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1 Overview: Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. 6O2 + C6H12O6 6H2O + CO2 + energy 2 Fermentation: The process of releasing energy in the absence of oxygen 3 How much energy is in food? • One calorie is the amount of energy needed to raise one gram of water by 1 degree Celsius. • One Calorie = one kilocalorie (food labels) • One gram of sugar yields 3811 calories of heat energy 4 Both processes begin with glycolysis (anaerobic) • The process in which one molecule of glucose is broken in half, producing 2 molecules of pyruvic acid. (3-C compound) • 2 ATPs are needed to start reaction, and 4 are produced, so there is a net gain of 2 ATP. • Electrons are passed to NAD+ molecules • Takes place in the cytoplasm 5 Glycolysis C6H12O6 + NAD+ 2 pyruvic acids + NADH 6 Fermentation • When oxygen is not present, fermentation releases energy from food molecules. • NADH is converted back to NAD+ by passing high energy electrons to pyruvic acid, allowing glycolysis to continue. 7 2 paths of fermentation Alchoholic fermentation: Yeasts and other microorganisms use pyruvic acid to form ethyl alchohol and CO2 and NAD+ Lactic Acid Fermentation: In some cells, such as muscle cells, pyruvic acid is converted to lactic acid and NAD+ 8 Krebs Cycle (citric acid cycle) • Pyruvic Acid is broken down to carbon dioxide in a series (5 steps) of energyextracting reactions • Takes place in the mitochondrial matrix • CO2 is the by-product • One glucose (2 turns of cycle) 6 NADH + 2 FADH2 + 2 ATP + 4 CO2 9 ELECTRON TRANSPORT CHAIN • Takes place in cristae (inner mitochondrial membrane) • 32 ATP produced in most eukaryotes; prokaryotes 34 • High-energy electrons (from NADH and FADH2 ) are passed along a series of carrier proteins (ETC) until the end where there is an enzyme that bonds the e-’s to hydrogen ions and oxygen water. • The energy passed along the ETC is used to move H+ ions into the intermembrane space. • ATP synthase provides channels for H+ ions to pass through. • Each time it “rotates” an ADP and a P are attached. • Aerobic respiration is about 40% efficient. The rest of the energy is lost as heat. 10 Energy and exercise • Muscle cells normally contain small amounts of ATP, enough for a few seconds of intense activity • Muscles use lactic acid fermentation (about 90 sec) Extra oxygen is needed to break it down. • Glycogen is used for about 20 minutes. Then, stored molecules must be broken down 11