• Draw:
    • An alpha glucose molecule
    • An amino acid
  • Name:
    • The reaction that breaks bonds between disaccharides and dipeptides
    • The bonds that join these structures
  • Describe:
    • The difference in structure between amylose and amylopectin
    • The tertiary structure of a protein

Objectives

  • Enzymes as catalysts lowering activation energy through the formation of enzyme-substrate complexes.
  • The lock and key and induced fit models of enzyme action.
  • The properties of enzymes relating to their tertiary structure.
  • Description and explanation of the effects of temperature, competitive and non-competitive inhibitors, pH and substrate concentration.

Globular proteins which act as a catalyst

“Alter the rate of reaction without undergoing permanent changes themselves”

  • As with any reaction: substrates → products
  • The energy of products must be lower than that of the substrates...however...
  • Substrate molecules must collide (or be pulled apart) with sufficient energy (known as the activation energy) to kick start the reaction
  • Enzymes lower the activation energy by stretching or pushing molecules, or changes conditions (e.g. pH) around them.
  • Enzymes work by lowering the activation energy level allowing reactions to take place at lower temperatures.

  • Only a small region of the enzyme is functional, known as the active site
  • The substrate fits into the active site to form an enzyme-substrate complex
  • The tertiary structure of the protein dictates the shape of the active site and therefore the action of the enzyme
  • Each enzyme is therefore specific to one substrate
  • Two models for how they function…

  • For enzymes to work, they must:
    • Come into physical contact with the substrate
    • Have an active site which fits the substrate

  • Two events most frequently measured to assess activity:
    • Formation of the product of the reaction
    • The disappearance of the substrate

  • In both cases, increasing concentration results in a linear increase in the rate of reaction
  • Rate of reaction plateaus when:
    • The enzymes present are working at a maximum rate so increasing substrate concentration has no effect
    • There is not enough substrate so increasing number of enzymes has no effect HOWEVER substrate is very rarely limiting
  • Each enzyme has an optimum temperature
  • A rise in temperature increase kinetic energy of the molecule
    • This results in greater collisions, the rate of reaction increases
  • High temperatures can cause hydrogen and other bonds to break
    • This alters the shape of the active site and prevents the substrate fitting within the active site
    • The enzyme becomes denatured

  • Each enzyme has its optimum pH (i.e. number of H+ ions in the medium around it)
  • Altering pH can:
    • Change the charge of amino acids that make up active site
    • Break ionic or hydrogen bonds of the tertiary structure
  • Significant changes in pH can result in the enzyme becoming denatured

Key pads ready

Objectives

  • The properties of enzymes relating to their tertiary structure.
  • Description and explanation of the effects of competitive and non-competitive inhibitors
  • They are substrates that directly or indirectly interfere with the function of the active site.
  • Competitive inhibitors – which bind the to active site of the enzyme
  • Non-competitive inhibitors – Which bind to the enzyme, not the active site.
  • Have similar shape than the substrate, allowing them to occupy the active site
  • Compete with the substrate for the available active site
  • Concentration of the inhibitor determines the effect it has on the enzyme activity
  • Not permanently bind to the active site
  • E.g. medicines

1

2

Non-competitive

Inhibitor

Revise

Rate of reaction

Substrate concentration

  • Attach themselves to the enzyme at a site which is not the active site
  • Alters the shape of the enzymes active site in a way that substrates can no longer occupy it
  • E.g. poisons

Station 1: Competitive & Non competitive inhibitors animations

Watch the two animations below then complete the card sorts

Rate of reaction

Substrate concentration

Enzymes - Google Slides