Proteins

• What are proteins made from?

  the monomers of proteins are amino acids.

  -a dipeptide is formed when 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

  carbon atom with attachments:

  -carboxyl group (-COOH)

  -an amine or amino group (-NH₂)

  -R group (variable side group)

  (all R group except glycine contain carbon which consists of just one hydrogen atom)

  
• Dipeptide and Polypeptide Formation

  -Amino Acids are linked together by condensation reactions to form dipeptides and polypeptides (this releases a molecule of water)
• Dipeptide and Polypeptide Formation

  -Amino acids are linked together by condensation reactions to form dipeptides and polypeptides (a molecule of water is released)

  -The bonds formed between amino acids are called peptide bonds

  
• Protein Primary Structure

  the sequence of amino acids in the polypeptide chain
• Protein Secondary Structure

  -Hydrogen bonds form between the amino acids in the chain which makes it coil into an α-helix or fold into a β-pleated sheet which makes up the secondary structure

  
• Protein Tertiary Structure

  -Coiled or folded chain of amino acid if coiled further

  -More bonds form between the different parts of the polypeptide chain, including hydrogen bonds and ionic bonds (attractions between negative and positive charges on different parts of the molecule)

  -Disulfide bridges also form whenever two molecules of the amino acid cysteine come close together - the sulfur atom in one cysteine bonds to the sulfur atom in the other.

  -For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure

  
• Protein Quaternary Structure

  -The way several different polypeptide chains are assembled together

  -For proteins made from more than one polypeptide chain (e.g. haemoglobin, insulin, collagen) the quaternary structure is the protein's final 3D structure.

  
• Biuret Test for Proteins

  • The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.
  • Then you add some copper (II) sulfate solution.
  • If a protein is present, the solution turns purple
  • If there is no protein the solution will remain blue