-lasted and steady will use
cellular respiration.
– Example: aerobic exercises like swimming, running,
dancing.
– Cell respiration generates a continuous, steady supply