Chapter 9

Cellular Respiration

Chemical Energy

• Living things get energy from the food they consume

• Calorie – the amount of energy needed to raise the temperature of 1 gram of water 1 °C

• 1 gram of glucose when burned in the presence of oxygen releases 3811 C

Cellular respiration

• Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen (aerobic)

• 6O2 + C6H12O6 → 6CO2 + 6H2O + energy • Oxygen + glucose → carbon dioxide + water + energy

• Three main stages:– Glycolysis– Krebs Cycle– Electron transport

Glycolysis

• 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 used to get the reaction going and will produce 4 ATP molecules when the process is complete

Cont.

• NAD+ (electron carrier) accepts 4 high energy electrons and becomes NADH

• This process can produce thousands of ATP molecules in a few milliseconds

• Does not require oxygen (anaerobic)

• Energy is used up quickly

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Fermentation

• Production of ATP in the absence of oxygen (anaerobic)

• Two types: Alcoholic fermentation and Lactic acid fermentation

• Alcohol fermentation: NADH is converted back to NAD+ by passing high energy electrons back to pyruvic acid

• Pyruvic acid + NADH → alcohol + CO2 and NAD+

Cont.

• Lactic fermentation: NADH is converted back to NAD+ by passing high energy electrons back to pyruvic acid and producing lactic acid

• Lactic acid is produced in muscle when the body cannot supply enough oxygen

• Pyruvic acid + NADH → lactic acid + NAD+

Krebs Cycle

• End of glycolysis, 90% of chemical energy in glucose is still unused, cell will use oxygen to extract the remaining energy

• Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion

• Pyruvic acid is used to make carbon dioxide, ATP, NADH, and FADH2

Electron Transport Chain

• Uses the high energy electrons from the Krebs cycle to convert ADP to ATP

• In eukaryotes: inner membrane of the mitochondrion

• In prokaryotes: in the cell membrane

• H+ builds up in the intermembrane space making it positively charged…other side, is now negatively charged

• As H+ escape through membrane, the mitochondria contain proteins (ATP synthase) which rotates, the enzyme grabs the low energy ADP and attaches a phosphate forming high energy ATP

• Process is repeated over and over

Energy for the body

• Quick – gylcolysis or fermentation

• Long term- cellular respiration

Summary

• Cellular respiration has 3 stages:– Glycolysis– Krebs cycle

• Electron transport chain