enzymes

• Biochemical pathways


  Chains or cycles of biochemical reactions, with each step controlled by a separate enzyme
• Biochemical reactions


  • Anabolic reactions - involve the synthesis of larger molecules from smaller subunits (energy is usually required for these reactions - endergonic)
  • Catabolic reactions - involve the breakdown of complex molecules into simpler ones (energy is usually released in these reactions - exergonic)
• Anabolic reactions


  Energy is required as bonds are formed to the final product has more energy than the initial (as there are more chemical bonds in which to store energy)
• Catabolic reactions


  Catabolic reactions release energy as bonds are broken. Therefore the products do not have as much energy as the initial substrate
• Energy cycle


  The energy that is released from the breaking of chemical bonds can be used to make chemical bonds (a chemical bond is a storage of energy, so breaking a bond releases it but making a bond requires energy to be put in)
• ATP


  Adenosine triphosphate, energy in living cells is stored and released in the form of ATP
• ATP-ADP cycle


  1. Phosphorylation - the addition of a phosphate group to an organic molecule (e.g. adenosine)

  2. This causes the molecule to become more reactive
• A typical adult human uses the equivalent of 2 BILLION ATP molecules a minute to stay alive! ATP gets recycled at a very FAST pace to keep up with energy demands
• Photosynthesis


  The biochemical process of converting light energy into the chemical energy stored within the bonds of glucose molecules
• Cellular respiration


  Breaking off of one phosphate of an ATP molecule releases energy to drive endergonic reactions
• Enzymes


  • Proteins that act as organic catalysts that speed up the rate of reactions without being used up in the reaction
  • Catalyse nearly all chemical reactions taking place in the cells of the body
  • Highly specific - they will only act on one particular substrate - shape of enzyme and substrate is important
• Activation energy


  The energy required to break the specific bonds in the reactant molecule(s) that allow new bonds to form and create the product molecule(s). Enzymes reduce the activation energy needed, so speed up the reaction
• Substrate


  The compound acted on by an enzyme
• Products


  The substances that are formed
• Active site


  A region of the enzyme where part of the substrate molecule fits
• Enzyme naming


  The suffix '-ase' is used to denote an enzyme. It is added to the end of the substrate name
• Lock and key model

  The active site has a rigid shape, only substrates with the matching shape can fit. The substrate is the key that fits the lock of the active site
• Induced fit model


  When enzymes and substrates bind, the active site is not completely rigid and may undergo a conformational change in shape to better fit the substrate. This conformational change may increase the reactivity of the substrate and be necessary for the enzyme's catalytic activity
• Cofactors


  Small inorganic compounds & ions that bind to enzymes to activate them, e.g. zinc, magnesium, iron, calcium
• Coenzymes


  Organic molecules that bind temporarily or permanently to enzymes near the active site, e.g. vitamins, NAD, FAD
• pH


  Each enzyme operates best at an optimum pH. A change in pH effects the shape of the enzyme and hence its ability to fit with the substrate molecule
• Temperature


  As temperature increases, enzymes and substrate move faster, so more chance of them meeting so activity increases. However, too high a temperature can cause the enzyme to denature and lose its shape and function
• Enzyme concentration


  The more enzymes you have, the more time the reaction can take place, the more product you will see. Consequently, if you increase the enzyme concentration, you will increase the overall rate of reaction
• Substrate concentration


  If you increase the substrate concentration, then you increase the likelihood of the enzyme and substrate colliding & reacting. The rate of the reaction increases as substrate concentration increases (at constant enzyme concentration)
• Inhibitors


  Chemicals that reduce the rate of enzyme catalysed reactions. They are usually specific and work at low concentrations. Some cause temporary loss of activity (reversible), others cause permanent loss of activity (irreversible)
• Competitive inhibitors


  Bind to the active site in place of the substrate so the enzyme can no longer act on the substrate. Can be reversible or irreversible. Its effect can be reduced by increasing the concentration of the substrate
• Non-competitive inhibitors


  Bind to a site other than the active site (allosteric site), causing a change in the shape of the active site so the substrate cannot bind. Effect cannot be reduced by increasing substrate concentration
• End-product inhibition


  A form of negative feedback where the end product inhibits the initial enzyme in the metabolic pathway, ensuring cells only make products when they are required
• Irreversible inhibitors


  Combine with the functional groups of the amino acids in the active site, irreversibly. They are retained by the body and are lost slowly. Examples: nerve gases, pesticides, heavy metals
• Enzymes affect the rate of photosynthesis and cellular respiration


  Anything that affects the rate at which the enzyme works will therefore affect the amount of photosynthesis and cellular respiration that occur
• Grass growth


  Grows more in spring, less in summer, less in winter
• Enzymes are not alive, so don't talk about them as DEAD