Ch. 6: Cellular Respiration Harvesting Chemical Energy

Cellular Respiration: An Overview A cellular process that breaks down nutrient molecules with the production of ATP Consumes oxygen and produces carbon dioxide (CO 2 ) ◦ Cellular respiration is an aerobic process. Usually involves the complete breakdown of glucose to CO 2 and H 2 O Occurs in 3 steps

Overview Cellular respiration is an exergonic ◦ produces up to 32 ATP molecules from each glucose molecule ◦ captures only about 34% of the energy originally stored in glucose  Other foods (organic molecules) can also be used as a source of energy.

Figure 6.2 Breathing Lungs Bloodstream CO 2 O2O2 O2O2 Muscle cells carrying out Cellular Respiration Glucose  O 2 CO 2  H 2 O  ATP

Cellular Respiration: An Overview

Terms to Know… ◦ Oxidation = the loss of electrons  Compound becomes more positive ◦ Reduction = the gain of electrons  Compound becomes more negative ◦ Electrons and protons (H + ) travel TOGETHER

energy glucose Reduction Oxidation 6H 2 O6CO 2 6O 2 C 6 H 12 O Electrons are removed from substrates and received by oxygen, which combines with H + to become water. Glucose is oxidized and O 2 is reduced

Important enzymes NAD + ◦ A coenzyme of oxidation-reduction. ◦ Each NAD + molecule is used over and over again ◦ Reduced into NADH  Accepts 2 electrons plus a hydrogen ion (H+) FAD ◦ Also a coenzyme of oxidation-reduction ◦ Sometimes used instead of NAD + ◦ Reduced into FADH 2  Accepts two electrons and two hydrogen ions (H + )

Cellular Respiration Respiration is a cumulative function of 3 metabolic stages ◦ Glycolysis  Only reactions that takes place outside of mitochondria and doesn’t require O2  Think back to the Endosymbiatic theory!!!! ◦ Citric acid cycle (Krebs Cycle)  Matrix of the mitochondria ◦ Oxidative Phosphorylation  Electron transport chain (ETC)  Occurs in the mitochondrial membrane because of the enzymes (proteins)

Cellular Respiration ATP Glucose Anaerobic Respiration (Fermentation) Aerobic Respiration (Krebs Cycle & ETC) Glycolysis Oxygen AbsentOxygen Present ATP 2

Glycolysis: “glucose-splitting” Big Picture: ◦ Glucose (6-C) is broken down into 2 molecules of pyruvate (3-C) Occurs in the cytoplasm ◦ Occurs without oxygen..again think evolution! Oxidation results in NADH and 2 ATP Made up of 2 phases: ◦ Energy investment phase ◦ Energy yielding (payoff) phase

Glycolysis: Energy Investment Phase Glucose is converted into 2 G3P (Glyceraldehyde-3- phosphate) Requires 2 ATP ENERGY IN

Glycolysis: Energy-Yielding Phase ◦ 2 G3P are converted into 2 Pyruvate (3C) molecules. ◦ Dehydrogenase enzymes remove H+ from intermediate compounds and attach them to 2 NAD to produce 2NADH

Substrate-Level Phosphorylation An enzyme transfers a phosphate group directly from an organic molecule to ADP to form ATP The ATP produced in Glycolysis & the Krebs Cycle is produced by this method.

P P P enzyme ADP ATP BPG 3PG

Net Gain in Glycolysis 2 ATP - 2 ATP (Energy investment phase) + 4 ATP (Energy yielding phase) + 2 ATP 2 NADH ◦ Electron carriers ◦ Will be used to make ATP later

Choices, Choices! Choices, Choices! If oxygen is absent, anaerobic respiration occurs ◦ Fermentation  Yeast & some bacteria  alcoholic fermentation  Animal muscle  lactic acid fermentation If oxygen is present, aerobic respiration occurs ◦ Krebs Cycle and Electron Transport Chain

Cellular Respiration ATP Glucose Anaerobic Respiration (Fermentation) Aerobic Respiration Glycolysis Oxygen AbsentOxygen Present ATP

Fermentation Fermentation is an anaerobic process that reduces pyruvate to either lactate or alcohol and CO 2 2 major types: ◦ Alcoholic and lactic acid fermentation NAD + acts as a hydrogen acceptor during glycolysis ◦ If the supply of NAD + runs out, then glycolysis would have to stop. ◦ Fermentation occurs as simply a means of recycling the NAD+, so that glycolysis can occur again.

