Learn: Anatomy & Physiology Chapter 3: Energy, Reactions, and Cellular Respiration

Energy

The capacity to do work; exists as potential energy or kinetic energy.

Potential energy

Stored energy, or energy of position.

Kinetic energy

Energy of motion.

Chemical energy

A form of potential energy stored in the bonds of a molecule, released when the bonds are broken.

Electrical energy

A form of kinetic energy resulting from the movement of charged particles.

Mechanical energy

A form of kinetic energy exhibited by objects in motion due to an applied force.

Radiant energy

The energy of electromagnetic waves, such as visible light.

Heat

Kinetic energy from the movement of atoms, ions, and molecules, measured as temperature.

First law of thermodynamics

Energy cannot be created or destroyed; it can only change from one form to another.

Second law of thermodynamics

Whenever energy is transformed, some usable energy is lost as heat.

Metabolism

The sum of all biochemical reactions occurring in living organisms.

Reactants

The substances present before a chemical reaction begins, written on the left side of a chemical equation.

Products

The substances formed by a chemical reaction, written on the right side of a chemical equation.

Decomposition reaction

A chemical reaction in which a larger molecule is broken down into smaller molecules.

Synthesis reaction

A chemical reaction in which smaller molecules are combined to form a larger molecule.

Exchange reaction

A chemical reaction in which parts of two reactants are switched, forming two new products.

Exergonic reaction

A chemical reaction in which the reactants have more energy than the products, releasing energy overall.

Endergonic reaction

A chemical reaction in which the reactants have less energy than the products, requiring an energy input.

ATP cycling

The continuous formation of ATP from ADP and phosphate using energy from exergonic reactions, and breakdown of ATP to fuel endergonic reactions.

Enzyme

A biological catalyst that accelerates a chemical reaction by decreasing its activation energy.

Active site

The unique three-dimensional region of an enzyme where a substrate binds to form an enzyme-substrate complex.

Enzyme-substrate complex

The temporary structure formed when a substrate binds to an enzyme's active site.

Induced fit model

The model describing how an enzyme's active site changes shape slightly to fit its substrate more closely.

Saturation (enzyme kinetics)

The point at which all enzyme molecules are engaged with substrate, so reaction rate cannot increase further with more substrate.

Competitive inhibitor

A molecule that resembles a substrate and competes with it for binding to an enzyme's active site.

Noncompetitive (allosteric) inhibitor

A molecule that binds to a site other than the active site, changing the enzyme's shape and reducing its activity, independent of substrate concentration.

Metabolic pathway

A series of enzymes in which the product of one reaction becomes the substrate for the next.

Multienzyme complex

A group of attached enzymes that work together in a sequence of reactions.

Phosphorylation

The addition of a phosphate group to a molecule, which can turn an enzyme on or off.

Dephosphorylation

The removal of a phosphate group from a molecule, which can turn an enzyme on or off.

Cellular respiration

The four-stage process (glycolysis, intermediate stage, citric acid cycle, electron transport system) that breaks down glucose to produce ATP.

Glycolysis

The first stage of cellular respiration; occurs in the cytosol without oxygen, splitting glucose into two pyruvate molecules with a net gain of 2 ATP and 2 NADH.

Pyruvate

The three-carbon end product of glycolysis, which enters the mitochondria if oxygen is available or is converted to lactate if not.

Intermediate stage

The stage of cellular respiration linking glycolysis to the citric acid cycle, converting pyruvate into acetyl CoA and releasing CO2 and NADH.

Acetyl CoA

The two-carbon molecule formed from pyruvate that enters the citric acid cycle.

Citric acid cycle

A cyclic metabolic pathway in the mitochondrial matrix that converts acetyl CoA into CO2 while producing ATP, NADH, and FADH2.

Electron transport system (chain)

A series of H+ pumps and electron carriers in the inner mitochondrial membrane that uses electrons from NADH and FADH2 to generate ATP.

Oxidative phosphorylation

The formation of ATP using energy from the H+ gradient created by the electron transport system, with oxygen as the final electron acceptor.

Substrate-level phosphorylation

The direct formation of ATP from the energy released by a substrate, occurring during glycolysis and the citric acid cycle.

ATP synthase

The enzyme that uses the kinetic energy of H+ moving down its concentration gradient to form ATP from ADP and phosphate.

Mitochondrial cristae

The folds of the inner mitochondrial membrane that house the electron transport system.

Mitochondrial matrix

The innermost space of the mitochondrion, containing the enzymes of the citric acid cycle.