Harvesting Chemical Energy
• ATP--main fuel for cells
• Cellular Respiration--process cells use to make ATP by breaking down organic compounds
Glucose
Glycolysis Krebs
cycle
Electrontransport
Fermentation (without oxygen)
Alcohol or lactic acid
Glucose Glycolysis
Cytoplasm
Pyruvic acid
Electrons carried in NADH
Krebs Cycle
Electrons carried in
NADH and FADH2 Electron
Transport Chain
Mitochondrion
Mitochondrion
The Cell Respiration Equation
• 6O2 + C6H12O6 6CO2 + 6H2O + Energy
• oxygen + sugar carbon dioxide + water + energy
Glycolysis
• The process of breaking 1 molecule of glucose in half
• Happens in the cytoplasm
• Produces pyruvic acid and NADH
• Produces 4 ATPs overall
• 2 ATPs used up to in the reaction
• Net gain = 2 ATPs
NAD+ and NADH
• NAD+ is a carrier molecule, it becomes NADH when it picks up energy (an electron)
• It is similar to NADPH, used in photosynthesis
• Carries high energy electrons to other places they are needed in the cell
Glycolysis• This is a FAST process
• Thousands of ATPs can be produced in a few milliseconds
• However, there are a limited number of NAD+ carriers, so more must be made
• Without additional NAD+, glycolysis cannot continue
Glucose
Glycolysis Krebs
cycle
Electrontransport
Fermentation (without oxygen)
Alcohol or lactic acid
• The next step of cell respiration depends on whether or not oxygen is available
• If no oxygen, then the next step is called FERMENTATION
• Fermentation is an anaerobic process
• Two types of fermentation--alcoholic fermentation and lactic acid fermentation
Alcoholic Fermentation
• Yeasts and a few other microorganisms use this
• pyruvic acid + NADH --> alcohol + CO2 + NAD+
• Used to produce bread,
• wine, beer, homeade rootbeer, etc.
The “holes” in bread are from pockets of CO2
that got trapped.
Lactic Acid Fermentation
• This type of fermentation happens in your muscles, and also in certain microorganisms
• pyruvic acid + NADH --> lactic acid + NAD+
Used to produce cheese, yogurt, soy sauce,
sauerkraut, etc. Lactic acid gives these things the
sharp, sour taste. YUMMMMY!
Lactic Acid Fermentation
• This is also the reason for runner’s fatigue or cramps
• When exercising strenously, your muscle cells use up all your oxygen and must switch to lactic acid fermentation
• Lactic acid burns when it builds up inside the cells
Lactic Acid Fermentation
• Since NAD+ is produced…
• pyruvic acid + NADH --> lactic acid + NAD+
• …glycolysis can continue and more ATP can be made
KrebsCycle
ElectronTransport
Chain
Carbon Dioxide
(CO2)+
Water(H2O)
Glucose(C6H1206)
+Oxygen
(02)
Glycolysis
After Glycolysis...
• Most of the energy in glucose is still not released even after glycolysis
• Oxygen is needed to release the remaining energy from the glucose molecule
• The next step is called the Krebs Cycle (if oxygen is available)
Krebs Cycle• What goes IN? pyruvic acid from glycolysis
• Where? Mitochondrial matrix (space inside the inner membrane of mitochondria)
• What comes OUT? NADH and FADH2 (both are carrier molecules for high energy electrons). These go to the next step of cellular respiration...
• When pyruvic acid enters mitochondria, it reacts with coenzyme A to make acetyl CoA & releases CO2
Krebs Cycle
christae
Krebs Cycle
• 5 Major Steps– 1) combines with oxalocetic acid to form citric
acid– 2) releases CO2 and NAD+ to NADH – 3) CO2 released and NAD to NADH, also ATP
synthesized– 4) FAD (carrier molecule) to FADH2– 5) NAD+ to NADH, more oxalocetic acid created
Mitochondrion
5 Major Steps
1) combines with oxalocetic acid to form citric acid
2) releases CO2 and NAD+ to NADH
3) CO2 released and NAD to NADH, also ATP synthesized
4) FAD (carrier molecule) to FADH2
5) NAD+ to NADH, more oxalocetic acid created
Electron TransportHydrogen Ion Movement
ATP Production
ATP synthase
Channel
Inner Membrane
Matrix
Intermembrane Space
Mitochondrion
Electron Transport Chain
• What goes IN? NADH and FADH2 from Krebs Cycle
• Where? Inner membrane of mitochondria
• What comes OUT? Lots and lots of ATP molecules!!!! (34 to be exact)
Electron TransportHydrogen Ion Movement
ATP Production
ATP synthase
Channel
Inner Membrane
Matrix
Intermembrane Space
Mitochondrion
Electron Transport Chain
• High energy electrons are passed from NADH and FADH2 along a series of molecules
• As they go from molecule to molecule, they lose their energy. It is used to pump H+ into the space between inner and outer mitochondrial membrane.
Electron Transport Chain
• Chemiosmosis takes place, H+ ions diffuse from high to low through ATP synthase
• As the ATP synthase spins, this generates ATP molecules
• Sound familiar?
Electron Transport Chain
• Oxygen is the final electron acceptor in this reaction
• This gets rid of low energy electrons and extra H+ ions
• Byproduct that results is H2O
The Totals (Net Gains)
• Glycolysis + Fermentation = 2 ATP
• Glycolysis + Krebs + ETC = 36 ATP
• Even 36 ATP is only about 66% of the energy available in one glucose molecule. Where does the rest of the energy go???
Pacing Yourself
• Fermentation--used during strenuous exercise (fast breakdown of sugar)
• Krebs Cycle and ETC--used during longer, paced exercises (like long-distance running) Slower, but more energy released