Microbial metabolism

Ch Microbial metabolism • Breakdown of carbohydrates, lipids and proteins to produce cellular energy (catabolism) • Redox (reduction/oxidation) reactions capture, store and use energy via electron transfers among molecules • Photosynthesis captures and stores energy from light • Biosynthesis of macromolecules and their precursors (anabolic reactions) Metabolism basics (Fig 5.1) • Metabolism is the sum of all biochemical reactions in the cell (pathways) • Catabolic pathways break down nutrients to yield smaller molecules and capture stored energy • Anabolic pathways synthesize larger molecules from smaller precursors and use energy Basic concepts of metabolic processes • Cells obtain nutrients from photosynthesis and/or transport from environment • Nutrients are catabolized to release and capture stored energy in form of ATP or NADH or electrochemical (chemiosmotic) gradients • Nutrients are converted to 12 basic precursors by enzymes in basic pathways (e.g., glycolysis, Krebs cycle and pentose phosphate cycle) • Anabolic reactions convert precursor molecules (12) into building blocks, building blocks into macromolecules (polymerization) and macromolecules into cell structures to form a new cell Redox reactions (Fig 5.2) • Fundamentally all biochemical reactions involve the transfer of electrons • Reduction is the gain of electrons; oxidation is loss of electrons and these are coupled • A molecule that has been reduced becomes relatively more negative, an oxidized molecules becomes relatively more positive Electron carriers • NAD+ /NADH, NADP+/NADPH and FAD/FADH2 are all cellular electron carriers used by cells • Electrons are transferred with protons (H transferred) • Many metabolic pathways require these electron carriers ATP production (Fig 5.3) • Substrate level phosphorylation involve transfer of high energy phosphate to ADP from another phosphorylated organic compound • Oxidative phosphorylation uses energy from high energy electron transfers during respiration to make ATP from ADP and Pi • Photophosphorylation uses energy from light to make electrons high energy Enzymes (Figs 5.4, 5.5) • Enzymes are usually proteins that catalyze (speed up) biochemical reactions • Enzymes often require cofactors • Ribozymes are enzymes made of RNA instead of protein Enzymatic reactions (Fig 5.7) • Substrate binds to active site of enzyme • Enzyme catalyzes reaction • Products leave active site 10 Krebs (aka TCA) cycle (Fig 5.19) 19 Respiration the electron transport system Fig 5.20 • Most of the ATP produced in microbes is produced by an electron transport system • The system is a series of membrane bound electron carriers • As electrons flow, energy is used to pump H+s out of cell • Many different ETSs occur in microbes 20 ATP production during respiration (Fig 5.21) • H+’s are pumped out as electrons pass through various carriers, especially cytochromes • As concentration of H+ builds, they are forced back through membrane bound ATP synthases, making ATP • When O2 is final electron acceptor, the most ATP is produced 21 Fermentation (Fig 5.22 and Table 5.3) • Fermentation yields of ATP small relative to respiration • Fermentation of sugars quickly uses up NAD+, which needs to be regenerated to keep up ATP production 22 Regenerating NAD+ Some fermentation products (Fig 5.23) 23 Fig 5.13 24 Photosynthesis overview • parts of photosynthesis, one light-dependent (photophosphorylation) and the other not (CO2 fixation, Calvin-Benson cycle) • Photophosphorylation uses light to generate high energy e’s that generate ATP in a process similar to respiration • The ATP from the light-dependent reactions is used to drive the reduction of CO2 to form 6C sugars from 5C sugars • CO2 fixation also requires NADPH 25 Photosystems and chlorophylls (Figs 5.26 and 5.27) • Photosystems are found on special membranes called thylakoids • Photosystems contain chlorophyll molecules embedded in sea of light harvesting pigments • Light energy collected and transferred to chls to acctivate electrons • High energy e-s transferred from chls through ETS produce H+ grad and then ATP 26 Cyclic photophosphorylation (Fig 5.28a) • ATP is generated from proton motive force generated as electrons move through ETS • The final e acceptor is the initial donor in a cycle • The NADPH needed for CO2 fixation must come from somewhere else 27 Non-cyclic photophosphorylation (Fig 5.28b) • light dependent steps are needed to elevate low energy e-s from H2O to high enough level to generate PMF and generate ATP + NADPH • O2 is the biproduct when H2O is e- donor 28 Table 5.5 29 Calvin cycle (Fig 5.29) 30 Calvin-Benson cycle • Uses RuBisCo to generate x 3C molecules per each CO2 molecule added to the 5C, ribulose bisphosphate • Cycle requires 3ATP and NADPH for each CO2 fixed (and reduced) • Energy from the ATP and NADH is stored and can later be recovered from the sugars produced • G3P feeds directly into glycolysis 31 32 33 [...]... glycolysis (Fig 5.14 • 2 NADH and 4 ATP produced • ATP production via substrate level phosphorylations • Fermentation occurs if pyruvic acid does not enter the Krebs cycle and if electrons from glucose metabolism don’t go down ETS • Fermentation typically anaerobic and yields acid bi-products 15 Substrate level phosphorylation (Fig 5.15) • These reactions are part of glycolysis • ATP only produced via