Problem 3
Contrasting milieux. Cerebrospinal fluid has a low content of albumin and other proteins compared with plasma. (a) What effect does this lower content have on the concentration of fatty acids in the extracellular medium of the brain? (b) Propose a plausible reason for the selection by the brain of glucose rather than fatty acids as the prime fuel. (c) How does the fuel preference of muscle complement that of the brain?
Problem 8
Sweet hazard. Ingesting large amounts of glucose before a marathon might seem to be a good way of increasing the fuel stores. However, experienced runners do not ingest glucose before a race. What is the biochemical reason for their avoidance of this potential fuel? (Hint: Consider the effect of glucose ingestion on the level of insulin.
Problem 9
An effect of diabetes. Insulin-dependent diabetes is often accompanied by hypertriglyceridemia, which is an excess blood level of triacylglycerols in the form of very low density lipoproteins. Suggest a biochemical explanation.
Problem 10
Sharing the wealth. The hormone glucagon signifies the starved state, yet it inhibits glycolysis in the liver. How does this inhibition of an energy- production pathway benefit the organism?
Problem 11
Compartmentation. Glycolysis takes place in the cytoplasm, whereas fatty acid degradation takes place in mitochondria. What metabolic pathways depend on the interplay of reactions that take place in both compartments?
Problem 12
Kuashiorkor. The most common form of malnutrition in children in the world, kwashiorkor, is caused by a diet having ample calories but little protein. The high levels of carbohydrate result in high levels of insulin. What is the effect of high levels of insulin on (a) lipid utilization? (b) protein metabolism? (c) Children suffering from kwashiorkor often have large distended bellies caused by water from the blood leaking into extracellular spaces. Suggest a biochemical basis for this condition.
Problem 13
Oxygen deficit. After light exercise, the oxygen consumed in recovery is approximately equal to the oxygen deficit, which is the amount of additional oxygen that would have been consumed had oxygen consumption reached steady state immediately. How is the oxygen consumed in recovery used?
Problem 14
Excess postexercise oxygen consumption. The oxygen consumed after strenuous exercise stops is significantly greater than the oxygen deficit and is termed excess postexercise oxygen consumption (EPOC). Why is so much more oxygen required after intense exercise?
Problem 15
Psychotropic effects. Ethanol is unusual in that it is freely soluble in both water and lipids. Thus, it has access to all regions of the highly vascularized brain. Although the molecular basis of ethanol action in the brain is not clear, ethanol evidently influences a number of neurotransmitter receptors and ion channels. Suggest a biochemical explanation for the diverse effects of ethanol.
Problem 16
Fiber type. Skeletal muscle has several distinct fiber types. Type I is used primarily for aerobic activity, whereas type II is specialized for short, intense bursts of activity. How could you distinguish between these types of muscle fiber if you viewed them with an electron microscope?
