Metabolism

1. Metabolism Microbiology for the Health Sciences

2. Definition of Metabolism Metabolism: the sum of all chemical reactions that occur in a living cell in order that the cell sustains its life’s processes

3. Metabolic Reactions Catabolism: decomposition reactions in a living organism, the breakdown of complex organic compounds into simpler ones. Catabolic reactions makes ATP Anabolism: all synthesis reactions in a living organism; the building of complex organic molecules from simpler ones. Anabolic reactions use ATP. Catabolism and Anabolism coupled rxns

4. Stages of Metabolism 1. Digestion 2. Movement of nutrients across cell membrane 3. The oxidation of glucose into two pyruvic acid molecules This is also known as Glycolysis. 4. The complete oxidation of pyruvic acid into carbon dioxide (CO2) and the formation of ATP. This is represented by the Kreb’s Cycle and the Electron Transport system

5. Digestion Enzymes needed to speed up chemical reactions Exoenzymes: enzymes the cell uses to break down large molecules outside of cell so can be transported across cell membrane Naming of enzymes substrate/enzyme Main nutrient groups: • Carbohydrates Amylase • Proteins Protease • Lipids Lipase

6. Movement of Nutrients Across Plasma Membrane Passive Diffusion: moves down concentration gradient (requires No Energy) Facilitated Diffusion: moves down a concentration gradient uses carrier molecule (requires No Energy) Active Transport: movement against concentration gradient (requires Energy) Endocytosis: (Eukaryotes) substance engulfed by cell membrane

7. Carbohydrate Catabolism [INSERT FIGURE 5.12]

8. Carbohydrate Catabolism

9. Glycolysis Beginning of oxidation glucose to two pyruvic acid molecules 1 glucose molecule contains 6 carbons. In glycolysis, glucose is broken down to 2, 3 carbon molecules called pyruvate Uses 2 ATP Make 4 ATP Net Energy is 2 ATP

10. Glycolysis

11. Summary of Glycolysis 2 ATP added to glucose (6C) to energize it. Through 10 steps glucose is converted to two pyruvate (3C), with energy transferred to make 4 ATP (substrate phosphorylation). Although glycolysis makes 4 ATP, the net ATP production by this step is 2 ATP (because 2 ATP were used to start glycolysis). The 2 net ATP are available for cell use. If oxygen is available to the cell, the pyruvate will move into the plasma membrane (P) or the mitochondria & aerobic respiration will begin.

12. Carbohydrate Catabolism [INSERT FIGURE 5.18]

13. Glycolysis and Kreb’s Cycle

14. Kreb’s Cycle (tricarboxylic acid cycle, or citric acid cycle) Pyruvic acid loses 1 molecule of carbon in form of carbon dioxide in preparatory step for Kreb cycle = 2 carbon compound called acetyl CoA Kreb cycle results in the complete oxidation of acetyl CoA to carbon dioxide and formation of ATP Carbon dioxide eventually released from cell 2 ATP equivalents produced H left with it’s corresponding electron

15. Kreb’s Cycle • Requires 2 cycles to metabolize glucose • Acetyl Co-A (2C) enters the Kreb's Cycle & joins with Oxaloacetic Acid (4C) to make Citric Acid (6C) • Citric acid is oxidized releasing CO2 , free H+, & e- and forming ketoglutaric acid (5C) • Free e- reduce the energy carriers NAD+ to NADHand FAD+ to FADH2 • Ketoglutaric acid is also oxidized releasing more CO2 , free H+, & e- • The cycle continues oxidizing the carbon compounds formed (succinic acid, fumaric acid, malic acid, etc.) producing more CO2, NADH, FADH2, & ATP • H2O is added to supply more H+ • CO2 is a waste product that diffuses out of cells

16. Kreb’s Cycle and Electron Transport Chain H’s need to be moved to where can be useful Carrier molecules NAD+ and FAD+ act as shuttles to move H’s to plasma membrane NAD can carry 1 H and FAD can carry 2 H H and corresponding electrons released into plasma membrane H pumped out of membrane and electron passed down carrier chain inside membrane

17. Hydrogen Shuttles Nicotinamide Adenine Dinucleotide NAD can carry 1 hydrogen NADH Flavin Adenine Dinucleotide FAD can carry 2 hydrogen FADH2

18. Carbohydrate Catabolism • Continuation of Cellular Respiration • Electron transport • Most significant production of ATP occurs through stepwise release of energy from series of redox reactions known as an electron transport chain (ETC) • Consists of series of membrane-bound carrier molecules that pass electrons from one to another and ultimately to final electron acceptor • Energy from electrons used to pump protons (H+) across the membrane, establishing a proton gradient • Located in cristae of eukaryotes and in cytoplasmic membrane of prokaryotes

19. Electron Transport Chain Excess protons outside membrane create potential energy due to high positive charge on one side of membrane Protons used to synthesize ATP Then protons, electrons and final electron acceptor, oxygen, combine with oxygen to form water Oxidative Phosphorylation

21. Electron Transport System NADH and FADH2 carry protons (H+) and electrons (e-) tothe electron transport chain located in the membrane. The energy from the transfer of electrons along thechain transports protons across the membrane and creates an electrochemical gradient. As the accumulating protons follow the electrochemical gradient back across the membrane through an ATP synthase complex, the movement of the protons provides energy for synthesizing ATP from ADP and phosphate. At the end of the electron transport system, two protons, two electrons, and half of an oxygen molecule combine to form water. Since oxygen is the final electron acceptor, the process is called aerobic respiration.

22. Electron Transport Chain Net result = 34 ATP from the Electron Transport System Note: 4 ATP were formed from glycolysis and kreb cycle Total ATP formed in prokaryotes is 38 for each glucose molecule

23. Role of ATP Synthase ATP synthase, also called complex, is the final enzyme in the oxidative phosphorylation pathway. This enzyme is found in all forms of life and functions in the same way in both prokaryotes and eukaryotes. The enzyme uses the energy stored in a proton gradient across a membrane to drive the synthesis of ATP from ADP and phosphate (Pi).

24. Electron Transport System

25. Electron Transport System • Found in the inner mitochondrial membrane or cristae • Contains 4 protein-based complexes that work in sequence moving H+ from the matrix across the inner membrane (proton pumps) • A concentration gradient of H+ between the inner & outer mitochondrial membrane occurs • H+ concentration gradient causes the synthesis of ATP by chemosmosis

26. Metabolism

28. Carbohydrate Catabolism [INSERT TABLE 5.3]

29. Anaerobic Respiration Terminal electron acceptor something other than oxygen Such as: Nitrate, nitrite, sulfate, or carbonate

30. Fermentation Releases energy from sugars or other organic molecules (amino acids) Does not require oxygen Does not require kreb cycle or electron transport chain Uses organic molecule as final electron acceptor Produces only small amounts of ATP Examples of end products are lactic acid or ethanol

31. Carbohydrate Catabolism • Fermentation • Sometimes cells cannot completely oxidize glucose by cellular respiration • Cells require constant source of NAD+ that cannot be obtained by simply using glycolysis and the Krebs cycle • In respiration, electron transport regenerates NAD+ from NADH • Fermentation pathways provide cells with alternate source of NAD+ • Partial oxidation of sugar (or other metabolites) to release energy using an organic molecule from within the cell as an electron acceptor

32. Carbohydrate Catabolism [INSERT TABLE 5.4]

33. Carbohydrate Catabolism [INSERT FIGURE 5.22]