Essential Nutrients

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I. Approximately 50 essential nutrients, listed in Table 4-9, are necessary for health but cannot be synthesized in adequate amounts by the body and must therefore be provided in the diet.

II. A large intake of water-soluble vitamins leads to their rapid excretion in the urine, whereas large intakes of fat-soluble vitamins lead to their accumulation in adipose tissue and may produce toxic effects.

SECTION C KEY TERMS

glycolysis pyruvate substrate-level phosphorylation aerobic anaerobic lactate

Krebs cycle citric acid cycle tricarboxylic acid cycle acetyl coenzyme A (acetyl CoA)

oxidative phosphorylation cytochrome electron transport chain chemiosmotic hypothesis hydrogen peroxide superoxide anion hydroxyl radical glycogen gluconeogenesis adipocyte adipose tissue beta oxidation a-glycerol phosphate protease oxidative deamination keto acid transamination urea essential amino acid negative nitrogen balance positive nitrogen balance essential nutrient water-soluble vitamin fat-soluble vitamin

SECTION C REVIEW QUESTIONS

What are the end products of glycolysis under aerobic and anaerobic conditions?

To which molecule are the hydrogen atoms in

NADH + H+ transferred during anaerobic glycolysis? During aerobic glycolysis?

What are the major substrates entering the Krebs cycle, and what are the products formed?

Why does the Krebs cycle operate only under aerobic conditions even though molecular oxygen is not used in any of its reactions?

10 11 12

18 19

Identify the molecules that enter the oxidative-phosphorylation pathway and the products that are formed.

Where are the enzymes for the Krebs cycle located? The enzymes for oxidative phosphorylation? The enzymes for glycolysis?

How many molecules of ATP can be formed from the breakdown of one molecule of glucose under aerobic conditions? Under anaerobic conditions? Describe the origin and effects of reactive oxygen molecules.

Describe the pathways by which glycogen is synthesized and broken down by cells. What molecules can be used to synthesize glucose? Why can't fatty acids be used to synthesize glucose? Describe the pathways used to catabolize fatty acids to carbon dioxide.

Why is it more efficient to store fuel as fat than as glycogen?

Describe the pathway by which glucose is converted into fat.

Describe the two processes by which amino groups are removed from amino acids.

What can keto acids be converted into?

What is the source of the nitrogen atoms in urea, and in what organ is urea synthesized?

Why is water considered an essential nutrient whereas glucose is not?

What is the consequence of ingesting large quantities of water-soluble vitamins? Fat-soluble vitamins?

CHAPTER 4 THOUGHT QUESTIONS

(Answers are given in Appendix A.)

1. A variety of chemical messengers that normally regulate acid secretion in the stomach bind to proteins in the plasma membranes of the acid-secreting cells. Some of these binding reactions lead to increased acid secretion, and others to decreased secretion. In what ways might a drug that causes decreased acid secretion be acting on these cells? In one type of diabetes, the plasma concentration of the hormone insulin is normal, but the response of the cells to which insulin usually binds is markedly decreased. Suggest a reason for this in terms of the properties of protein binding sites. Given the following substances in a cell and their effects on each other, predict the change in compound H that will result from an increase in compound A, and diagram this sequence of changes. Compound A is a modulator molecule that allosterically activates protein B. Protein B is a protein kinase enzyme that activates protein C.

Protein C is an enzyme that converts substrate D to product E.

Compound E is a modulator molecule that allosterically inhibits protein F.

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

Protein Activity and Cellular Metabolism CHAPTER FOUR

Protein Activity and Cellular Metabolism CHAPTER FOUR

Protein F is an enzyme that converts substrate G to product H.

4. Shown below is the relation between the amount of acid secreted and the concentration of compound X, which stimulates acid secretion in the stomach by binding to a membrane protein.

Plasma concentration of compound X (pM)

At a plasma concentration of 2 pM, compound X produces an acid secretion of 20 mmol/h.

a. Specify two ways in which acid secretion by compound X could be increased to 40 mmol/h.

b. Why will increasing the concentration of compound X to 28 pM not produce more acid secretion than increasing the concentration of X to 18 pM.

5. How would protein regulation be affected by a mutation that causes the loss of phosphoprotein phosphatase from cells?

How much energy is added to or released from a reaction in which reactants A and B are converted to products C and D if the energy content, in kilocalories per mole, of the participating molecules is: A = 55, B = 93, C = 62, and D = 87? Is this reaction reversible or irreversible? Explain. In the following metabolic pathway, what is the rate of formation of the end product E if substrate A is present at a saturating concentration? The maximal rates (products formed per second) of the individual steps are indicated.

If the concentration of oxygen in the blood delivered to a muscle is increased, what effect will this have on the rate of ATP production by the muscle? During prolonged starvation, when glucose is not being absorbed from the gastrointestinal tract, what molecules can be used to synthesize new glucose? Why does the catabolism of fatty acids occur only under aerobic conditions?

Why do certain forms of liver disease produce an increase in the blood levels of ammonia?

Vander et al.: Human Physiology: The Mechanism of Body

Vander et al.: Human Physiology: The Mechanism of Body

CHAPTER

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Responses

  • selassie
    What pathway is used to catabolize fatty acids to carbon dioxide?
    8 years ago
  • jonathan
    What are the major substrates entering the kreb cycle and what are the products formed?
    8 years ago
  • andrea
    Why is glucose not an essential nutrient?
    8 years ago
  • claire cameron
    What are the 50 essential nutrients?
    8 years ago
  • cedivar
    Why cant fatty acids be broken down under anaerobic conditoona?
    8 years ago
  • ursula
    Is glucose a body's essential nutrient?
    8 years ago

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