Chemical Pathways Chapter 9 Section 1

Chemical Energy and Food How much energy is really in food? One gram of sugar glucose releases 3811 calories of heat energy Calorie: Amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius Calorie on the food labels is a kilocalorie, or 1000 calories

Chemical Energy and Food Cells don’t burn glucose……Then why is it so important???? Process begins with a pathway called Glycolysis Glycolysis releases only a small amount of energy If oxygen is present, it prepares the glucose molecule

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 Processes of Cellular Respiration: Glycolysis Kreb’s Cycle Electron Transport Chain

Overview of Cellular Respiration

Glycolysis 1st stage of Cellular Respiration Occurs in the cytoplasm Glycolysis is the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid At the beginning of glycolysis, 2 ATP molecules are put in to get the process started When glycolysis is finished, 4 ATP molecules are gained Net ATP: 4 (created) – 2 (invested)=2 ATP

Glycolysis One of the reactions that makes ATP also makes another high energy molecule, NADH An electron carrier, NAD+, accepts a pair of high-energy electrons to form NADH 2 Pyruvic acid will then go onto either the Kreb’s cycle (if oxygen is present) or fermentation (if oxygen is not present)

Glycolysis Advantage: Disadvantage: Speed Does not require oxygen (produces thousands of ATP in milliseconds Disadvantage: Will run out of NAD+

Overview of Glycolysis Reactants: Glucose 2 ATP 4 ADP 2 NAD+ Products: 2 Pyruvic Acid 4 ATP 2 ADP 2 NADH H2O

Fermentation When oxygen is not present, pyruvic acid moves to fermentation Since fermentation does not require oxygen, it is said to be anaerobic Fermentation recycles NADH back to NAD+ for glycolysis Two main types of fermentation: Alcoholic Fermentation Lactic Acid Fermentation

Alcoholic Fermentation Yeast and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide Used by bakers to cause bread to rise or brewers to make beer Pyruvic Acid +NADH→Alcohol +CO2+NAD+

Lactic Acid Fermentation In many cells, the pyruvic acid accumulated can be converted into lactic acid Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues Buildup of lactic acid is the burning, painful sensation in your muscles Some prokaryotes produce lactic acid to produce: cheese, yogurt, buttermilk, sour cream, pickles, and sauerkraut Pyruvic Acid +NADH→Lactic Acid +NAD+