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Metabolism

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All chemical and physical workings of a cell

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Catabolism

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Degradative; breaks the bonds of larger molecules forming smaller molecules; releases energy

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Anabolism

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Biosynthesis; process that forms larger macromolecules from smaller molecules; requires energy input

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Enzymes

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Enzymes are biological catalysts that increase the rate of a chemical reaction by lowering the energy of activation (the resistance to a reaction); The enzyme is not permanently altered in the reaction; Enzyme promotes a reaction by serving as a physical site for specific substrate molecules to position

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Cofactors

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Micronutrients; act as carriers to assist the enzyme in its activity; metal ions and vitamins

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Coenzymes

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Micronutrients; vitamins only

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Exoenzymes

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Transported extracellularly, where they break down large food molecules or harmful chemicals; examples are Cellulase, amylase, penicillinase

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Endoenzymes

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Retained intracellularly and function there; Most enzymes are endoenzymes

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Constitutive Enzymes

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Always present, always produced in equal amounts or at equal rates, regardless of the amount of substrate

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Regulated enzymes

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Not constantly present; production is turned on (induced) or turned off (repressed) in response to changes in the substrate concentration

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Synthesis or Condensation Reactions

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Anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond formed

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Hydrolysis Reactions

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Catabolic reactions that break down substrates into small molecules; requires the input of water to break bonds

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Sensitivity of Enzymes to Their Environment

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Activity of an enzyme is influenced by the cell’s environment; Enzymes operate under temperature, pH, and osmotic pressure of organism’s habitat; When enzymes are subjected to changes in organism’s habitat they become unstable

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Labile

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Chemically unstable enzymes

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Denaturation

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Weak bonds that maintain the shape of the apoenzyme are broken

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Competitive Inhibition

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Substance that resembles the normal substrate competes with the substrate for the active site

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Noncompetitive Inhibition

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Enzymes are regulated by the binding of molecules other than the substrate away from the active site

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Enzyme repression

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Inhibits at the genetic level by controlling synthesis of key enzymes

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Enzyme induction

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Enzymes are made only when suitable substrates are present

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The Pursuit and Utilization of Energy

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Energy: the capacity to do work or to cause change; Forms of energy include: Thermal, radiant, electrical, mechanical, atomic, and chemical

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Cell Energetics

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Cells manage energy in the form of chemical reactions that make or break bonds and transfer electrons; Energy released is temporarily stored in high energy phosphate molecules. The energy of these molecules is used in endergonic cell reactions.

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Endergonic reactions

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Consume energy

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Exergonic reactions

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Release energy

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Redox reactions

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Always occur in pairs; There is an electron donor which gets reduced and electron acceptor which gets oxidized then constitute a redox pair; Process salvages electrons and their energy; Released energy can be captured to phosphorylate ADP or another compound

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Electron and Proton Carriers

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Repeatedly accept and release electrons and hydrogen to facilitate the transfer of redox energy; Most carriers are coenzymes: NAD, FAD, NADP, coenzyme A, and compounds of the respiratory chain

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Adenosine Triphosphate: ATP

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Metabolic “currency”; Three part molecule consisting of: Adenine – a nitrogenous base, Ribose – a 5-carbon sugar, 3 phosphate groups; Removal of the terminal phosphate releases energy; ATP utilization and replenishment is a constant cycle in active cells

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Formation of ATP

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Substrate-level phosphorylation; Oxidative phosphorylation; Photophosphorylation

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Substrate-level phosphorylation

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Transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP – occurs in all cells

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Oxidative phosphorylation

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Series of redox reactions occurring during respiratory pathway

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Photophosphorylation

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ATP is formed utilizing the energy of sunlight

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Metabolic Pathway

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a sequence of chemical reactions where each reaction is catalyzed by a different enzyme. Initial reaction produces substrate for next enzyme – enzymes are regulated in a number of ways: Environmental factors and Feedback

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Bioenergetics

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Study of the mechanisms of cellular energy release. Includes Anabolic and Catabolic Reactions.

