3.1 Biological Molecules

• The key molecules that are required to build structures that enable organisms to function are:

  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
  • Water
• Monomers are the smaller units from which larger molecules are made
• Polymers are molecules made from a large number of monomers joined together in a chain
• Each carbon atom can form four covalent bonds. This makes the compounds very stable
• Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur
• Carbon atoms can bond to form straight chains, branched chains or rings
• Carbon compounds can form small single subunits (monomers) that bond with many repeating subunits to form large molecules (polymers) by a process called polymerisation
• Macromolecules are very large molecules that contain 1000 or more atoms therefore having a high molecular mass
• The three types of carbohydrates are monosaccharides, disaccharides and polysaccharides
• Condensation reactions are also known as dehydration synthesis
• A condensation reaction occurs when monomers combine together by covalent bonds to form polymers (polymerisation) or macromolecules (lipids) and water is removed
• Hydrolysis means breaking with water
• In the hydrolysis of polymers, covalent bonds are broken when water is added
• Hydrolysis of lipids produces fatty acids and monoglycerides
• The monomer of carbohydrates is a monosaccharide
• The polymer of carbohydrates is a polysaccharide
• The monomer of a protein is an amino acid
• The polymer of a protein is a polypeptide
• The monomer of a nucleic acid is a nucleotide
• The polymer of a nucleic acid is a polynucleotide
• The general formula for a carbohydrate is Cx(H2O)y
• Functions of carbohydrates in living organisms:

  • Energy supply for cells - This is the main role of carbohydrates. 
  • Energy storage - Sugars can be stored as complex carbohydrates (e.g. starch or glycogen). 
  • Structural components Cellulose and chitin are used in cell walls. 
  • Cellular recognition - Glycoproteins help cells identify each other and communicate. 
  • Building blocks for biological molecules - Deoxyribose and ribose can be used to make nucleic acids.
• The main function of a monosaccharide is to be an energy source
• The main function of a disaccharide is to be a form of transport
• The main function of a polysaccharide is to be a storage form
• Monosaccharides are soluble, sweet-tasting and are found in many foods such as fruits, vegetables, and grains.
• Monosaccharides have the general formula (CH2O)n where 'n' can be any number from 3 to 7
• Pentose sugars have 5 carbon atoms. These include ribose and deoxyribose sugars
• Hexose sugars have 6 carbon atoms. These include glucose, fructose, and galactose
• There are two isomers of glucose:

  A) alpha-glucose

  B) beta-glucose

  
• Features of glucose which help it to function as an energy source:

  • Soluble
  • Bonds store a lot of energy
• The hydroxyl groups of glucose can form hydrogen bonds with water, so it can be transported around organisms
• Disaccharides are formed when two monosaccharides join together
• Maltose is made up of:

  A) Glucose

  B) Glucose

  
• Sucrose is made up of:

  A) Glucose

  B) Fructose

  
• Lactose is made up of:

  A) Glucose

  B) Galactose

  
• Disaccharides are created via condensation reactions
• Disaccharides are broken down via hydrolysis reactions
• When two monosaccharides join, the hydroxyl group on carbon 1 of one monosaccharide reacts with the hydroxyl group on carbon 4 of another monosaccharide.

  A 1-4 glycosidic bond is formed and a water molecule is released.

  
• When a water molecule is added to a disaccharide, the glycosidic bond is broken to release the 2 monosaccharides.