Proteins

• Sulfur atoms are required for synthesis of proteins.
• What takes place to form the bond between valine and alanine?

  Condensation reaction which forms a peptide bond.
• What are conjugated proteins?

  • Proteins with a non-protein group attached
  • contain a prosthetic group
  • commonly globular
  • Attached by covalent bonds and hydrogen bonds
• Some globular proteins are conjugated proteins
• Haemoglobin is a conjugated protein, contains the prosthetic group of haem.
• . * Describe how the structure of llama haemoglobin is likely to be different from that of camel haemoglobin with reference to the four levels of protein structure.

  • difference in primary structure
  • one amino acid is changed
  • amino acid could cause change to secondary structure
• collagen is a fibrous protein. State three properties of fibrous proteins that are different to globular proteins.

  • strong
  • insoluble
  • unreactive
• Globular proteins are compact, spherical and soluble in water.
• When do globular proteins form a spherical shape? and why?

  When folding into tertiary structure.

  Their non-polar hydrophobic R groups are orientated towards the centre of the protein away from aqueous surroundings.
• How many polypeptide chains are in haemoglobin's quarternary structure?

  four
• What are the four globin subunits held together by?

  disulphide bonds
• Why is the arrangement of the R group important?

  Important to the functioning. If changes occur to sequence of amino acids it can result in properties of haemoglobin changing.
• What are fibrous proteins?

  long strands of polypeptide chains with cross-linkages due to hydrogen bonds.
• Fibrous proteins have little or no tertiary structure.
• • Fibrous proteins have a limited number of amino acids with the sequence usually being highly repetitive
• What are some examples of fibrous proteins?

  Keratin

  Elastin

  Collagen
• Fibrous proteins are generally insoluble in water
• • Collagen is the most common structural protein found in vertebrates
• • Collagen is formed from three polypeptide chains closely held together by hydrogen bonds to form a triple helix (known as tropocollagen)
• • In the primary structure of collagen almost every third amino acid is glycine
  • This is the smallest amino acid with a R group that contains a single hydrogen atom
  • Glycine tends to be found on the inside of the polypeptide chains allowing the three chains to be arranged closely together forming a tight triple helix structure
• • Covalent bonds also form cross-links between R groups of amino acids in interacting triple helices when they are arranged parallel to each other. The cross-links hold the collagen molecules together to form fibrils
• • The collagen molecules are positioned in the fibrils so that there are staggered ends (this gives the striated effect seen in electron micrographs)
  • When many fibrils are arranged together they form collagen fibres
  • Collagen fibres are positioned so that they are lined up with the forces they are withstanding