Download 1 - SMIC Nutrition Science

1.
What is the difference between catabolic and anabolic pathways?
Answer (key points): Catabolic pathways release energy through the breakdown of complex molecules into simpler ones,
whereas anabolic pathways require energy (ATP) to construct complex molecules from simpler ones. (pp. 272-273)
2.
What is the difference between coenzymes and cofactors, and where do we get them from?
Answer (key points): Cofactors are inorganic substances, or minerals, such as zinc, potassium, iron, and magnesium. Some
enzymes require that cofactors be attached to their active sites in order to function. Coenzymes are organic molecules derived
from vitamins such as niacin and riboflavin. Unlike cofactors, coenzymes are not actually a part of the enzyme structure.
Rather, they assist enzymes by accepting and donating hydrogen ions (H +), electrons (e-), and other molecules during
chemical reactions. The vitamins in our diet provide coenzymes and the minerals provide cofactors. (pp. 274-275)
3.
Describe briefly what each of the primary hormones involved in the regulation of catabolic and anabolic pathways does and
identify where each is made.
Answer (key points): (p. 276)
4.
Primary
hormones
Insulin
Glucagon
Where made
Pancreas
Pancreas
Cortisol
Adrenal glands
Epinephrine
Adrenal glands
Function(s)
Activates anabolic pathways and inactivates catabolic pathways.
Promotes catabolic pathways and inhibits anabolic pathways, thus
increasing energy availability by mobilizing energy-yielding molecules
that have been “stored for a rainy day.”
Stimulates catabolic pathways that help increase fuel availability; for
example, cortisol and epinephrine stimulate the breakdown of muscle
glycogen to increase glucose availability.
Stimulates catabolic pathways that help increase fuel availability; for
example, cortisol and epinephrine stimulate the breakdown of muscle
glycogen to increase glucose availability.
Mitochondria have often been referred to as the body’s “powerhouses.” Why is this an appropriate statement?
Answer (key points): The electron transport chain is located in the inner membrane of the mitochondria. The oxidative
phosphorylation that takes place through a series of linked chemical reactions that make up the chain accounts for
approximately 90% of the body’s ATP production. (pp. 278-279)
5.
Why might someone who eats a diet that contains inadequate amounts of niacin and riboflavin experience fatigue and feel
tired?
Answer (key points): Without sufficient niacin and riboflavin from the diet the body will not have the coenzymes essential to
the operation of the electron transport chain, which produces about 90% of the body’s ATP. (pp. 275, 278-279)
6.
Why would a bioterrorism agent that shut down the electron transport chain be of urgent concern for Homeland Security?
Answer (key points): Oxidative phosphorylation accounts for approximately 90% of ATP production and involves a series
of linked chemical reactions that make up the electron transport chain. If the body could not generate ATP via the electron
transport chain, death would result. (pp. 278-279)
7.
Describe/summarize the four major stages of catabolism.
Answer (key points):
8.

Stage 1: complex molecules are broken down into their fundamental building blocks.
glycogenolysis – glycogen → glucose
proteolysis – protein → amino acids
lipolysis – triglycerides → fatty acids and glycerol molecules

Stage 2: glucose, amino acids, fatty acids, and glycerol enter specific pathways in which each is converted into an
intermediate product that can enter the citric acid cycle.

Stage 3: intermediate products formed during Stage 2 enter the citric acid cycle and are broken down further to form
carbon dioxide, releasing energy in the process. Much of the energy released during Stage 3 of metabolism is transferred
to the coenzymes NAD+ and FAD, forming NADH + H + and FADH2, respectively. In addition, small amounts of ATP
are formed via substrate phosphorylation.

