Chapter 9 Cellular Respiration

Chemical Energy and Food Food - fats, sugars, and protein - serves as a source of chemical energy for cells The chemical energy in food is measured in calories, the amount of energy needed to raise the temperature of 1g of water 1ºC 1 Calorie = 1 kilocalorie = 1000 calories Cells release the energy from glucose and other food compounds through cellular respiration

Both plant and animal cells carry out the final stages of cellular respiration in the mitochondria. Animal Plant Mitochondria

Outer membrane Intermembrane space Inner membrane Matrix Mitochondrion

Overview of Cellular Respiration Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen 6 O 2 + C 6 H 12 O 6 6 CO H 2 O

Overview of Cellular Respiration In the presence of oxygen, cellular respiration takes place in three stages – Glycolysis Krebs Cycle Electron Transport Chain Each of the three stages captures some of the chemical energy available in food and uses it to produce ATP

Glycolysis The process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid, a 3-carbon compound.

Glycolysis ATP Production At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction. 2 ADP 4 ADP 4 ATP 2 Pyruvic acid 2 ATP

Glycolysis When glycolysis is complete, 4 ATP molecules have been produced. 2 ADP 4 ADP 4 ATP 2 ATP 2 Pyruvic acid

Glycolysis This gives the cell a net gain of 2 ATP molecules. 4 ADP 4 ATP 2 ADP 2 ATP 2 Pyruvic acid

Glycolysis NADH Production One reaction of glycolysis removes 4 high- energy electrons, passing them to an electron carrier called NAD +. 2 Pyruvic acid 4 ADP 4 ATP 2 ADP 2 ATP 2NAD +

Glycolysis Each NAD + accepts a pair of high- energy electrons and becomes an NADH molecule. 2 Pyruvic acid 4 ADP 4 ATP 2 ADP 2 ATP 2NAD + 2

Glycolysis The NADH molecule holds the electrons until they can be transferred to other molecules. To the electron transport chain 2NAD + 2 Pyruvic acid 4 ADP 4 ATP 2 ADP 2 ATP 2

Glycolysis Advantages of Glycolysis The process is so fast that cells can produce thousands of ATP molecules in a few milliseconds. Glycolysis does not require oxygen. However, when a cell produces a large amount of ATP from glycolysis, all of the cell’s NAD + molecules are filled up in a few seconds. Glycolysis stops!

Fermentation When oxygen is present, glycolysis is followed by the Krebs cycle and the electron transport chain When oxygen is not present, energy can be released from food by the process of fermentation Two main types of fermentation: Lactic acid fermentation Alcoholic fermentation

Fermentation Cells convert NADH to NAD + by passing high-energy electrons back to pyruvic acid. Allows glycolysis to continue producing a steady supply of ATP Because does not require oxygen—it is an anaerobic process.

Alcoholic Fermentation Yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes. The equation for alcoholic fermentation after glycolysis is: pyruvic acid + NADH → alcohol + CO 2 + NAD +

Alcoholic Fermentation Alcoholic fermentation causes bread dough to rise. When yeast in the dough runs out of oxygen, it begins to ferment, giving off bubbles of carbon dioxide that form the air spaces you see in a slice of bread. The small amount of alcohol produced in the dough evaporates when the bread is baked.

Lactic Acid Fermentation Pyruvic acid from glycolysis is converted to lactic acid Lactic acid fermentation regenerates NAD + so that glycolysis can continue.

Lactic Acid Fermentation Lactic acid fermentation converts glucose into lactic acid. Glycolysis

Lactic Acid Fermentation The equation for lactic acid fermentation after glycolysis is: pyruvic acid + NADH → lactic acid + NAD+

Lactic Acid Fermentation Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the muscles

Why can’t cellular respiration take place without oxygen? ATP ATP synthase Channel