ENZYMES

ENZYMES

  • Enzymes are biological catalysts that increase the rate of chemical reaction in the body
  • They are all produced inside cells
  • Some are intracellular and they catalyse reactions within the cells
  • Others are extracellular and are secreted out of the cells where they work e.g. digestive enzymes

Properties of Enzymes

  • Enzymes are protein in nature
  • Enzymes are specific to the type of reaction they catalyse
  • This is referred to as substrate specificity
  • Enzymes work in very small amounts
  • They remain unchanged after the reaction
  • They catalyse reversible reactions
  • They work very fast (high turnover numbers) e.g. the enzyme catalase works on 600 thousand molecules of hydrogen peroxide in one second

Naming of enzymes

Enzymes are named by adding the suffix -ase to:

  • Name of substrate that they work on e.g.
  • Carbohydrates – carbohydrases e.g. sucrase
  • Starch (amylose) – amylase
  • Protein – proteinase (protease)
  • Lipids -lipases
  • Type of chemical reaction catalised e.g.
  • Oxidation – oxidase
  • Reduction – reductase
  • Hydrolysis – hydrolase

Factors Affecting Enzyme Action

Temperature

  • Enzymes are sensitive to temperature changes
  • Generally, the rate of an enzyme¬controlled reaction doubles with every 10OC increase in temperature
  • However, temperatures above 40°C do not favour enzyme reaction
  • This is because enzymes are denatured by high temperatures

pH

  • Every enzyme has a particular pH range over which it works best
  • Some enzymes work best in acidic media while others function better in alkaline media
  • Many enzymes function well under neutral conditions
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Enzyme Concentration

  • Under conditions where the substrate is in excess, the rate of an enzyme-controlled reaction increases as the enzyme concentration is increased

Substrate Concentration

  • If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for sometime and then become constant
  • Any further increase in substrate concentration will not result in corresponding increase in the rate of the reaction

Enzyme Inhibitors

  • These are substances that either compete with substrates for enzyme active sites or combine with enzymes and hence they inhibit the enzyme reaction
  • e.g. certain drugs, cyanide and nerve gas

Co-factors

  • Most enzymes require the presence of other compounds known as co-factors which are non-proteins
  • There are three groups of co-factors
  • Inorganic ions – e.g. iron, magnesium, copper and zinc
  • Complex organic molecules known as prosthetic groups are attached to the enzyme e.g. flavin adenine dinucleotide (FAD) derived from vitamin B2 (riboflavin)
  • Co-enzymes e.g. co¬enzyme A is involved in respiration
  • All co-enzymes are derived from vitamins

Also See:

POLYSACCHARIDES

PROCESS OF PHOTOSYNTHESIS

NUTRITION IN PLANTS

BIOLOGY PRACTICAL

ACTIVE TRANSPORT

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