B4

  • General
    • Definition: protein that functions as a biological catalyst
    • Made in all living cells
    • Can be used over and over again
      • Not used up during reaction
      • Only little is needed to speed up reaction
  • Enzyme action
    • Function:
      • Enzyme can join two molecules -> forms complicated substance
      • 2 glucose molecules -> maltose (larger molecule)
      • Enzyme + substrate need complementary shapes
      • Other substrate molecules don’t work
      • 2 molecules can join without enzyme, but takes very long
      • Enzyme brings molecules close together -> reaction is fast
      • Catalase (enzyme found in most cells) can break down 40,000 hydrogen peroxide molecules a second
      • Can join molecules -> create long chains
        • Hundreds of glucose molecules joined together -> long starch molecules used in cytoplasm
      • Glucose molecules built into cellulose molecules -> added to cell wall
      • Protein molecules built up by enzymes -> joined 10s – 100s amino acid molecules -> added to cell membrane, cytoplasm or nucleus or act as enzymes
    • Enzymes & temperature
      • Most chemical reactions: temperature increases -> increase in rate
      • Enzymes stop working at 50 degrees celcius (shape on enzyme changes: denature)
        • Reason a lot of organisms die under long heat exposure
      • Test for enzymes:
        • Heat substance to boiling point
        • Still carries out reaction after this -> not enzyme
      • Rise of 10 degrees celcius -> doubles rate of enzyme-controlled reactions in cells (up to 37 degrees celcius)
      • Reason:
        • Enzyme & substrate always move
        • Reaction occurs when they touch
        • Warmer temperatures -> more kinetic energy -> more movement -> more collisions
        • Over optmal temperature: begin to deform (denature)
        • Not all enzyems are affected right away
        • Reactions don’t suddenly stop
        • Gradual process when temperature > 37 degrees celcius
      • Once enzyme denatures -> can’t work anymore (permanent)
        • Egg white (protein albumin
          • Before it’s cooked: liquid, transparent + colorless
          • Can’t go back
    • Enzymes & pH
      • Acid & alkaline conditions -> change chemical properties of protein (enzyme)
      • Enzymes work best at specific pH
        • Protein-digesting enzyme in stomach works best pH 2
          • Amylase enzyme in saliva would not survive
        • Enzyme in cells work best pH 7
        • Duodenum: slightly alkaline
        • Pancreating lipase: pH 8
      • Optimum pH & temperature: when enzyme works best
      • pH affects activity of enzymes, but usually reversible
        • Enzyme inactivated by low pH will resume normal activity at optimum pH
      • Extreme pH denatures some enzymes -> irreversible
      • Denatured -> shapes don’t fit together