Enzymes Notes

2.5 Enzymes

Understandings

  • Enzymes have an active site to which specific substrates bind.

    • Enzymes are proteins that speed up specific chemical reactions, both anabolic and catabolic.
    • Each enzyme possesses an active site that facilitates binding to a specific substrate.

  • Enzyme catalysis involves molecular motion and the collision of substrates with the active site.

    • The structure and chemical properties of an enzyme’s active site are complementary to the substrate molecule it binds to.
    • To catalyze a reaction, the substrate must collide with the enzyme’s active site, forming an enzyme-substrate complex.

  • After binding to the active site, the substrate is broken down by the enzyme, and the products are released.

    • The enzyme remains unchanged and can bind to another substrate.

  • The specificity of enzymes is often called the lock-and-key model, where only one specific substrate can bind to each active site.

  • Enzymes can be denatured when exposed to conditions that interfere with internal amino acid interactions.

    • Each enzyme has optimum conditions in which it most effectively catalyzes reactions, usually related to the organism's habitat or the cell’s location within the body.

  • Immobilized enzymes are widely used in industry.

    • Immobilized enzymes are attached to a material so that it stays in place.
      • Bound to solid or porous materials.
      • Mixed in with a matrix.
      • Embedded in a soluble membrane.
    • These enzymes are not changed in reactions and so can be used many times when substrates pass over them.

Key Terms

  • Enzyme: A protein that speeds up specific chemical reactions.
  • Active Site: The specific region of an enzyme that binds to a substrate.
  • Substrate: The molecule upon which an enzyme acts.
  • Denaturation: The process by which proteins lose their structure due to external factors.
  • Immobilized Enzymes: Enzymes attached to a material so that it stays in place.
  • Lactase: Enzyme used in producing lactose-free milk.
  • Lactose-Free Milk: Milk in which lactose has been broken down into glucose and galactose.

Enzyme Catalysis

  • Enzyme catalysis requires molecular motion and substrate collision with the active site.
  • Example:
    • Enzymes are like scissors.
    • Substrates are like paper, skin, trees, fabric, or shrubs.
    • Active sites are where the scissors touch the material.
    • Products are strips of paper, an open cut, branches of trees, small pieces of jagged fabric, or leaves from shrubs.

Factors Affecting Enzyme Activity

Temperature

  • Low temperatures result in insufficient thermal energy for enzyme-catalyzed reactions to proceed.
  • Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity.
  • At an optimal temperature (which varies for different enzymes), the rate of enzyme activity will be at its peak.
  • Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the enzyme’s hydrogen bonds.
  • This causes the enzyme (particularly the active site) to lose its shape, resulting in the loss of activity (denaturation).

pH

  • Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape.
  • Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function.
  • Enzymes have an optimal pH (which may differ between enzymes), and moving outside this range diminishes enzyme activity.

Substrate Concentration

  • Increasing substrate concentration will increase the activity of a corresponding enzyme.
  • More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period.
  • After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels because the environment is saturated with substrate, and all enzymes are bound and reacting.

Immobilized Enzymes

  • Immobilized enzymes are used in carbon capturing. Polluted air is passed over enzymes, which traps CO_2 for storage. This technology is being used to reduce emissions from factories.

Applications

Lactose-Free Milk

  • Immobilized enzymes are used in producing lactose-free milk.
  • Lactase is immobilized in alginate beads, and then milk is passed over, which breaks lactose into glucose and galactose monomers.
  • Since the enzymes are bound, they do not wash away and can be used many times.
  • Because lactose-free milk has more sugar monomers, it tastes sweeter, and manufacturers use this to sweeten dairy products without adding extra sugars.

Enzymes in Everyday Usage

  • Enzymes can be taken out of organisms, purified, and then used in science and industry.
  • Example: The use of amylase, lipases, and proteases in biological washing powder to break down any stains that contain carbohydrate, fat, and protein.

Review Questions

  1. How is a lock and key process similar to an enzyme-substrate complex?
  2. What human body system would have the most enzymatic activity?