Stage 4: begins when NADH + H+ and FADH2 enter the electron transport chain. The energy-yielding pathways of
oxidative phosphorylation operate in nearly all cells to produce energy for cellular activities. (pp. 279, 281)
What are the pathways involved in the first stage of catabolism and what are the substrate and product(s) of each?
Answer (key points): (p. 279)
Pathways
glycogenolysis
proteolysis
lipolysis
9.
Substrates
glycogen
proteins
triglycerides
Products
glucose
amino acids
fatty acids and glycerol
Describe the process that permits a cyclist or other endurance athlete to continue to exercise even when he or she cannot take
in sufficient oxygen to support the electron transport chain’s continued generation of ATP.
Answer (key points): When endurance athletes cannot take in enough oxygen to meet the body’s demands for the large
amounts of oxygen needed to produce ATP via the electron transport chain, pyruvate remains in the cytoplasm and is
converted to lactate. Lactate is then released into the blood and taken up by the liver, where it is converted to glucose via
gluconeogenesis. The glucose that is formed from pyruvate can then undergo glycolysis. This sequence of chemical reactions,
called the Cori cycle, provides a means by which small amounts of ATP can be produced in the relative absence of oxygen.
Because very little ATP is actually produced, the Cori cycle cannot sustain vigorous physical activity for very long before the
muscle begins to fatigue. (pp. 282-283)
10. Why is the citric acid cycle considered to be an amphibolic pathway?
Answer (key points): Because intermediate products of the citric acid cycle can “leave” and enter anabolic pathways, the
citric acid cycle is both catabolic and anabolic and thus is considered an amphibolic pathway. (p. 283)
11. How does transamination differ from deamination?
Answer (key points): Protein catabolism involves removing the nitrogen-containing amino group and using the remainder of
the amino acid to generate energy. Transamination, the first step in this process, includes transferring the amino group from
an amino acid to a compound called an -ketoacid to form a new amino acid.
Deamination, the second step of amino acid catabolism, occurs primarily in the liver. This process removes the amino group
from an amino acid, leaving an -ketoacid. The amino group removed from the amino acid is converted to ammonia. Because
ammonia is toxic to cells, it is quickly converted to a less toxic substance called urea, which is released into the blood. Urea is
removed from the blood by the kidneys and excreted in the urine. Deamination also produces NADH + H+, which then
produces energy through oxidative phosphorylation via the electron transport chain.
After transamination and deamination are complete, an -ketoacid is able to enter the citric acid cycle at various points. (pp.
284-286)
12. How is it possible for both anabolic and catabolic processes to take place at the same time?
Answer (key points): Anabolism tends to take place in the cytoplasm, whereas catabolism takes place primarily in
mitochondria. This separation or compartmentalization is important, because it enables both anabolic and catabolic pathways
to function simultaneously. Catabolic pathways that break down compounds are distinctly different from anabolic pathways
that synthesize compounds. (p. 289)
13. It takes considerable energy to fuel the “energetically expensive” reactions of gluconeogenesis. Why, then, does the body
have such a process?
Answer (key points): Although most cells can use glucose and fatty acids for energy, the brain and central nervous system
use glucose preferentially, and red blood cells use glucose exclusively. To ensure that these and other tissues have a continual
supply of glucose, small amounts of glucose are stored as glycogen in the liver and skeletal muscle. However, when glycogen
stores are depleted, noncarbohydrate molecules are transformed into glucose by various anabolic pathways. This process,
called gluconeogenesis, occurs primarily within liver cells and, to a lesser extent, kidney cells. During periods of starvation,
gluconeogenesis provides an important source of glucose to cells that depend on it as their major or sole source of energy.
(pp. 291, 296-297)
14. What is the purpose of ketogenesis?
Answer (key points): Ketogenesis is an anabolic process that feeds into the catabolic processes of energy generation in the
brain and other tissues. Ketogenesis, which results in the synthesis of ketones, can spare the body from having to use amino
acids to synthesize large amounts of glucose via gluconeogenesis.
Ketogenesis, which occurs mostly in the liver, provides the body with an important source of energy during times of glucose
insufficiency (such as starvation and diabetes). However, only muscle, brain, and kidney tissue have the enzymes needed to
metabolize ketones for energy. (pp. 292-293, 297-298)
15. Assuming that one has enough oxygen, what pathways are active during the fed state for the generation of ATP?
Answer (key points): Most of the ATP produced during the fed state is the result of glycolysis, the citric acid cycle, and the
electron transport chain. (p. 294)
16. Why is it important for long-term health and well-being that weight reduction diets not mimic starvation?
Answer (key points): During starvation, the body’s priority is to supply the nervous system and red blood cells with
sufficient glucose. Once glycogen stores have been depleted within the first 24-36 hours of no food intake, glucose must be
synthesized from noncarbohydrate substances via gluconeogenesis. Muscles contribute to gluconeogenesis by supplying
amino acids, lactate, and glycerol, all of which are used by the liver to generate small amounts of glucose. The loss of lean
tissue during the early stages of acute starvation reduces the body’s total energy requirements. The body goes into “survival
mode” by dramatically reducing its metabolically active lean tissue. This defensive action is important because it helps
prolong survival if starvation continues. In this way, less energy is needed to maintain lean body mass, thus decreasing the
body’s overall energy needs. Similarly, self-imposed energy restriction, as with some eating disorders and very low-calorie
diets, also sacrifices lean tissue to support gluconeogenesis. Successful weight-loss diets advocate slow and gradual weight
loss to minimize the loss of lean tissue and thus muscle mass and strength. (p. 298)