1.4 Proteins

• Amino acid structure

  -4 chemical groups arranged around a central carbon atom

  
• Amino acid

  -20 different amino acids that make proteins

  -R group differs for each amino acid

  -2 bonded amino acids= dipeptide

  -more than 2= polypeptide
• Dipeptide

  Two amino acids bonded together

  
• primary structure


  The specific sequence of amino acids that make up a protein

  
• Secondary structure

  Coiling and pleating of parts of the polypeptide molecule

  Alpha helix and beta pleated sheets

  
• Alpha helix

  -right hand coil

  -as it coils, hydrogen bonds form

  -stabilises the protein

  
• Beta pleated sheets

  -Amino acid chain folds up on itself

  -hydrogen bonds form across sheets

  -stabilises the protein

  
• Tertiary structure


  -overall 3D structure of a protein molecule

  -Held in place by:

  -polar interactions

  -disulphide bonds

  -Ionic interactions

  -covalent bonds

  
• quatenary structure

  more than one polypeptide chain

  
• Polar interactions

  -Hydrophobic R groups cluster to interior of protein molecule

  - forms hydrophobic interactions

  -stabalises protein

  -Hydrophilic R groups on outside of proteins

  - water soluable
• Disulphide bonds/ bridges/ linkages

  -covalent bonds

  -will bond as soon as two R groups with sulphur are close
• Ionic interactions

  -Carboxyl and amino groups form charges in solutions

  -Opposite charges come together
• 3D proteins shapes

  -Fibrous

  -Globular
• Fibrous

  -Structural functions

  -repetitive amino acid sequences

  -usually insoluable
• Globular

  -metabolic functions

  -formed through hydrophobic and hydrophillic interactions

  -water soluable