LSM1401 Semester 2 2007‐08
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Tutorial 2
(17, 18, and 19 March 2008)
Questions
1. According to the fluid mosaic model, a biological membrane is composed of a lipid bilayer with proteins embedded in or loosely attached to the bilayer structure.
(a) The lipid bilayer is composed principally of phospholipids. Why are phospholipids ideal for the formation of the bilayer?
(b) Egg yolks are rich in phosphatidylcholine, a glycerophospholipid. Egg yolks are added into mixtures of water and melted butter to prevent separation during baking. How do the egg yolks prevent the separation?
(c) The integral proteins embedded in the bilayer have transmembrane segments that may consist of α‐helices. Assuming that the membrane is 50 Å in thickness, what is the minimum number of residues required for an α‐helix to span the lipid bilayer?
(d) It is said that the differences between integral proteins and water‐soluble proteins are skin‐deep. What are the differences between integral and water‐soluble proteins?
2. Consider to the following structure of D‐glucose.
(a) Glucuronic acid is a product of the oxidation of the C6 position of glucose. Draw the six‐ membered ring structure of β‐D‐glucuronate.
(b) Hyaluronate is a glycosaminoglycan composed of repeating disaccharides. Each disaccharide unit consists of a D‐glucuronic acid and one N‐acetyl‐β‐D‐glucosamine linked by a β(1→3) O‐glycosidic bond. Draw the structure of the disaccharide unit in its ionised form.
3. Suggest a reason why animals that live in cold climates tend to have higher proportions of polyunsaturated fatty acid residues in their lipids than do animals that live in warm climates.
LSM1401 Semester 2 2007‐08
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4. Prostaglandin H2 synthase‐1 is an enzyme that catalyses the synthesis of prostaglandins and thromboxanes from arachidonate.
(a) The action of prostaglandin H2 synthase‐1 may be inhibited by a group of drugs. (i) What is the general name for this group of drugs that block the synthesis of
prostaglandins and thromboxanes from arachidonate? (ii) List two examples of this group of drugs.
(b) Prostaglandin H2 synthase‐1 is a membrane‐bound protein which is partially embedded in the membrane, as shown in the diagram below.
(i) What are the main differences between the amino acid residues of the α‐helices of the portion of the enzyme embedded in the membrane and the segment that lies along the outer surface of the membrane?
(ii) Explain why the localisation of the enzyme in the membrane is crucial to its function.
5. Fructose in its β‐D‐pyranose form accounts for the powerful sweetness of honey. The β‐D‐ furanose form, although sweet, is not as sweet as the pyranose form. The furanose form is the more stable form. Draw the two forms and explain why it may not be wise to cook with honey.
6. Some athletes eat diets high in carbohydrates before an event. Suggest a biochemical basis for this practice.
7. IVLE Review Questions on topics of (a) “Life and Aqueous Solutions”, (b) “Cell Biology”, and
(c) “Protein Structure and Function”.
