Chapter 3 and 4: Biological molecules and enzymes

• Carbohydrates: Organic molecules made of carbon, hydrogen and oxygen
• Simple sugars:

  • Basic unit of carbohydrate
  • C6H12O6
  • Glucose: found in plants and animals
  • Fructose: common in plants, rare in animals
• Double sugars:

  • formed when 2 single sugars are joined together
  • Maltose: formed with 2 glucose molecules, can be broken down by maltase
  • Sucrose: formed with 1 glucose and 1 fructose joined together
• Reducing sugars:

  • Glucose, fructose, maltose and lactose
  • Can be tested for using Benedict's solution
• Benedict's test:

  1. Mix equal amount of food samples and Benedict's solution in a test tube
  2. Place test tube in boiling water bath for 2-3 mins

  Results:

  • Solution remains blue: No reducing sugars present
  • Solution turns from blue to green: Traces of reducing sugars present
  • Solution turns from blue to yellow/orange: Moderate amount of reducing sugars present
  • Solution turns from blue to red: Large amounts of reducing sugars present
• Complex carbohydrate: contains many molecules of single sugars joined together

  Examples: Starch, glycogen and cellulose
• Starch:

  • storage form of carbohydrates in plants that can be broken down to glucose to provide energy for cell activity
  • found in storage organs of plants; potato tubers and tapioca
• Cellulose:

  • protects plants from bursting or damage
  • cannot be digested by our intestines, serving as dietary fibre that helps to prevent constipation
  • found in cell walls of plant cells
• Glycogen:

  • storage form of carbohydrates in mammals and could be digested into glucose to provide energy for cell activities
  • stored in liver and muscles of mammals
• Stores of glucose (Glycogen and starch):

  • Are insoluble in water thus would not affecting the water potential of cells
  • Are large molecules that cannot diffuse through the cell membrane thus they would not be lost from cell
  • Are easily broken down into glucose when needed
  • Have compact shape, making them more space efficient than individual glucose molecules
• Breakdown of starch:

  • Amylase breaks down starch into maltose
  • Maltase then breaks down maltose into glucose
• Functions of carbohydrates:

  • Respiration to provide energy for cell activities
  • To form supporting structures (cellulose)
  • Formation of nucleic acid (DNA)
  • Synthesize lubricants (mucus) and nectar
• Fats:

  • organic molecules made of carbon, hydrogen and oxygen but it does not have as much oxygen in proportion to hydrogen as compared to carbohydrates
  • Shaped as one long oval (glycerol) with 3 wiggly lines attached (fatty acids)
• Fats can be broken down by lipase into glycerol and 3 fatty acids molecules
• Functions of fats:

  • Energy source and storage
  • Insulation
  • Solvent for fat soluble vitamins
  • Essential part of cell membrane
  • Way to reduce water loss through sweat
• Ethanol emulsion test for fats:

  For liquid samples:

  1. Add equal volumes of water and ethanol to sample
  2. Shake the mixture and observe

  For solid samples:

  1. Crush solid sample using pestle and mortar
  2. Add 2ml of ethanol to test tube and shake
  3. Pour off top layer of ethanol into test tube of water and shake

  Results: Fat is present when there is white emulsion
• Proteins:

  • Organic molecules made of carbon, hydrogen, oxygen and nitrogen. Sulfur may also be present
  • Built up from amino acids
• Amino acids:

  • Made of amino group (-NH2), acidic group (-COOH) and a side chain (R)
  • Can be joined to form polypeptide
  • Polypeptide can also join and fold to form protein molecule with 3 dimensional shape
• Functions of protein:

  • Synthesis of new cytoplasm for growth and repair
  • Synthesis of enzymes, hormones and antibodies
• Test for protein (biuret test):

  1. Add in equal volumes of sample and dilute sodium hydroxide into test tube
  2. Add in a few drops of copper (II) sulfate solution into the test tube
  3. Shake well

  Observation:

  • Solution turned blue: protein is absent
  • Solution turned violet: protein is present
• Starch test:

  1. Add a few drops of iodine to sample

  Observation:

  • Iodine remains brown: starch absent
  • Iodine turns blue black: starch present
• Enzymes:

  • Biological catalysts that speed up rate of reaction and remains chemically unchanged at the end of reactions
  • Lowers activation energy needed to start a chemical reaction
  • Can build up complex substance (building up of proteins using enzymes in cytoplasm) or break down complex substances (Digestive enzymes)
• Types of enzymes:

  • Carbohydrases: digests carbohydrates
  • Proteases: digests proteins
  • Lipases: digests lipids (fats)
• Lock and key hypothesis:

  • Enzymes has a specific 3 dimensional shape with a depression know as its active site
  • The substance of which an enzyme acts on is called the substrate
  • Substrates only bind to enzymes when the have a 3 dimensional shape complimentary to the enzyme's active site, forming an enzyme-substrate complex
  • Substrate fits into enzyme like how a key fits into a lock
• Characteristics of enzymes:

  • Enzymes speed up chemical reactions
  • Enzymes are specific in action
  • Enzymes are required in minute amount and remain unchanged at the end of reactions
  • Enzymes are affected by temperature and pH
• 0-10 degrees: enzymes are less active at low temperatures as it lacks kinetic energy, thus causing there to be less collision of enzymes and substrate

  10-30 degrees: As temperature increase, rate of enzyme reaction increase

  Optimum temperature: At optimum temperature, enzyme is most active

  40-60 degrees: Increasing the temperature above optimum temperature causes rapid decrease in rate of enzyme reaction

  >60 degrees: Enzymes are denatured

  
• Denaturation: change in 3 dimensional structure of enzyme due to heat or chemicals such as acids and alkalis