Chapter 6 Acquiring Energy

Energy for Life All energy comes from the sun Producers convert light into chemical energy (glucose bonds) Consumers eat/break bonds to release energy Energy coupling reactions recycle components Cellular respiration (break): 6O2 + C6H12O6  6CO2 + 6H2O + ATP Photosynthesis (make): ATP + 6CO2 + 6H2O  C6H12O6 + 6O2 Which reaction term applies to each?

Redox Reactions Coupled reactions that move electrons between molecules Review: electrons form bonds and energy is released when they break (endergonic or exergonic?) LEO goes GER Lose an electron = oxidation Glucose oxidized to CO2 Gain an electron = reduction O2 reduced to H20 NAD+ reduced to NADH What do all these reactions have in common?

Electron Carriers NADH and NADPH hold e-’s = high energy bonds Carry 2 e-’s and a H+ Precursor = NAD + and NADP + Molecules oxidized  e-’s released & captured Dehydrogenase

Cellular Respiration Aerobic respiration Anaerobic respiration Requires O2 High energy (ATP) yield Glycolysis Common to all paths Energy from sugar (glucose) Citric acid cycle (Kreb’s cycle) Oxidative phosphorylation (ETS and Chemiosmosis) Anaerobic respiration Doesn’t require O2 Organisms w/o mitochondria Low energy yield

Step 1: Glycolysis Aerobic and anaerobic In the cytoplasm Starts with: Glucose (6C’s) 2 ATP Ends with: 2 pyruvate (3C’s) Important products of this process: Net 2 ATP 4 ATP  substrate-level phosphorylation 2 NADH

Intermediate Step: ‘Grooming’ Starts with: 2 Pyruvate (3C’s) High energy product Ends with: 2 Acetyl-CoA (2C’s) Important products of this process: 2 CO2 Decarboxylation 2 NADH

Step 2: Citric Acid Cycle In the mitochondrial matrix Starts with: 2 Acetyl CoA Ends with: 4 CO2 Important products of this process: 2 ATP  substrate level phosphorylation 6 NADH 2 FADH2 6 C’s 4 C’s

Step 3: Electron Transport System (ETS) In the inner mitochondrial membrane Starts with: 10 NADH (previous steps) 2 FADH2 (citric acid cycle) O2 Ends with: H2O Important products of this process: H + gradient

Electrons and the Importance of Oxygen Review Electron energy determined by arrangement e-’s further from the nucleus = more PE e-’s dropping levels release E Oxygen is highly electronegative Integral protein complexes use a little less energy to ‘hold’ the electrons Extra energy transports a H+ across out of the matrix into the intermembrane space O2 is the last molecule to accept e-’s to become water Electrons from reactions in glycolysis and Kreb’s cycle

Step 4: ATP Generation (Chemiosmosis) In the inner mitochondrial membrane Starts with: H + gradient Ends with: 32 – 34 ATP ATP synthase facilitates

A Review of Cellular Respiration Substrate level phosphorylation

Fermentation If no O2 available Starts with: Ends with: Glucose Ends with: Lactate or CO2 and ethanol Important products of this process: 2 pyruvate 2 ATP 2 NADH/NAD+ Makes yogurt, bread, alcoholic beverages