Chapter 7: Energy for Cells

Cellular Respiration ATP molecules are produced during cellular respiration with the help of the mitochondria Respiration is the reverse of photosynthesis In photosynthesis, CO 2 is reduced to make carbohydrate In respiration, carbohydrate is oxidized along with O 2 consumption and CO 2 and H 2 O are formed as by-products

Phases of Glucose Breakdown Glucose is broken down slowly so that energy is not lost as heat Coenzymes are nonprotein helpers that assist in carrying out oxidation during cellular respiration Coenzymes NAD + and FAD receive hydrogen atoms and become NADH and FADH 2 Glycolysis: the breakdown of glucose to 2 molecules of pyruvate in the cytoplasm 2 ATP invested, 4 ATP and 1 NADH produced Preparatory reaction: pyruvate is broken down to a 2-carbon acetyl group carried by coenzyme A (CoA) Occurs in the matrix of mitochondria NADH and CO 2 produced Citric Acid Cycle: takes place in the matrix of mitochondria 1 spin produces 3 NADH, 1 FADH 2, 1 GTP and 2 CO 2 ETC: NADH and FADH 2 give up electrons to the chain in the cristae of mitochondria This energy is used for the production of ATP O 2 is the final electron acceptor and H 2 O is produced

Glycolysis Glycolysis takes place within the cytoplasm outside the mitochondria Glucose, a C 6 molecule, is broken down into 2 pyruvates, C 3 molecules 2 steps: In the energy-investment step, 2 ATPs are used to activate the substrates In the energy-harvesting step, substrates are oxidized by the removal of hydrogen atoms - 2 NADH and 4 ATP are produced - 2 pyruvates are the end product of glycolysis - If O 2 is available, pyruvate will move into the mitochondria - If no O 2 is available, pyruvate is reduced to lactate o What is the net gain of ATP for glycolysis?

Glycolysis

Inside the Mitochondria Preparatory Reaction: Occurs in the mitochondrial matrix This reaction occurs 2X per glucose Pyruvate is oxidized, CO 2 is given off NAD +  NADH C 2 acetyl group will attach to coenzyme A (CoA) to form acetyl- CoA Products: 2 CO 2, 2 NADH, 2 acetyl- CoA Citric Acid Cycle: Occurs in the mitochondrial matrix Acetyl-CoA is joined to a C 4 molecule to make a C 6 citrate molecule The acetyl group is oxidized and the CO 2 is given off NAD + and FAD accept hydrogen atoms to make NADH and FADH 2 Substrate-level ATP synthesis occurs resulting in GTP  ATP The cycle turns 2X

Inside the Mitochondria

Electron Transport Chain ATP synthase carried out ATP synthesis in the inner mitochondrial membrane (cristae of the membrane) H + gradient is created as a result of oxidation/reduction The flow of H + through the ATP synthase complex causes a conformational change and the synthase produces ATP The ETC is located in the cristae of the mitochondria The hydrogen atoms attached to NADH and FADH 2 consist of an electron (e - ) and a hydrogen ion (H + ) The ETC accepts only e - and not H + A series of oxidation-reduction occurs as the electron pairs are passed form carrier to carrier Energy is released and captured for ATP production O 2 is the final electron acceptor because it attracts electrons more than the carriers of the chain O 2 is combined with H + to form H 2 O Electrons from NADH make 3 ATP molecules, electrons from FADH 2 make 2 ATP NAD +, FAD, and ADP are recycled

Energy Yield from Glucose Metabolism Per glucose: Net gain of 2 ATP from glycolysis 2 ATP from citric acid cycle 10 NADH  30 ATP 2 FADH 2  4 ATP Total maximum number of ATP is 38 ATP

Alternative Metabolic Pathways Proteins, Fats and Oils can be used to make ATP Glycerol is a carbohydrate and can enter glycolysis Fatty acids can be broken down to acetyl groups and enter the citric acid cycle The hydrocarbon backbone from an amino acid can enter cellular respiration at the pyruvate, acetyl-CoA, or the citric acid cycle

Fermentation When O 2 is not available, fermentation takes place Fermentation is the anaerobic breakdown of glucose and the production of 2 ATP per glucose Pyruvate formed by glycolysis accepts 2 hydrogen atoms and is reduced to lactate Why is this beneficial? o Fermentation is a way to produce ATP when O 2 is in limited supply o Although fermentation results in only 2 ATP, it still provides a quick burst of ATP energy for short-term, strenuous muscular activity

Microorganisms and Fermentation Bacteria use fermentation to make organic acid, alcohol, and CO 2 Yeasts generate ethyl alcohol and CO 2 Yeasts are used to ferment grapes for wine production The desired product is ethyl alcohol