AP BIO METABOLISM

Metabolism

The totality of all chemical reactions occurring in a cell or organism

Metabolic Pathway

A series of enzyme-controlled reactions converting a substrate into a final product

Catabolic Pathway

Metabolic pathway that breaks down complex molecules into simpler ones, releasing energy

Anabolic Pathway

Metabolic pathway that builds complex molecules from simpler ones, requiring energy input

Bioenergetics

The study of how energy flows through living systems

Energy

The capacity to do work or cause change

Kinetic Energy

Energy associated with motion

Potential Energy

Energy stored due to position or structure

Chemical Energy

Potential energy stored in chemical bonds

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed

Second Law of Thermodynamics

Every energy transfer increases the entropy of the universe

Entropy

A measure of disorder or randomness

Enthalpy (H)

Total energy of a system

Gibbs Free Energy (G)

Energy available to do work at constant temperature and pressure

Free Energy Change (ΔG)

Difference in free energy between reactants and products

Exergonic Reaction

Reaction that releases free energy (ΔG < 0)

Endergonic Reaction

Reaction that requires free energy input (ΔG > 0)

Spontaneous Reaction

Reaction that can occur without added energy input (ΔG < 0)

Equilibrium

State in which forward and reverse reactions occur at the same rate

ATP (Adenosine Triphosphate)

Primary energy currency of the cell

Phosphorylation

Transfer of a phosphate group to a molecule

Energy Coupling

Using energy released from exergonic reactions to drive endergonic reactions

ADP (Adenosine Diphosphate)

Molecule formed when ATP loses a phosphate group

Inorganic Phosphate (Pi)

Free phosphate released during ATP hydrolysis

Enzyme

A biological catalyst that speeds up chemical reactions by lowering activation energy

Catalyst

Substance that increases reaction rate without being consumed

Protein

Polymer of amino acids that folds into a specific three-dimensional shape

Ribozyme

RNA molecule that functions as an enzyme

Substrate

Reactant that an enzyme acts upon

Product

Molecule produced by a chemical reaction

Activation Energy (Ea)

Minimum energy required to start a chemical reaction

Transition State

Unstable, high-energy intermediate state during a reaction

Reaction Rate

Speed at which reactants are converted to products

Active Site

Region of the enzyme where substrate binds

Enzyme-Substrate Complex

Temporary complex formed when an enzyme binds its substrate

Specificity

Ability of an enzyme to bind only a specific substrate

Lock-and-Key Model

Model in which the enzyme’s active site exactly matches the substrate

Induced Fit Model

Model in which enzyme changes shape upon substrate binding

Orientation of Substrates

Enzyme positions substrates to favor bond formation

Strain

Enzyme-induced stress on substrate bonds that lowers activation energy

Microenvironment

Local environment within the active site that favors the reaction

Optimal Temperature

Temperature at which enzyme activity is highest

Denaturation

Loss of enzyme structure due to heat, pH, or chemicals

Optimal pH

pH at which an enzyme functions best

Saturation

Condition in which all enzyme active sites are occupied

Substrate Concentration

Amount of substrate available for enzyme binding

Inhibitor

Substance that reduces enzyme activity

Competitive Inhibitor

Inhibitor that competes with substrate for the enzyme’s active site

Noncompetitive Inhibitor

Inhibitor that binds to an allosteric site and alters enzyme shape

Allosteric Site

Binding site on an enzyme separate from the active site

Cofactor

Nonprotein helper required for enzyme activity

Metal Ion Cofactor

Inorganic ion such as Mg²⁺ or Zn²⁺ that assists enzyme function

Coenzyme

Organic cofactor, often derived from vitamins

NAD⁺ (Nicotinamide Adenine Dinucleotide)

Electron carrier used in redox reactions

FAD (Flavin Adenine Dinucleotide)

Electron carrier involved in cellular respiration

Coenzyme A

Coenzyme involved in acetyl group transfer

Allosteric Regulation

Regulation of enzyme activity through binding at an allosteric site

Activator

Molecule that increases enzyme activity

Feedback Inhibition

End product of a metabolic pathway inhibits an early enzyme

Pathway Intermediate

Molecule formed between steps in a metabolic pathway

Rate-Limiting Step

Slowest step in a metabolic pathway that determines overall rate

Homeostasis

Maintenance of stable internal conditions

Hydrolysis

Breaking chemical bonds using water

Condensation (Dehydration Synthesis)

Formation of bonds by removing water

Redox Reaction

Reaction involving transfer of electrons

Oxidation

Loss of electrons

Reduction

Gain of electrons