1. Biological molecules: Biochemicals and bonds

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  • Biochemicals & bonds
    • Carbon chains & rings
      • Because carbon atoms have 4 electrons in their outer orbitals, they can gain stability by sharing the 4 electrons with other atoms
        • The sharing of electrons forms a strong bond between the atoms (covalent bond) and the bonded atoms are called a moelcule
      • Carbon is able to make 4 covalent bonds, which can be between other carbon atoms or other elements
      • Carbon can form a vast variety of molecules by bonding with other atoms and by forming chains or rings of carbon atoms with other atoms bonded to the chain
    • Double bonds can occur
      • Carbon can form 2 bonds with another atom, key examples in biology include c=c double bonds in hydrocarbon chains
        • and  c=o double bonds found in many molecules, including organic acids
    • Monomers & polymers
      • Biological molecules are grouped according to their chemical properties
      • The most important groups are the carbohydrates, proteins, nucleic acids and lipids
        • in the first 3 types large molecules are made by bonding together similar smaller molecules
      • The term monomer refers to a single, small molecule, many of which can be joined together to form a polymer
        • Although they are made of smaller molecules bonded together, lipids are not polymers because the smaller molecules are very different from each other
    • Condensation & hydrolysis
      • The chemical reaction that links biological monomers together is called a condensation reaction
        • In making a polymer, the same reaction is repeated many times in order to link many monomers together to form a polymer
          • they also link the different subunits together in lipid molecules
      • In condensation reactions: a water molecule is released, a new covalent bond is formed and a larger molecule is formed by the bonding together of smaller molecules
      • The chemical reaction that splits larger molecules to monomers is called a hydrolysis reaction, this is the reverse of a condensation reaction
        • In all hydrolysis reactions: a water molecules is used, a covalent bond is broken and smaller molecules are formed by the splitting of a larger molecule
    • Hydrogen bonds
      • Polymers can be very large molecules, they often have specific functions that rely on their shape
      • Hydrogen bonds form when a slightly -ve charged part of a molecule comes close to a slightly +ve charged hydrogen atom in the same (or another) molecule
        • This is most easily seen in water
          • Hydrogen  bonds are not strong bonds, they are often described as 'interaction'
            • However, in some polymers many thousands of hydrogen bonds can form and this helps to stabilise the structure of the molecule



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