2.5 - Enzymes

Essential Idea: Enzymes control the metabolism of the cell.

2.5 Enzymes Understandings: Enzymes have an active site to which specific substrates bind   Enzyme catalysis involves molecular motion and the collision of substrates with the active site Temperature, pH and substrate concentration affect the rate of activity of enzymes Enzymes can be denatured Immobilized enzymes are widely used in industry Application: Methods of production of lactose-free milk and its advantages Skills: Design experiments testing the effect of temperature, pH and substrate concentration on the activity of enzymes. Experimental investigation of a factor affecting enzyme activity

I. Catalysts A. Speed up the rate of a reaction without being changed by the reaction

B. Chemical reactions = breaking and reforming bonds Activation Energy – the amount of energy needed get a reaction started (have bonds of reactants break and reactants bump into each other) For a reaction to get started, reactants have to bump into each other and bonds have to break

Catalysts lower the activation energy of a reaction 1. Help break the bonds of reactants and increase the frequency at which reactants bump into each other

In chemistry, heat is a great catalyst 1. Puts stress on chemical bonds, causing them to break 2. Increases molecular motion, meaning molecules bump into each other more frequently and with more force

2. Not specific 1. Damages cells D. In living organisms, heat is not a great catalyst for 2 major reasons 1. Damages cells 2. Not specific

II. Enzymes Proteins that act as catalysts 1. Proteins have a very specific shape due to tertiary folding 2. Specific folding creates an active site – location where substrate fits into the enzyme 3. Substrate – reactants in a metabolic reaction *Enzyme names usually end in -ase

B. Enzymes lower activation energy for metabolic reactions 1 B. Enzymes lower activation energy for metabolic reactions 1. Can stress bonds that need to be broken or hold reactants in a position favorable to bonding 2. The enzyme does not provide any energy! *Still requires molecular motion and collision of molecules involved Reminder – enzymes not changed by the reaction

III. Factors that affect enzyme activity Temperature Each enzyme has an ideal (optimum) temperature range Too hot – heat stresses bonds in protein causing it to change shape Too cold – molecular motion is too slow

B. pH (proportion of H+ and OH- ions) Each enzyme has an ideal (optimum) pH range Change in H+ and OH- ions can bind with enzyme (changes bonding between amino acids which changes its shape) or substrate and influence bonding between the two

C. Temperature and pH changes outside the optimum range can cause denaturation of the protein

D. Substrate concentration - as substrate concentration increases, enzyme activity increases until a maximum rate is achieved

IV. Enzymes in Industry Immobilized enzymes - fixed to a static surface (like beads) in order to improve the efficiency of the catalyzed reaction and prevent denaturation of the enzyme

Many uses including the production of lactose-free milk 1. Some humans produce the enzyme lactase which breaks down the lactose sugar in milk in glucose and galactose

Some humans are lactose-intolerant – do not produce lactase a. If lactose is consumed, it is not broken down in the small intestine, so it continues to the large intestine where symbiotic bacteria break it down, but also produce various gases, which cause bloating and intestinal discomfort.

Lactose-free milk can be produced using immobilized enzymes a. The lactase is purified from yeast or bacteria and then bound to an inert substance (such as alginate beads) b. Milk is then repeatedly passed over the immobilized enzyme, becoming lactose-free.

4. The generation of lactose-free milk can be used in a variety of ways: As a source of dairy for lactose-intolerant individuals As a means of increasing sweetness in the absence of artificial sweeteners (monosaccharides are sweeter tasting) As a way of reducing the crystallization of ice-creams (monosaccharides are more soluble, less likely to crystalize) As a means of reducing production time for cheese and yogurts (bacteria ferment monosaccharides more readily)