⚡ Metabolism &amp; Bioenergetics

Metabolism

The sum of all chemical reactions in an organism, including anabolic building and catabolic breakdown.

Anabolism and Catabolism

Anabolic reactions build complex molecules using energy; catabolic reactions break them down to release energy.

ATP

The cell's energy currency, whose phosphate bond hydrolysis powers work in the cell.

Cellular Respiration

The process of releasing energy from glucose to make ATP, using oxygen in the aerobic form.

Aerobic and Anaerobic Respiration

Aerobic uses oxygen for a large ATP yield; anaerobic occurs without oxygen with much less ATP.

Glucose as Fuel

The main sugar broken down to supply cellular energy.

Photosynthesis vs Respiration

Photosynthesis stores energy in glucose and releases oxygen; respiration releases that energy and consumes oxygen.

Lactic Acid Fermentation

Pyruvate is converted to lactate when oxygen is lacking, regenerating NAD+ for glycolysis.

Alcoholic Fermentation

Yeast convert pyruvate to ethanol and carbon dioxide, regenerating NAD+.

Metabolic Rate

The speed at which the body uses energy, affected by size, age, activity and hormones.

Respiratory Equation

Glucose plus oxygen yields carbon dioxide, water and energy released as ATP and heat.

Energy Flow in Ecosystems

Energy enters from the sun, flows through food chains and is lost as heat at each step.

Intermediate topics (16)

Glycolysis

A ten-step pathway in the cytoplasm that splits glucose into two pyruvate, yielding net 2 ATP and 2 NADH.

Link Reaction

Pyruvate is oxidised to acetyl-CoA in the mitochondrial matrix, releasing carbon dioxide and forming NADH.

Krebs Cycle

A cyclic pathway that oxidises acetyl-CoA to carbon dioxide, producing NADH, FADH2 and a little ATP.

Electron Transport Chain

Protein complexes in the inner mitochondrial membrane pass electrons to oxygen while pumping protons.

Oxidative Phosphorylation

ATP synthesis driven by electron transport and the proton gradient across the inner membrane.

Chemiosmosis

Protons flowing back through ATP synthase down their gradient drive the formation of ATP.

NAD and FAD

Electron carrier coenzymes that shuttle electrons from catabolic reactions to the electron transport chain.

ATP Yield from Glucose

Complete aerobic oxidation yields about 30 to 32 ATP, compared with 2 from fermentation.

Gluconeogenesis

Synthesis of glucose from non-carbohydrate precursors such as lactate and amino acids, mainly in the liver.

Glycogen Metabolism

Glycogenesis stores glucose as glycogen and glycogenolysis breaks it down when energy is needed.

Beta-Oxidation

Fatty acids are broken into acetyl-CoA two carbons at a time for use in the Krebs cycle.

Protein Catabolism

Amino acids are deaminated and their carbon skeletons enter respiration, with nitrogen excreted as urea.

Respiratory Quotient

The ratio of carbon dioxide produced to oxygen consumed, indicating which fuel is being used.

Pentose Phosphate Pathway

Produces NADPH and ribose sugars for biosynthesis and antioxidant defence.

Metabolic Pathways Regulation

Key enzymes are controlled by feedback, allosteric effectors and hormones like insulin.

Light Reactions and ATP Synthesis

Photosynthetic electron flow builds a proton gradient across the thylakoid to drive photophosphorylation.

Advanced topics (25)

Cori Cycle

Lactate from muscle is converted to glucose in the liver and returned, costing net ATP.

Proton Motive Force

The combined chemical and electrical gradient of protons that powers ATP synthase and transport.

ATP Synthase Rotary Mechanism

Proton flow turns the F0 rotor, driving conformational changes in F1 that make ATP, like a molecular turbine.

Mitochondrial Uncoupling

Uncoupling proteins dissipate the proton gradient as heat, as in brown adipose tissue.

Reactive Oxygen Species

Electron leakage produces superoxide and other oxidants that cause damage but also act as signals.

Metabolic Flux Analysis

Uses isotope tracers and models to measure reaction rates through metabolic networks.

Warburg Effect

Cancer cells favour glycolysis and lactate production even when oxygen is abundant.

AMPK and mTOR Signalling

Energy sensors AMPK and mTOR balance catabolism and growth according to nutrient availability.

Ketone Body Metabolism

During fasting the liver makes ketones from fatty acids as alternative fuel for the brain.

Urea Cycle

A liver pathway that converts toxic ammonia into urea for excretion.

Thermodynamics of Metabolism

Coupled reactions and negative free energy changes determine pathway direction.

Brown Fat Thermogenesis

Specialised adipocytes burn fuel to produce heat via UCP1 for non-shivering warmth.

Metabolic Syndrome

A cluster of high blood pressure, insulin resistance, obesity and dyslipidaemia raising heart disease risk.

Anaerobic Respiration in Prokaryotes

Bacteria use alternative terminal acceptors such as nitrate or sulfate in the electron transport chain.

Chemosynthesis

Bacteria at hydrothermal vents fix carbon using energy from inorganic chemical reactions.

Lipid Biosynthesis

Fatty acid synthase builds fatty acids from acetyl-CoA and malonyl-CoA using NADPH.

Cholesterol Metabolism

Synthesis through the mevalonate pathway is regulated by HMG-CoA reductase, the target of statins.

Metabolomics

Large-scale measurement of small metabolites to profile the physiological state of cells and tissues.

Mitochondrial Dynamics

Fusion, fission and mitophagy keep the mitochondrial population healthy.

Oxygen Debt and Recovery

Extra oxygen consumption after exercise restores ATP and phosphocreatine and clears lactate.

Hormonal Control of Metabolism

Insulin, glucagon, cortisol, adrenaline and thyroid hormone coordinate fuel use across tissues.

Metabolic Engineering

Rewiring pathways in microbes to produce fuels, drugs and chemicals.

Circadian Metabolism

Clock genes align metabolic enzymes and hormones with daily feeding and fasting cycles.

Bioenergetics of Muscle

Phosphocreatine, glycolysis and oxidative metabolism supply ATP at different timescales of exercise.

Systems Biology of Metabolism

Genome-scale models predict growth and pathway usage under constraints.