Microbiology - Microbial Metabolism - Quick Guides | Microbiology

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Study GuideMicrobiology–Microbial Metabolism1.Cellular RespirationMicroorganisms need energy to grow, move, and carry out life processes. Some microorganisms,such ascyanobacteria, can capture energy from sunlight throughphotosynthesisand store it incarbohydrates. The main carbohydrate produced during photosynthesis isglucose.However, many microorganisms—such asnon-photosynthetic bacteria, fungi, and protozoa—cannot make their own food. These organisms must obtainpreformed carbohydratesfrom theenvironment. To release energy from these carbohydrates, they use a process calledcellularrespiration.1.1What Is Cellular Respiration?Cellular respirationis the process by which microorganisms break down carbohydrates, especiallyglucose, to release energy.During this process:•Glucose is broken down step by step•Energy is captured and stored asATP (adenosine triphosphate)•Carbon dioxide (CO₂)is released as a waste product•Oxygenis used as the final acceptor of electronsThe ATP produced is used later for cellular activities. The carbon dioxide released can be reused byphotosynthetic organisms to make new carbohydrates.1.2Major Stages of Cellular RespirationCellular respiration occurs infour main stages:1.Glycolysis2.Krebs cycle3.Electron transport system4.Chemiosmosis

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Study GuideFigure 1An overview of the processes of cellular respiration showing the major pathways andthe places where ATP is synthesized.GlycolysisGlycolysisis the first stage of cellular respiration.Key Features•Occurs in thecytoplasm•Doesnot require oxygen(anaerobic)•Involves multiple enzyme-controlled steps

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Study GuideWhat Happens in Glycolysis?•One glucose molecule (6 carbons) is broken intotwo pyruvic acid molecules(3 carbonseach)•2 ATP moleculesare used early in the process•4 ATP moleculesare produced laterNet Energy Gain•Net gain: 2 ATP moleculesIn addition:•2 NADH moleculesare produced•NADH carries high-energy electrons to later stagesFor some anaerobic organisms, glycolysis is theonly source of energy, but it is inefficient becausemuch energy remains in pyruvic acid.Krebs Cycle (Citric Acid Cycle)After glycolysis, cellular respiration continues with theKrebs cycle, also called:•Citric acid cycle•Tricarboxylic acid (TCA) cycleLocation•Bacterial cells: cell membrane•Eukaryotic cells: mitochondriaMitochondria have:•An outer membrane•A highly folded inner membrane calledcristae, which holds important enzymes for ATPproduction

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Study GuidePreparation Step: Pyruvic Acid to Acetyl-CoABefore entering the Krebs cycle:•Each pyruvic acid molecule loses one carbon asCO₂•The remaining two carbons combine withcoenzyme A•This formsacetyl-CoA•NADHis produced in the processEvents in the Krebs Cycle•Acetyl-CoA combines withoxaloacetic acidto formcitric acid•Citric acid undergoes a series of enzyme-controlled reactions•During these reactions:oNADHandFADH₂are formedoATPis producedoCarbon dioxideis releasedEnergy Yield (per glucose)•2 ATP molecules•ManyNADH molecules•SomeFADH₂molecules•6 CO₂moleculesreleased in totalAt the end of the cycle, oxaloacetic acid is regenerated and ready to start the cycle again.Electron Transport System (ETS)Theelectron transport systemis where most energy is released.Location•Bacteria: cell membrane•Eukaryotes: cristae of mitochondria

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Study GuideWhat Happens?•NADH and FADH₂donate electrons•Electrons pass through a chain ofcytochromes and coenzymes•Energy from electrons is used topump protons (H⁺)across the membraneEach:•NADHmoves about6 protons•FADH₂moves about4 protonsThe final electron acceptor isoxygen, which combines with electrons and protons to formwater(H₂O).Without oxygen:•Electrons cannot flow•ATP cannot be produced•Cellular respiration stopsChemiosmosisChemiosmosisis the stage where ATP is actually synthesized.How It Works•Proton pumping creates aproton gradient•Protons flow back through special protein channels•Energy from proton movement is used to convertADP + phosphate into ATPATP Yield•Prokaryotes:36 ATP molecules•Eukaryotes:34 ATP molecules•Plus2 ATP from glycolysisTotal ATP per Glucose•Prokaryotes: 38 ATP•Eukaryotes: 36 ATP

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