Enzyme Notes

Enzymes

Basics of Enzymes

  • Enzymes help speed up chemical reactions by either breaking or creating bonds.
  • They make reactions happen faster and easier.

Enzymes as Proteins

  • Enzymes are proteins, which are coded by DNA.
  • DNA codes for the primary structure which is the list of amino acids in a protein polymer.
  • Proteins can be:
    • Structural (e.g., collagen, keratin).
    • Functional (e.g., enzymes like maltase, hormones like insulin, hemoglobin).
  • Hemoglobin is a quaternary protein that carries oxygen in red blood cells.

Structural vs. Functional Proteins

  • Two main groups of proteins: structural and functional.

Protein Fragility and Denaturation

  • Proteins are fragile; their globular shape is crucial for their function.
  • If the shape changes, the protein can become denatured (e.g., egg whites turning white when cooked).

Factors Affecting Enzyme Activity

  • Factors that can destroy enzyme activity:
    • Temperature: Heat can denature proteins (e.g., cooking egg whites).
    • pH: Drastic changes in pH can break hydrogen bonds, altering the shape and function of the enzyme; extreme changes can completely denature a protein.
    • Heavy Metals/Pesticides: Lead, mercury, and other heavy metals can affect or destroy enzyme activity.

Enzymes as Biological Catalysts

  • Enzymes are biological catalysts that speed up chemical reactions without being destroyed.
  • They can be used repeatedly.
  • Many enzyme names end in "-ase" (e.g., maltase, lipase, helicase).
  • Examples in the digestive system: pepsin and trypsin.

Catalysts Defined

  • A catalyst is a substance that alters or speeds up a chemical reaction without being chemically used up or changed at the end of the reaction.
  • Example: Decomposition of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2) is sped up by manganese dioxide (MnO_2).
  • 2H2O2 \rightarrow 2H2O + O2
  • Manganese dioxide (MnO_2) can be recovered and reused.

Enzymes in Reactions

  • Enzyme + Substrate(s) → Enzyme-Substrate Complex → Enzyme + Product(s)
  • The enzyme remains unchanged and can be reused.

Metabolism and Enzymes

  • Metabolism is the sum of all chemical reactions in the body.
  • Almost all reactions need an enzyme to proceed at an appropriate rate.
  • Examples of processes needing enzymes:
    • Digestion:
      Breakdown of large complex molecules into small, diffusible and soluble forms.
    • Cellular respiration:
      Breakdown of glucose in the presence of oxygen to release energy.
    • Protein synthesis.
    • Blood clotting.

Chemical Reactions

  • General Chemistry: Reactants → Catalyst → Products
  • Biology: Substrate(s) → Enzyme → Product(s)
  • All chemical reactions require activation energy to begin.

Activation Energy

  • Reactants (substrates) must collide in a certain way to react.
  • Enzymes lower the activation energy by fitting the substrate into the enzyme, forming an enzyme-substrate complex.
  • After the reaction, the enzyme remains and can be used again.

How Enzymes Work

  • Enzymes lower the activation energy needed for a reaction.
  • The straining of bonds increases the energy needed to break the bonds for the reaction to continue.
  • Enzymes position molecules to interact in ways that don't normally occur.

Energy Content and Reaction Progress

  • Activation energy without a catalyst is high; with a catalyst, it is dramatically lower.
  • Reaction rate depends on activation energy.
  • Activation energy is needed to reach the transition state.
  • The transition state involves strained bonds and is an unstable intermediate step.
  • Lower activation energy allows more molecules to achieve the necessary energy, yielding a greater rate of reaction.

Activation Energy Examples

  • Body temperature provides activation energy for enzyme reactions.
  • ATP from other reactions can activate enzymes or proteins.

Enzyme-Substrate Interactions

  • All enzymes have an active site where the reaction occurs.
  • Substrates enter the active site, forming an enzyme-substrate complex.
  • Substrate entry can change the enzyme's shape to facilitate the reaction.
  • The product is released, and the enzyme is ready to be used again.

Lock and Key Hypothesis

  • Enzymes and substrates fit together like a lock and key.
  • Active sites are depressions on the enzyme surface where specific substrates fit.
  • When the substrate binds, the enzyme-substrate complex forms.
  • Reactions convert substrates into products (synthesis - building up; lysis - breaking down).

Enzyme Review

  • Enzymes are proteins that catalyze or stimulate chemical reactions.
  • They lower activation energy by:
    • Binding specifically to substrates.
    • Orienting substrates optimally for the reaction.
    • Straining specific bonds.
    • Accepting or donating protons and electrons.
  • The chemical reaction occurs in the active site.
  • The 3D shape and chemical nature of the active site determine which substrates bind.

Enzyme Models

  • Lock and Key Model: Specific molecules fit to activate change.
  • Induced Fit Model: Enzymes change shape in response to substrate binding or other factors.

Uses of Enzymes in Daily Life

  • Alcohol production: Converting sugars to alcohol.
  • Animal feed: Making feed easier to digest.
  • Baking: Modifying flour with natural enzymes to prevent staleness.
  • Brewing.
  • Cheese and yogurt production.
  • Detergents: Cleaning oils and fats.
  • Leather tanning.
  • Personal care products.
  • Pulp and paper industry.
  • Textiles: Producing a range of colors in clothing.