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 3-carbon 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