Metabolism

Terms (60)

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   Metabolism

   Metabolism is the sum of all chemical reactions in a cell that maintain life, including breaking down molecules for energy and building complex molecules from simpler ones.

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   Catabolism

   Catabolism is the phase of metabolism that involves breaking down complex molecules into simpler ones, releasing energy in the process, such as during cellular respiration.

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   Anabolism

   Anabolism is the phase of metabolism that uses energy to construct complex molecules from simpler ones, essential for growth and repair in cells.

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   ATP

   ATP, or adenosine triphosphate, is the primary energy currency of the cell, storing and transferring energy through the hydrolysis of its phosphate bonds.

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   ADP

   ADP, or adenosine diphosphate, is a molecule that forms when ATP loses a phosphate group, releasing energy, and can be phosphorylated back to ATP.

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   Glycolysis

   Glycolysis is the metabolic pathway that breaks down one glucose molecule into two pyruvate molecules in the cytoplasm, producing a net gain of two ATP molecules.

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   Krebs Cycle

   The Krebs cycle, also known as the citric acid cycle, is a series of reactions in the mitochondria that generate energy through the oxidation of acetyl-CoA, producing ATP, NADH, and FADH2.

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   Electron Transport Chain

   The electron transport chain is a series of protein complexes in the inner mitochondrial membrane that use electrons from NADH and FADH2 to create a proton gradient for ATP synthesis.

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   Oxidative Phosphorylation

   Oxidative phosphorylation is the process in cellular respiration where ATP is produced using the energy from the electron transport chain and a proton gradient.

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    Substrate-level Phosphorylation

    Substrate-level phosphorylation is a method of ATP production where a phosphate group is directly transferred from a substrate to ADP, as seen in glycolysis.

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    Photosynthesis

    Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, stored as glucose, using carbon dioxide and water.

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    Light-dependent Reactions

    Light-dependent reactions in photosynthesis use light energy to split water molecules, producing ATP, NADPH, and oxygen in the thylakoid membranes of chloroplasts.

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    Calvin Cycle

    The Calvin cycle is the light-independent phase of photosynthesis that uses ATP and NADPH to fix carbon dioxide into glucose in the stroma of chloroplasts.

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    Enzymes

    Enzymes are biological catalysts that speed up chemical reactions in cells by lowering the activation energy, without being consumed in the process.

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    Enzyme-Substrate Complex

    The enzyme-substrate complex is the temporary binding of a substrate to an enzyme's active site, facilitating the reaction and leading to product formation.

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    Active Site

    The active site is the specific region on an enzyme where the substrate binds and the catalytic reaction occurs, often shaped to fit the substrate precisely.

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    Activation Energy

    Activation energy is the minimum energy required to start a chemical reaction, which enzymes reduce to make reactions proceed more quickly in metabolic pathways.

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    Catalyst

    A catalyst is a substance that increases the rate of a chemical reaction by lowering its activation energy, and enzymes serve this role in biological systems.

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    Lock and Key Model

    The lock and key model describes enzyme function where the substrate fits perfectly into the enzyme's active site like a key into a lock, ensuring specificity.

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    Induced Fit Model

    The induced fit model suggests that an enzyme's active site changes shape slightly upon substrate binding, enhancing the reaction and improving catalytic efficiency.

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    Michaelis-Menten Kinetics

    Michaelis-Menten kinetics describe the rate of enzymatic reactions, where the reaction velocity depends on substrate concentration, reaching a maximum at enzyme saturation.

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    Km

    Km, or the Michaelis constant, is the substrate concentration at which an enzyme operates at half its maximum velocity, indicating the enzyme's affinity for the substrate.

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    Vmax

    Vmax is the maximum rate of an enzymatic reaction when the enzyme is fully saturated with substrate, reflecting the enzyme's catalytic efficiency.

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    Competitive Inhibition

    Competitive inhibition occurs when an inhibitor molecule competes with the substrate for the enzyme's active site, reducing the reaction rate by decreasing effective substrate binding.

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    Non-competitive Inhibition

    Non-competitive inhibition happens when an inhibitor binds to an enzyme at a site other than the active site, altering the enzyme's shape and reducing its activity regardless of substrate concentration.

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    Allosteric Regulation

    Allosteric regulation is the control of enzyme activity through the binding of a molecule at a site other than the active site, which can activate or inhibit the enzyme.

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    Feedback Inhibition

    Feedback inhibition is a form of enzyme regulation where the end product of a metabolic pathway inhibits an earlier enzyme, preventing overproduction of the product.

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    Phosphorylation

    Phosphorylation is the addition of a phosphate group to a molecule, often used to activate or deactivate enzymes in metabolic signaling pathways.

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    Dephosphorylation

    Dephosphorylation is the removal of a phosphate group from a molecule, which can reverse the effects of phosphorylation and regulate metabolic processes.

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    Second Messengers

    Second messengers are small molecules or ions, like cAMP, that relay signals from receptors on the cell surface to target molecules inside the cell, affecting metabolism.

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    Hormonal Regulation of Metabolism

    Hormonal regulation of metabolism involves hormones like insulin and glucagon controlling metabolic pathways, such as glucose uptake and storage in response to blood sugar levels.