Alcoholic Fermentation Occurs in some BACTERIA and YEAST 2 step process: ◦ Carbon dioxide is released from pyruvate (3-C), forming acetaldehyde (2-C) ◦ Acetaldehyde is reduced by NADH forming ethanol ◦ NAD + is regenerated Used to produce beer and wine

Lactic Acid Fermentation Occurs in ANIMALS 1 step process: ◦ Pyruvate is reduced by NADH forming lactic acid NAD + is regenerated Occurs in muscle cells, causing muscle pain and fatigue Used to make yogurt and cheese

Cellular Respiration ATP Glucose Anaerobic Respiration (Fermentation) Aerobic Respiration Glycolysis Oxygen AbsentOxygen Present ATP

Aerobic Respiration After glycolysis, most of the energy from glucose remains “locked” in 2 molecules of pyruvate If oxygen is present, the pyruvate enters the mitochondrial matrix to complete the Krebs Cycle Preparatory Phase: Pyruvate (3-C) is converted to Acetyl CoA (2-C) ◦ CO 2 is released as a waste product ◦ NADH is produced

The Krebs Cycle Yield per pyruvate molecule (two turns): ◦ 3 NADH ◦ 1 FADH 2 ◦ 1 ATP  (produced via substrate level phosphorylation) ◦ 2 CO 2 CO 2 released as a waste product ◦ We exhale this

Figure 6.9A Acetyl CoA Citric Acid Cycle CoA CO NAD  3 H  NADH ADP ATP P FAD FADH 2

Electron Transport Chain (ETC) Collection of cytochrome molecules embedded in the cristae membrane ◦ 4 reactions plus ATP synthase Occurs in inner membrane of mitochondrion Proton pump that produces a proton gradient that will be used to create ATP

ETC Electrons from NADH and FADH 2 from glycolysis and the Krebs Cycle lose electrons, proton gradient The energy in each NADH molecule moves enough protons (H + ) into the mitochondrial matrix to create 3 ATP ◦ 1 FADH 2  2 ATP

ETC The electrons from NADH and FADH 2 are passed from one electron acceptor molecule to another. Each electron acceptor is more electronegative than the last. Oxygen is the final electron acceptor, producing water e- oxygen

Steps of the ETC I- NADH reductase oxidizes NADH to NAD+ resulting in high energy electron II- high energy electron transfers through coenzyme Q to cytochrome reductase III- travels through the cytochrome c IV- travels into cytochrome oxidase where it is now low energy and binds to oxygen to form water

Chemiosmosis the energy the electrons lose along the way moves H + out of the matrix and into the intermembrane space of the mitochondria As H + ions diffuse through the membrane, ATP synthase uses the energy to join ADP and a phosphate group  ATP

Oxidative Phosphorylation: ETC & Chemiosmosis

Figure 6.12 NADH FADH 2 NADH FADH 2 NADH or NADH Mitochondrion CYTOPLASM Electron shuttles across membrane Glycolysis Glucose 2 Pyruvate Pyruvate Oxidation 2 Acetyl CoA Citric Acid Cycle Oxidative Phosphorylation (electron transport and chemiosmosis) Maximum per glucose: by substrate-level phosphorylation by oxidative phosphorylation ATP  2 about  ATP About ATP ATP  2

ProcessATP Produced Directly by Substrate-level Phosphorylation Reduced Coenzyme ATP Produced by Oxidative Phosphorylation Total GlycolysisNet 2 ATP2 NADH4 to 6 ATP6-8 Oxidation of Pyruvate NADH6 ATP6 Krebs cycle2 ATP6 NADH 2 FADH 2 18 ATP 4 ATP24 Total: This number is okay for prokaryotes but with eukaryotes this number is more like 30 ATP