Chapter 5 Bacterial Metabolism

1. Chapter 5Bacterial Metabolism • Metabolism is sum total of all biochemical processes taking place in an organism. • Two categories • Anabolism – synthesis of chemical compounds • Form bonds • Require energy • Endergonic • Catobolism hydrolysis of chemical compounds • Break bonds • Release energy • Exergonic

3. Enzymes and Energy in Metabolism Pg 163 - 170 • Enzymes – are a group of organic compounds made of proteins that increase the rate of a chemical reaction. • Enzymes are reusable. • One enzyme is used for one reaction. • The substance acted on by an enzymes is called the substrate. • Product formed is called the product.

4. Enzyme • The same enzyme can sometimes act to build up a product or break it down dependent on the circumstance. • Enzymes are usually named for the reaction they perform and end in “ase” • Like lactase which breaks down lactose or sucrase that break downs sucrose. • There are exceptions lysozyme which lysis bacterial cell walls.

5. Enzymes Act Through Enzyme-Substrate Complex • How an enzyme works is by aligning the substrate(s) in a specific way to make the reaction more likely to occur. • In a hydrolysis reaction, the enzyme forces the substrate to stretch or weaken causing the bond to break. • In a synthesis reaction, the enzyme brings the substrates together were the chemical bond will form. • The area on the enzyme where the substrates reactions are brought together is called the active site

7. Enzymes • Some enzymes are made up of only proteins like lysozyme. • Other enzymes need small non-protein substances that help carry out the reaction. • Some of these are metal ions, Mg2+, Fe2+ or ZN2+ and are called cofactors. • If the non-protein is a small organic molecule it is called a coenzyme. • Two important coenzymes are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD). • NAD+ and FAD help carry electrons in metabolism.

8. Enzymes Often Act In Metabolic Pathways • A metabolic pathway is a sequence of chemical reactions, each reaction is carried out by a different enzyme, and the product of one reaction serves as a substrate for the next reaction • The pathway starts with a specific substrate and ends with a final end product.

10. Adenosine Triphosphate Pg 168 – 169 • In many enzyme reactions energy is required to drive the reaction • This energy comes from adenosine triphosphate • Adenosine triphosphate (ATP) is a high energy molecule and serves as an energy source for cells • The energy is supplied when the covalent bond between the third and second phosphates of the ATP molecule is broken • The breaking of this chemical bond releases 12,000 calories of usable energy • In a bacteria cell ATP is formed on the cell membrane • In a eukaryotic cell it is produced in the mitochondria

11. ATP

12. Catabolism of Glucose p. 170 to 179 • The best studied metabolic activity in a cell is the breakdown of glucose • Glucose is the key source of energy for production of ATP • A mole of glucose (180 g) contains 686,000 calories of energy • Breakdown of glucose is a controlled process that takes all the energy available in the molecule and converts it to ATP • The extraction of the energy of glucose happens down a metabolic pathway

13. Glycolysis • Glycolysis is the first process of energy extraction from glucose. • Glycolysis is the chemical breakdown of glucose. • Glycolysis occurs in the cytosol of bacteria. • In this process glucose is converted from a 6 carbon molecule into two 3 carbon molecules called pyruvate

14. Cellular Respiration • The production of ATP through the harvesting of energy down a metabolic pathway is called Cellular Respiration • If a cell uses oxygen in making ATP it is called Aerobic Respiration • C6H12O6 + 6O2 + 38 ADP + 38P → 6CO2 + 6H2O + 38ATP • If no oxygen is used it is called Anaerobic Respiration

15. The Steps of Glycolysis

16. Glycolysis • Energy Requiring Steps • Each step in the breakdown uses a specific enzyme • The first three steps of gylcolysis requires 2 ATP molecules • Glucose is broken down into two 3 carbon molecules dihydroxyacetone phosphate (DHAP) • Energy Producing Steps • The removal of the phosphate groups from these molecules helps to produce 2 ATP from each of the 3 carbon molecules • The end product of glycolysis is 2 ATP, 2 Nicotinamide adenine dinucleotide (NADH) and 2 pyruvate molecules • Note: The 2 NADH molecules will be used in the production of energy in the electron transport chain

17. Krebs Cycle (Citric Acid Cycle) • This metabolic pathway is called a cycle pathway because the starting product is identical to the finishing product • All steps are carried out by enzymes • All reactions take place along the bacterial cell membrane • Eukaryotic cells it occurs in the mitochondria • The initial product added to the Krebs cycle is not pyruvate • Pyruvate first has to loss a carbon in the form of CO2 • The remaining two carbons are attached to a molecule called coenzyme A

