Chapter 4 Cells and Energy Cellular Respiration

Cellular respiration  Process by which food molecules are broken down to release energy  Glucose and other 6-carbon sugars are major sources of energy  Aerobic processes require oxygen  Anaerobic processes don’t need oxygen

Releasing energy with O 2  process involves 4 steps Glycolysis Converting pyruvic acid to acetic acid Citric acid cycle (Kreb’s cycle) Electron transport chain

Glycolysis  6-carbon glucose breaks down to 2 molecules of pyruvic acid (each with 3- carbons)  No oxygen required  Also produces 2H+ ions and 2electrons that are picked up by 2NAD+  Uses 2ATP and produces 4ATP (net production of 2ATP)  Occurs in cytoplasm

Section 9.3 Summary – pages Glycolysis Glucose 2ATP 2ADP 2PGAL 4ADP + 4P 2NAD+ 2NADH + 2H + 4ATP 2 Pyruvic acid

Fermentation  Lactic Acid Pyruvic acid from glycolysis is converted to lactic acid NADH + H+ is recycled to NAD+  Alcoholic Pyruvic acid from glycolysis is converted to ethyl alcohol and carbon dioxide NADH + H+ is recycled to NAD+

Fermentation  Lactic acid fermentation occurs in cytoplasm of muscle cells (causes muscle soreness)  Alcoholic fermentation occurs in bacteria and yeast  Both forms occur in the cytoplasm WITHOUT oxygen

Pyruvic acid to acetic acid  2 Pyruvic acids moves from the cytoplasm into the mitochondria  Each pyruvic acid loses a C to CO 2 to make acetic acid  2 Acetic acids are combined with coenzyme A to make 2 acetyl-CoA  2H+ and 2 electrons are picked up by NAD+

Section 9.3 Summary – pages Pyruvic acid Outside the mitochondrion Mitochondrial membrane Inside the mitochondrion Pyruvic acid Intermediate by-product NAD + NADH + H + CO 2 Coenzyme A - CoA Acetyl-CoA Pyruvic Acid

Citric acid cycle (Kreb’s cycle)  Each acetyl-CoA enters the cycle and combines with the 4-carbon oxaloacetic acid to make citric acid  Citric acid loses a C to CO 2 and releases H+ to NAD+ to become ketoglutaric acid  Ketoglutaric acid loses a C to CO 2, stores energy in an ATP and releases H+ and electrons to NAD+ to make succinic acid

Kreb’s continued  Succinic acid releases H+ and electrons to NAD+ and FAD and converted back to oxaloacetic acid  Products of Kreb’s cycle 4 CO 2 2 ATP 6 NADH + H+ 2 FADH

Section 9.3 Summary – pages The Citric Acid Cycle (Acetyl-CoA) Citric acid NAD + NADH + H + O==O (CO 2 ) NAD + O==O (CO 2 ) ADP + ATP FAD FADH 2 Citric Acid Cycle NAD + NADH + H + Oxaloacetic acid The mitochondria host the citric acid cycle. NADH + H +

Electron Transport Chain  All NADH + H+ and FADH produced go to the electron transport chain  Each NADH + H+ produces 3 ATP (30 ATP)  Each FADH produces 2 ATP (4 ATP)  Electron transport chain produces a total of 34 ATP

Section 9.3 Summary – pages The electron transport chain Enzyme Electron carrier proteins e - NADH FADH 2 NAD + FAD Electron pathway 4H + + O electrons H2OH2O H2OH2O ADP +ATP Inner membrane Center of mitochondrion Space between inner and outer membranes

Total ATP production  Net ATP in glycolysis is 2  ATP production in Kreb’s is 2  ATP production in ETC is 34  Total = 38 ATP