Chapter 9 & 10: Enzymes

• An enzyme is a biological catalyst that is made of protein.

• A catalyst is a substance that speeds up a reaction, without itself being used up in the reaction.

• A substrate us the substance on which an enzyme reacts.

• The product is the substance(s) the enzyme forms.

e.g Amylase → Starch = Maltose

• Enzymes are large molecules that are highly folded into a 3D shape.

• Enzymes have areas along their surface called active sites. It is these that a particular substrate becomes attached. These make the enzyme specific.

Enzyme reactions are reversible. This means that an enzyme’s reaction can be anabolic and catabolic. Examples of chemical reactions controlled by enzymes are:
Respiration, Photosynthesis, Digestion, Protein Synthesis, and DNA Replication.

Anabolic Enzymes

• DNA Ligase
  Used in genetic engineering, joins two pieces of DNA together.

• DNA Polymerase
  An enzyme that repairs and forms DNA.

Enzymes involved in photosynthesis are also anabolic because they convert carbon dioxide and water into glucose.

Catabolic Enzymes

• Amylase
  An enzyme that converts starch into maltose and seed germination.

• Catalase
  Converts hydrogen peroxide into water and oxygen.

Factors Affecting Enzyme Activity

pH

• Enzyme shape changes when the pH changes. If the pH becomes too high or low the enzyme changes shape (denatured).

Temperature

• At low temperatures enzyme activity is reduced. An increase in temperature increases enzymes activity.

• Human enzymes are designed to work at 37OC while plants work at 20-20OC.

• Above a certain temperature, enzymes change their 3D shape - as a result the rate of the reaction falls.

Denaturing Enzymes

Active sites are destroyed when denaturing occurs, substrates cannot attach and enzymes cannot function. Dentaturing cannot be reversed.