Cellular Respiration: Harvesting Chemical Energy Chapter 9

Life Is Work Living cells require energy from outside sources Plants  E from ? Animals  E from ?

Energy flows into ecosystem as light Photosynthesis in chloroplasts CO2 + H2O Cellular respiration in mitochondria Organic molecules + O2 ATP powers most cellular work Heat ATP ATP powers work Energy leaves as heat

Photosynthesis Cellular respiration Organelle = ? Generates O2 and organic molecules Cellular respiration Uses organic molecules to generate ATP

Catabolic Pathway review Organic molecules have potential (chemical) energy Exergonic rxns break down organic molecules  energy (and heat)

Cellular Respiration Aerobic respiration Anaerobic respiration Uses O2 ATP produced Anaerobic respiration Does not use O2 ATP produced

Cellular respiration Glycolysis Anaerobic Occurs in cytoplasm Anaerobic Glucose + 2NAD+ + 2ATP  2 pyruvate+ 2NADH + 4ATP 1 glucose  2 ATP and 2 pyruvate Glucose oxidized to pyruvate (loses electron) NAD+ reduced to NADH (gains electron)

Glycolysis CYTOSOL Electron donor mitochondrion Electrons carried Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH Electron donor mitochondrion CYTOSOL

Glycolysis 1. Energy investment phase uses 2 ATP 2. Energy payoff phase  4 ATP produced 2NAD+ reduced to 2NADH 1 glucose split to 2 pyruvate Glucose + 2NAD+ + 2ATP  2 pyruvate+ 2NADH + 4ATP

Energy investment phase Glucose 2 ADP + 2 P 2 ATP used formed 4 ATP Energy payoff phase 4 ADP + 4 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net 4 ATP formed – 2 ATP used 2 NADH + 2 H+

10 enzymatic steps in glycolysis

2. Citric acid cycle (Krebs cycle) mt matrix Matrix is enclosed by the inner membrane What’s in the matrix? Enzymes (acetyl CoA) mtDNA Ribosomes

Citric acid cycle Where did the pyruvate come from? 2Pyruvate + NAD+ + FADH  2ATP + NADH + FADH2 + CO2 + H2O Where did the pyruvate come from? How did it get into the mt matrix? # ATP generated? Waste product? Where does it go? NADH and FADH2 can donate electrons later What happened to the sugar? O2?

MITCHONDRION Mitochondrion Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH Electrons carried via NADH and FADH2 Citric acid cycle MITCHONDRION

citric acid cycle 1. Convert 2pyruvate to 2acetyl A (before cycle) Acetyl CoA links glycolysis to cycle

Pyruvate diffuses into mt matrix and is converted to acetyl CoA CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Pyruvate Transport protein CO2 Coenzyme A Acetyl CoA Cellular Respiration: Bioflix animation

2. The citric acid cycle

8 enzymatic steps ATP: For each pyruvate? For each glucose? NAD+ NADH + H+ Acetyl CoA CO2 CoA Citric acid cycle FADH2 FAD 2 3 3 NAD+ + 3 H+ ADP + P i ATP 8 enzymatic steps ATP: For each pyruvate? For each glucose? For each turn of cycle?

Summary of citric acid cycle Per molecule glucose =2 pyruvate NADH and FADH 2 electron donors 2 ATP (1 per turn) per glucose CO 2 produced (2 per turn)  out mt matrix BIO 231 TCA cycle animation: Acetyl CoA formation Text Activity: The Citric Acid Cycle

3. oxidative phosphorylation in mt cristae Cristae compartmentalize mt inner membrane = more surface area

What happens? NADH and FADH 2 donate electrons in the series of steps Oxygen accepts electrons  water H+ proton gradient ADP + P  ATP 34 ATP produced Add up the ATP yield per glucose: Glycolysis + Citric acid cycle + Ox Phos =

Oxidative phosphorylation:  34 ATP Mitochondrion Substrate-level phosphorylation ATP Cytosol Glucose Pyruvate Glycolysis Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidative Citric acid cycle phosphorylation: electron transport and chemiosmosis

Stepwise Energy Harvest via Electron Transport Chain 1. Controlled rxns Free energy, G (a) Uncontrolled reaction H2O H2 + 1/2 O2 Explosive release of heat and light energy (b) Cellular respiration Controlled energy for synthesis of ATP 2 H+ + 2 e– 2 H + 1/2 O2 (from food via NADH) 2 H+ 2 e– Electron transport chain

NADH NAD+ 2 FADH2 FAD Multiprotein complexes Fe•S FMN Q  Cyt b   Cyt c1 Cyt c Cyt a Cyt a3 IV Free energy (G) relative to O2 (kcal/mol) 50 40 30 20 10 (from NADH or FADH2) 2 H+ + 1/2 O2 H2O e– 2. electron transport is a fall in energy during each step to control release of fuel energy FADH2 donates its electrons later – so provides less energy than NADH

