How Cells Release Chemical Energy

 Photosynthesis  Light energy converted into stored energy (glucose)  CO 2 + H 2 O => C 6 H 12 O 6 (glucose) + O 2  Endergonic  Cellular Respiration  Stored energy (glucose) converted into useable energy (ATP)  C 6 H 12 O 6 (glucose) + O 2 => CO 2 + H 2 O  Exergonic

 Aerobic Respiration  Requires oxygen  High energy (ATP) yield  Glycolysis—cytoplasm  Kreb’s Cycle—mitochondrial matrix  Electron Transport System—cristae  Anaerobic Respiration  Doesn’t require oxygen  Organisms without mitochondria  Low energy yield

 Step 1—Glycolysis  Glucose (6C) broken down into two PGAL (3C)  PGAL restructured into pyruvate  Produces 2 NADH  Requires 2 ATP to start  Produces 4 ATP  Net gain of 2 ATP  Glucose  P-Glucose  2 Pyruvate

 Step 2a—Acetyl-CoA  Pyruvate (3C) combines with CoA  Releases CO 2  NAD +  NADH  Forms acetyle-CoA (2C)  2 Pyruvate => 2 CO NADH

 Step 2b—Krebs Cycle  2 Acetyl-CoA enter  Transfers carbons to oxaloacetate (C4), forming citrate (C6)  Cycles through steps to rearrange citrate  2 CO 2 released  Ends forming oxaloacetate  Cycle starts again  Net gain of 4 CO 2, 6 NADH, 2 FADH 2, 2 ATP

 Step 3—Electron Transfer Phosphorylation  NADH & FADH 2 from previous steps start chain  Electrons flow through “chain” of membrane proteins  Each protein then takes H+ from above molecules and pumps them into intermembrane space  This sets up concentration gradient  H + moves down gradient through ATP synthase  Movement forms ATP from ADP & P (32 net gain)  Ends with electrons passed to O 2, combines with H + to form H 2 O

 If no oxygen, electrons can’t pass on  This backs up to NADPH, so no H + gradients  No ATP forms, starving cells

 Glycolysis  Glucose + 2ATP  4ATP + 2NADH + 2 Pyruvate  Intermediate  2 Pyruvate  2CO 2 + 2NADH + 2 Acetyl-CoA  Krebs Cycle  2 Acetyl-CoA  6NADH + 2ATP + 2FADH 2  Electron Transfer  10NADH + 2FADH 2  32ATP + 4CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2  6H 2 O + 6CO ATP + heat

 Fermenters  Protists, bacteria  Marshes, bogs, deep sea, animal gut, sewage, canned food  Some die when exposed to O 2  Some indifferent to O 2  Some can use O 2, but switch to fermentation when none around

 Glycolysis happens normally  2 Pyruvate, 2 NADH, 2 Net ATP form  Enough energy for many single-celled species  Not enough energy for large organisms

 Glucose  2 Pyruvate  2 Acetaldehyde + 2 CO 2  NADH + Acetaldehyde  Ethanol

 Yeasts  Bread  Beer  Wine

 Glucose  Pyruvate  Lactate

 Can spoil food  Some bacteria create food  Cheese, yogurt, buttermilk  Cure meats  Pickle some fruits & vegetables

 Muscle cells  Slow-twitch—light, steady, prolonged activity Marathons, bird migrations Many mitochondria Only aerobic respiration “dark” meat in birds  Fast-twitch—immediate, intense energy Weight lifting, sprinting Few mitochondria Lactate fermentation Produce ATP quickly, but not for long “white” meat in birds

 Glucose absorbed through intestines  When glucose level rises, glucose converted to glycogen  Diverts at glucose-6- phosphate in glycolysis

 Glycogen is storage polysaccharide  Stores in liver & muscles  With low blood glucose, insulin released  This triggers glycogen to convert back to glucose  If too many carbohydrates/glucose in blood, acetyl-CoA diverted & made into fatty acid

 Body stores most fats as triglycerides  When glucose levels fall, triglycerides used  Enzymes remove glycerol

 Glycerol converted to PGAL  PGAL converted to pyruvate as in glycolysis

 Happens when eat too many proteins, or when carbohydrates & fats used  Enzymes break down protein molecules  Ammonia (NH 3 ) removed  Leftover carbon backbone split  Forms acetyl-CoA, pyruvate, or intermediate of Krebs cycle  Specific amino acid determines which is formed