Biochemical Pathways: Cellular Respiration Chapter 6 2-

Energy and Organisms Organisms are classified based on the kind of energy they use. Autotrophs Use the energy from sunlight to make organic molecules (sugar) Use the energy in the organic molecules to make ATP Heterotrophs Obtain organic molecules by eating the autotrophs Autotrophs use photosynthesis. To use the energy from light to make organic molecules All organisms use cellular respiration. To harvest the energy from organic molecules and use it to make ATP 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Energy Transformation 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cellular Respiration Respiration is a metabolic pathway of Redox Reactions Respiration oxidizes carbohydrates and transfers the energy to produce ATP The type of molecule that is reduced determines the type of respiration The energy produced is in the form of ATP 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cellular Respiration Three Types of Respiration Aerobic Respiration Oxygen is reduced to produce water Anaerobic Respiration A molecule other that oxygen is reduced may produce acids, methane, etc. Fermentation Another carbohydrate is reduced to produce alcohols 5- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1. Aerobic Respiration Glucose is Oxidized to become Carbon Dioxide Oxygen is reduced to become water The protons and electrons from the oxidation of glucose are used to produce ATPs 5- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

C6H12O6 + 6O2 + 38 ADP + 38 P 6 H2O + 6CO2 + 38 ATP 1. Aerobic Respiration C6H12O6 + 6 O2 6 H2O + 6 CO2 + Energy C6H12O6 + 6O2 + 38 ADP + 38 P 6 H2O + 6CO2 + 38 ATP 5- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1. Aerobic Respiration Aerobic Respiration is a three stage process: Stage 1: Glycolysis Stage 2: The Krebs Cycle Stage 3: Oxidative Phosphorylation (Electron Transport Chain) Each of these stages produce ATP At the end of all three stages, there is a net gain of ~38 ATP’s 5- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 1: Glycolysis Glycolysis is a 10 step metabolic pathway that cleaves glucose Glyo-lysis = “splitting glucose” Glycolysis occurs in the cell’s cytoplasm 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 1: Glycolysis Glycolysis splits glucose to make two pyruvate molecules Produces 4 ATP molecules 4 ATP made -2 ATP invested = net production of 2 ATP Reduces 2 NAD+ to make 2 NADH 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 1: Glycolysis During Glycolysis, Glucose (a 6 carbon molecule) is chopped up into 2 Pyruvates (pyruvate is a 3 carbon molecule) This is a 9 step metabolic process 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 6_07

9 Steps of Glycolysis Summary Glucose is phosphorylated - costs 1 ATP to become Glucose-6-Phosphate Glucose-6-P is converted to Fructose-6-P Fructose-6-P is phosphorylated - costs 1 ATP to become Fructose-1,6-bisphosphate Fructose-1,6-bisphosphate is split into two molecules - each with 3 carbons and a phosphate: Dihydroxyacetone (DHAP) Glyceraldehyde-3-Phoshate (G-3-P) 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9 Steps of Glycolysis Summary G-3-P DHAP 5. G-3-P is phosphorylated to 5. DHAP is phosphorylated to become 1,3-bisphosphoglycerate become 1,3 bisphosphoglycerate 6. 1,3-bisphosphglycerate gives up 6. 1,3-bisphosphoglycerate gives up a a phosphate to an ADP, G-3-P left phosphate to an ADP, G-3-P left 7. G-3-P converted to 7. G-3-P converted to 2-Phosphoglycerate 2-Phospoglycerate 8. 2-Phosphoglycerate converted to 8. 2-Phosphoglycerate converted to Phosphoenolpyruvate Phosphoenolpyruvate 9. Phosphoenolpyruvate gives up 9. Phosphoenolpyruvate gives up its phosphate to an ADP its phosphate to an ADP 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glucose Pyruvate1 Pyruvate 2 2 ATP 4 ATP, 2 NADH

NAD+, NADH NAD+ is an electron carrier for the redox reactions of cellular respiration NAD+ accepts 2 electrons and 1 proton to become NADH Functions of NAD+, NADH NAD+ is reduced so Redox reactions can occur NAD+ is used to carry electrons from one part of the cell to another NAD+ keeps protons out of solution 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

