Enzymes- Biological catalyst

Enzymes- Biological catalyst

1. Speed up metabolic reactions in living organisms and remain unchanged, able to be used again. A small amount of catalyst can catalyse the conversion of a large number of molecules. The number of reactions that an enzyme molecule can catalyse per second is called its turnover number

2. Why are enzymes so remarkable?

   • Enzymes speed up metabolic reactions by up to 10^12 times at lower temperatures, neutral pH and normal pressures- conditions that sustain life
   • Enzymes are more specific that chemical catalysts- do not produce unwanted by-products and rarely make mistakes
   • The cells where they are made can regulate their production and activity to fit the needs of the cell/organism at the time

3. Enzyme structure determines function

   • They may need help from cofactors
   • Instructions for making enzymes are encoded in genes. If a mutation alters the sequence of amino acids, then this may alter the tertiary structure preventing it functioning
   • If an enzyme that catalyses a metabolic reaction is deficient, then a metabolic disorder occurs
   • Enzymes also catalyse the formation of the organism's structural components, collagen in bone, cartilage in blood-vessel wall, joints and connective tissue

4. The active site

   • The active site consists of around 6 to 10 amino acids
   • The tertiary structure of the active site is crucial, as its shape is complementary to the shape of the substrate molecule
   • Each type of enzyme is highly specific in its function
   • The shape of enzymes active site can be altered by changes in temperature and pH- affect the bonds that hold proteins in their tertiary structure

5. Intracellular enzymes

   • In any cell there may be up to 1000 metabolic reactions going on at the same time
   • Each metabolic pathway is one in a series of consecutive reactions, ever step catalysed by a specific enzyme
   • Various reactants and intermediates (known as metabolites) act as substrates for specific enzymes
   • In some metabolic pathways (described as catabolic), metabolites are broken down to smaller molecules to release energy
   • In other metabolic pathways (anabolic) energy is used to synthesise larger molecules from smaller ones
   • Respiration and photosynthesis are examples of complex metabolic pathways

6. Extracellular enzymes

   • Fungi release hydrolytic enzymes from their thread like hyphae, they digest carbs, proteins and lipids and glucose, amino acids, glycerol and fatty acids are absorbed to be used in respiration and growth
   • In our digestive system enzymes are secreted to the gut lumen, where they extracellularly digest large molecules (proteins, lipids and nucleic acids)
   • Amylase produced in salivary glands, acts in the mouth to digest starch and in the pancreas to catalyse the same reaction in the lumen of small intestine
   • Trypsin made in pancreas and acts in the lumen of small intestine to digest proteins by hydrolysing peptide bonds- optimum pH 7.5-8.5

7. Catalase

   • It protects cells from damage by oxygen by quickly breaking down hydrogen peroxide to water and oxygen
   • Catalase consists of 4 polypeptide chain and contains a haem group with iron
   • Highest turnover no. known 6million per sec
   • Found in small vesicles called peroxisomes
   • When white blood cells ingest pathogens they use catalase to kill the invading microbe
   • Optimum pH varies 4-11, optimum temp 45 (humans)- 90