Bio 110 Lec Chapter 9 Cellular Respiration And Fermentation

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Fermentation

Back 1

- ATP-producing catabolic pathway in which both electron donors and acceptors are organic compounds

- can be anaerobic catabolism of organic nutrients

- results in partial degradation of sugars

- yields 18x less ATP than fermentation

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Cellular respiration

Back 2

- ATP-producing catabolic process where inorganic molecule (e.g. oxygen) accepts electron

- Organic compounds (food) + Oxygen -> Carbon dioxide + Water + Energy

- carbs, proteins, and fats can all be metabolized, but most often described as glucose:

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP + heat)

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Redox reactions

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- involves partial or complete transfer of electrons

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Oxidation

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- GE R OA

- in cellular respiration: C6H12O6 -> 6CO2

- not oxidzed in one explosive step, but enzymes gradualy lower activation energy so oxidation can happen in a stepwise fashion

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Reduction

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- LE O RA

- in cellular respiration: 6O2 + 6H2O

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Reducing agent

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- substance that is oxidized

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Oxidizing agent

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- substance that is reduced

- NAD+ functions as oxidizing agent: NAD+ to NADH

- NAD+ reaction catalyzed by dehydrogenases, which:

(1) remove 2E2P from substrate

(2) deliver 2E1P to NAD+

(3) release remaining H+ in surrounding solution

substrate + NAD+ -dehydrogenase-> oxidized substrate + NADH + H_

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NAD+

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- electron acceptor to which hydrogens stripped from glucose are passed

- Nicotinamide adenine dinucleotide: dinucleotide that functions as a coenzyme in redox reactions of metabolism

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Glycolysis

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- in cytosol

- glucose (6C) into two pyruvate (3C)

- 2 ATP invested, 4 ATP 2NADH produced

(1) Energy-investment

i. C6 of glucose phosphorylated by hexokinase (1 ATP) -> glucose-6-phosphate

ii. isomerase rearranges G6P -> fructose-6-phosphate

iii. C1 of F6P phosphorylated by phosphofructokinase (1 ATP) -> fructose-1,6-diphosphate

iv. F16D cleaved by aldolase -> dihydroxyacetone phosphate and glyceraldehyde phosphate

v. dihydroxyacetone phosphate pulled towards glyceraldehyde phosphate by isomerase

(2) Energy-yielding

via. Glyceraldehyde phosphate oxidized by triose phosphate dehydrogenase -> 1,3-diphosphoglycerate; NAD+ reduced -> NADH + H+

vib: C1 of 1,3-dipg phosphorylated with inorganic phosphate in cytosol

vii. High-energy bond in 1,3-dipg transferred to ADP -> 2ATP!!~~ and 3-phosphoglycerate

viii. C3 phosphate group on 3-phosphoglycerate transferred to C2 -> 2-phosphoglycerate

ix. water molecule removed, creating double bond between C1 and C2 -> phosphoenolpyruvate

x. PEP phosphorylated, transferred to ADP -> 2 ATP!!UIOFU)(# + pyruvate

- can also hydrolyze: starch -> glucose, proteins -> amino acids (excess converted to intermediates) -> fats oxidized to ATP

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Krebs cycle

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- in mitochondrial matrix

- acetyl CoA (pyruvate derivative) -> carbon dioxide

- pyruvate to acetyl CoA: 2 NADH

- produces 2 ATP (6), 6 NADH (4, 5, 9), 2 FADH2 (7)

- 2 rounds required to oxidize glucose

(1) Pyruvate oxidized -> acetyl CoA

i. CO2 from carboxyl group of pyruvate removed, releasing CO2

ii. 2C-fragment oxidized to acetate, and NAD+ reduced to NADH

iii. CoA attached to acetyl group

(2) 2C acetyl bonds to 4C acetylate -> 6C citrate (when conc. up, Gly step 3 slows, keeps rates in sync)

(3) Citrate isomerized -> isocitrate

(4) Isocitrate loses CO2 -> 5C a-ketogluterate; NAD+ reduced -> NADH

(5) CO2 removed from a-keto, CoA attached -> 4C Succinyl CoA; NAD+ reduced -> NADH

(6) CoA displaced by a phosphate group, transferred to GDP -> GTP and succinate; GTP transfers phosphate group to ADP -> ATP !!#!#

(7) Succinate oxidized -> fumarate; FAD reduced -> FADH2

(8) Fumarate + water -> malate

(9) Malate oxidized -> oxoacetate; NAD+ reduced -> NADH

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Oxidative phosphorylation

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- ATP synthesis

- NADH and FADH2 pass electrons down electron transport chain to oxygen -> every successive carrier has higher EN

- NADH -> H2O + 2-3 ATPs per electron pair from NADH

- FADH contributes e- at lower energy level -> worth 2 ATPs max

- resulting protein gradient stores potential energy which can be sed to phosphorylate ATP

(1) NADH oxidized, flavoprotein reduced -> e- transferred from NADH to flavin mononucleotide (FMN)

(2) FMN oxidized -> passes electrons to iron-sulfur protein

(3) Iron-sulfur proteins oxidized -> passes electrons to ubiquinone (Q)

(4) Q oxidized -> passes electrons to cytochromes

(5) Cyta3, last cytochrome, passes electrons to O2

(6) O2 reduced to H2O

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Substrate-level phosphorylation

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- ATP production by direct enzymatic transfer of phosphate from an intermediate substrate to ADP

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Acetyl CoA

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- acetyl coenzyme A

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Cytochrome (cyt)

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- type of protein molecule that contains a heme prosthetic group and functions as electron carrier

- prosthetic groups: accept and donate electrons

- heme prosthetic group: 4 organic rings surrounding single iron atom -> iron transfers electrons

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ATP synthase

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- enzyme that makes ATP using proton gradient

- allows H+ to diffuse back across the membrane, which causes phosphorylation of ADP

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Chemiosmosis

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- coupling between chemical reactions (phosphorylation) and transport processes (proton transport)

- pumps H+ across membrane from mitochondrial matrix -> inner membrane -> intermembrane space

- phospholipid bilayer is imp[ermeable to H+ so no backflow

- surface area for chemiosmosis increasd by cristae

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Protein-motive force

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- pH in intermembrane space is lower than in matrix, but sae as cytosol because outer mitochondrial membrane is permeable to proons

- potential energy stored in proton gradient: two components

(1) chemical gradient: concentration gradient of protons

(2): electrical gradient: voltagee across membrane

- drives cellular work!

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Aerobic

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- existing in the presence of oxygen

- pyrvate oxidized further by substrate-level phosphorylation and oxidative phosphorylation

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Anaerobic

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- existing in the absence of free oxygen

- pyruvate reduced, no dditional ATP produced

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Alcohol fermentation

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- pyruvate -> ethanol

(1) pyruvate loses CO2 -> converted to 2C acetaldehyde

(2) NADH oxidized -> NAD+; acetaldehyde redudced -> ethanol

- bacteria and yeast

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Lactic acid fermentation

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(1) pyruvate reduced -> lactate

(2) NADH oxidized -> NAD+

- cheese and yogurt

- muscle cells switch to lactic acid fermentation when O2 scarce -> lactate accumulates -> carried to liver -> converted back to pyruvate

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Facultative anaerobe

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- capable of growth in either aerobic or anaerobic environments

- e.g. yeasts, bacteria, mammalian muscle cells

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Beta oxidation

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- converts energy in fats to acetyl CoA

- resulting 2C fragments can enter Krebs cycle