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Chapter 5: Problem 19

Explain how energy is obtained from the metabolism of amino acids. Why does a starving person have a high concentration of urea in the blood?

Short Answer

Expert verified
Energy is obtained from the metabolism of amino acids through the deamination process, which removes the amino group from the amino acid molecule, producing ammonia as a byproduct. This ammonia is then converted to urea through the urea cycle, which is less toxic and more easily excreted. The remaining deaminated amino acid molecule (keto acid) is further metabolized for energy production, entering pathways such as glycolysis or the citric acid cycle, ultimately producing ATP. In a starving person, the high concentration of urea in the blood indicates increased protein breakdown for energy purposes, as the body has exhausted its carbohydrate and fat stores.

Step by step solution

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1. Amino Acid Metabolism Overview

Amino acids are the building blocks of proteins, which are essential for various biological functions in our body. When we digest proteins from our diet, they break down into individual amino acids. Our body can use these amino acids to synthesize new proteins, or they can be metabolized to provide energy.
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2. Deamination Process

The first step to obtain energy from amino acids is the process of deamination. It involves the removal of the amino group (-NH2) from the amino acid molecule. This process primarily occurs in the liver and produces ammonia (NH3) as a byproduct. Since ammonia is toxic to the body, it must be converted into a less harmful substance to be excreted.
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3. Urea Cycle

The urea cycle is a series of biochemical reactions that convert ammonia to urea. Urea is less toxic and more easily excreted by the kidneys in the urine. The process takes place mainly in the liver, but some steps also occur in the kidneys. In this cycle, two ammonia molecules are combined with carbon dioxide (CO2) to form urea, which is safe for the body to eliminate.
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4. Conversion to Energy

After the deamination and urea cycle processes, the remaining deaminated amino acid molecule, now a keto acid, can be further metabolized for energy production. Depending on the specific amino acid, its keto acid can enter various pathways, such as glycolysis or the citric acid cycle. These pathways ultimately lead to the production of ATP, the primary energy currency of the cell.
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5. Starvation and High Urea Concentration

In a starvation state, the body exhausts its carbohydrate and fat stores to produce energy. When these reserves are depleted, the body starts to break down proteins (mainly from muscle tissue) for energy. This mechanism results in an increased release of amino acids in the bloodstream which will be broken down and metabolized for energy through the deamination process and the urea cycle. Consequently, the metabolism of a large amount of amino acids generates a higher concentration of urea in the blood, indicative of increased protein breakdown during starvation.

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Most popular questions from this chapter

The conversion of glucose 6-phosphate to free glucose, which can be secreted into the blood, occurs in a. the liver. b. skeletal muscles. c. both \(a\) and \(b\).

The net gain of ATP per glucose molecule in lactic acid fermentation is _____; the net gain in aerobic respiration is generally _____. a. \(2 ; 4\) b. \(2 ; 30\) c. \(30 ; 2\) d. \(24 ; 38\)

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What purpose is served by the formation of lactic acid during anaerobic metabolism? How is this accomplished during aerobic respiration?

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