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    Insulin

    Insulin is a hormone that promotes the uptake of glucose into cells and stimulates anabolic processes like glycogenesis, lowering blood sugar levels.

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    Glucagon

    Glucagon is a hormone that stimulates the breakdown of glycogen and gluconeogenesis in the liver, raising blood sugar levels during fasting.

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    Gibbs Free Energy

    Gibbs free energy measures the energy available to do work in a chemical reaction, with a negative change indicating a spontaneous, exergonic process.

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    ΔG

    ΔG, or change in Gibbs free energy, determines the direction of a reaction; if negative, the reaction is spontaneous and releases energy.

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    Exergonic Reaction

    An exergonic reaction releases energy and has a negative ΔG, commonly occurring in catabolic pathways like cellular respiration.

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    Endergonic Reaction

    An endergonic reaction requires energy input and has a positive ΔG, typically driven by coupling with exergonic reactions in anabolism.

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    Equilibrium

    Equilibrium in a metabolic reaction is the point where the forward and reverse rates are equal, and the concentrations of reactants and products remain constant.

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    Metabolic Pathways

    Metabolic pathways are sequences of enzyme-catalyzed reactions that convert substrates to products, such as glycolysis leading to energy production.

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    Amphibolic Pathways

    Amphibolic pathways serve both catabolic and anabolic functions, like the Krebs cycle, which provides intermediates for biosynthesis while generating energy.

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    Coenzymes

    Coenzymes are organic molecules, such as NAD+ and FAD, that assist enzymes by carrying chemical groups or electrons in metabolic reactions.

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    Redox Reactions

    Redox reactions involve the transfer of electrons between molecules, with oxidation losing electrons and reduction gaining them, fundamental to energy metabolism.

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    Oxidation

    Oxidation is the loss of electrons from a molecule, often involving the addition of oxygen or removal of hydrogen, as in the conversion of glucose to CO2.

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    Reduction

    Reduction is the gain of electrons by a molecule, typically involving the addition of hydrogen or removal of oxygen, like in the formation of NADH.

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    Fermentation

    Fermentation is an anaerobic process that regenerates NAD+ from NADH by converting pyruvate to products like lactate, allowing glycolysis to continue without oxygen.

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    Lactic Acid Fermentation

    Lactic acid fermentation converts pyruvate to lactate in animal cells, regenerating NAD+ for glycolysis during oxygen debt, as in muscle cells during exercise.

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    Alcoholic Fermentation

    Alcoholic fermentation converts pyruvate to ethanol and carbon dioxide in yeast and some bacteria, regenerating NAD+ for continued glycolysis.

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    Gluconeogenesis

    Gluconeogenesis is the metabolic pathway that synthesizes glucose from non-carbohydrate precursors like lactate, occurring mainly in the liver during fasting.

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    Glycogenesis

    Glycogenesis is the process of synthesizing glycogen from glucose, storing energy in the liver and muscles for later use.

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    Glycogenolysis

    Glycogenolysis is the breakdown of glycogen into glucose, providing quick energy during periods of low blood sugar.

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    Lipolysis

    Lipolysis is the hydrolysis of triglycerides into glycerol and fatty acids, releasing energy for use in metabolic processes.

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    Lipogenesis

    Lipogenesis is the synthesis of fatty acids and triglycerides from acetyl-CoA and other precursors, storing excess energy as fat.

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    Common Trap: Confusing Aerobic and Anaerobic Respiration

    A common error is mixing up aerobic respiration, which requires oxygen and produces more ATP, with anaerobic respiration, which does not and yields less energy, like in fermentation.

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    Strategy for Enzyme Kinetics Problems

    For enzyme kinetics problems, plot reaction rates against substrate concentrations to identify Vmax and Km, and determine if inhibitors affect these values to solve for enzyme efficiency.

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    Example: Net ATP from Glucose

    In complete oxidation of one glucose molecule, glycolysis yields 2 ATP net, the Krebs cycle produces 2 ATP, and oxidative phosphorylation generates about 26-28 ATP, totaling around 30-32 ATP.

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    Bioenergetics of Photosynthesis

    Bioenergetics in photosynthesis involves capturing light energy to produce ATP and NADPH, which drive the Calvin cycle to fix CO2 into sugars, with an overall efficiency influenced by wavelength.

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    Regulation by Phosphofructokinase

    Phosphofructokinase is a key regulatory enzyme in glycolysis, inhibited by high ATP and citrate levels, preventing unnecessary glucose breakdown when energy is abundant.

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    Coupled Reactions in Metabolism

    Coupled reactions link an exergonic reaction, like ATP hydrolysis, to an endergonic one to make it spontaneous, such as in anabolic pathways for synthesizing complex molecules.

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    NAD+ and FAD in Electron Carriers

    NAD+ and FAD act as electron carriers in metabolism, accepting electrons during catabolism to become NADH and FADH2, which then donate electrons to the electron transport chain.

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    Energy Charge of the Cell

    The energy charge of the cell is a measure of the cell's energy status, calculated from the ratio of ATP, ADP, and AMP, influencing the regulation of metabolic pathways.