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Ch. 9 - The Molecular Biology of Translation
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 9, Problem B.2a

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.
Why do you think eating a low-methionine diet is critical to controlling homocystinuria?

Verified step by step guidance
1
Understand that homocystinuria is caused by a mutation leading to the absence of a critical enzyme needed to break down methionine, an essential amino acid.
Recognize that because the enzyme is missing or nonfunctional, methionine cannot be properly degraded, causing a buildup of homocysteine, a toxic intermediate compound.
Realize that a high level of homocysteine in the body leads to the symptoms associated with homocystinuria, such as mental impairment and heart problems.
Conclude that by eating a low-methionine diet, the intake of methionine is reduced, which in turn decreases the amount of homocysteine produced and accumulated.
Therefore, controlling methionine intake through diet is critical to managing the symptoms and preventing the harmful effects of homocystinuria.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Autosomal Recessive Inheritance

Autosomal recessive inheritance means a person must inherit two copies of a mutated gene, one from each parent, to express the disorder. Carriers with only one mutated gene typically do not show symptoms. Understanding this helps explain why homocystinuria appears in newborn screening and the genetic risk for families.
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Autosomal Pedigrees

Methionine Metabolism and Enzyme Deficiency

Methionine is an essential amino acid broken down through a metabolic pathway involving several enzymes. In homocystinuria, a mutation causes deficiency of a key enzyme, leading to accumulation of homocysteine, a toxic intermediate. This disruption explains the biochemical basis of the disease and its symptoms.
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Translation initiation

Dietary Management in Metabolic Disorders

Dietary control, such as a low-methionine diet, reduces substrate availability for the defective metabolic pathway, preventing toxic buildup. In homocystinuria, limiting methionine intake helps lower homocysteine levels, reducing symptoms and improving outcomes. This principle is common in treating inherited metabolic disorders.
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Related Practice
Textbook Question

Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein. What is the amino acid sequence of the polypeptide produced from this sequence?

Textbook Question

Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein.

What term is used to identify a functional protein like this one formed when two identical polypeptides join together?

Textbook Question

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

The low-methionine diet must be maintained throughout life to manage homocystinuria. Why do you think this is the case?

Textbook Question

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

Describe how the codon for phenylalanine was identified.

Textbook Question

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

What was the result of studies of synthetic mRNAs composed exclusively of cytosine?

Textbook Question

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

What result was obtained for synthetic mRNAs containing AG repeats, that is, AGAGAGAG...?