NAD+, NADH

NAD+ Reduced to NADH

FAD, FADH2 FAD is very similar to NAD+ It has the same functions of collecting and carrying electrons and protons FAD can carry 2 Hydrogen atoms FAD is Reduced to FADH2 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 2: Kreb’s Cycle Also known as The Citric Acid Cycle or the Tricarboxylic Acid (TCA) Cycle The Krebs cycle is a metabolic pathway that further oxidizes pyruvate The Krebs Cycle occurs in the Cell membrane of Prokaryotic Cells and in the mitochondria of Eukaryotic Cells In mitochondria, a multienzyme complex called pyruvate dehydrogenase catalyzes the reaction 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 2: Kreb’s Cycle The Krebs Cycle begins with pyruvate (from Glycolysis) Remember, there are 2 pyruvates made from each Glucose, so there are 2 Krebs Cycles for every glucose molecule During a Kreb’s Cycle the pyruvate (a 3 carbon molecule) will be completely oxidized to become 3 carbon dioxide molecules (one carbon atom each) 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cellular Respiration C6H12O6 + 6O2 6H2O + 6CO2 + Energy Glucose Oxygen Water Carbon Dioxide The Kreb’s Cycle produces the CO2 that we exhale 5- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 2: Kreb’s Cycle Important steps in the Kreb’s Cycle Pyruvate is converted to acetyl-CoA Acetyl-CoA combine with Oxaloacetate (in the mitochondria) to make Citrate The cycle ends with the production of oxaloacetate, ready for anther turn of the cycle 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 6_05

Stage 2: Kreb’s Cycle During the Kreb’s Cycle enough energy is released from one pyruvic acid molecule to produce: 1 ATP 4 NADH from 4 NAD+ 1 FADH2 from 1 FAD. 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 6_08

Glucose 2 ATP Pyruvate1 Pyruvate 2 4 ATP, 2 NADH 2 ATP 1 ATP, 2 CO2 Pyruate converted to Acetyl Co-A 2 ATP 1 ATP, 2 CO2 4 NADH, 1 FADH2

Stage 2: Kreb’s Cycle After glycolysis and the Krebs cycle glucose has been completely oxidized to form: 6 CO2 ~5 ATP ~10 NADH ~2 FADH2 We are still short of our 36-38 ATP goal The third stage of cellular respiration uses the protons and electrons of the hydrogens on the NADH’s and FADH2’s that were produced during the first 2 stages 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Electron Transport Chain NADH, FADH2 Glucose Pyruvate1 Pyruvate 2 2 ATP 4 ATP, 2 NADH Pyruate converted to Acetyl Co-A 2 ATP 2 ATP, CO2 8 NADH, 2 FADH2 34 ATP Electron Transport Chain NADH, FADH2

Stage 3: Electron-Transport System The electron transport chain (ETC) is a series of membrane-bound electron carrier molecules called cytochromes embedded in the mitochondrial inner membrane Electrons from NADH and FADH2 are transferred to cytochromes of the ETC Each cytochrome transfers the electrons to the next cytochromes in the chain 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 7.13a

Stage 3: Electron-Transport System As the electrons are transferred, some electron energy is released with each transfer This energy is used by the cytochromes to pump protons (H+) across the membrane from the matrix to the inner membrane space A proton concentration gradient is established 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Stage 3: Electron Transport Chain

Figure 6_06

Stage 3: Electron-Transport System There are other channel proteins in the membrane known as ATP synthases ATP synthases provide a channel for protons to rush through by diffusion The rushing protons provides the energy for ATP synthase to phosphorylate ADP to ATP 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 6_06

Figure 6_09

Cellular Respiration Recall Three Types of Respiration Aerobic Respiration Oxygen is reduced to produce water Anaerobic Respiration A molecule other that oxygen is reduced may produce acids, methane, etc. Fermentation Another carbohydrate is reduced to produce alcohols 5- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1. Aerobic Respiration Oxygen is the final molecule to receive the electrons as they are passed down the Electron Transport Chain Oxygen is reduced with two electrons and picks up two protons The result is water: 2O2 + 8e-’s and 8H+’s 4H2O Oxygen is the Final Electron Acceptor in Aerobic Respiration 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Electron Transport Chain

