Enzymes are globular proteins that act and biological catalysts (They speed up chemical reactions). There is a depression on the surface of the enzyme molecule called the active site.
LOCK AND KEY THEORY:
• a molecule with a complimentary shape can fit into the active site
• the substrate molecules form temporary bonds with the amino acids of the the active site to produce an enzyme substrate complex
• the enzyme holds the substrate molecules in a way that they react more easily
• when the reaction is finished the products are released, leaving the enzyme unchanged
• the substrate is known as the ‘key’ which fits into the enzyme’s ‘lock’
INDUCED FIT THEORY:
• active site is flexible
• when the substrate enters the active site the enzyme molecule changes shape slightly fitting more closely round the substrate