IB BIology 2025 Enzymes

Enzyme

a substance produced by a living organism that acts as a catalyst to bring about a specific biochemical reaction.

Catalyst

(n.) a substance that causes or hastens a chemical reaction; any agent that causes change

Active Site

a region on an enzyme that binds to a protein or other substance during a reaction.

Substrate

reactant of an enzyme-catalyzed reaction

Enzyme-Substrate Complex

A temporary complex formed when an enzyme binds to its substrate molecule(s).

Activation Energy

the minimum amount of energy required to start a chemical reaction

Product

A substance produced in a chemical reaction

Lock-and-Key Model

The model of the enzyme that shows the substrate fitting perfectly into the active site

Induced Fit Model

enzyme model where the substrate induces the enzyme to alter its shape slightly so it fits better

Denaturation

In proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive. In DNA, the separation of the two strands of the double helix.

Optimal Temperature

Temperature at which an enzyme works the best

Optimal pH

specific pH at which an enzyme works the fastest

Enzyme Activity

a measure of the ability of an enzyme to catalyse a specific reaction.

enzyme turnover rate

rate at which the enzyme that comes out with the product is recycled through the process again

Cofactor

Non-protein helpers that may be bound tightly to the enzyme as a permanent resident, or may bind loosely and reversibly along with the substrate.

Coenzyme

If the cofactor is an organic molecule.

Prosthetic Group

A non-protein, but organic, molecule (such as vitamin) that is covalently bound to an enzyme as part of the active site.

Competitive Inhibition

substance that resembles the normal substrate competes with the substrate for the active site

Non-Competitive Inhibition

a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate.

Allosteric Site

The place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active.

Allosteric Inhibition

inhibition by a binding event at a site different from the active site, which induces a conformational change and reduces the affinity of the enzyme for its substrate

Feedback Inhibition

A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

Reversible Inhibition

inhibitor bonds noncovalently to the active site and prevents substrate from binding, when inhibitor leaves enzyme function resumes

Irreversible Inhibition

active site is made unavailable for prolonged period of time or enzyme is permanently altered usually when a covalent bond is formed between the inhibitor and the enzyme itself

Enzyme Kinetics

the study of the rates of enzyme-catalyzed reactions

Vmax

maximum initial velocity or rate of an enzyme-catalysed reaction.

Saturation point - Enzymes

The point is where there are too many substrates for enzymes, and their reaction rate stays the same. All active sites are full of substrates

Inhibitor

A substance that slows down or stops a chemical reaction

Enzyme Specificity

Enzyme specificity is the concept that each enzyme catalyzes only one kind of reaction.

Catalytic Cycle

substrate + enzyme --> enzyme substrate complex --> product + enzyme

Metabolic Pathway

A series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.

Immobilized Enzymes

are enzymes that can be attached to each other or to inert substances and can be used repeatedly. (to each other, insoluble supports: glass, within a gel: sodium Alginate)

Transition State

a high-energy intermediate state of the reactants during a chemical reaction that must be achieved for the reaction to proceed

competative inhibition

regulatory molecule is similar in size and shape to the enzyme's natural substrate and inhibits catalysis by binding to the enzyme's active site

Non-competative inhibition

The inhibitor binds to the allosteric site, changing the shape of the enzyme so that the substrate can no longer bind the active site.

Effect of temperature on enzyme activity

Enzyme activity increases as temperature increased (often doubles with every 10 degree rise) because collisions between substrate and active site occur more frequently due to faster molecular motion

At too high temperatures, enzymes denature and stop working

Effect of pH on enzyme activity

All enzymes work best at optimal pH. above and below the optimal pH the rate of reaction decreases. Extreme pH changes can denature the enzyme.

substrate concentration on enzyme activity

As the substrate concentration increases, so does the rate of reaction, until all of the active sites are bound and the rate of reaction levels off.

temp enzyme activity graph

ph enzyme activity graph

Substrate Concentration on Enzyme Activity graph

mechanism-based inhibition

- inhibitor acts as a substrate and forms a covalent bond with the enzyme so the reaction cannot take place as the substrate cannot fit in the enzyme

- often irreversible

eg: covalent "suicide" inhibition