Enzymes

What are enzymes?

• Biological catalysts that increase the rate of metabolic reactions

• Globular tertiary/quaternary structure proteins

• Are water-soluble as hydrophilic R-groups point outwards

• Have an active site that is specific to a certain substrate and complementary in shape

What is the function of an enzyme?

• A substrate molecule binds to the enzyme when its R-groups interact with the R-groups of the active site to form bonds

• This forms an enzyme-substrate complex

• The reaction is finished when the substrate is converted to product

What are the two theories for the formation of enzyme-substrate complexes?

Lock and Key Theory

Induced Fit Hypothesis

Lock and Key Theory

• Enzymes are specific to one type of substrate molecule only; the enzyme active site is the lock and the substrate is the key

• The substrate is exactly complementary in shape to the active site

• When the substrate enters the active site, it is temporarily held in place by bonds that form between the R-groups of the substrate and amino acids of the enzyme

Induced Fit Hypothesis

• The enzyme changes shape slightly when the substrate molecule enters the active site, ensuring a perfect fit

• When the R-groups interact, the active site slightly changes shape when bonds form between the substrate and active site

• Enzymes are still specific to only one type of substrate as certain bonds need to be formed

Example of the “Induced Fit Hypothesis”

Lysosyme Enzymes

• Can be found in tears and saliva or inside lysosome sacs in a cell

• Break down the polysaccharide cell call of bacterial cells