Cellular Respiration

Principles of Energy Harvest Ultimately, the NRG in an ecosystem begins as sunlight and leaves as heat Chemical elements are recycled Photosynthesis and Respiration are essential processes that allow NRG to flow through an ecosystem

NRG from food Catabolic pathways produce ATP from organic compounds Fermentation Partially degrades sugars Occurs when no O2 present Cellular Respiration C6H12O6 + 6O2  6CO2 + 6H2O + E (ATP + heat)

Redox reactions In order to make ATP, electrons must be rearranged Oxidation/Reduction LEO the lion says GER Lose Electrons = Oxidation Gain Electrons = Reduction Reducing agent: e- donor Oxidizing agent: e- acceptor

Oxidizing agent in Respiration NAD+ (nicotinamide adenine dinucleotide) Removes electrons from food (series of reactions) NAD+ is reduced to NADH Enzyme action: dehydrogenase (removes 2 e- and 2 H+) NRG in NADH is used to make ATP (controlled production of NRG)

Electron Transport Chains Electron carrier molecules (membrane proteins) Shuttle e- that release NRG used to make ATP Sequence of reactions that prevents NRG release in one explosive step Electron route: food NADH  ETC O2 Oxygen is the final e- acceptor

Cellular respiration Glycolysis: Citric Acid (Kreb’s) Cycle: cytosol degrades glucose into pyruvate Citric Acid (Kreb’s) Cycle: mitochondrial matrix pyruvate into CO2 Electron Transport Chain: inner membrane of mitochondrion electrons passed to oxygen NRG trapped to make ATP

Glycolysis 1 Glucose ---> 2 pyruvate molecules Energy investment phase: cell uses 2 ATP to phosphorylate fuel Energy payoff phase: 4 ATP produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation Net NRG yield per glucose: 2 ATP, 2 NADH

Kreb’s Cycle For each pyruvate: If molecular O2 is present… Each pyruvate (2 from glycolysis) converted into acetyl CoA CO2 released NAD+ ---> NADH coenzyme A (from B vitamin) attached; makes molecule very reactive In each turn, 2 C atoms enter (pyruvate) and 2 exit (CO2) For each pyruvate: 3 NAD+ reduced to NADH 1 FAD+ reduced to FADH2 1 ATP molecule

Electron Transport Chain e- carriers, NADH and FADH2 donate e- to the chain e- passed “downhill” to more electronegative molecules as they move on Most carrier molecules are cytochromes have a heme group that accepts and donates e-

Chemiosmosis Electron Transport chain sets up a H+ concentration gradient e- flow is exergonic; released NRG is used to pump protons across the membrane “proton-motive force” As H+ diffuses back in, ATP synthase makes ATP Chemiosmosis: energy coupling mechanism NRG of H+ gradient drives cellular work

ATP Production ATP synthase: produces ATP using the H+ gradient harnesses flow of H+ back into matrix phosphorylates ADP to ATP (oxidative phosphorylation) Produces 32-34 molecules of ATP

Review: Cellular Respiration Glycolysis: 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6 ATP 2 NADH (acetyl CoA) = 6 ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose

Fermentation Occurs when no O2 is present Produces some ATP and replenishes NAD+ Keeps glycolysis going so some ATP can be produced Facultative anaerobes (yeast/bacteria) can survive off of fermentation alone

Types of fermentation Alcoholic Lactic acid pyruvate to ethanol Bacteria, yeast, most plants Production of bread and alcoholic beverages Lactic acid pyruvate to lactate Fungi, bacteria, human muscle cells Production of cheese and yogurt Causes muscle fatigue and pain during strenuous exercise

Other Metabolic Pathways Proteins broken down into amino acids Converted into intermediates used in glycolysis and Kreb’s Lipids Broken down into glycerol and fatty acids Glycerol transformed into an intermediate in glycolysis Fatty acids broken down by beta-oxidation and transformed into Acetyl Co-A