Problem 21
BIOCHEMICAL CONNECTIONS Crisco is made from vegetable oils, which are usually liquid. Why is Crisco a solid? Hint: Read the label.
Problem 23
In lipid bilayers, there is an order-disorder transition similar to the melting of a crystal. In a lipid bilayer in which most of the fatty acids are unsaturated, would you expect this transition to occur at a higher temperature, a lower temperature, or the same temperature as it would in a lipid bilayer in which most of the fatty acids are saturated? Why?
Problem 24
Briefly discuss the structure of myelin and its role in the nervous system.
Problem 26
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.
Problem 29
How can fluorescence techniques be used to monitor the motion of lipids and proteins in membranes?
Problem 32
A membrane consists of \(50 \%\) protein by weight and \(50 \%\) phosphoglycerides by weight. The average molecular weight of the lipids is 800 Da, and the average molecular weight of the proteins is 50,000 Da. Calculate the molar ratio of lipid to protein.
Problem 34
Suppose that you are studying a protein involved in transporting ions in and out of cells. Would you expect to find the nonpolar residues in the interior or the exterior? Why? Would you expect to find the polar residues in the interior or the exterior? Why?
Problem 35
Which statements are consistent with the fluid-mosaic model of membranes? (a) All membrane proteins are bound to the interior of the membrane. (b) Both proteins and lipids undergo transverse (flip-flop) diffusion from the inside to the outside of the membrane. (c) Some proteins and lipids undergo lateral diffusion along the inner or outer surface of the membrane. (d) Carbohydrates are covalently bonded to the outside of the membrane. (e) The term mosaic refers to the arrangement of the lipids alone.
Problem 38
Suggest a reason why inorganic ions, such as \(\mathrm{K}^{+}, \mathrm{Na}^{+}, \mathrm{Ca}^{2+},\) and \(\mathrm{Mg}^{2+},\) do not cross biological membranes by simple diffusion.
Problem 39
Which statements are consistent with the known facts about membrane transport? (a) Active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher. (b) Transport does not involve any pores or channels in membranes. (c) Transport proteins may be involved in bringing substances into cells.
