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Transcript
Microbial Metabolism Overview A. Energy flows through the cell as a flow of electrons Compound that loses electrons → oxidized Compound that gains electrons → reduced -energy is released by an electron during its transfer from one compound to another -this energy is captured → converted into high energy bonds on ATP B. Energy storage molecules ATP, NADH, NADPH, FADH ex. NADH – reduced, NAD+ - oxidized these molecules carry energy from cell respiration to the electron transport chain C. Cell Respiration 1. Glycolysis – glucose is partially digested into 2 smaller molecules (pyruvate) and the released energy is captured as NADH 2. Krebs Cycle (also called the TCA cycle or the Citric Acid cycle) -oxidation of these smaller molecules is completed -produces more energy-carrying molecules such as NADH Both of the above pathways combined → make only a small amount of ATP 3. Electron Transport Chain -energy-carrying molecules made in first 2 pathways (NADH, FADH) are oxidized - molecules like O2 (aerobes) or N, S, etc. (anaerobes) are reduced -released energy is captured as ATP -most of the cell’s ATP is made here D. Bacteria/Archaea have 3 pathways to catabolize (digest) glucose → pyruvate 1. Glycolysis (EMP) pathway (prokaryotes and eukaryotes) 2. Enter-Doudoroff (ED) pathway (only prokaryotes) 3. Pentose Phosphate Shunt (PPS) (prokaryotes and eukaryotes) E. Electron Transport System (ETS or ETC - electron transport chain) -Series of electron carriers that transfer electrons to electron acceptors -Results in a flow of electrons through the ETS -ETS generates Proton Motive Force (PMF), which pushes H+ into the cell -As electrons are passed through the electron transport chain → energy released is used to pump protons (H+) across the membrane, which is called the PMF. PMF drives: ATP synthase – enzyme complex to produce ATP Ion transport – to move compounds across the cell membrane Flagella motion - makes flagella move or spin ATP production – more variable in anaerobic respiration because fewer carriers in ETC Proton Gradient - low H+ inside the cell – high outside the cell (lots of H+) - causes proton gradient across the cell membrane 1. H+ cannot easily diffuse back inside the cell 2. H+ can only flow back in through an enzyme complex called ATP synthase, which has a channel to pump H+ back into the cell: a. also binds ADP + P (ADP + P = ATP) b. as H+ flow back into the cell through the channel they release energy → ATP c. enzyme complex spins making ATP Fermentation If a cell runs out of electron acceptor (O2 or N or S), respiration can only proceed through glycolysis. Prokaryotes – some only go this far to make energy, they only do fermentation and do not have the capability to do respiration. 6C molecule (glucose) → two 3 carbon molecules (pyruvate) this makes ATP and NADH if NADH forms → recycle NAD+ so cell regenerates NAD+ by oxidizing NADH and reducing pyruvate (waste products from this reaction are valuable, such as ethanol, lactic acid, propionic acid, etc.) Molecules besides glucose can be used for energy: lipids → lipases are enzymes that breakdown lipids proteins → proteases and peptidases are enzymes that breakdown proteins many other compounds (such as aromatic biological compounds) can also be used bacteria - insecticides etc. are metabolized - biodegradation - petroleum can be metabolized - bioremediation -often look for microorganisms that can do these reactions – commercial value General Types of Microorganisms Heterotrophs - energy from biological molecules, must absorb (eat) biological molecules Autotrophs - can make their own biological molecules from N2, CO2, etc Photoautotrophs – convert light energy → ATP Chemoautotrophs – convert chemical energy → ATP Instead of light they can use ammonia, methane, hydrogen sulfide, etc. Photosynthesis – opposite of aerobic cell respiration (respiration starts with sugars while photosynthesis produces sugars) 1. Light reactions, light energy → ATP e- → ETS → chlorophylls → H+ gradient → ATP synthase → ATP 2. Carbon cycle, ATP + NADPH + CO2 → sugars - also called Carbon Fixation