Answers
Tutorial 3: Amino Acids & Proteins
1. Draw the general chemical structure of amino acids.
(2 marks)
2. Give two examples from each classes of amino acids:
a) Hydrophobic – Gly, Ala, Val, Leu, Ile, Pro, Met, Phe and Trp
b) Polar, uncharged - Ser, Thr, Cys, Tyr, Asn, Gln, His
c) Polar, charged - Asp, Glu, Lys, Arg
(6 marks)
3. Answer the following questions:
a) Name one amino acid that have aromatic ring – Phe, Trp, Tyr
b) Which amino acid that can form disulfide bond - Cys
c) Which amino acid that actually is an imino acid - Pro
d) What is the smallest amino acid - Gly
e) What is the largest amino acid - Trp
(5 marks)
4. Give the full name for each abbreviation of amino acid below:
a) Asn - Asparagine
b) Asp - Aspartate
c) Arg - Arginine
d) W - Tryptophan
e) Q - Glutamine
f) Y - Tyrosine
(6 marks)
5. Calculate the isoelectric pH or pI of aspartic acid that has pK1 = 2.09 and pK2 = 3.96.
(2 marks)
pH = 2.09 + 3.96 = 3.03
2
6. Give an example for each protein function below.
a) Oxygen transport – Hb
b) Oxygen storage - Mb
c) Electron transport – Cyt c
d) Enzyme – Ribonuclease/ Amylase/ DNA polymerase
e) Structural proteins - Collagen
f) Regulatory or receptors proteins – G protein
g) Immune proteins – Ig (Antibodies)
h) Muscle contraction - Actin
(8 marks)
7. Draw a structure of dipeptide. Shows the peptide bond.
(3 marks)
8. Describe what are globular and fibrous proteins. Give two examples for each type of
proteins.
(10 marks)
 Globular proteins
- Water soluble, more dynamic and flexible – presents in biological fluids (blood)
or cytoplasm
- play a role in transport, immune protection and catalysis
- Amino acids residues with polar and charged R groups
- Examples: Hb, Mb, Ribonuclease, Lysozymes, Cyt c, Ig, Actin
 Fibrous proteins
- Water insoluble, rigid conformation and have high tensile strength
- structural proteins collagen and keratin
- Amino acids residues with nonpolar R groups
- Examples: Silk, collagen, keratin, myosin & elastin
9. Name and describe all four levels of proteins structures.
(8 marks)
Primary structure
- Sequence of amino acid residues in a protein
Secondary structure
- Localized regions of primary sequence fold into regular and repeated structure –
e.g. -helix and -helix sheets
Tertiary structure
- Secondary structure of a protein interact and pack into a compact globular unit
Quaternary structure
- Association of two or more polypeptide chains to form a multisubunit protein
molecule
10. Polypeptide chains in  configuration can combine to form -sheet in two possible
orientations. Explain this statement by drawing the schematic structure of both -sheets.
(4 marks)
Anti- parallel -sheet:
Parallel -sheet:
TOTAL MARKS: 54