Pathways that Harvest and Store Chemical Energy 6 Pathways that Harvest and Store Chemical Energy

Chapter 6 Pathways that Harvest and Store Chemical Energy Key Concepts 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy

Chapter 6 Pathways that Harvest and Store Chemical Energy 6.4 Catabolic and Anabolic Pathways Are Integrated 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates

Chapter 6 Opening Question Why does fresh air inhibit the formation of alcohol by yeast cells?

Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Cellular respiration is a major catabolic pathway. Glucose is oxidized: Photosynthesis is a major anabolic pathway. Light energy is converted to chemical energy (CO2 is reduced): LINK Concept 2.5 reviews the principles of catabolism and anabolism

Figure 6.7 ATP, Reduced Coenzymes, and Metabolism

Five principles governing metabolic pathways: Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Five principles governing metabolic pathways: 1. Chemical transformations occur in a series of intermediate reactions that form a metabolic pathway. 2. Each reaction is catalyzed by a specific enzyme. 3. Most metabolic pathways are similar in all organisms.

Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism 4. In eukaryotes, many metabolic pathways occur inside specific organelles. 5. Each metabolic pathway is controlled by enzymes that can be inhibited or activated.

1. How do heterotrophs obtain free energy? From food! A lot of energy is released when reduced molecules (ex: glucose) are fully oxidized to CO2.

Figure 6.8 Energy Metabolism Occurs in Small Steps

This is the equation for aerobic cellular respiration: Endergonic or exergonic? Catabolic or Anabolic? Require or Release energy? Positive or Negative change in Free Energy?

This is the equation for aerobic cellular respiration: Which substance is being oxidized? To what is this substance oxidized to? Which substance is being reduced? To what is this substance being reduced to?

Figure 6.9 Energy-Releasing Metabolic Pathways

NAD+ and FAD (oxidized forms) NADH and FADH2 (reduced form) What is an “electron shuttle” or “electron carrier”? What are the two major electron carriers in respiration? Transfer electrons and protons to other areas of cells to continue metabolism (transfer of energy!) NAD+ and FAD (oxidized forms) NADH and FADH2 (reduced form)

Glycolysis:

f. Substrate Level Phosphorylation g. NAD+ is reduced to NADH; 2 Glycolysis: a. Cytoplasm b. 10 reactions c. Glucose, 2NAD+, 2ATP d. 2 ATP e. 4 ATP f. Substrate Level Phosphorylation g. NAD+ is reduced to NADH; 2 h. 2 ATP, 2 NADH, 2 Pyruvate

Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 1)

Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 2)

Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 3)

Why is glycolysis considered to be anaerobic? Glycolysis does not require oxygen!

Why is glycolysis considered to be the most ancient metabolic pathway? It occurs in the cytoplasm of ALL living things!

Acetyl CoA a. Mitochondria b. CO2 c. Reduced 8. Before each Pyruvate molecule can enter the citric acid cycle, it is converted into... Acetyl CoA a. Mitochondria b. CO2 c. Reduced

Comparing inputs/outputs per pyruvate and per glucose molecule Acetyl CoA preparation reaction per Pyruvate 1 Pyruvate 1 NAD+ 1 Coenzyme A 1 Acetyl CoA 1 NADH 1 CO2 (waste product) Acetyl CoA preparation reaction per Glucose 2 Pyruvate 2 NAD+ 2 Coenzyme A 2 Acetyl CoA 2 NADH 2 CO2 (waste product)

Figure 6.11 The Citric Acid Cycle

9. Citric Acid Cycle (The Krebs Cycle): 2 Turns per Glucose Molecule a. Mitochondrial Matrix b. CO2; 2 c. 3 d. No; FAD is also used in this cycle e. 1 f. 1; Substrate Level Phosporylation g. To enable the cycle to continue

g. Citric Acid Cycle Summary Inputs Outputs Per Acetyl CoA Molecule 1 Acetyl CoA 3 NAD+ 1 FAD 1 ADP 2 CO2 3 NADH 1 FADH2 1 ATP Per Glucose Molecule 2 Acetyl CoA 6 NAD+ 2 FAD 2 ADP 4 CO2 6 NADH 2 FADH2 2 ATP

Although the CAC doesn’t produce a lot of ATP… **Most of the energy from glucose is stored in electron shuttles (NADH, FADH2) during this process…This energy will be released in the next step!**

