Weight control. As disturbing as the obesity epidemic is, an equally intriguing, almost amazing observation is that many people are able to maintain an approximately constant weight throughout adult life. A few simple calculations of a simplified situation illustrates how remarkable this feat is. Consider a 120-pound woman whose weight does not change significantly between the ages of 25 and 65. Let us say that the woman requires 8,400 kJ (2000 kcal) day⁻¹. For simplicity’s sake, let us assume that the woman’s diet consists predominantly of fatty acids derived from lipids. The energy density of fatty acids is 38 kJ (9 kcal) g⁻¹. How much food has she consumed over the 40 years in question?

Spare tire. Suppose that our test subject from problem 1 gained 55 pounds between the ages of 25 and 65 (a sadly common occurrence), and that her weight at 65 years of age is 175 pounds. Calculate how many excess calories she consumed per day to gain the 55 pounds over 40 years. Assume that our test subject is 5 feet 6 inches tall. What is her BMI? Would she be considered obese at 175 lbs?

Depot fat. Adipose tissue was once only considered a storage site for fat. Why is this view no longer considered correct?

Balancing act. What is meant by caloric homeostasis?

Dynamic duo. What are the key hormones responsible for maintaining caloric homeostasis?

Dual roles. What two biochemical roles does CCK play? GLP-1?

Failure to communicate. Leptin inhibits eating and is secreted in amounts in direct proportion to body fat. Moreover, obese people have normal amounts of leptin and leptin receptor. Why, then, do people become obese?

Many signals. Match the characteristic (a–i) with the appropriate hormone (1–6).

A key chemical. What are the sources of glucose 6-phosphate in liver cells?

Neither option is good. Differentiate between type 1 and type 2 diabetes.

Fighting diabetes. Leptin is considered an “anti-diabetogenic” hormone. Explain.

Metabolic energy and power. The rate of energy expenditure of a typical 70-kg person at rest is about 70 watts (W), like that of a light bulb.

Respiratory quotient (RQ). This classic metabolic index is defined as the volume of CO₂ released divided by the volume of O₂ consumed.

Camel’s hump. Compare the H₂O yield from the complete oxidation of 1 g of glucose with that of 1 g of tripalmitoylglycerol. Relate these values to the evolutionary selection of the contents of a camel’s hump.

Hungry–nourished. What is meant by the starved–fed cycle?

Of course, too much is bad for you. What are the primary means of processing ethanol?

Started out with burgundy, but soon hit the harder stuff. Describe the three stages of ethanol consumption that lead to liver damage and possibly death.

The wages of sin. How long does a person have to jog to offset the calories obtained from eating 10 macadamia nuts (75 kJ, or 18 kcal, per nut)? (Assume an incremental power consumption of 400 W.)

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.)

Lipodystrophy. Lipodystrophy is a condition in which an individual lacks adipose tissue. The muscles and liver from such individuals are insulin resistant, and both tissues accumulate large amounts of triacylglycerols (hyperlipidemia). The administration of leptin partly ameliorates this condition. What does it indicate about the relation of adipose tissue to insulin action?

Therapeutic target. What would be the effect of a mutation in the gene for PTP1B (protein tyrosine phosphatase 1B) that inactivated the enzyme in a person who has type 2 diabetes?

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.

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?

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?

Kwashiorkor. 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

One for all, all for one. How is the metabolism of the liver coordinated with that of skeletal muscle during strenuous exercise?

A little help, please? What is the advantage of converting pyruvate into lactate in skeletal muscle?

Fuel choice. What is the major fuel for resting muscle? What is the major fuel for muscle under strenuous work conditions?

Hefty reimbursement. Endurance athletes sometimes follow the exercise-and-diet plan described here: 7 days before an event, do exhaustive exercises so as to all but deplete glycogen stores. For the next 2 to 3 days, consume few carbohydrates and do moderate- to low-intensity exercises. Finally, 3 to 4 days before the event, consume a diet rich in carbohydrates. Explain the benefits of this regime.

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?

Excess post-exercise oxygen consumption. The oxygen consumed after strenuous exercise stops is significantly greater than the oxygen deficit and is termed excess post-exercise oxygen consumption (EPOC). Why is so much more oxygen required after intense exercise?

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.

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Fiber type. Skeletal muscle has several distinct fiber types. Type I is used primarily for aerobic activity, whereas type IIb 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?

Tour de France. Cyclists in the Tour de France (more than 2000 miles in 3 weeks) require about 836,000 kJ (200,000 kcal) of energy, or 41,840 kJ (10,000 kcal) day⁻¹ (a resting male requires 8368 kJ, or 2000 kcal, day⁻¹).

Responding to stress. Why does it make good physiological sense that regular bouts of prolonged exercise will result in mitochondrial biogenesis?

Burning fats. How does the activation of AMP-activated protein kinase (AMPK) during aerobic exercise foster the switch to fatty acid oxidation for distance running?

Saving protein. What metabolic and hormonal changes account for decreased gluconeogenesis during the first several weeks of starvation in humans?

Did I do that!? Alcohol consumption on an empty stomach results in some interesting biochemical as well as embarrassing behavioral alterations. We will ignore the latter. Gluconeogenesis falls; there are increases in intracellular ratios of lactate to pyruvate, of glycerol 3-phosphate to dihydroxyacetone phosphate, of glutamate to α-ketoglutarate, and of d-3-hydroxybutyrate to acetoacetate. Hypoglycemia develops rapidly. Blood pH also falls. Alcohol consumption by a well-fed individual does not lead to hypoglycemia or alteration in blood pH.

Skip the candy bar. Humans can survive longer by total fasting than on a diet consisting entirely of small amounts of carbohydrates. What is going on?

Too much of a good thing. What is the relation between fatty acid oxidation and insulin resistance in the muscle?

Aneurin? Really? Why are the symptoms of beriberi similar to those of Wernicke–Korsakoff syndrome?

Lactate threshold. The graph shows the relation between blood-lactate levels, oxygen consumption, and heart rate during exercise of increasing intensity. The values for oxygen consumption and heart rate are indicators of the degree of exertion.

Feeling the burn. Under certain circumstances, the respiratory quotient (RQ value) for an athlete exercising intensely can rise above one. How is this possible?

So many channels. Like cable TV. Describe the role of ion channels in insulin secretion by the β cells of the pancreas.