Enzymes: Mechanism of Action, Specificity, and Factors Affecting Activity

Vocabulary practice flashcards covering enzyme definitions, lock-and-key action, 3D structure and specificity, factors affecting activity (temperature and pH), and key terminology for describing graphical trends.

Catalyst

A chemical substance that speeds up a chemical reaction and is not changed or affected by the reaction.

Enzyme

A protein molecule that acts as a biological catalyst to speed up chemical reactions by lowering the activation energy.

Active Site

The specific region of an enzyme that has a complementary shape to a specific substrate, allowing the substrate to fit and bind.

Enzyme-Substrate Complex

The intermediate complex formed when a substrate molecule fits and binds into the complementary active site of an enzyme.

Lock and Key Mechanism

The model describing enzyme action in which an enzyme has a specific shape of active site that is complementary to a specific substrate, joining together to form an enzyme-substrate complex.

Anabolic Reaction

A build-up (condensation) metabolic reaction where two or more substrate molecules enter the enzyme's active site to form a single product.

Catabolic Reaction

A break-down (hydrolysis) metabolic reaction in which an enzyme catalyses the splitting of a larger substrate molecule into smaller product molecules.

Enzyme Specificity

The property that an enzyme only catalyses one specific reaction because its active site is determined by a specific sequence of amino acids that curls into a unique 3D shape complementary to only one substrate.

Factors Affecting Enzyme Activity

The five physical and chemical variables that alter the rate of enzyme reactions: temperature, pH, surface area, substrate concentration, and enzyme concentration.

Optimum Temperature

The temperature at which enzyme activity is at its peak (e.g., $40\,^\circ\text{C}$), showing the maximum number of enzyme-substrate complexes formed.

Denaturation

The irreversible loss of an enzyme's functional 3D shape caused by high temperatures or extreme pH, altering the active site so that it is no longer complementary and substrates can no longer fit and bind.

Optimum pH

The specific pH value at which an enzyme works at its maximum activity and forms the maximum number of enzyme-substrate complexes (e.g., pH 8 or pH 6 depending on the enzyme).

Sucrase

The specific enzyme that catalyses the hydrolysis (breakdown) of sucrose into glucose and fructose.

Amylase

The enzyme that catalyses the breakdown of starch into sugar.

Levelling Off

A graphical trend where the rate of reaction stops changing and remains constant (horizontal) despite a continued increase in an independent variable.

Catalyst

A chemical substance that speeds up a chemical reaction without being changed or affected by the reaction.

Enzymes

Protein molecules that act as biological catalysts to speed up chemical reactions by lowering the activation energy.

Active site

A region on an enzyme with a specific 3D shape that is complementary to a specific substrate molecule, allowing the substrate to fit and bind.

Enzyme-substrate complex

The temporary complex formed when a substrate fits and binds into the complementary active site of an enzyme.

Lock and key mechanism

A model explaining enzyme action where an enzyme with a specific active site shape binds a complementary substrate like a key in a lock, catalysing a breakdown or formation reaction under optimum conditions and releasing products unchanged.

Anabolic reaction

A metabolic reaction involving condensation (building up), where two or more smaller substrate molecules enter the enzyme's active site to form a single larger product.

Catabolic reaction

A metabolic reaction involving hydrolysis (breaking down), where an enzyme catalyses the breakdown of a large substrate molecule into smaller products.

Enzyme specificity

The ability of an enzyme to catalyse only one specific reaction, arising because its unique sequence of amino acids curls into a specific 3D shape that creates an active site complementary only to its specific substrate.

Factors affecting enzyme activity

The key physical and chemical variables that alter the rate of enzyme-catalysed reactions: temperature, pH, surface area, substrate concentration, and enzyme concentration.

Optimum temperature

The temperature (commonly $40\,^{\circ}\text{C}$ in human enzyme examples) at which an enzyme works at its maximum rate, showing a peak with the maximum number of enzyme-substrate complexes formed.

Denaturation

The process at high temperatures or extreme pH values (far from optimum) where energetic vibrations cause the enzyme to lose the shape of its active site, making it no longer complementary to the substrate so no enzyme-substrate complexes can form.

Optimum pH

The specific pH value at which an enzyme displays its maximum activity and forms the maximum number of enzyme-substrate complexes.

Sucrase

An enzyme with an active site complementary to sucrose that catalyses the hydrolysis breakdown of sucrose into glucose and fructose.

Amylase

An enzyme that breaks down starch (which normally turns blue-black with iodine solution) into sugar.

Peak / Maximum (in graph description)

The highest point on a curve representing the optimum condition where the measured variable or rate of reaction reaches its greatest value.

Level off / Stay constant (in graph description)

The portion of a graph curve that flattens out horizontally, showing that the rate or measured variable stops changing despite changes in the independent variable.

Fluctuates (in graph description)

A pattern on a graph characterized by repeated increases and decreases over an interval rather than following a continuous trend.