2.1.2o- Globular and Fibrous proteins

Question 1

Explain how a change in the amino acid sequence can result in the formation of a non-functional enzyme. (6)

Answer 1

• the base sequence determines the amino acid sequence.
• a different base sequence therefore codes for a different amino acid sequence. - amino acids interact with each other by H-bonds, ionic bonds, and disulphide bridges.
• when the amino acid sequence changes, these interactions and bonds also change.
• proteins are shaped by interactions between their amino acids.
• when the interactions between amino acids change, the 3D shape of the protein changes (tertiary structure).
• enzymes work by interacting with substrates via their ‘active site’.
• a change in protein shape will change the shape of the active site.
• the substrate cannot bind to the new shape of the active site so no enzyme-substrate complexes are formed so the enzyme cannot function.

Question 2

What categories do the tertiary and quarternary structures of proteins fall into?

Answer 2

they fall into two categories: fibrous and globular

Question 3

What are globular proteins?

Answer 3

• spherical shaped proteins that have chemical function and take part in specific reactions within living organisms
• globular proteins form a spherical mass with a specific 3-D shape (tertiary and quaternary structure)
• they fold up so that hydrophillic groups are on the outside and hydrophobic groups are inside the molecule

Question 4

What are fibrous proteins?

Answer 4

• proteins that play a structural role in a cell (may give elasticity in some tissues)
• form long chains/ fibres => primary, secondary, tertiary and quarternary structure
• insoluble in water => useful for structure and support
• fibres form a triple-helix of polypeptide chains
• these chains are held together by hydrogen bonds