exam questions

• Describe how the primary structure of leptin enables it to be soluble in water (3) 

  -       Primary structure determines the folding of the polypeptide (tertiary structure) 

  -       Forming a globular protein 

  -       Hydrophobic R groups located in the centre of the protein and hydrophilic on the outside

  -       So, water forms hydrogen bonds with the hydrophilic groups 
•  Explain why these two types of mutation have different effects on protein structure (4) 

  -       Deletion of a base effect all codons in the DNA, so codons mostly code for a different amino acid so changes amino acid sequence of the polypeptide chain 

  -       Also, may change the position of the start and stop codon

  -       Changing one base(substitution) may have no affect due to degenerate nature of the genetic code 

  -       The new codon may code for the same amino acid causing no change in primary structure.
• Explain the importance of the primary structure for the functioning of this enzyme (3) 

  -       Primary structure determines interaction between amino acids and R groups

  -       Primary structure determines folding of polypeptide chain/tertiary structure

  -       Folding affects the shape of the active site of the enzyme 

  -       Active site shape must be complementary to the shape of the substrate.
• Explain why enzymes which are incorrectly folded cannot carry out their function (3)

  -       if the protein is not folded correctly, the tertiary structure would be different 

  -       therefore, the active site of the enzyme would not bind to the substrate

  -       therefore, it would not be able to catalyse the reaction
• describe how tertiary structure of myosin is related to its function (3) 

  -       top folded into specific shape with a globular head 

  -       that can bind to actin 

  -       myosin has a site that can bind with ATP

  -       body of myosin straight to form a bundle with other myosin molecules
• compare and contrast the molecular structures of globular and fibrous proteins (4) 

  -       both have polypeptide chains made from amino acids

  -       both contain bonds such as hydrogen or ionic which hold molecule into 3D shape

  -       globular proteins have hydrophilic groups on outside whereas fibrous proteins have hydrophobic groups on outside (means globular are soluble-hydrogen bonds with water molecules) 

  -       globular have tertiary or quaternary structure whereas fibrous have little or none 

  -       globular are folded into compact shapes whereas fibrous have long chains.
• Explain how a change of one amino acid could lead to a change in structure and properties of haemoglobin protein (4) 

  -       different sequence of amino acids 

  -       a diff amino acid will have a diff R group 

  -       therefore, its tertiary structure will change

  -       due to a change in hydrogen or ionic bonds which hold the molecule together 

  -       thus, haemoglobin may not bond to oxygen
• Compare and contrast the chemical bonds found at secondary and tertiary structure (2)

  -       Peptide and hydrogen bonds can be found at secondary and tertiary 

  -       Tertiary structure of a protein can be formed by disulphide/ionic bonds and hydrophobic interactions- not found at secondary level
• Explain why the reaction rate of amylase decreased after 40 degrees (2)

  -       Enzyme had denatured and active site no longer complementary to the substrate 

  -       Breaking of bonds in high heat causes change in folding/tertiary structure