ENZYMES and METABOLIC REACTIONS

 How do reactions occur in cells ?  Molecules are in constant motion  Collisions between molecules allow reactions to occur

ENZYMES and METABOLIC REACTIONS  Enzymes  Are protein catalysts that allow chemical reactions to take place in our body without increasing the temperature  Usually end with the suffix ‘-ase’  Examples: urease, amylase, sucrase

Catalysts  Control the speed of reactions without changing the products formed  They do this by reducing the activation energy

Enzymes…  Work on molecules called the substrate  Can be anything

Enzymes…  Work on molecules called the substrate  Can be anything  Are substrate-specific

Enzymes…  Work on molecules called the substrate  Can be anything  Are substrate-specific  Alter the substrate in some way

Substrate approaches an enzyme The enzyme- substrate complex is formed Reaction is complete. Enzyme remains unchanged. Products are formed.

Enzymes Models  Where the substrate joins the enzyme is called the active site  ‘Lock and Key Model’  The active site of an enzyme is a perfect match to a specific substrate

Enzymes Models  ‘Induced-Fit Model’  The active site changes shape slightly when the E-S complex join together  Makes a tighter fit

Factors that Affect Enzymes  What happens at cooler temperatures? 1. Temperature  Reaction rates increase as temperature increases  Peaks at ~ °C then drops rapidly  Why?  E.g. egg frying

Factors that Affect Enzymes 2. pH  Enzymes function within an optimal pH range  Stomach pH  Small intestine pH

Factors that Affect Enzymes 3. Concentration of Substrate Molecules  Reaction rate increases as the substrate concentration increases up to a point  The limiting factor in the reaction may be the amount of substrate or the amount of enzyme available

4. Inhibitor molecules  Molecules that attach to the enzyme and reduce its ability to bind substrate  There are two types of inhibitors Competitive inhibitors Non-competitive inhibitors

4. Inhibitor molecules a. Competitive inhibitors Attach to enzyme’s active site Shape is similar to substrate Compete with the substrate E.g. drugs and poisons - CO - Cyanide

4. Inhibitor molecules b. Non-competitive inhibitors Attach elsewhere on the enzyme (not the active site) Attachment changes the 3D shape of enzyme Reaction still occurs, but is inhibited