Chapter 8 Reading Question 1

Genetic disorders of metabolism occur when individuals inherit a defect in one or more genes that result in the lack of a specific enzyme. Without appropriate enzyme activity, byproducts can accumulate in the body, sometimes with toxic effects. There is no cure for genetic disorders of metabolism, but early detection and specific diet modifications can control symptoms and prevent complications for many of these disorders. Select all of the sentences below that correctly describe the genetic disorder phenylketonuria (PKU).

Currently, blood tests are done at birth to screen for PKU. For a person with PKU, fruits, vegetables, grains, and special prescription formulas should compose the bulk of the diet. Individuals with PKU cannot metabolize phenylalanine.

The most metabolically active organ in the body is the __________.

Liver

The only source of energy that can be used directly by the cells is __________.

adenosine triphosphate (ATP)

The primary pathway to metabolize low volumes of alcohol is the __________.

alcohol dehydrogenase (ADH) enzyme system

During the absorptive state, metabolism favors energy storage and __________.

anabolism

Maple syrup urine disease is a metabolic disorder caused by the inability to metabolize __________.

branched chain amino acids. Maple syrup urine disease is a metabolic disorder caused by the inability to metabolize branched chain amino acids.

The first stage of metabolism to use glucose for energy is glycolysis. This is an example of a(n) __________.

catabolic reaction

The anabolic process of lipogenesis is efficient for __________.

fatty acids

Protein can be converted to glucose through the anabolic reaction __________.

gluconeogenesis

Which of the following is an anabolic reaction?

gluconeogenesis

Excess carbohydrates in the diet are first stored as __________.

glycogen

The first step in forming ATP from glucose is _________

glycolysis

In the electron transport chain, the passing of electrons to complete the production of ATP can be slowed by __________.

iron deficiency. If you are iron deficient, the cytochromes, which contain the minerals iron and copper, are less able to pass the electrons along the chain to complete the production of ATP.

The compounds used for gluconeogenesis include _________

lactate

Metabolism takes place within cells. The powerhouse of the cell is the __________.

mitochondrion

Which bond is the source of a large amount of energy in reactions involving ATP?

the breaking of one phosphate bond (forming ADP)

Genetic disorders of metabolism are problematic because they lead to __________.

the buildup of abnormal byproducts. The buildup of byproducts to toxic levels causes the medical complications of metabolic disorders.

Metabolism is defined as __________.

the sum of all chemical reactions in the body

Which of the following statements correctly describes protein metabolism during the postabsorptive state? Protein metabolism is halted during the postabsorptive state. Beta-oxidation is a series of metabolic reactions in which amino acids are oxidized to yield energy. Amino acids provide energy at a steady pace throughout the postabsorptive state. Amino acids are used to produce glucose through gluconeogenesis during the postabsorptive state.

Amino acids are used to produce glucose through gluconeogenesis during the postabsorptive state. Once liver glycogen has been depleted during fasting, gluconeogenesis uses amino acids, glycerol, pyruvate, and lactate to produce glucose.

Carmen has started a low-carb diet to lose weight quickly. She watches her food intake very carefully, and begins by eating no carbohydrates at all. After three days of being deprived of carbohydrates, her body uses what process for fuel?

Carmen's body forms ketone bodies to use as fuel via ketogenesis.

Anabolic Processes Excess glucose is stored as glycogen in the liver and muscle.Excess fatty acids combine with glycerol to form triglycerides, which are stored in adipose tissues.Amino acids from the amino acid pool are used to synthesize proteins.Excess glucose is converted to fatty acids and stored as part of the triglyceride molecule in adipose tissue.

Catabolic Processes Dietary protein from a meal is digested and absorbed as single amino acids.Glucose is used as the primary fuel for energy.Dietary carbohydrate from a meal is digested and absorbed as monosaccharides, mainly glucose.Fatty acids are used as fuel sources for some tissues.

Excess alcohol is stored as __________.

Fats

Which of the following statements correctly describes lipid metabolism during the postabsorptive state? Ketogenesis is stimulated by the breakdown of stored muscle glycogen during the early stages of the postabsorptive state. Ketone bodies can be used by the red blood cells during long-term starvation but not by the brain, which relies on glucose produced by gluconeogenesis. Lipogenesis creates triglycerides from excess carbohydrates, proteins, and fats, which are stored during the later stages of the postabsorptive state. Fatty acids are rapidly broken down from adipose tissues and converted to ketone bodies during the later stages of the postabsorptive state.

Fatty acids are rapidly broken down from adipose tissues and converted to ketone bodies during the later stages of the postabsorptive state. Fatty acids are broken down in ketogenesis to produce ketone bodies, the brain's preferred fuel source during long-term starvation.

Both catabolic and anabolic reactions are regulated by hormones. When the endocrine system detects a change in the concentration of nutrients, such as glucose levels dropping below normal, hormones are released to activate or deactivate the enzymes in the metabolic pathways. Which of the following statements is correct regarding the hormonal control of catabolism during the absorptive state?

Glucagon from the pancreas stimulates protein degradation, glycogenolysis, and lipolysis when blood glucose levels are low. Glucagon is released from the pancreas when blood glucose levels are low and stimulates protein degradation, glycogenolysis, and lipolysis.

Anabolic reactions are those that combine smaller compounds to build larger compounds. Anabolic reactions are favored during the absorptive state compared to catabolic reactions. Which of the following statements is correct regarding the anabolic reactions that occur during the absorptive state? Hints

Glycogenesis is the favored method for storing energy from carbohydrates during the absorptive state.

Understanding Metabolic Pathways

Glycolysis This is an anaerobic pathway that produces pyruvate.Glucose, six of the glucogenic amino acids, and glycerol enter here. TCA Cycle One trip through this pathway produces four reduced coenzymes, two CO2 molecules, and guanosine triphosphate (GTP), which will be converted to ATP.Acetyl CoA and oxaloacetate combine to form citrate in this stage. Electron Transport Chain The enzyme ATP synthase works to produce ATP through oxidative phosphorylation.The majority of ATP is produced here.

Which of the following statements correctly describes carbohydrate metabolism during the postabsorptive state? Liver glycogen stores are utilized to supply the blood with glucose even during long-term fasting. Muscle glycogen stores are depleted early in the postabsorptive state. Excess glucose is converted to a fatty acid, attached to a glycerol backbone, and stored as a triglyceride in adipose tissue in the postabsorptive state. In the later stages of the postabsorptive state, fatty acids can be converted to glucose to supply the brain and red blood cells with fuel.

Muscle glycogen stores are depleted early in the postabsorptive state. Glycogen stores are used during short periods of fasting overnight or between meals. These stores are depleted early when fasting becomes prolonged.

Metabolic Events During the Postabsorptive State

Short-Term Fasting Glucose from muscle glycogenolysis is used for energy by the muscle cells.Liver glycogenolysis helps maintain blood glucose levels. Long-Term Fasting Muscle protein catabolism yields single amino acids.Liver utilizes single amino acids from the catabolism of muscle for gluconeogenesis.Fatty acids in the liver are converted to ketone bodies that can be utilized for fuel by all cells and tissues except red blood cells. Both Short- and Long-Term Fasting Glucose is used as a fuel source for red blood cells, brain cells, and other tissues.Lipolysis breaks down triglycerides in adipose tissue to provide fatty acids for energy.

Which of the following is one of the four stages of carbohydrate metabolism to produce ATP?

TCA cycle