Biological molecules

• Nutrients are needed to provide energy, to supply materials for creation of protoplasm and to keep us healthy
• There are three main types of nutrients, Carbohydrates, Fats and Proteins
• Carbohydrates are made up of carbon, hydrogen and oxygen.

  A) C

  B) H

  C) O

  
• The ratio of hydrogen atoms to oxygen atoms is 2:1
• There are three sub-categories of carbohydrates, Monosaccharides or single sugars, Disaccharides or double sugars and Polysaccharides or complex carbohydrates
• Types of Monosaccharides

  1. Glucose
  2. Fructose
  3. Galactose
• Types of Disaccharides

  1. Maltose
  2. Sucrose (Not a reducing sugar)
  3. Lactose
• Types of Polysaccharides

  1. Starch
  2. Glycogen
  3. Cellulose
• All Monosaccharides and Disaccharides are reducing sugars
• Disaccharides are formed by a condensation reaction when two simple molecules join together to form a larger molecule with the removal of one molecule of water.

  
• Disaccharides can be split back into smaller molecules by Hydrolysis. The Large molecule is broken down into smaller molecules by the use of a water molecule and a respective enzyme.

  
• To test for reducing sugars,

  1. Add 2cm^3 of Benedicts Solution t o2cm^3 of a food sample
  2. Shake the mixture
  3. Heat the contents in a boiling water bath for 3 minutes

  Positive result

  1. Small amount of reducing sugar - green precipitate
  2. Good amount of reducing sugar - yellow precipitate
  3. High amount of reducing sugar - Brick-red precipitate
• Types of complex carbohydrates

  Glycogen

  1. Is a form of carbohydrate storage in mammals
  2. Digested to form glucose

  
• Types of complex carbohydrates

  Cellulose

  1. Cellulose cell wall protects plant cells
  2. Serves as dietary fibre to prevent constipation

  
• Types of complex carbohydrates

  Starch

  1. Form of storage of carbohydrates in plants
  2. Found in storage organs in plants

  
• Hydrolysis of starch

  Starch breaks down into maltose via amylase, Maltose breaks down into glucose via maltase
• Functions of carbohydrates

  • To provide energy for cell activities
  • To form supporting structures
  • For conversion into other organic compounds
  • To form nucleic acids
  • To synthesise lubricants
  • To synthesise nectar in flowers
• Fats are made up of Carbon, Hydrogen and Oxygen. Fats contain less oxygen than hydrogen and the proportions are not fixed.
• Fat molecules are made of glycerol and three fatty acid chains.

  A) Glycerol

  B) Fatty acid

  C) Fatty acid

  D) Fatty acid

  
• Hydrolysis of Fats

  Fats can be broken down by 3 water molecules into glycerol and fatty acids

  A) Fat

  B) Water

  C) 3H2O

  D) Glycerol

  E) Fatty acid

  
• To test for fats,

  1. 2cm^3 ethanol to 2cm^3 food sample in tube
  2. Shake contents
  3. Decant 3cm^3 of water in the mixture and shake

  Postive Test

  • If fats are present a white cloudy emulsion is formed
• Functions of fats

  • Energy storage
  • Insulation material
  • Solvent for fat soluble vitamins and hormones
  • Form main part of cell membrane
  • Reduces water loss from skin surface
• Proteins are amino acids which are made of

  • An amino group
  • An acid group
  • A side chain

  
• Amino acids are the building blocks of Proteins.

  Peptide bonds link Amino acids to form polypeptide

  2 or more polypeptide chains fold to form a 3-D molecule called protein
• To test for proteins

  1. 2cm^3 sodium hydroxide solution to 2cm^3 of food sample in tube
  2. Shake mixture
  3. Drop 1% copper(II) sulfate solution and shake after every drop

  Positive test

  • If protein is present, A purple or violet solution is formed
• Proteins are organic compounds made of Carbon, Hydrogen, Oxygen and Nitrogen
• Functions of proteins

  • Synthesis of new protoplasm for growth and repair of worn out cells
  • Synthesis of enzymes and hormones
  • Synthesis of antibodies