Figure 6.12 Electron Transport and ATP Synthesis in Mitochondria

a. Inner mitochondrial membrane (cristae) Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy a. Inner mitochondrial membrane (cristae) b. NADH and FADH2 are oxidized to NAD+ and FAD Move back to the Cytoplasm (glycolysis) or the Matrix (Citric Acid Cycle) to be reused c. Chain of membrane-associated electron carriers that electrons from NADH and FADH2 pass through d. Actively Pump protons from the matrix into the inter-membrane space creating an electrochemical gradient e. Oxygen, Water is formed

How is ATP generated? ATP synthase in the membrane uses the H+ gradient to synthesize ATP by chemiosmosis. ANIMATED TUTORIAL 6.2 Electron Transport and ATP Synthesis

Summary of Oxidative Phosphorylation Inputs Outputs Oxidative Phosphorylation: ETC and Chemiosmosis 10 NADH 2 FADH2 Oxygen ~32-34 ATP Water 10 NAD+ 2 FAD

How much ATP is produced per glucose molecule? Between 32 and 36 molecules of ATP are produced from 1 glucose molecule (Hypothetical yield is 38 ATP) APPLY THE CONCEPT Carbohydrate catabolism in the presence of oxygen releases a large amount of energy

Why isn’t it an exact number? ATP synthesis and oxidation of electron carriers are NOT directly coupled, and therefore we cannot give an exact number of ATP produced ~ 3ATP per NADH, ~2 ATP per FADH2 APPLY THE CONCEPT Carbohydrate catabolism in the presence of oxygen releases a large amount of energy

Other macromolecules can enter various points of cell respiration: Polysaccharides are hydrolyzed to glucose, which enter glycolysis. Lipids break down to fatty acids and glycerol. Fatty acids can be converted to acetyl CoA. Proteins are hydrolyzed to amino acids that can feed into glycolysis or the citric acid cycle.

Cellular Respiration is a highly regulated process: This is accomplished by regulation of enzymes— allosteric regulation, feedback inhibition. Example: Glycolytic enzymes (a glycolysis enzyme) are a major site of control; It is stimulated by AMP, and inhibited by ATP and citrate (produced in the Krebs cycle) LINK Concept 3.4 Review the discussion of enzyme regulation

Overview of Glycolysis: Location, Inputs, Net Outputs Cytoplasm Glucose, 2NAD+, 2 ATP 2 Pyruvate, 2 NADH, 2 ATP

Two types of anaerobic respiration/fermentation pathways:

What happens after glycolysis if oxygen is not available? To prevent a cell from depleting its NAD+ molecules, fermentation occurs Fermentation allows the NADH produced in glycolysis to be oxidized back to NAD+ to enable anaerobic respiration to occur NAD+ is needed for glycolysis Fermentation takes place in the cytoplasm

In both types of anaerobic respiration, what is the overall yield of ATP? Where are these ATPs produced? 2 ATPs Glycolysis

Lactic acid fermentation: End product is lactic acid. Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy Lactic acid fermentation: End product is lactic acid. NADH is used to reduce pyruvate to lactic acid, thus regenerating NAD+. Which type of animal cells can carry out lactic acid fermentation? Why? Skeletal Muscle Cells when experiencing an Oxygen debt

Figure 6.13 A Fermentation

Alcoholic fermentation: End product is ethanol. Alcohol Fermentation Alcoholic fermentation: End product is ethanol. Pyruvate is reduced to ethanol, CO2 is produced, and NADH is regenerated.

Figure 6.13 B Fermentation

To regenerate NAD+ so glycolysis can continue to occur! If the ATP is generated during glycolysis in both types of fermentation, what is the major purpose of fermentation? To regenerate NAD+ so glycolysis can continue to occur!

Which process is more efficient? Aerobic is 19x more efficient than anaerobic respiration in terms of usable energy production (~38 ATP compared to 2 ATP) LINK Concept 3.4 Review the discussion of enzyme regulation

Mitochondria incubated with glucose Absent Cell Fraction CO2 Lactic Acid Mitochondria incubated with glucose Absent Mitochondria incubated with pyruvate Present Cytoplasm incubated with glucose Cytoplasm incubated with pyruvate

Figure 6.14 Relationships among the Major Metabolic Pathways of the Cell

Answer to Opening Question Pasteur’s findings: Catabolism of the beet sugar is a cellular process, so living yeast cells must be present. With air (O2) yeasts used aerobic metabolism to fully oxidize glucose to CO2. Without air, yeasts used alcoholic fermentation, producing ethanol, less CO2, and less energy (slower growth).

Figure 6.23 Products of Glucose Metabolism