Electron Transport Chain powered by redox reactions Overview: Wiley Electron Transport: Wiley Watch the electrons Prokaryotes carry out electron transport in the plasma membrane. In mitochondria, the proteins are embedded in the crisate – the folds provide surface area. The proteins are numbered I – IV. There are non-protein prosthetic groups which provide function for enzymes. BIO 231 Electron transport animation Watch the electrons

In addition to electron transfer……. 3. H+ ions pumped out

H+ gradient, a proton force ET chain e- pumps H+ across mt membrane H+ gradient drives ATP production Interactive concepts Watch the H+ ions

Mcgraw hill electron transport Watch the H+, no audio

Chemiosmosis couples energy of electron transport to ATP synthesis

ATP synthase H+ ion enters for one turn ADP + P  ATP INTERMEMBRANE SPACE Rotor H+ Stator Internal rod Catalytic knob ADP + P ATP i MITOCHONDRIAL MATRIX ATP synthase H+ ion enters for one turn ADP + P  ATP Virtual Cell: Electron Transport Chain animation

Electron transport chain 2 H+ + 1/2O2 H2O Protein complex of electron carriers H+ Cyt c Q    V FADH2 FAD NAD+ NADH (carrying electrons from food) Electron transport chain 2 H+ + 1/2O2 H2O ADP + P i Chemiosmosis Oxidative phosphorylation ATP synthase ATP 2 1

An Accounting of ATP Production by Cellular Respiration Most energy: glucose  NADH  electron transport chain  proton-motive force  ATP = ~38 ATP total

Maximum per glucose: About 36 or 38 ATP + 2 ATP +2ATP + about 32 or 34 ATP Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA Glycolysis Glucose Pyruvate 2 NADH 6 NADH 2 FADH2 CYTOSOL Electron shuttles span membrane or MITOCHONDRION Glycolysis Citric Acid Cycle Ox. Phos. Cytosol mt mt

Anaerobic respiration (no O2)

Anaerobic respiration (cytoplasm) Prokaryotes Eukaryotes Generate ATP without O2 Glycolysis Fermentation

Fermentation No electron transport chain NAD+ reused in glycolysis (way to keep generating ATP without O2)

Alcohol fermentation Pyruvate + NADH  ethanol + NAD+ + CO2 Bacteria Yeast by humans for:

(a) Alcohol fermentation 2 2 ADP + 2 P i 2 ATP Glucose Glycolysis 2 Pyruvate 2 NADH 2 NAD+ + 2 H+ CO2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2

Lactic acid fermentation Pyruvate + NADH  lactate + NAD+ Bacteria, fungi in cheese making Human muscle cells use lactic acid fermentation to generate Pyruvate + NADH  lactate + NAD+ ATP when O2 is low.

(b) Lactic acid fermentation Glucose 2 ADP + 2 P i 2 ATP Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate 2 Lactate (b) Lactic acid fermentation

Fermentation (no O2) vs. Aerobic Respiration Both use glycolysis to oxidize glucose (and other organic fuels ) to pyruvate ATP Cellular respiration  38 ATP per glucose Fermentation  2 ATP per glucose

Facultative anaerobes Obligate anaerobes fermentation cannot survive in the presence of O2 Ex. clostridium botulinum Facultative anaerobes Yeast and many bacteria can survive using either fermentation or cellular respiration (pyruvate can be used either way) Ex. E. coli, Streptococcus In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

Facultative anaerobe Glucose Glycolysis CYTOSOL Pyruvate O2 present: No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Acetyl CoA Ethanol or lactate Citric acid cycle

The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms Glycolysis probably evolved in ancient prokaryotes before O2 on planet

Glycolysis and the citric acid cycle connect to other metabolic pathways

The Versatility of Catabolism Glycolysis and fuel Carbohydrates – many accepted Proteins  amino acids;  glycolysis or the citric acid cycle Fats  glycerol  glycolysis Fatty acids  acetyl CoA An oxidized gram of fat produces >2X ATP as oxidized gram of carbohydrate

Citric acid cycle Oxidative phosphorylation Proteins Carbohydrates Amino acids Sugars Fats Glycerol Fatty Glycolysis Glucose Glyceraldehyde-3- Pyruvate P NH3 Acetyl CoA Citric acid cycle Oxidative phosphorylation

Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Most cellular respiration requires O2 to produce ATP Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions) In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP

Regulation of Cellular Respiration via Feedback Mechanisms Feedback inhibition is the most common mechanism for control If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway

Biosynthesis (Anabolic Pathways) The body uses small molecules to build other substances These small molecules may come directly from food, from glycolysis, or from the citric acid cycle