Unit 2 Section 1.2 Proteins

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  • Proteins
    • what are proteins made from?
      • proteins are polymers. these are large complex molecules composed of long chains of monomers
        • the monomer of proteins are amino acids.
          • a dipeptide is formed when more than two amino acids join together
            • a polypeptide is formed when more than two amino acids join together.
              • proteins are made up of one or more polypeptides
    • Amino acid structure
      • all amino acids have the same general structure
        • a carboxyl group (-COOH) and an amino group (-NH2) attached to a carbon atom. the difference between different amino acids is the variable group they contain
    • Polypeptide Formation
      • amino acids are linked together by condensation reactions to form dipeptide and polypeptides. a molecule of water is released during the reaction
      • the bonds formed between amino acids are called peptide bonds. a peptide bond forms between the amino group of one amino acid and the carboxyl group of another amino acid
      • the reverse reaction adds a molecule of water to break the peptide bond - this is called a hydrolysis reacion
    • Protein Structure
      • proteins are big, complicated molecules
      • they're much easier to explain if you describe their structure in four 'levels'. these levels are a proteins primary secondary and tertiary and quaternary structures.
        • the four structural levels of a protein are held together by different kinds of bonds
        • Primary Structure
          • this is the sequence of amino acids in the polypeptide chain.
            • it is held together by the peptide bonds between amino acids
        • Secondary structure
          • the polypeptide chain doesnt remain flat and straight
            • Hyrogen bonds form between the -NH and -CO groups  of amino acids in the chain
              • this makes it automatically curl into a alpha helix or fold into a beta pleated sheet
        • Tertiary Structure
          • the coiled or folded chain of amino acids is often coiled and folded further.
            • more bonds form between different parts of the polypeptide chain such as
              • Ionic Interactions, Disulfide bridges, Hydrophobic and hydrophilic interactions and hydrogen bonds
        • Quaternary structure
    • Functions of Proteins
      • a proteins shape relates to its function
        • Fibrous Proteins
          • are tough and rope - shaped. they tend to be found in connective tisssue eg tendons
        • Globular proteins
          • are round and compact. they're soluble, so they're easily transported in fluids
  • some proteins are made of two or more polypeptide chains held together by bonds
    • the quaternary structure is the way these poly peptide chains are assembled together
      • it tends to be determined by the tertiary structure of the individual polypeptide chains
        • because of this, it can be influenced by all the bonds mentioned above
    • Quaternary structure


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