1. Biochemical Energy Production
Chapter Twenty Three
Biochemical Energy Production

2. Metabolism
The sum total of all the biochemical reactions that take place in a living organism

3. Cell Structure
Metabolic Reactions occur in specific sites within cells
Typical animal cell
Nucleus
Chromosomes in the nucleus contain genetic material
Cytoplasm is material between nucleus and cell membrane
Mitochondria are where energy-producing reactions occur

4. Biochemical Energy Production

5. Biochemical Energy Production
© R. Bhatnagar / Visuals Unlimited
(a) Representation of a mitochondria. (b) micrograph of a mitochondria crista.

6. ATP Energy is released as food is oxidized
Used to form ATP from ADP and Pi
ADP + Pi Energy ATP
In cells, energy is provided by the hydrolysis of ATP (31 kJ/mole of ATP)
ATP ADP + Pi Energy

7. Biochemical Energy Production

8. High-Energy Phosphate Compounds
Phosphate containing compounds that have a greater free energy of hydrolysis than that of a typical compound
The energy of hydrolysis is large because of strong repulsive forces between electronegative atoms
Enough energy is released by their hydrolysis to compensate for the energy needed for ATP production

9. Major Coenzymes in Metabolic Reactions
NAD+/NADH
FAD/FADH2
Coenzyme A (CoA-SH)

10. Major Coenzymes in Metabolic Reactions
(a) Flavin adenine nucleotide (b) nicotinamide adenine dinucleotide

11. Major Coenzymes in Metabolic Reactions

12. Biochemical Energy Production
Structural formula for coenzyme A CoA-SH

13. Coenzyme NAD+
In cells, the oxidation of compounds provides 2H as 2H+ and 2e- that reduce coenzymes
NAD+ (nicotinamide adenine dinucleotide) participates in reactions that produce a carbon-oxygen double bond (C=O)
Oxidation
CH3-CH2-OH  CH3-CHO + 2H+ + 2e-
Reduction
NAD+ + 2H+ + 2e-  NADH + H+

14. Coenzyme FAD
FAD participates in reactions that produce a carbon-carbon double bond (C=C)
Oxidation
-CH2-CH2-  -CH=CH- + 2H+ + 2e-
Reduction
FAD + 2H+ + 2e-  FADH2

15. Biochemical Energy Production
Classification of metabolic intermediate compounds in terms of function.

16. Free Energies of
Hydrolysis of
Phosphate
Containing
Compounds

17. Biochemical Energy Production
Hans Adolf Krebs received the Nobel Prize in medicine.
Hulton Archive / Getty Images

18. Stages of Metabolism Catabolic reactions are organized as stages
In Stage 1, digestion breaks down large molecules into smaller ones that enter the bloodstream.
In Stage 2, molecules in the cells are broken down to two- and three-carbon compounds

19. Digestion of Foods Digestion is the first step of catabolism
Carbohydrates glucose, fructose, galactose
Proteins amino acids
Lipids glycerol
fatty acids

20. Stages of Metabolism
In Stage 3, compounds are oxidized in the citric acid cycle to provide NADH and FADH2 molecules (reduced forms of coenzymes)
In Stage 4, NADH and FADH2 are oxidized in order to provide energy for the production of ATP

22. Citric Acid Cycle The citric acid cycle:
Operates under aerobic conditions only
Oxidizes the two-carbon acetyl group in acetyl CoA to CO2
Produces reduced coenzymes NADH and FADH2 and one ATP directly

24. Reaction 1: Formation of Citrate
Oxaloacetate combines with the two carbon acetyl group to form citrate

25. Reaction 2: Formation of Isocitrate
Citrate isomerizes to isocitrate
The tertiary –OH group in citrate is converted to a secondary –OH group that can be oxidized

26. Reaction 3: Oxidative Decarboxylation (1)
A decarboxylation removes a carbon as CO2 from isocitrate.
The –OH group is oxidized to a ketone, releasing H+ and 2e- that form reduced coenzyme NADH

27. Reaction 4: Oxidative Decarboxylation (2)
In a second decarboxylation, a carbon is removed as CO2 from a-ketoglutarate
The 4-carbon compound bonds to coenzyme A, providing H+ and 2e- to form NADH

