Role and structure of enzymes

Metabolism

All the chemical reactions that take place inside living cells or organisms.

Anabolic reactions

Molecules are synthesised and energy is required. An example would be photosynthesis.

Catabolic reactions

Molecules are broken down and energy is released. An example would be cellular respiration.

What are enzymes commonly described as

Biological catalysts

Why are enzymes referred to as catalysts

They increase the rate of chemical reactions but remain unchanged at the end.

Why are enzymes referred to as biological

They are produced by cells and catalyse metabolic reactions inside cells or organisms.

How do enzymes increase the rate of metabolic reactions

By binding a specific substrate and converting it into a product. The enzyme is unchanged in the reaction and is able to bind to another substrate.

Turnover number

The number of reactions that can be catalysed by a particular enzyme per second.

Metabolic pathways

Metabolic reactions that are linked together. Each step is catalysed by a different specific enzyme and the product of one enzyme is the substrate for the next.

Advantages of using enzymes over chemical catalysts

Specific to a particular substrate/reaction so enzymes do not produce unwanted byproducts.

High turnover.

Work at lower temperatures and pressures and often at neutral pH.

Production and activity of enzyme can be regulated by cell.

Disadvantages of using enzymes over chemical catalysts

Less stable.

May require specific cofactors to work.

Enzymes a proteins coded for by genes so mutations mat affect their tertiary structure and activity and cause a metabolic disorder.

Intracellular enzymes

Enzymes that act inside cells.

What is an example of an intracellular enzyme

Catalase

Where is catalase found

In peroxisomes

What reaction does catalase catalyse

The breakdown of hydrogen peroxide to oxygen and water (2H₂O₂ → O₂ + 2H₂O).

Why is it important that catalase has a high turnover

So that hydrogen peroxide is broken down quickly as it can damage DNA and cause mutations.

What is the structure of catalase

4 identical polypeptide chains each with an iron containing haem prosthetic group (similar to haemoglobin).

Extracellular enzymes

Enzymes that act outside of cells.

Example of an extracellular enzyme

Amylase

What reaction does amylase catalyse

The hydrolysis of starch into maltose.

Where does amylase act if it is produced in the salivary glands

The mouth

Where does amylase act if it is produced in the pancreas

The small intestines

What are extracellular enzymes important for

Extracellular digestion which many organisms rely on to obtain nutrients.

Extracellular digestion

Enzymes are secreted onto food and digest the complex macromolecules into smaller molecules that can be absorbed and used in respiration or for synthesis of molecules for growth.

What type of proteins are enzymes

Globular

What part of the enzyme does the substrate bind to

The active site

What are the shapes of the active site and substrate described as

Complementary to each other

If enzymes are soluble in water, what will the positioning of their R groups be

The hydrophilic R groups will be on the outside, while the hydrophobic R groups will be on the inside.

Why are enzymes unstable

Their tertiary structure is maintained by many weak hydrogen bonds and ionic bonds, which can be broken by extremes of pH and high temperatures.

Denaturation

An irreversible change in the tertiary structure of a protein.

Why is it important to ensure enzymes do not denature

If the shape of the active site of an enzyme is changed, then it will no longer be complementary in shape to the substrate and will therefore not be able to catalyse that reaction.