• There is a massive variety of life within and between organisms however the biochemical basis of life is similar for all living things
• 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
• 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
  • They contain 1000 or more atoms and so have a?high molecular mass
  • Polymers can be macromolecules, however,?not?all?macromolecules are polymers as the subunits of polymers have to be the?same?repeating units

   

Covalent bonding

• A?covalent bond?is the sharing of two or more electrons between two atoms
  • The electrons can be shared equally forming a?nonpolar?covalent bond or unequally (where an atom can be more?electronegative?δ-) to form a?polar?covalent bond

   

• Generally, each atom will form a certain number of covalent bonds due to the number of free electrons in the outer orbital e.g. H = 1 bond, C = 4 bonds
• Covalent bonds are very stable as high energies are required to break the bonds
• Multiple pairs of electrons can be shared forming?double?bonds (e.g. unsaturated fats C=C) or?triple?bonds

Different types of covalent bonds

• When two monomers are close enough that their outer orbitals overlap this results in their?electrons being shared?and a covalent bond forming. If more monomers are added then?polymerisation?occurs (and / or a macromolecule forms)

Condensation

• Also known as dehydration synthesis (‘to put together while losing water’)
• A?condensation reaction?occurs when?monomers?combine together by?covalent bonds?to form?polymers?(polymerisation) or macromolecules (lipids) and?water?is?removed

Written and symbolic illustrations of the removal of water to form a covalent bond between two or more monomers during a condensation reaction

Hydrolysis

• Hydrolysis means ‘lyse’ (to break) and ‘hydro’ (with water)
• In the hydrolysis of polymers,?covalent bonds?are?broken?when?water?is?added

Written and symbolic illustrations of the addition of water to break down covalent bond/s during a hydrolysis reaction

Covalent Bonds in Organic Molecules Table

• Carbohydrates, lipids, proteins and nucleic acids contain the chemical elements?carbon?(C) and?hydrogen?(H) making them?organic compounds
• Carbon atoms?are key to organic compounds because:
  • Each carbon atom can form?four?covalent bonds?– this makes the compounds very stable (as covalent bonds are so strong they require a large input of energy to break them)
  • Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur
  • Carbon atoms can form?straight chains,?branched?chains?or?rings

   

Carbohydrates

• All carbohydrates contain the chemical elements?C,?H?and?O
• As?H?and?O?atoms are always present in the?ratio?of?2:1?(eg. water H2O, which is where ‘hydrate’ comes from in 'carbohydrate') they can be represented by the formula?Cx?(H2O)y
• The three types of carbohydrates are?monosaccharides,?disaccharides?and?polysaccharides
• Carbohydrates have many different functions:
  • Source of energy?e.g. glucose is used for energy-release during cellular respiration
  • Store of energy?e.g. glycogen is stored in the muscles and liver of animals
  • Structurally important?e.g. cellulose in the cell walls of plants

   

Types of Carbohydrates Table

Lipids

• All lipids?contain the chemical elements?C,?H?and?O
  • However, the proportion of?O?in lipids is?low?compared to carbohydrates

   

• There are many types of lipids, including triglycerides (fats and oils), phospholipids, waxes, and steroids (such as cholesterol)
• Lipids have many different functions:
  • Source of energy?that can be respired (lipids have a high energy yield)
  • Store of energy?e.g. lipids are stored in animals as fats in adipose tissue and in plants as lipid droplets
  • Insulating layer?e.g.?thermal?insulation?under the skin of mammals and?electrical?insulation?around nerve cells
  • An essential component of?biological membranes

   

Proteins

• Like carbohydrates and lipids, all proteins contain the chemical elements?C,?H?and?O
  • However, all proteins also contain?N?(nitrogen) and some proteins contain?S?(sulphur)

   

• Proteins have many different functions:
  • Required for cell?growth, cell?repair?and the replacement of biological materials
  • Structurally important?e.g. in muscles, collagen and elastin in the skin, collagen in bone and keratin in hair
  • Proteins can also act as?carrier molecules?in cell membranes,?antibodies,?enzymes?or?hormones

   

Nucleic Acids

• Like carbohydrates, lipids and proteins, all nucleic acids contain the chemical elements?C,?H?and?O
  • However, all nucleic acids also contain?N?(nitrogen) in their?bases?and?P?(phosphorous) in the form of?phosphate groups

   

• Nucleic acids (DNA and RNA) have?one?function:
  • Carrying the?genetic code?in all living organisms
  • Nucleic acids are essential in the?control?of all cellular?processes?including?protein synthesis

   

The key biological molecules for living organisms