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Cellular Energetics Fermentation and Cellular Respiration Fermentation and Cellular Respiration • Both reactions are catabolic/anabolic? • Chemical equation for respiration: – C6H12O6 + 6O2 6CO2 + 6H2O + ATP • Both involve redox reactions (LEO says GER): – LEO: glucose to CO2 – GER: O2 to H2O • Electrons = energy! Cellular Respiration • In respiration there are 2 e- carriers: – NAD+ and FAD (oxidized forms) – NADH and FADH2 (reduced forms) • These help carry the energy from glucose to the mitochondria where it will be harnessed Cellular Respiration Cellular Respiration: 4 parts • 1. Glycolysis (splitting of sugar) – Takes place in cytoplasm – Glucose (6-C sugar) is split into 2 pyruvates (3-C molecules) – NAD+ is reduced to NADH – From 1 glucose: produces 2 (net) ATP, 2 NADH, 2 pyruvate Gycolysis Cellular Respiration: 4 parts • 2. Shuttle Step – Takes place in mitochondria – Pyruvate is decarboxylated (take off a carboxyl group) to form acetate (2-C compound) – CoA is attached to form Acetyl-CoA – Produces 1 NADH and 1 CO2 (waste) Shuttle Step Cellular Respiration: 4 parts • 3. Krebs Cycle – Takes place in the mitochondrial matrix – Produces the majority of NADH, FADH2, and CO2 (waste) – The 2-C fragment from acetyl-CoA is added to oxaloacetate to make 3-C citrate (citric acid) • Produces (x2) 3 NADH, 1 FADH2, 1 ATP and CO2 (waste) Krebs Cycle Cellular Respiration: 4 parts • 4. Electron Transport Chain and Oxidative Phosphorylation • ETC proteins embedded in the inner mitochondrial membrane • ETC membrane proteins accept e- from NADH and FADH2 • e- are passed down the ETC via redox reactions until they reach the final e- acceptor (O2) to form water • No ATP is made by ETC; must be coupled to oxidative phosphorylation via chemiosmosis (diffusion of H+ across the membrane) Cellular Respiration: 4 parts • 4 cont’d. Electron Transport Chain and Oxidative Phosphorylation • As NADH and FADH2 are oxidized, H+ inside the mitochondrial matrix is transported to the intermembrane space. This creates a proton-motive force and H+ moves back across the membrane thru ATP synthase and ATP is produced ETC Fermentation • What if O2 is not present? • Objective of fermentation is to replenish NAD+ so that glycolysis can proceed again • Takes place in the cytoplasm Lactic Acid Fermentation • Prokaryotes and humans • Pyruvate (product of glycolysis) is converted to lactate (lactic acid). In this process NADH gives up its e- to form NAD+, which can now be used again for glycolysis • Produces only 2 ATP and 2 NADH (better than zero) Alcoholic Fermentation • Fungi (yeast) • Pyruvate converted to acetaldehyde and then ethanol (ethyl alcohol) producing NAD+ which can now be used again for glycolysis • Produces only 2 ATP, 2 NADH, and 2 CO2 (carbonation in beer!) Fermentation Photosynthesis • Used by producers (autotrophs) • Takes place in the chloroplast • 2 parts: – light-dependent (the photo part- produces NADPH, ATP, and O2 (waste) – light-independent or Calvin Cycle (the synthesis part- carbon fixation- produces sugar) Photosynthesis Photosynthesis- the light reactions • Occurs in thylakoids • Chlorphyll a and b, in the photosystems, absorb photons of light and become excited when their e- gain energy • Photosystem 2 (P680) absorbs light and e- are excited • e- are now boosted to a higher level and must be replaced • H2O is split (photolysis) and the e- are replaced (and oxygen is produced) • e- pass down an ETC and ATP is produced by chemiosmosis • e- are passed to photosystem 1 Photosynthesis- the light reactions • e- are passed from P680 to Photosystem 1 (P700) where they are again boosted to a higher level • e- are passed down a 2nd ETC that produces NADPH Light Reactions Calvin Cycle • Occurs in stroma • Uses e- from NADPH and energy from ATP produced in the light reactions • One molecule of G3P exits the cycle per 3 CO2 molecules fixed and is converted to glucose • ADP and NADP+ are returned to the light reactions Calvin Cycle All together now!