Introduction - Prior knowledge - Exercises

12 important questions on Introduction - Prior knowledge - Exercises

Which bond is/are used to stabilise the tertiary/quaternary structure of a protein?

  • Disulphide bonds (covalent)
  • Electrostatic interactions
  • Hydrophobic interactions


How can this be classified? Fibrillar, globular or random coil?
Proteins that provide structure to tissues (e.g. muscle).

Fibrillar

How can this be classified? Fibrillar, globular or random coil?
Combination of α-helices and β-sheets, alternated by random coils.

Globular
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How can this be classified? Fibrillar, globular or random coil?
Low solubility in water, leading to a tendency to cluster.

Fibrillar

How can this be classified? Fibrillar, globular or random coil?
Entire peptide chain of the protein is packed or arranged within a single secondary structure.

Fibrillar

Which amino groups from amino acids and proteins can react in this reaction?

  • Free amino acids and amino group at N-terminal of a peptide or protein.
  • Free amino acids, amino group at N-terminal of a peptide or protein and all amino-groups at side-chains of amino acid (residues).
  • Amino group at N-terminal of a peptide or protein, and all amino-groups at side-chains of amino acid (residues).
  • Free amino acids, amino-group at N-terminal of a peptide or protein, and side chain groups of lysine and arginine.

Free amino acids, amino-group at N-terminal of a peptide or protein, and side chain groups of lysine and arginine.

Indicate for each property of proteins whether it will be lower or higher after denaturation compared to before denaturation.
  1. sans-serifSolubility of the protein
  2. sans-serifEnzymatic activity of the protein
  3. sans-serifAggregation reactions between proteins
  4. sans-serifArea of hydrophobicity of the protein
  5. sans-serifTime needed to break down the protein with enzyme

  1. Solubility of the protein --> lower
  2. Enzymatic activity of the protein --> lower
  3. Aggregation reactions between proteins --> higher
  4. Area of hydrophobicity of the protein --> higher
  5. Time needed to break down the protein with enzyme --> lower

How is the proportion of charged amino acid residues and the amount of hydrophobic amino acid residues related to the solubility?

A high proportion of charged amino acid residues and a low proportion of hydrophobic amino acid residues will result in the highest solubility.

What method do you use to determine the solubility of a protein in a simple way?

Spectrophotometrical determination (e.g. A280). Proteins give an absorption maximum at 280 nm because of aromatic amino acids. The more proteins are dissolved, the more aromatic amino acids are present and the more absorption you will find.

Proteins are best soluble at their pI value. T/F

False

Amino acids have side groups which may contribute to the overall charge of the protein. T/F

True

At pH = 2.3, casein (pI = 4.6) is net positively charged. T/F

True

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