Proteins

Question 1

What are the effects of heating proteins on solubility?

Answer 1

Solubility decreases as the hydrophobic attraction increases. The more a protein is heated it denatures, the more the hydrophobic inside is exposed. These tend to attract other proteins and aggregate. As the aggregate grow, it is decreasing their ability to dissolve.

Question 2

Enzymes of the digestive tract are built to process only one stereo isomer of AA, which one is that?

Answer 2

Alpha-L-AA.

Question 3

What are charged polar AA side chains? What are their properties?

Answer 3

Carboxyl groups (-COOH and -COO-)
Amino groups (-NH3+ and NH2)

Properties:
- Hydrophilic
- High solubility
- Mainly present at the outside of the protein
- Reactive
- Charge depends on pH

Question 4

What are non-charged polar AA side chains? Also give their properties.

Answer 4

• Hydroxyl group (-OH)
• Sulfhydryl group (-SH)
• Amide group (CO-NH2)

Properties:
- Hydrophilic
- High solubility
- Mainly present on the outside of the protein
- Reactive

Question 5

What are non-charged non-polar AA side chains? Also give their properties.

Answer 5

• Aliphatic group
• Aromatic groups
• Imino acid group, thio-ether

Properties:
- Hydrophobic
- Low solubility
- Mainly present on the inside of the protein

Question 6

What is a primary structure?

Answer 6

AA configuration into peptide, but also peptide configuration into protein (polypeptide).

Question 7

What is a secondary structure?

Answer 7

E.g. Alpha-helix or beta sheet

Peptide chains that are stabilized by hydrogen bonds between the strands.

Question 8

What is a tertiary structure?

Answer 8

Spatial arrangement of secondary structure elements. Stabilized by electrostatic and hydrophobic interactions, disulphide bonds, and van der Waals interaction.

Question 9

What is a quarternairy structure?

Answer 9

Spatial arrangement of different polypeptide chains. Stabilized by hydrophobic interactions, disulphide bonds, and charge.

Question 10

What are the different levels of classification based on solubility? Starting from an insoluble source?

Answer 10

1) Albumins (extracted with water)
2) Globulins (extracted with 5% NaCl)
3) Prolamins (extracted with 70% ethanol)
4) Glutelins (residue)

Question 11

What is strecker degradation?

Answer 11

Combination between decarboxylation and deamination. Aldehydes are formed, which are quite reactive.