General Biology/Cells/Respiration

Glucose + O2 → CO2 + H2O + ATP (Adenosine Triphosphate) Energy Energy is primarily in C-H bonds (C-O too) Chemical energy drives metabolism Autotrophs: harvest energy through photosynthesis or related process (plants, algae, some bacteria) Heterotrophs: live on energy produced by autotrophs (most bacteria and protists, fungi, animals) Digestion: enzymatic breakdown of polymers into monomers Catabolism: enzymatic harvesting of energy Respiration: harvesting of high energy electrons from glucose Respiration Transfer of energy from high energy electrons of glucose to ATP Energy depleted electron (with associated H+) is donated to acceptor molecule Aerobic respiration: oxygen accepts electrons, forms water Anaerobic respiration: inorganic molecule accepts hydrogen/electron Fermentation: organic molecule accepts hydrogen/electron Respiration of glucose C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy ΔG = -720 kcal/mole under cellular conditions Largely from the 6 C-H bonds Same energy whether burned or catabolized In cells, some energy produces heat, most is transferred to ATP Alternative anaerobic respiration Methanogens (Archaebacteria). CO2 is electron acceptor, forming CH4 Sulfur bacteria SO4 reduced to H2S Formation of H2S set stage for evolution of photosynthesis (H2S as electron donor before H2O) About 2.7 by, based on ratio of 32S/34S, where only biological processes produce 32S enrichment Glycolysis overview Glycolysis accounting Oxidation Two electrons (one proton) are transferred from each G3P to NAD+ forming NADH 2NADH Substrate level phosphorylation G3P to pyruvate forms 2 ATP molecules 4 ATP (from 2 G3P) –2 ATP (priming) 2 ATP (net gain) Summary: The net input of glycolysis is 2 ATP molecules which are used to split one glucose molecule. The net yield of this step is 2 ATP and 2 pyruvate. Regeneration of NAD+ Reduction of NAD+ to NADH can deplete NAD+ supply; it must be regenerated Two pathways, coupled to fate of pyruvate With oxygen: enter electron transport chain, forming water (and ATP) Without oxygen: fermentation lactate ethanol Alcohol fermentation Lactate formation Either lactic acid or alcohol can be formed as a result of anaerobic respiration in cells. Krebs cycle: overview Matrix of mitochondrion Priming steps Joining of acetyl-CoA to oxaloacetate Isomerization reactions Energy extraction steps in Krebs cycle Per glucose 6 NADH 2 FADH2 2 ATP (from GTP) 4 CO2 ATP production Chemiosmosis (Mitchell) H+ (from NADH and FADH2) is pumped against a gradient into the intermembranal space of the mitochondrion (creates voltage potential) Diffusion back into matrix through ATP synthase channels drives synthesis of ATP (ADP + Pi → ATP) ATP exits mitochondrion by facilitated transport Evolution of aerobic respiration Preceded by evolution of photosynthesis (O2 needed; also, prior evolution of electron transport and chemiosmosis) High efficiency of ATP production compared to glycolysis Fostered evolution of heterotrophs Fostered evolution of mitochondria by endosymbiosis in eukaryotes