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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.
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