BIOLOGY - AS Level - 2.4 - Enzymes

What are enzymes?

Biological catalysts

What are enzymes made up of?

Globular proteins with tertiary structures.

How do enzymes work?

They lower the activation energy for a reaction.

What is activation energy?

A minimum amount of energy needed to break bonds and have a reaction occur.

What are intracellular enzymes?

Enzymes act within the cell that produce them.

What is an example of an intracellular enzyme?

Catalase- this catalyses the breakdown of hydrogen peroxide into O2 + H2O which prevents the accumulation of toxic hydrogen peroxide inside cells.

What are metabolic pathways?

A series of consecutive reactions with every step catalysed by a specific enzyme that produces a specific product.

What are catabolic reactions?

Metabolic pathways that breakdown larger molecules into smaller ones releasing energy in the process.

What are anabolic reactions?

Mastic pathways that use energy to build complex molecules from simpler ones.

What are extracellular enzymes?

Enzymes that act outside of the cells that produce them.

What are examples of extracellular enzymes?

• Amylase - this is secreted by the salivary glands, pancreas and small intestine to break down starch into maltose.

• Trypsin- this is secreted by the pancreas into the small intestine to breakdown proteins into smaller polypeptides

What is the process of enzyme action?

• The enzyme by the active site to form an enzyme-substrate complex

• Temporary bonds form between the R groups within the active site and the substrate (these bonds lower activation energy)

• The products are released from the active site

What is the lock and key model?

When the subject fits perfectly into the enzymes active site.

What is the induced fit model?

When the substrate doesn’t fit perfectly into the enzymes active site, So when the substrate enters the enzyme, the active site changes slightly.

What are inhibitors?

Molecules that bind to enzyme to reduce their activity.

What do reversible inhibitors do?

Form weak bonds with the enzyme.

What do irreversible inhibitors do?

From strong bonds with the enzyme.

What are the two types of inhibitors?

Reversible and irreversible.

What’s do competitive inhibitors do?

Bind to the active site to prevent enzyme substrate-complexes.

How do competitive inhibitors work?

They have a similar shape to the substrate and they bind to the active site of the enzyme, this prevents the substrate from binding and reduces the formation of enzyme–substrate complexes, this decreases the rate of reaction.

What do non-competitive inhibitors do?

A bind away from the active site to prevent enzymes-substrate complexes.

How do non competetive inhibitors work ?

When non-competitive inhibitors bind to the enzyme, it changes the tertiary structure causing the active site to change shape, this results in the active site no longer being complimentary to the substrate thus the substrate and enzyme cannot bind, so less enzyme subject complexes can be formed and the rate of reaction decreases.

What are cofactors?

Non-protein substances that bind to enzymes to increase activity.

What is an example of a cofactor?

Chloride ions are cofactors for amylase

What are coenzymes?

Organic cofactors that bind temporarily to the active site of enzyme molecules.

What is an example of coenzymes?

Vitamins

What are prosthetic groups?

A co-factor that is permanently bound to an enzyme.

What is enzyme denaturation?

Where enzyme tertiary structure changes.

What is the effect of temperature on enzymes?

• As temperature increases so does the rate of reaction, the molecules have more kinetic energy causing more collisions and enzyme substrate complexes

• The maximum rate of reaction is reached at optimum temperature

• As temperature increases past optimum the rate of reaction decreases and reaction stops, this is because too much kinetic energy causes the active site to change shape and enzyme denatures.

What is the effect of pH on enzymes?

• Below the optimum pH, the rate of reaction is low or zero, because in acidic conditions H ions break ionic/hydrogen bonds and denature enzymes

• The max rate of reaction is reached at optimum pH

• Above the optimum pH at the rate of reaction is low or zero, because in alkaline conditions OH ions break ionic/hydrogen bonds and denature enzymes

• What is the effect of substrate concentration on enzymes?

• As the substrate concentration increases, the rate of reaction increases, because there are more substrate molecules to form more enzyme-substrate complexes.

• As the subject concentration increases further, the rate of reaction plateaus, because all active sites are occupied by a substrate and enzymes become the limiting factor

• What is the effect of enzyme concentrations on enzymes?

• As enzyme concentration increases, the rate of reaction increases, because there are more enzyme molecules to form enzyme-substrate complexes

• As the enzyme concentration increases further, the rate of reaction plateaus, all subject molecules are acted on and substrate concentration becomes a limiting factor