Metabolism and Enzymes

Metabolism:

The sum of all the catabolic and anabolic processes that occur in the body (including matter and energy).

Catabolic vs. Anabolic Reactions

    Catabolic Reaction:

  • Breaks down larger molecules (energy rich and complex) into smaller ones (many energy poor and simple)
  • Releases excess energy
  • Exergonic reaction
  • Remember: Cats break down house of cards
  • Example: cellular respiration

    Anabolic Reaction:

  • Builds energy rich and complex molecule from many energy poor and simple molecules
  • Water as a byproduct of condensation reaction
  • Endergonic reaction
  • Example: photosynthesis

Enzymes

    What are Enzymes

  • Biological catalysts that speed reactions up. Life processes such as digestion, growth, cell respiration, etc, would slow down severely without enzymes.
  • Enzymes are produced to speed up specific reactions within the cell, allowing cells to control which reactions happen
  • Each cell produces thousands of different enzymes
  • Enzymes typically catalyse small chemical reactions, while major reactions happen via a series of reactions (product of one enzyme’s reaction is the substrate of the next)
  • Metabolism is also the complex network of interdependent and interaction chemical reactions catalysed by enzymes occurring in living organisms

    How Enzymes Work

  • Enzymes are globular proteins with active sites where catalysis occurs
  • Enzymes fold, making 3d structures, so that amino acids can be next to each other and make active sites
  • Amino acids interact with each other to provide ideal chemical environments for substrate-product transformation. Some active sites include non-amino acid components (e.g. metal ion)
  • Active sites and substrates are not rigid structures, but rather interact during binding to modify and fit to the other (induced-fit binding). Changes during this time weaken bond in substrate, making transformation into product faster
  • Enzymes are sometimes smaller than substrate molecules
  • Random movement of molecules in liquid is needed for substrate molecules
    • Meeting of substrate and active site is referred to as a collision
    • When close enough and in proper orientation, the two are attracted to each other and fit together
    • This makes successful collision (substrate binds to active site)

Rate of Enzyme Activity

The rate of enzyme activity is how frequently reactions are catalysized, and can be measured by amount of product formed per unit time. Factors influencing this include:


    Temperature

  • Temperature affects molecular movement, thus affecting the amount of successful collisions per unit time
  • Can also cause denaturation
  • Temperature increase → increased molecular movement → more successful substrate-active site collisions
  • Too high of a temperature leads to enzyme denaturation and breaks bonds within enzymes needed to maintain structure

    Substrate Concentration

  • More substrate allows for more successful substrate-active site collisions to occur
  • As the substrate concentration increases, more active sites are occupied
  • At some point it will top out, because eventually there will not be enough active sites to bond with substrates

    pH

  • pH affects the ionization of COOH and NH₂ groups
  • This alters the enzyme structure and can cause denaturation
  • Most enzymes have an optimum pH of 7
  • If the pH increases or decreases from the optimum, enzyme activity drops because the active site is altered
  • At above or below the optimum pH, all enzymes are permanently denatured, so no reactions occur at all

Enzymes Lowering Activation Energy

    Bond Energy

  • Energy is required to break chemical bonds, and energy is released when these bonds are made
  • To convert reactants into products, bonds must be broken or weakened in reactants
  • The amount of energy needed to break bonds and reach the transition state is called the activation energy
  • Transition State: the stage between breaking and making bonds, when energy within bonds is at a maximum for a short period of time

    Enzymes Reduce the Activation Energy of Reactants

  • They do this by weakening the bonds of substrates so that an alternate transition state is reached at lower energy
  • This makes it likely that substrates already have the activation energy, so the reaction rate is greatly increased