A-Level Biology Enzymes: Action, Factors and Inhibition

Activation energy

Energy required to bring about a reaction.

Active Site

A group of amino acids that makes up the region of an enzyme into which the substrate fits to catalyse a reaction.

Competitive inhibitor

A form of inhibitor which binds to the active site of the enzyme preventing the binding of substrate.

Complimentary

Describes the relationship between the active site of an enzyme and the substrate molecule - the way in which they fit together.

Enzyme

A protein that acts as a catalyst and so lowers the activation energy needed for a reaction.

Enzyme-substrate (ES) complex

The intermediate formed when a substrate molecule interacts with the active site of an enzyme.

Induced fit model

A mechanism of interaction between an enzyme and a substrate where the active site changes shape to allow an enzyme-substrate complex to be formed.

Inhibitor

A substance which reduces the activity of an enzyme.

Kinetic Energy

The energy of motion, observable as the movement of an object, particle or set of particles.

Lock and key model

An analogy for how enzymes work - only the correctly sized key (substrate) fits into the keyhole (active site) of the lock (enzyme).

Metabolism

All the chemical processes that take place in living organisms.

Non-competitive inhibitor

A form of inhibitor which does not bind at the active site of the enzyme which prevents the binding of substrate.

pH

A figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acidic and higher values are more alkaline.

Rate of reaction

The speed of a chemical reaction - can be worked out by looking at the decrease in concentration of a reactant over time or increase in concentration of a product over time.

Specific

Describes how each enzyme only catalyses a certain chemical reaction.

Substrate

A substance that is acted on or used by another substance or process. Fits into the active site of an enzyme.

Enzyme Concentration

Increasing enzyme concentration increases the number of active sites available for the substrate to collide with.

Substrate Concentration

Increasing the substrate concentration will increase the rate of reaction as there are more substrate molecules.

Temperature

As temperature increases so does the rate of reaction as there is more kinetic energy so the molecules move faster.

pH effect on enzymes

Above and below the optimum pH for each enzyme, the H+ ions and OH- ions disrupt the ionic and hydrogen bonds holding the enzyme's tertiary structure in place.

Competitive Inhibition

Have a similar shape to that of substrate molecules and compete with the substrate to bind to the active site of the enzyme.

Non-Competitive Inhibition

Do not bind to the active site as have different shape to the substrate and bind to a site away from the active site.

Denaturation

At high temperatures, the enzyme molecules vibrate too much, and bonds are broken which maintain the tertiary structure.

Saturation point

When all the enzyme active sites are occupied, increasing the substrate concentration will have no further effect on the rate.

Induced-fit Model

The updated model suggesting that the active site can change shape slightly to fit around the substrate and form an ES complex.

Enzyme-catalysed reaction

A reaction that is accelerated by the presence of an enzyme.

Temperature effect on enzyme reaction

The rate of an enzyme-controlled reaction can vary with temperature.

Controlled factor in enzyme experiments

One other factor the technician would have controlled.

Rate of reaction at 25 °C

The calculated speed of the enzyme reaction at this temperature.

Enzyme specificity

An enzyme catalyses only one reaction due to its specific active site.

Gout

A disease caused by the build-up of uric acid crystals in joints.

Xanthine oxidase

An enzyme that catalyses the production of uric acid from xanthine.

Allopurinol

A drug used to treat gout by inhibiting xanthine oxidase.

Protease

An enzyme that digests protein.

Effect of temperature on protease activity

The graph shows how protease activity varies with temperature.

Enzyme shape and function

The shape of an enzyme molecule is crucial for its specific function.

Vinegar's effect on bacterial enzymes

Vinegar, being acidic, can prevent the action of bacterial enzymes.

Temperature decrease and enzyme activity

A decrease in temperature decreases the kinetic energy of molecules.

Urea's effect on enzyme reactions

Urea breaks hydrogen bonds, affecting the rate of enzyme-controlled reactions.

Potassium ions in respiration

Concentrations of potassium ions are measured to study respiration.

Inhibitor in respiration

A substance that prevents respiration in plant roots.

Malonate

An inhibitor of respiration with a structure similar to the substrate.

Malonate's mechanism of inhibition

Malonate inhibits respiration by competing with the substrate for the enzyme.

Enzymes

Speed up the rate of chemical reactions in organisms by acting as catalysts.

Enzyme-Substrate Complex

Formed when an enzyme binds to a substrate.

Metabolic Reactions

Reactions that occur at a cellular level, such as respiration and digestion.

Optimum Temperature

The temperature at which an enzyme works best.

Optimum pH

The pH level at which most enzymes work best, typically around pH 7.

Enzyme Inhibitors

Molecules that bind to enzymes and slow or prevent their activity.

Hydrogen Bonds

Bonds that can be disrupted by changes in pH, affecting enzyme structure.

Ionic Bonds

Bonds that can be disrupted by changes in pH, affecting enzyme structure.

Enzyme Activity

Can be affected by factors such as temperature, pH, enzyme concentration, and substrate concentration.

ES-complex

The complex formed when an enzyme and substrate bind together.

Proton Tunneling

A phenomenon where protons can tunnel through energy barriers, allowing reactions to occur.

Specificity

The ability of an enzyme to only bind to a specific substrate due to its unique shape.

3D Structure

The three-dimensional shape of an enzyme that is crucial for its function.

Metabolic Rate

The speed at which metabolic reactions occur, influenced by enzyme activity.

Collisions

Interactions between molecules that lead to the formation of ES-complexes.

Limiting Factor

A condition that restricts the rate of a reaction, such as substrate or enzyme concentration.