TOPIC 1

• Magnification


  The number of times bigger an image appears compared to the size of the specimen
• Resolution


  The smallest distance between two objects that can be distinguished
• Enzymes

  Biological catalysts that increase the rate of a chemical reaction without being permanently altered themselves
• Active site

  The region of an enzyme to which a substrate molecule binds and the reaction takes place
• Enzyme specificity

  Only substrates with a specific, complementary shape can fit into an enzyme's active site
• Lock and key model

  1. Substrate collides with the active site of an enzyme

  2. Substrate binds, enzyme-substrate complex forms

  3. Substrate converted to products

  4. Products released from the active site which is now free to bind to another substrate
• Factors affecting rate of enzyme-controlled reaction

  • Temperature
  • pH
  • Substrate concentration

  
• As temperature increases

  Molecules have more kinetic energy, movement increases, probability of successful collision increases, more enzyme-substrate complexes form, rate of reaction increases
• As temperature increases above optimum

  Increased vibrations break bonds in enzyme's structure, active site changes shape, enzyme is denatured, no more enzyme-substrate complexes can form, rate of reaction decreases
• As pH shifts from optimum

  Bonds in enzyme's structure are altered, active site changes shape, enzyme is denatured, rate of reaction decreases
• As substrate concentration increases


  Number of substrate molecules in the same volume increases, probability of successful collision increases, more enzyme-substrate complexes form, rate of reaction increases, once all active sites become full, rate plateaus

  
• Rate of enzyme-controlled reaction


  1000 divided by time in units s-1
• what needs to happen to Large organic molecules

  Need to be broken down into smaller, simpler molecules in the body as they are too big to be absorbed across the gut wall
• Breakdown of large molecules in plants

  • Starch is broken down by enzymes into simpler sugars which are respired to release energy
• Monomers of carbohydrates

  Simple sugars
• Enzymes that catalyse breakdown of carbohydrates

  Carbohydrases
• Enzyme that catalyses breakdown of starch

  Amylase
• Monomers of proteins

  Amino acids
• Enzymes that catalyse breakdown of proteins


  Proteases
• Function of lipases

  Enzymes which catalyse the breakdown of lipids into fatty acids and glycerol
• Reason for synthesising small molecules into larger organic molecules in the body

  Large molecules are used for storage (e.g. glycogen) or are used to build structures (e.g. organelles)
• Method to measure energy content of food

  Calorimetry - a method of measuring the heat transfer during a chemical reaction
• Procedure to measure energy in food sample

  1. Add a set volume of water to a boiling tube, record initial temperature

  2. Record the mass of a small sample of food (e.g. bean)

  3. Stick the sample onto a mounted needle

  4. Using a bunsen burner light the food sample

  5. Hold the sample under the boiling tube until it burns up

  6. Record the maximum temperature reached by the water

  7. Record the final mass of the food sample
• how can the amount of energy in a food sample be caculated

  4.2 x change in mass of food x change in temperature of water
• how can total magnification be calculated from lens powers 


  eyepiece lens x objective lens
• how do you calculate magnification 


  image size divided by real size
• how else can energy be calculated 


  energy in food divided by mass of food burnt
• why are enzymes needed in the human


  they speed up the rate of chemical reactions