Chemistry of Life Topic 3.6 - Enzymes

1. Chemistry of LifeTopic 3.6 - Enzymes

2. Enzymes • Globular proteins • Catalysts which speed up chemical reactions • Unchanged by reaction, therefore are reusable • Specific to their substrate • Affected by pH and Temp

3. Substrate • The substance on which an enzyme works • Active site • Part of the enzyme that attaches to substrate by weak chemical bonds

4. Lock and Key Mechanism • Globular enzyme • Active site • substrate • Activated complex • Unchanged enzyme • products • Active site is often composed of loops of polar amino acids • Enzyme specificity is due to the complementary shape of the active site and substrate • Enzymes work at low concentrations because they can be reused

5. Induced Fit • As substrate enters the active site it induces a slight change in the shape of the protein that causes the active site to embrace the substrate

6. Effect of Temp on Enzymes • As temp goes up (B) molecules are excited and have a greater chance of colliding; increasing enzyme activity • Optimum temp (C) = max rate of reaction • (D) rapid decrease of enzymatic reaction because protein enzyme denatures and not available for bindin

7. Effect of substrate conc. on Enzymes • As substrate conc. goes (A) up, increases chance of collision w/enzyme and rate of reaction increases • At (B) active sites start to become saturated and reaction does not speed up w/addition of substrate • At (C) addition of more substrate does nothing • Only way to speed it up is to add more enzyme

8. Effects of pH on Enzymes • If pH is too low (increase in H+ ions) • If too high (increase in OH-) • Either of these can bond to portions of the amino acids on the enzyme • Changes the active site or protein structure and cause specificity to go down thus lowering reaction activity (pH denaturing) • Pepsin acts at a pH of 3 (blue) • Salivary amylase acts at a pH of 7.2 (red)

9. Protein Denaturing (heat) • Denature – structural change in a protein that results in a loss (usually permanent) of its biological properties • Enzymes are globular proteins (tertiary structure) • Protein structure is maintained by covalent, ionic and hydrogen bonds (polar) • Adding heat excites the molecule and bonds that hold the globular structure and bonds in the active site break, thus changing the shape of both

10. Optimum Temperature for Enzymes • Most organisms have and optimum temp at which their enzymes act • 35-40 C • Some micro-organisms in sulfur pools or geothermal hotspots are 80 C

11. Explain the use of lactase in the production of lactose-free milk. lactase in producing lactose-reduced milk • lactose is the sugar that is naturally present in milk • lactase is obtained by artificially culturing a fungus, Kluveromyces lactis • the fungus grows naturally in milk where it uses lactase to hydrolyze lactose into glucose and galactose • biotechnology companies culture the yeast, extract the lactase from the yeast, and purify it for sale to food manufacturing companies there are several reasons for using lactase in food processing: • some people are lactose-intolerant and cannot drink more than about 250 ml of milk per day, unless it is lactose-reduced • galactose and glucose are sweeter than lactose, so less sugar needs to be added to sweet foods containing milk, such as milk shakes or fruit yoghurt • lactose tends to crystallize during the production of ice cream, giving a gritty texture; because glucose and galactose are more soluble than lactose they remain dissolved, giving a smoother texture • bacteria ferment glucose and galactose more quickly than lactose, so the production of yoghurt and cottage cheese is faster