Biological Molecules

• Carbohydrates, proteins and fats


  Very important biological molecules
• Carbohydrates


  • Contain carbon, hydrogen and oxygen
  • Sugars like glucose and lactose are 'simple' carbohydrates made of one or two basic sugar units
  • Good sources of energy
  • Glucose is normally used in respiration
  • Lactose is the sugar and energy source in milk
  • Sugars are 'fast-release' energy stores
• Foods rich in sugars


  • Some fizzy drinks
  • Cakes
• Complex carbohydrates


  • Include starch, glycogen and cellulose
  • Made up of many glucose units linked together
  • Starch and glycogen are storage molecules
  • Cellulose provides structural support in plant cell walls
• Starch and glycogen


  • Contain branches and can coil up, making them very compact
• Proteins


  • Long chains of amino acids bonded together
  • Many different arrangements of the 20 different amino acids
• Proteins


  • Can be structural (e.g. in muscle) or functional (e.g. as enzymes or antibodies)
• Sources of protein


  • Lean meat
  • Lentils
  • Fish
• Fats


  • Basic sub-unit is one molecule of glycerol and three fatty acid molecules
  • High in energy, approximately twice as much as carbohydrates or proteins
• Oils


  • Olive oil
  • Rapeseed oil
• Rich sources of fat


  • Sausages
  • Streaky bacon
  • Butter
  • Lard
• Too much fat in the diet can lead to health problems
• Measuring the energy content of food


  1. Burn food

  2. Measure rise in temperature of water

  3. Use equation: energy released in joules (J) = mass of water (g) x rise in temp (°C) x 4.2
• Some energy will be lost to the air, lost to heat the glass, and left in the burned food remains
• Food tests


  Indicators and positive tests for carbohydrates, lipids and proteins
• Food testing methods


  1. Identify the positive result observed

  2. Samples are tested with reagents

  3. Reagents cause a chemical reaction that produces a visible colour change, precipitation or emulsion
• Qualitative test


  Indicates if starch is present or not but no idea of quantity
• Iodine test


  Qualitative test for starch
• Main biological molecules in diet


  • Carbohydrates
  • Lipids (fats)
  • Proteins
• Organic molecules


  Mostly made of carbon (C), also contain oxygen (O), hydrogen (H), nitrogen (N) and sulphur (S)
• Carbohydrates


  • 2 main types: simple sugars and complex carbohydrates
• Simple sugars (monosaccharides)

  Sweet, soluble molecules that dissolve readily in water. Can be made up of one sugar (e.g. glucose, fructose, galactose) or two sugars (disaccharides e.g. maltose, sucrose, lactose)
• Monosaccharides


  Simple sugars that are absorbed into the blood in the small intestine and used for respiration to produce energy
• Disaccharides


  Two monosaccharides joined together. Release energy rapidly but can't be stored easily due to high solubility
• Complex carbohydrates


  • Long chains of monosaccharides. Humans store as glycogen, plants store as starch. Cellulose forms plant cell walls and is indigestible fibre
• Lipids


  Fats and oils made up of fatty acids and glycerol. Provide energy storage, insulation and protection for organs
• Saturated fats


  Have single bonds in fatty acid chains, are solid at room temperature
• Unsaturated fats


  Have double bonds in fatty acid chains, are liquid at room temperature
• Proteins


  • Made up of a chain of amino acids. Order of amino acids determines protein structure and function. Can be structural, functional (enzymes, hormones) or used as energy source
• Proteins are coded by the DNA in cells
• The order of amino acids determines how the protein folds
• Food molecules

  • Carbohydrates
  • Fats
  • Proteins
• Smaller molecules they are made from

  • glucose
  • glycerol
  • fatty acids
  • amino acids
• Main function in the body

  • Respiration to produce energy
  • Energy store
  • Growth and repair
• amino acids

  Smaller units that make up proteins
• peptide

  Smaller chain of amino acids
• protein

  Larger molecule made up of amino acids
• Method

  1. Add 10ml of cold water to a test tube

  2. Secure the test tube in the retort stand

  3. Place the heat proof mat underneath the test tube

  4. Connect the Bunsen burner to a gas tap, ensuring that it is not too close to the test tube

  5. Record the starting temperature of the water

  6. Light the Bunsen burner and turn to the blue flame

  7. Hold the first sample in the flame until it begins to burn

  8. Place it under the test tube of water

  9. If it goes out, relight

  10. When the food has stopped burning, all the energy has been released

  11. Record the final temperature of the water

  12. Calculate the temperature difference

  13. Pour out the water and fill to the line marked

  14. Repeat with an identical food sample and calculate the average temperature change for food sample 1

  15. Repeat the method with each food sample, changing the water before each new attempt
• The energy in the potato crisp is calculated using the formula: Energy/J = mass of water/g x temperature rise/°C x 4.2
• Potato crisps contain carbohydrates