Biological molecules

• How are most of molecules in living organisms categorised?

  • Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids
  • These all contain carbon and so are described as organic molecules

  
• Carbohydrates


  Molecules containing carbon, hydrogen and oxygen
• Monosaccharide


  A simple sugar e.g. glucose (C6H12O6) or fructose
• Glucose molecules contain lots of energy which can be released in respiration by breaking the bonds between the carbon atoms
• Disaccharide


  Made when two monosaccharides join together
• Disaccharides


  • Maltose (two glucose molecules)
  • Sucrose (one glucose and one fructose molecule)
• Polysaccharide


  Formed when lots of monosaccharides join together
• Polysaccharides


  • Starch
  • Glycogen
  • Cellulose
• Polysaccharides are insoluble and therefore useful as storage molecules
• Fats in molecules:

  • Most fats (lipids) in the body are made up of triglycerides
  • Their basic unit is one glycerol molecule chemically bonded to three fatty acid chains
  • The fatty acids vary in size and structure
  • Lipids are divided into fats (solids at room temperature) and oils(liquids at room temperature)

  
• Proteins in molecules:

  • Proteins are formed from long chains of amino acids
  • There are 20 different amino acids
  • When amino acids are joined together a protein is formed
  • Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins
  • Examples of proteins include enzymes, haemoglobin, ligaments and keratin

  
• What is the shape of protein?

  • Different proteins have different amino acid sequences resulting in them being different shapes
  • Even a small difference in the amino acid sequence will result in a completely different protein being formed
  • The different sequences of amino acids cause the polypeptide chains to fold in different ways and this gives rise to the different shapes of proteins
  • In this way, every protein has a unique 3-D shape that enables it to carry out its function
  • The shape of a protein determines its function
• How does proteins shape help its function?

  • Enzymes have a specifically shaped active site - this is where a specific substrate molecule fits in order for a reaction to take place
  • If the shape of the active site does not match the shape of the molecule that fits into it, the reaction will not take place
  • Antibodies are proteins produced by certain types of white blood cells that attach to antigens on the surface of pathogens
  • The shape of the antibody must match the shape of the antigenso that it can attach to it and signal it for destruction

  
• How do you test for glucose?

  • Add Benedict's solution to the sample solution in a test tube
  • Heat in a boiling water bath for 5 minutes
  • Take the test tube out of the water bath and observe the colour
  • A positive test will show a colour change from blue to orange / brick red

  
• How do you test for starch?

  • We can use iodine to test for the presence or absence of starch in a food sample
  • Add drops of iodine solution to the food sample
  • A positive test will show a colour change from orange-brown to blue-black

  
• How to test for protein?

  • Add drops of Biuret solution to the food sample
  • A positive test will show a colour change from blue to violet / purple

  
• How to test for lipids?

  • Mix the food sample with 4cm3 of ethanol and shake
  • Allow time for the sample to dissolve in the ethanol
  • Strain the ethanol solution into another test tube
  • Add the ethanol solution to an equal volume of cold distilled water (4cm3)
  • A positive test will show a cloudy emulsion forming

  
• Food Tests Results Table

  Here..

  
• What are the hazards in the food tests?

  • Whilst carrying out this practical you should try to identify the main hazards and be thinking of ways to reduce harm
  • Biuret solution contains copper (II) sulfate which is dangerous particularly if it gets in the eyes, so always wear goggles
  • Iodine is also an irritant to the eyes
  • Sodium hydroxide in biuret solution is corrosive, if any chemicals get onto your skin wash your hands immediately
  • Ethanol is highly flammable; keep it away from any Bunsen burner
  • The Bunsen burner itself is a hazard due to the open flame
• CORMS evaluation


  • C - We are changing the type of food in the sample
  • O - This is not relevant to this investigation as we aren't using an organism
  • R - We will repeat the investigation several times for each food sample to ensure a reliable result
  • M1 - The presence of the specific biological molecule in each food type by noting the colour change
  • M2 - ....after testing with each specific testing agent
  • S - We will control the volume of each testing agent used, the quantity of the food sample, the concentration of the testing agents, the temperature of the water bath for the Benedicts test. There may be other examples that you can think of
• What are enzymes?

  • Enzymes are proteins that act as biological catalysts to speed upthe rate of a chemical reaction without being changed or used up in the reaction
  • They are biological because they are made in living cells
  • Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life
  • For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours
  • Often the products of one reaction are the reactants for another (and so on)
• Enzymes

  • Specific to one particular substrate(s)
  • Active site of the enzyme is a complementary shape to the substrate
• Enzyme-substrate complex formation

  1. Enzyme and substrate randomly move about in solution

  2. Enzyme and complementary substrate randomly collide

  3. Enzyme-substrate complex forms

  4. Reaction occurs

  5. Product(s) form from substrate(s)

  6. Product(s) released from active site

  7. Enzyme unchanged and will catalyse further reactions
• After the reaction has occurred, the products leave the enzyme's active site as they no longer fit it and it is free to take up another substrate
• How do enzymes work?

  Here..

  
• Enzymes

  Proteins with a specific shape, determined by the amino acids that make the enzyme and held in place by bonds
• Enzyme shape


  • Specific shape is extremely important around the active site as it ensures the substrate will fit into the active site and enable the reaction to proceed
• Optimum temperature


  Temperature at which enzymes work fastest
• In the human body, the optimum temperature for enzymes is 37⁰C
• Denaturation


  Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape
• What happens when the enzymes denature?

  • Substrates cannot fit into denatured enzymes as the shape of their active site has been lost
  • Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop
• What does increasing temperature mean for enzymes?

  • Increasing the temperature towards the optimum increases the activity of enzymes as the more kinetic energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
• What happens to enzymes at lower temperatures?

  • This means that low temperatures do not denature enzymes, they just make them work more slowly due to a lack of kinetic energy
• Graph showing the effect of temperature on the rate of enzyme activity


  Here..

  
• Apparatus in practical to test how temperature tests the rate of enzymes

  • Spotting tile
  • Measuring cylinder
  • Test tube
  • Syringe
  • Pipette
  • Stopwatch
  • Water
  • Thermometer
  • Water bath
  • Iodine
  • Starch solution
  • Amylase solution
• Method for Practical: Investigating Temperature & Enzyme Activity

  1. Add 5cm3 starch solution to a test tube

  2. Heat to a set temperature using beaker of water with a Bunsen burner

  3. Add a drop of Iodine to each of the wells of a spotting tile

  4. Use a syringe to add 2cm3 amylase to the starch solution and mix well

  5. Every minute, transfer a droplet of solution to a new well of iodine solution (which should turn blue-black)

  6. Repeat this transfer process until the iodine solution stops turning blue-black (this means the amylase has broken down all the starch)

  7. Record the time taken for the reaction to be completed

  8. Repeat the investigation for a range of temperatures (from 20°C to 60°C)
• Amylase


  An enzyme which breaks down starch
• Reaction rate


  The quicker the reaction is completed, the faster the enzyme is working
• Investigation findings

  1. At optimum temperature, iodine stopped turning blue-black fastest

  2. At colder temperatures, iodine took longer to stop turning blue-black

  3. At hotter temperatures, iodine turned blue-black throughout
• Optimum temperature


  The enzyme is working at its fastest rate and has digested all the starch