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Metabolic Pathways

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Nutrient processing is varied, yet in many cases is based on three catabolic pathways that convert glucose to CO2 and gives off energy

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Aerobic respiration

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Glycolysis, the Kreb’s cycle,respiratory chain

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Anaerobic respiration

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Glycolysis, the Kreb’s cycle, respiratory chain; molecular oxygen is not the final electron acceptor

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Fermentation

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Glycolysis, organic compounds are the final electron acceptors

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Aerobic Respiration

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Series or enzyme-catalyzed reactions in which electrons are transferred from fuel molecules (glucose) to oxygen as a final electron acceptor. Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C), NADH is generated. TCA – processes pyruvic acid and generates 3 CO2 molecules , NADH and FADH2 are generated. Electron transport chain – accepts electrons from NADH and FADH; generates energy through sequential redox reactions called oxidative phosphorylation

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Electron Transport and Oxidative Phosphorylation

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Final processing of electrons and hydrogen and the major generator of ATP. Chain of redox carriers that receive electrons from reduced carriers (NADH and FADH2).

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Oxidative phosphorylation

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ETS shuttles electrons down the chain, energy is released and subsequently captured and used by ATP synthase complexes to produce ATP

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Chemiosmosis

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As the electron transport carriers shuttle electrons, they actively pump hydrogen ions (protons) across the membrane setting up a gradient of hydrogen ions – proton motive force. Hydrogen ions diffuse back through the ATP synthase complex causing it to rotate, causing a 3-D change resulting in the production of ATP

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The Terminal Step

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Oxygen accepts 2 electrons from the ETS and then picks up 2 hydrogen ions from the solution to form a molecule of water. Oxygen is the final electron acceptor 2H+ + 2e- + ?O2 > H2O

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AEROBIC RESPIRATION SUMMARY

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The energy yielding process in which: Initial electron donor is carbohydrate, the final electron acceptor is oxygen gas. The location of pathway: Eukaryotes: glycolysis – cytoplasm, CAC – mitochondria, ETC - mitochondria; Prokaryotes: glycolysis – cytoplasm, CAC – cytoplasm, ETC – cell membrane. Substrates include proteins, carbohydrates, lipids. C6H12O6 + 6O2 + 38 ADP + 38 P INTO 6CO2 + 6H2O + 38 ATP.

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Anaerobic Respiration

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Functions like aerobic respiration except it utilizes oxygen containing ions, rather than free oxygen, as the final electron acceptor is Nitrate (NO3-) and nitrite (NO2-); Most obligate anaerobes use the H+ generated during glycolysis and the Kreb’s cycle to reduce some compound other than O2

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Fermentation

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Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen; Uses organic compounds as terminal electron acceptors; Yields a small amount of ATP; Production of ethyl alcohol by yeasts acting on glucose; Formation of acid, gas, and other products by the action of various bacteria on pyruvic acid

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Photosynthesis: The Earth’s Lifeline

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The ultimate source of all the chemical energy in cells comes from the sun. The chemical formula - 6CO2 + 6H2O to produce C6H12O6 + 6O2

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Photosynthesis

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Occurs in 2 stages: Light Dependent and Light Independent.

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Light-dependent

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Photons are absorbed by chlorophyll, carotenoid, and phycobilin pigments; Water split by photolysis, releasing O2 gas and provides electrons to drive photophosphorylation; Released light energy used to synthesize ATP and NADPH

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Light-independent Reaction

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Dark reactions go into the Calvin Cycle; Uses ATP to fix CO2 to ribulose-1,5-bisphosphate and convert it to glucose

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Photosynthesis

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Metabolic process converting light energy to chemical energy and stored as carbohydrates or other organic compounds

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Classical Photosynthesis

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Performed by PHOTOAUTOTROPHS: – plants, algae and Cyanobacteria. The initial electron donor is CO2, the final electron acceptor is water (H2O). The Products are O2 gas, H2O and Carbohydrates. There is NO net production of ATP

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Classical Photosynthesis

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Consists of 2 sets of reactions: 1.Energy-fixing reactions (sunlight) 2.Carbon-fixing reactions (CO2) Net result is 6CO2 + 6H2O + light INTO C6H12O6 + 6O2.

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Bacterial Photosynthesis

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Two different processes: 1. Photoautotrophs – Green & Purple Sulfur Bacteria – never produce oxygen gas. – Initial electron donor – CO2 – Final electron acceptor - H2S – Products: carbohydrates, H2O, sulfur (S?) – Bacteriochlorophyll – primary photosynthetic pigment. The chemical formula is CO2 + 2H2S + light ?C6H12O6 + 2S + H2O. 2. Photoheterotrophs - Green & Purple Non-sulfur Bacteria – Initial electron donor - CO2 – Final electron acceptor – organic acids & alcohols – Products: carbohydrates, oxidized organic acids & alcohols – Bacteriochlorophyll – primary pigment CO2 + org acid + light INTO C6H1206 + oxidized org acids.

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