1. CHAPTER 23: Metabolism & Energy Production
General, Organic, & Biological Chemistry
Janice Gorzynski Smith

2. CHAPTER 23: Metabolism & Energy Production
Learning Objectives:
Stages of Metabolism
ATP: structure, hydrolysis, & formation
Coupling reactions
Coenzymes
NAD+ & NADH
FAD & FADH2
Coenzyme A
Citric Acid Cycle: all 8 steps
Electron Transport Chain
ATP synthesis by Oxidative Phosphorylation
CH 23 Homework:
End of Chapter problems: 20, 22, 24, 26, 28, 32, 34, 36, 40, 42, 46, 48, 50, 52, 56, 60, 64, 74
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

3. Metabolism Definition
Metabolism is the sum of all the chemical reactions that take place in an organism.
Catabolism is the breakdown of large molecules into smaller ones; energy is generally released during catabolism.
Anabolism is the synthesis of large molecules from smaller ones; energy is generally absorbed during anabolism.
Often, the process is a series of consecutive reactions called a metabolic pathway, which can be linear or cyclic.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

4. Stage [2] – Formation of Acetyl CoA
Metabolism
Overview
Stage [1] – Digestion
Stage [2] – Formation of Acetyl CoA
Stage [3] – The Citric Acid Cycle
Stage [4] – Electron Transport Chain
& Oxidative Phosphorylation
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

5. Metabolism Stage [1] – Digestion Carbohydrates Proteins
Triacylglycerols
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

6. Stage [2] – Formation of Acetyl CoA
Metabolism
Stage [2] – Formation of Acetyl CoA
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

7. Stage [3] – The Citric Acid Cycle
Metabolism
Stage [3] – The Citric Acid Cycle
The citric acid cycle is based in the mitochondria, where the acetyl CoA is oxidized to CO2.
The cycle also produces energy stored as a nucleoside triphosphate and the reduced coenzymes.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

8. Stage [4] – Electron Transport Chain & Oxidative Phosphorylation
Metabolism
Stage [4] – Electron Transport Chain
& Oxidative Phosphorylation
Within the mitochondria, the electron transport chain and oxidative phosphorylation produce ATP (adenosine 5’-triphosphate).
ATP is the primary energy-carrying molecule in the body
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

9. ATP
Definition
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

10. Hydrolysis: Energy Released
ATP
Hydrolysis: Energy Released
Hydrolysis of ATP cleaves 1 phosphate group.
This forms ADP and hydrogen phosphate (HPO42−),
releasing 7.3 kcal/mol of energy.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

11. Phosphorylation: Energy Absorbed
ATP
Phosphorylation: Energy Absorbed
Phosphorylation is the reverse reaction, where
a phosphate group is added to ADP, forming ATP
requiring 7.3 kcal/mol of energy.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

12. ATP
Coupled Reactions
Coupled reactions are pairs of reactions that occur together.
The energy released by one reaction is absorbed by the other reaction.
Coupling an energetically unfavorable reaction with a favorable one that releases more energy than the amount required is common in biological reactions.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

13. Coenzymes Oxidation & Reduction
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

14. Coenzyme A (HS-CoA) is neither an oxidizing nor a reducing agent.
Coenzymes
Coenzyme A
Coenzyme A (HS-CoA) is neither an oxidizing
nor a reducing agent.
When the thioester bond is broken, 7.5 kcal/mol
of energy is released.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

15. Citric Acid Cycle Overview
The citric acid cycle produces high-energy compounds for ATP synthesis in stage [4] of catabolism.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

16. Citric Acid Cycle Overview
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

17. Citric Acid Cycle Steps 1 - 4
Step [1] reacts acetyl CoA with oxaloacetate to form citrate, and it is catalyzed by citrate synthase.
Step [2] isomerizes the 3o alcohol in citrate to the 2o alcohol in isocitrate; it is catalyzed by aconitase.
Step [3] isocitrate loses CO2 in a decarboxylation reaction catalyzed by isocitrate dehydrogenase. Also, the 2o alcohol of isocitrate is oxidized by the oxidizing agent NAD+ to form the ketone a-ketoglutarate and NADH
Step [4] releases another CO2 with the oxidation of a-ketoglutarate by NAD+ in the presence of coenzyme A to form succinyl CoA and NADH. Catalyzed by a-ketoglutarate dehydrogenase
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

18. Citric Acid Cycle Steps 5 - 8
Step [5] the thioester bond of succinyl CoA is hydrolyzed to form succinate, releasing energy that converts GDP to GTP.
Step [6] succinate is converted to fumarate with FAD and succinate dehydrogenase; FADH2 is formed.
Step [7], water is added across the C=C; this transforms fumarate into malate, which has a 2o alcohol.
Step [8], the 2o alcohol of malate is oxidized by NAD+ to form the ketone portion of oxaloacetate and NADH. The product of step [8] is the starting material for step [1].
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

19. The main function of the citric acid cycle is to
Overall Reaction
The main function of the citric acid cycle is to
produce reduced coenzymes (NADH and FADH2).
These molecules enter the electron transport chain
and ultimately produce ATP.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

20. The electron transport chain is a multistep
Definition
The electron transport chain is a multistep
process using 4 enzyme complexes (I, II, III and IV)
located along the mitochondrial inner membrane.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

21. Electron Transport Chain
The reduced coenzymes (NADH and FADH2) are
reducing agents, and can donate e− when oxidized.
NADH is oxidized to NAD+ and FADH2 is oxidized
to FAD when they enter the electron transport
chain.
The e− donated by the coenzymes are passed
down from complex to complex in a series of
redox reactions, which produces some energy.
These e− and H+ react with inhaled O2 to form water.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

22. Oxidative Phosphorylation
ATP Synthesis
Oxidative Phosphorylation
The electron transport chain provides the energy
to pump H+ ions across the inner membrane
of the mitochondria.
The concentration of H+ ions in the inter membrane space becomes higher than that inside the matrix creating a potential energy gradient.
To return to the matrix, H+ ions travel through a
channel in the ATP synthase enzyme (catalyzes phosphorylation of ADP to ATP).
It is called oxidative phosphorylation because
the energy used to transfer the phosphate group
results from the oxidation of the coenzymes.
The energy released as the H+ ions return to the
matrix is the energy stored in the ATP molecule.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

23. Oxidative Phosphorylation
ATP Synthesis
Oxidative Phosphorylation
Each NADH entering the electron transport chain
produces enough energy to make 2.5 ATPs.
Each FADH2 entering the electron transport chain
produces enough energy to make 1.5 ATPs.
The citric acid cycle produces overall:
3 NADH x 2.5 ATP = 7.5 ATP
It is called oxidative phosphorylation because
the energy used to transfer the phosphate group
results from the oxidation of the coenzymes.
1 FADH2 x 1.5 ATP = 1.5 ATP
1 GTP = 1 ATP
10 ATP
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.

24. Oxidative Phosphorylation
ATP Synthesis
Oxidative Phosphorylation
It is called oxidative phosphorylation because
the energy used to transfer the phosphate group
results from the oxidation of the coenzymes.
Smith, Janice Gorzynski. General, Organic, & Biological Chemistry 2nd Ed.