Electron Transport Chain NADH, FADH2 Glucose Pyruvate1 Pyruvate 2 2 ATP 4 ATP, 2 NADH Pyruate converted to Acetyl Co-A 2 ATP 2 ATP, CO2 8 NADH, 2 FADH2 30+ ATP And H2O Electron Transport Chain NADH, FADH2

Aerobic Cellular Respiration: Overview 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Total Yields for Aerobic Cellular Respiration per Glucose Molecule Glycolysis 2 ATP 2 NADH (converted to 2 FADH2) Kreb’s cycle 8 NADH 2 FADH2 Electron transport chain Each NADH fuels the formation of 3 ATP. 8 NADH x 3 ATP = 24 ATP Each FADH2 fuels the formation of 2 ATP. 4 FADH2 x 2 ATP = 8 ATP Total ATP=2+2+24+8=36 ATP made from the metabolism of one glucose molecule. 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Anaerobic Cellular Respiration Some cells do not require O2 as the final electron acceptor for the electron transport chain These cells perform Anaerobic Respiration Anaerobic Respiration produces fewer ATPs per glucose molecule compared to Aerobic Respiration – it is not as efficient and the exact amount of ATP production depends on the organism and the electron acceptors that are used 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Anaerobic Cellular Respiration Anaerobic respiration by methanogens methanogens use CO2 CO2 is reduced to CH4 (methane) Anaerobic respiration by sulfur bacteria inorganic sulphate (SO4) is reduced to hydrogen sulfide (H2S) 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3. Fermentation Fermentation reduces organic molecules as the final electron acceptors Ethanol fermentation occurs in yeast fermentation of sugars produces alcohol Lactic acid fermentation occurs in animal cells (especially muscles) electrons are transferred from NADH to pyruvate to produce lactic acid 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 6_10

Alcoholic Fermentation Starts with glycolysis Glucose is metabolized to pyruvic acid. A net of 2 ATP is made. During alcoholic fermentation Pyruvic acid is reduced to form ethanol. Carbon dioxide is released. Yeasts do this Leavened bread Sparkling wine 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lactic Acid Fermentation Starts with glycolysis Glucose is metabolized to pyruvic acid. During lactic acid fermentation Pyruvic acid is reduced to form lactic acid. No carbon dioxide is released. Muscle cells have the enzymes to do this, but brain cells do not. Muscle cells can survive brief periods of oxygen deprivation, but brain cells cannot. Lactic acid “burns” in muscles. 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Metabolizing Other Molecules Cells will use the energy in carbohydrates first. Complex carbohydrates are metabolized into simple sugars. Cells can use the energy in fats and proteins as well. Fats are digested into fatty acids and glycerol. Proteins are digested into amino acids. Cells must convert fats and proteins into molecules that can enter and be metabolized by the enzymes of glycolysis or the Kreb’s cycle. 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fat Respiration Fats are broken down into Glycerol Fatty acids Converted to glyceraldehyde-3-phosphate Enters glycolysis Converted to acetylCoA Enter the Kreb’s cycle Each molecule of fat fuels the formation of many more ATP than glucose. This makes it a good energy storage molecule. 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lipids Amino Acids Preparatory Steps

Protein Respiration Proteins are digested into amino acids. Then amino acids have the amino group removed. Generates a keto acid (acetic acid, pyruvic acid, etc.) Enter the Kreb’s cycle at the appropriate place 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Interconversion of Fats, Carbohydrates and Proteins 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Energy Resources Carbohydrates, fats and proteins can all be used for energy. Glycolysis and the Kreb’s cycle allow these types of molecules to be interchanged. If more calories are consumed than used The excess food will be stored. Once the organism has all of the proteins it needs And its carbohydrate stores are full The remainder will be converted to and stored as fat. 6- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.