biological molecules

• why temperature affects enzyme activity?

  • higher temperature = enzymes gain kinetic energy & collide more often, increasing formation of enzyme-substrate complexes & increasing rate of reaction
• How does pH affect enzyme activity?

  • Extreme pH values cause enzymes to denature and no longer fit into the substrate
  • this means reaction can no longer take place
• Why pH affects enzyme activity

  Changing the pH of its surroundings will also change the shape of the active site of an enzyme
• enzymes are biological catalysts that speed up metabolic reactions
• metabolic meaning?

  • chemical reactions/processes in cells
• carbohydrates, lipids and proteins are all large molecules made from smaller basic units
• carbohydrates contain the elements carbon, hydrogen & oxygen
• all sugars taste sweet and are soluble in water
• glucose, fructose & galactose are all simple sugars called monosaccharides
• sucrose is made of glucose & fructose joined together

  • called a disaccharide
• starch & glycogen are polymers of glucose called polysaccharides

  • made from simple sugars
• lipids (fats) contain the elements hydrogen & oxygen
• fats are made up of one molecule of glycerol joined to 3 fatty acids
• proteins are made up of long chains of amino acids
• proteins contain the elements carbon, hydrogen, oxygen & nitrogen
• testing for starch?

  add iodine solution to sample

  • if present = iodine changes from orange to black
• testing for glucose?

  add benedict's solution & place in hot water bath

  • if present = change from blue to orange/red
• testing for protein?

  add biuret reagent

  • if present = change from blue to purple (lilac)
• testing for lipids?

  add ethanol, then add water & mix

  • if present = change from clear to white emulsion
• enzymes work as catalysts produced by living things
• enzymes are biological catalysts for living things
• catalysts are substances that speed up a chemical reaction without being used up or changed
• enzymes are specific

  • each enzyme has an active site which the substrate joins onto
  • the substrate must be complementary to the active site, or it will not fit
• substrate = molecule that changes during a reaction
• the substrate fitting into the active site like a key in a lock is called the lock & key theory
• enzymes speed up one reaction as they are specific to one substrate
• enzymes reduce the need for higher temperatures and speeds up the rate of reaction
• higher temperature means that the enzyme gains kinetic energy & moves around more, colliding & forming enzyme-substrate complexes
• an enzyme works best at optimum temperature
• if temperature becomes too high:

  • bonds holding enzyme together break & active site changes shape
  • the substrate can no longer fit into the active site
  • enzyme is said to be denatured and reaction can no longer take place
• what affects enzyme activity?

  temperature & pH
• if enzymes pH is too high/low:

  • bonds break
  • substrate no longer fits
  • enzyme is denatured
• enzymes have an optimum pH of neutral 7
• enzymes use a lock & key method so they can only bind with a certain substrate, by binding together in the active site