18. Krebs Cycle (Citric Acid Cycle) • The new molecule is called acetyl coenzyme A (Acetyl CoA) • The removal of the CO2 also produces another NADH molecule for the electron transport chain • The remaining 2 carbons from the 3 carbon pyruvate are now able to enter the Krebs cycle • This happens when a four carbon oxaloacetate molecule reacts with the acetyl CoA molecule and forms citrate (citric acid cycle)

20. Krebs Cycle (Citric Acid Cycle) • From each removal of carbon along the cycle an NADH molecule is produced • With pyruvate the end product of Kreb’s Cycle is 3 NADH molecules and 1 flavin adenine dinucleotide (FADH2) • So all totaled from the breakdown of glucose through glycolysis and the Krebs cycle 10 NADH and 2 FADH2 are produced

22. Electron Transport Chain (Pg 175 – 179) • Oxidative Phosphorylation – is a sequence of reactions were electrons are moved from one molecule to another (electron transport) and the energy released is captured in ATP molecules • Oxidative means the loss of electron pairs from a molecule • Reduction means to the gain of a pair of electron • Oxidative phosphorylation produces 34 molecules of ATP for each glucose molecule broken down

23. Oxidative Phosphorylation in Bacteria

24. Oxidative Phosphorylation • Oxidative phosphorylation, like the Krebs cycle, occurs in the cytoplasmic membrane in bacteria and mitochondria in eukaryotes • The NADH and FADH2 molecules produced in glycolysis and the Kreb’s cycle are used to shunt electrons to the electron transport chain • Once at the electron transport chain the electrons from either NADH and FADH2 are transferred to the first cytochrome in the cell membrane • The oxidized NAD+ and FAD are returned to the cytosol to be reused in glycolysis and the Kreb’s cycle

25. Electron Transport • The electrons from the first cytochrome are transported to another cytochrome and then to the next down the chain • This is why the process is referred to as the electron transport chain because it helps transfer electrons down a chain of cytochromes to be finally transferred to an oxygen molecule • The final stage of the electron transport is were the electron pair is accepted by oxygen • The oxygen then requires two protons (H+) to stabilize itself and water is formed water • O2 is essential in the electron transport chain • If oxygen is not present the flow of electrons stops and the whole process stops

26. ATP Synthesis • What makes the electron transport chain so important is that as electrons move down the cytochromes the energy released is used at three pumps • These pumps move protons (H+) out of the cytosol to the outside of the membrane • This movement results in build up of protons (H+) outside the membrane and creates an electrical potential • The protons are then moved back into the cell through a protein channel which has an enzyme called ATP synthase attached

27. ATP Synthesis • As the protons (H+) move back into the cell the free energy potential is used to synthesize ADP into ATP • For each pair of electrons released by a NADH molecule 3 ATP molecules can be produced • 2 ATP for each FADH2 • Electron transport chain coupled to ATP synthesis

28. ATP Produced By Glycolysis

29. Anaerobic Respiration and Fermentation (Pg 183) • Anaerobic respiration oxygen is not used as the final electron acceptor in electron transport • NO3- ,SO2= , CO2 • When sulfate is used the final product is H2S the gas that gives the rotten egg smell • Fermentation can make ATP in the absence of cellular respiration • Krebs and oxidative respiration is shut down

32. Chapter 5 Summary of Key Concepts • Enzymes and Energy in Metabolism • Enzymes Catalyze Chemical Reaction • Enzymes Act Through Enzyme-Substrate Complex • Enzymes Often Act in Metabolic Pathways • Energy in The Form of ATP Is Required for Metabolism

33. The Catabolism of Glucose • Glucose Contains Stored Energy that Can Be Extracted • Cellular Respiration Is a Series of Catabolic Pathway for the Production of ATP • Glycolysis Is the First Stage of Energy Extraction • The Kreb’s Cycle Extracts More Energy from Pyruvate • Oxidative Phosphorylation Is the Process by which Most ATP Molecules Form

34. Other Aspects of Catabolism • Other Carbohydrates, Proteins and Fats Can be used to Extract Energy From • Anaerobic Respiration Produces Using Other Electron Acceptors • Fermentation Produces ATP Using an Organic Final Electron Acceptor