Metabolism & Energy
Connect fuel breakdown, electron transfer, membranes, and ATP production in one learning path.
See how the pieces connect
- Step 1Glucoseenters fuel pathways
- Step 2Glycolysismakes pyruvate and NADH
- Step 3Electron carriersdeliver electrons
- Step 4Oxidative phosphorylationuses a proton gradient
- Step 5ATPpowers cellular work
During glycolysis, glucose is rearranged into pyruvate. The pathway also makes ATP directly and transfers electrons to NADH. In many human cells, those electrons can support mitochondrial ATP production; the stages are connected but are not all one reaction.
Read the supporting reference: Molecular Biology of the Cell · How Cells Obtain Energy from FoodFrom glucose to ATP
Follow carbon through fuel breakdown and electrons toward oxygen; ATP is made at more than one stage.
Carbon route
The carbon skeleton is rearranged and eventually released as CO₂
- GlycolysisCytosolGlucose becomes two pyruvate; the pathway also produces net ATP and NADH.Open record ↗
- splits glucose intoPyruvate oxidationMitochondrial matrixPyruvate is converted to acetyl-CoA; CO₂ and NADH are produced.Open record ↗
- oxidative decarboxylation formsCitric acid cycleMitochondrial matrixAcetyl carbon is released as CO₂ while electron carriers are reduced.Open record ↗
- oxidizes acetyl groups toElectron carriersTo inner membraneNADH and FADH₂ carry high-energy electrons to the respiratory chain.Open record ↗
Energy coupling
Electron transfer builds a gradient that powers ATP synthase
- Respiratory chainInner mitochondrial membraneElectron transfer ends when oxygen accepts electrons and is reduced to water.Open record ↗
- transfer electrons toProton gradientAcross inner membraneThe chain pumps H⁺ to the intermembrane space, storing potential energy.Open record ↗
- use electron energy to pumpATP synthaseInner mitochondrial membraneH⁺ flow back toward the matrix drives this molecular machine.
- flow back throughATPMatrix and cytosolA usable energy carrier for cellular work.Open record ↗
Simplified aerobic route in a typical human cell. Glycolysis makes some ATP directly; most ATP from glucose oxidation is associated with oxidative phosphorylation. If oxygen is limited, cells can use other routes such as lactate fermentation to regenerate NAD⁺.
What directly powers ATP synthase during oxidative phosphorylation?
Topics in this branch
Cellular Metabolism
The connected reactions cells use to obtain energy and build the molecules they need.
Explore this idea 02Cellular Respiration
How cells transfer energy from fuel molecules into ATP, often using oxygen in the final electron-accepting step.
Explore this idea 03Amino Acids
Meet the 20 standard amino acids that build most proteins, plus selenocysteine and pyrrolysine, two rare amino acids that some organisms encode directly.
Explore this idea 04Oxidation And reduction
Paired chemical changes in which electrons move from one molecule to another.
Explore this idea 05Electron Carriers
Small molecules such as NADH that collect and deliver electrons between metabolic reactions.
Explore this idea 06Substrate-level Phosphorylation
Direct formation of ATP or GTP when an enzyme transfers a phosphate group from a reaction intermediate.
Explore this idea 07Oxidative Phosphorylation
The respiratory chain transfers electrons from NADH and FAD-linked sources to oxygen. Complexes I, III, and IV pump protons; ATP synthase uses the proton-motive force to make ATP from ADP and phosphate.
Explore this idea 08Chemiosmosis
The use of an ion gradient across a membrane to power a cellular process such as ATP synthesis.
Explore this idea 09Proton-motive Force
Stored electrochemical energy created by differences in proton concentration and charge across a membrane.
Explore this idea 10Allosteric Regulation
Control of a protein's activity when a molecule binds at a site other than its main working site.
Explore this idea 11Feedback Inhibition
A control pattern in which a later product reduces activity earlier in the process that makes it.
Explore this idea 12Glycogen Storage and breakdown
How cells build glycogen from glucose and break it down when glucose or energy is needed.
Explore this idea 13Fatty-acid Oxidation
The stepwise breakdown of fatty acids that supplies acetyl-CoA and electron carriers to other pathways.
Explore this idea 14Ketone Bodies
Small molecules made mainly by the liver from acetyl-CoA and used as fuel by several tissues during prolonged fasting.
Explore this idea 15Fed And fasting states
Coordinated changes in hormones and fuel use that help the body respond to eating and time without food.
Explore this idea 16Enzymes
Biological catalysts that speed reactions; most known enzymes are proteins, while some RNA molecules also catalyze reactions.
Explore this ideaThe 20 Standard Amino Acids + Two Rare Encoded Forms
Alanine
Alanine is a compact amino acid used to build proteins. Its small, nonpolar side chain can fit into many protein structures.
Open record MoleculeArginine
Arginine is a protein-building amino acid with a nitrogen-rich side chain that is usually positively charged in cells.
Open record MoleculeAsparagine
Asparagine is a polar amino acid whose side chain can form hydrogen bonds with water and other parts of a protein.
Open record MoleculeAspartate
Aspartate is the negatively charged form commonly present in cells of the amino acid also called aspartic acid.
Open record MoleculeCysteine
Cysteine is a sulfur-containing amino acid. Its reactive thiol group can form a covalent link with another cysteine.
Open record MoleculeGlutamine
Glutamine is a polar amino acid and a major way cells carry nitrogen between tissues.
Open record MoleculeGlutamate
Glutamate is a negatively charged amino acid that helps cells handle nitrogen and supports many protein interactions.
Open record MoleculeGlycine
Glycine is the smallest amino acid, with a hydrogen atom as its side chain. This lets parts of a protein chain bend tightly.
Open record MoleculeHistidine
Histidine is an amino acid with an imidazole ring that can gain or lose a proton near biologically relevant pH.
Open record MoleculeIsoleucine
Isoleucine is one of the three branched-chain amino acids. Its nonpolar side chain often packs inside folded proteins.
Open record MoleculeLeucine
Leucine is a branched-chain amino acid with a hydrophobic side chain that helps proteins fold and pack.
Open record MoleculeLysine
Lysine has a long side chain ending in a positively charged amino group, which can interact with negatively charged molecules.
Open record MoleculeMethionine
Methionine is a sulfur-containing amino acid and is often the first amino acid inserted when a protein is translated.
Open record MoleculePhenylalanine
Phenylalanine has a bulky aromatic side chain that is usually hydrophobic inside a folded protein.
Open record MoleculeProline
Proline has a ring that locks part of the protein backbone into a restricted shape, often introducing a bend.
Open record MoleculeSerine
Serine is a polar amino acid with a hydroxyl group that can form hydrogen bonds and be chemically modified.
Open record MoleculeThreonine
Threonine is an essential amino acid with a hydroxyl group that can form hydrogen bonds.
Open record MoleculeTryptophan
Tryptophan has a large indole ring that can contribute to protein packing and absorb ultraviolet light.
Open record MoleculeTyrosine
Tyrosine is an aromatic amino acid with a hydroxyl group that makes it more polar than phenylalanine.
Open record MoleculeValine
Valine is a branched-chain amino acid with a hydrophobic side chain that helps shape protein interiors.
Open record MoleculeSelenocysteine
Selenocysteine is a rare amino acid that cells can insert into certain proteins using a special recoding system.
Open record MoleculePyrrolysine
Pyrrolysine is a rare amino acid used by some microbes, where a special decoding system can insert it into proteins.
Open record