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Biology Unit 2 - Cellular Respiration and Photosynthesis

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Western University
Biology 1001A
Charles Jones

Biology Unit 2 – Review Chapter 9 – Cellular Respiration Introduction - The energy stored in organic food ultimately comes from the sun Organic molecules + O 2 Light  Photosynthesis Cellular Resp.  ATP  Heat CO +2H O 2 - Catabolic pathway: energy stored in bonds, enzymes break bonds, energy is released to do work/heat - Fermentation: catabolic pathway, degrading of sugar w/o O 2 - Cellular respiration: most prevalent and efficient catabolic pathway for production of ATP, O an2 organic molecules are consumed, happens in mitochondria Organic compound + oxygen  carbon dioxide + water + energy C 6 O12 O6 CO 2 H O 2 2 - An exergonic rxn, can happen spontaneously Redox Rxns - - OIL RIG (oxidation = losing, reduction = gaining e ) - Reducing agent: e donor - - Oxidizing agent: e acceptor - Sometimes change the degree of e sharing (change covalent bonds) Oxidized CH + 2 O  CO + 2 H O + energy 4 2 2 2 Reduced - CH 4CO – the 2 move closer to oxygen and farther from carbon - - O 2H O – 2he e move closer to oxygen * Oxygen is very electronegative, one of the most potent oxidizing agents - Glucose is oxidized (seen in cell. resp. reaction) - Hydrogen transfer from glucose to oxygen, liberates energy for ATP synthesis - Glucose oxidized in various steps, increases control, not all energy released at once - H atoms passed to coenzyme NAD , e acceptor, takes 2 e and 1 p (other p is released + + as H ) - NAD most versatile acceptor in cell. resp. , very little energy is lost w/ transfer - - Electron transport chain: a sequence of e carrier molecules (membrane proteins) that - shuttle e during redox rxns o Releases energy gradually - o At the end of the chain, oxygen accepts the e o More efficient than one explosion (lose less energy) Stages of cellular respiration: 1. Glycolysis 2. The citric acid cycle (Krebs cycle) - 3. Oxidative phosphorylation (e transport and chemiosmosis) - Glycolysis: the splitting of glucose into pyruvate, the one metabolic path. Occurring in ALL cells, occurs in cytoplasm, no O is r2quired - Citric acid cycle: chem. Cycle involving 8 steps, completes the breakdown of glucose into CO ,2occurs in mitochondria - Oxidative phosphorylation: the production of ATP using energy derived from redox rxns of the e transport chain, happens in inner mitochondrion, accounts for 90% of ATP - * b/w citric a. cycle and oxy. phos. There is the e transport chain - Substrate-level phosphorylation: the formation of ATP by directly transferring a phosphate group to ADP from intermediate substrate in catabolic rxn - 1 glucose = 36-38 ATP Glycolysis - Glucose (6-C) split into 2 3-C sugars, 3-C sugars oxidized into pyruvate - Energy investment phase = 2 ATP used Net products: 2 ATP, 2 NADH - Energy payoff phase = 4 ATP and 2 NADH made - Glyc. Only releases ¼ energy in glucose - Occurs whether O pre2ent or not (if present, continue to Krebs cycle) Summary of glycolysis: 1. Glucose - enzyme transfers P from ATP to sugar (traps it in cell, membrane impermeable to ions) 2. Glucose-6-phosphate  fructose-6-phosphate (isomer) 3. Fructose-6-phosphate - Enzyme transfers P from ATP to sugar 4. Fructose-1,6-biphosphate - enzyme cleaves sugar into 2 3-C sugars 5. Dihydroxyacetone phosphate & glyceraldehyde-3-phosphate – enzyme makes it possible to switch b/w isomers, only glyceraldehyde-3-phosphate is used in rest of process + 6. glyceraldehyde-3-phosphate – an enzyme catalyzes 2 rxns: sugar is oxidized by NAD (and H ) formed, this rxn releases energy attaching another P to sugar 7. 1,3-biphosphoglycerate – the P added in step 6 is transferred to ADP ATP, no longer a sugar, now an organic acid 8. 3-phosphoglycerate - enzyme relocates P 9. 2-phosphoglycerate - enzyme extracts H O crea2ing a double bond 10. Phosphenolpyruvate (PEP) – this is an unstable molecule, enzyme transfers P to ADP  ATP 11. Pyruvate – final product * remember that steps 6-11 happen to both sugars formed in step 4  2x the products Citric Acid/ Krebs Cycle - If O is present, pyruvate enters c.a.c. via active transport 2 - Junction b/w glycolysis and c.a.c. is when pyruvate is changed to Acetyl CoA: o Pyruvate’s carboxyl group is removed, giving off a CO molec. 2 o The remaining 2-C molec. Is oxidized to create acetate, e transferred toNAD + o Coenzyme A (sulfur-containing, derived from B Vitamin) attached with unstable bond  reactive - Produces 3 CO mol2c. (including 1 in transition step ) Per cycle - Generates 1 ATP, most chem. energy is transferred to 3 NAD and 1 FAD + Summary of C.A.C: 1. Acetyl CoA + oxaloacetate  citrate (CoA-SH removed) 2. Citrate - converted to isocitrate, H O rem2ved and then added again 3. Isocitrate - loses CO , pr2duct is oxidized by NAD NADH 4. -ketoglutarate - another CO is lost2 product is oxidized by NAD NADH, product is attached to CoA by unstable bond 5. Succinyl CoA - CoA is displaced by P, P then transferred to GDP  GTP ADP ATP 6. Succinate - 2 H atoms transfer to FAD  FADH 2 7. Fumarate - H O add2d, rearranges bonds 8. Malate - oxidized, changing NAD  NADH + 9. Oxaloacetate – continues through cycle Oxidative Phosphorylation Electron transport: - - e transport chain : collection of molec. and proteins embedded in membrane of mitochondria, multi-protein complex - prosthetic groups: bound to proteins, non-protein compound essential for enzyme fnc - free energy drops as going down chain - - - e carriers get reduced from “uphill” neighbour, passes e to “downhill” neighbour - Summary of e Transp-rt Chain: st 1. NADH e transferred to 1 molec (a flavoprotein, its prosthetic group is flavin mononucleotide) 2. FMN passes e to iron-sulfur protein - 3. FeS passes e to ubiquinone (Q; small, hydrophobic, non-protein) 4. Continues down the chain in this order: Q, Cyt b, FeS, Cyt c , Cyt c, C1t a, Cyt a 3 - + 5. At the end oxygen picks up 2 e and 2 H forming H O 2 * FADH e enter too, @ II protein through Q: FADH  FAD  FeS  Q, Cyt b, FeS, Cyt 2 2 c1, Cyt c, Cyt a, Cyt a 3 (⅓ less energy released) - - Cytochromes: iron-containing protein (heme prosthetic group attracts/carries e ) Chemiosmosis: - Inner mitochondrial membrane is populated w/ ATP synthase (ADP + P  ATP) + + - Hydrogen (p ) gradient fuels ATP synthase, diff. [C] of p - Chemiosmosis: energy coupling mechanism, uses energy stored in H gradient to do+ cellular work Summary of ATP Synthase: 1. Rotor w/in the membrane spins as H passes through it and the stator (in the membrane, holds knob in place) 2. A rod attached to a rotor spins as well, activating 3 catalytic sites in
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