28. Reaction 5: Hydrolysis
The hydrolysis of the thioester bond releases energy to add phosphate to GDP and form GTP, a high energy compound

29. Reaction 6: Dehyrogenation
In this oxidation, two H are removed from succinate to form a double bond in fumarate
FAD is reduced to FADH2

30. Reaction 7: Hydration of Fumarate
Water is added to the double bond in fumarate to form malate

31. Reaction 8: Dehyrogenation
Another oxidation forms a C=O bond
The hydrogens from the oxidation form NADH + H+

32. Summary of Products in the Citric Acid Cycle
Oxaloacetate bonds with an acetyl group to form citrate
Two decarboxylations remove two carbons as 2CO2
Four oxidations provide hydrogen for 3NADH and one FADH2
A direct phosphorylation forms GTP

33. Overall Chemical Reaction for the Citric Acid Cycle
Acetyl CoA + 3NAD+ + FAD
+ GDP + Pi + 2H2O
2CO2 + 3NADH + 2H+ + FADH2
+ HS-CoA + GTP

34. Regulation of Citric Acid Cycle
Low levels of ATP stimulate the formation of acetyl CoA for the citric acid cycle
High ATP and NADH levels decrease the formation of acetyl CoA and slow down the citric acid cycle

35. Regulation of Citric Acid Cycle
The citric acid cycle:
Increases its reaction rate when low levels of ATP or NAD+ activate isocitrate dehydrogenase
Slows when high levels of ATP or NADH inhibit citrate synthetase (first step in cycle)

36. Electron Carriers Electron carriers:
Accept hydrogen and electrons from the reduced coenzymes NADH and FADH2
Are oxidized and reduced to provide energy for the synthesis of ATP

37. Oxidation-Reduction
Electron carriers are continuously oxidized and reduced as hydrogen and/or electrons are transferred from one to the next
Electron carrier A (reduced)
Electron carrier B (oxidized)
Electron carrier A (oxidized)
Electron carrier B (reduced)

38. Electron Transport Chain
A series of biochemical reactions in which electrons and hydrogen ions from NADH and FADH2 are passed to intermediate electron carriers and then ultimately react with molecular oxygen to produce water
Most of the enzymes for the Electron Transport Chain are found in the inner mitochondrial membrane (found in the order in which they are needed)

39. Biochemical Energy Production

40. Biochemical Energy Production
(a) The oxidized form and reduced form of the electron carrier flavin mononucleotide. (b) The oxidized form and reduced form of the electron carrier coenzyme Q.

41. Biochemical Energy Production
(a) CoQH2 carries electrons from both complexes I and II to complex III. (b) NADH is the substrate for the complex I and FADH2 is the substrate for complex II.

42. Biochemical Energy Production
Electron movement through Complex III is initiated by the electron carrier CoQH2.

43. Biochemical Energy Production
The electron-transfer pathway through Complex IV.

44. Biochemical Energy Production

45. Biochemical Energy Production
Protein complexes I, III, and IV also act as proton pumps.

47. Chemiosmotic Model In the chemiosmotic model:
Complexes I, III, and IV pump protons into the intermembrane space, creating a proton gradient.
Protons must pass through ATP synthase to return to the matrix
The flow of protons through ATP synthase provides the energy for ATP synthesis (oxidative phosphorylation)
ADP + Pi + Energy  ATP

48. ATP Synthase ATP Synthase has two portions:
Protons flow back to the matrix through a channel in the F0 complex.
Proton flow provides the energy that drives ATP synthesis by the F1 complex

50. ATP Production for the Common Metabolic Pathway
For every mole of NADH oxidized in the ETC, 2.5 moles of ATP are formed
3 formed in one turn of citric acid cycle (7.5 ATP)
For every mole of FADH2 oxidized in the ETC, 1.5 moles of ATP are formed
1 formed in one turn of citric acid cycle (1.5 ATP)
GTP is the equivalent of ATP
1 formed in one turn of the citric acid cycle (1 ATP)
10 ATP Overall!!!

51. Biochemical Energy Production
The interconversion of ATP and ADP is the principal medium for energy exchange in the biochemical processes.