Cell Respiration

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

Glucose 2 Pyruvic acid

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)

Mitochondrion

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???

• The remaining 34% is given off as body heat (keeps you warm in this chilly room!)

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

Why do runners breathe heavily after a race?

They are “repaying” the oxygen debt they have built

up!

• Photosynthesis--removes CO2 from the

atmosphere, puts back O2

• Cellular Respiration--removes O2 from the

atmosphere, puts back CO26O2 + C6H12O6 6CO2 + 6H2O + Energy

6H2O + 6CO2 + light energy C6H12O6 + 6O2