Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

11. Translation

Proteins

Genetics

11. Translation

Proteins

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1:20 minutes

Problem 13

Textbook Question

Individuals with phenylketonuria cannot convert phenylalanine to tyrosine. Why don't these individuals exhibit a deficiency of tyrosine?

Verified step by step guidance

Phenylketonuria (PKU) is a genetic disorder caused by a deficiency in the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine to tyrosine.

In individuals with PKU, phenylalanine accumulates because it cannot be converted to tyrosine, but this does not necessarily lead to a deficiency of tyrosine.

Tyrosine is a non-essential amino acid, meaning that it can be synthesized by the body from other sources besides phenylalanine.

Individuals with PKU can obtain tyrosine directly from their diet, as it is present in many protein-containing foods.

Therefore, despite the inability to convert phenylalanine to tyrosine, dietary intake can compensate for the potential deficiency of tyrosine in individuals with PKU.

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Key Concepts

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

Phenylketonuria (PKU)

Phenylketonuria is a genetic disorder caused by a deficiency in the enzyme phenylalanine hydroxylase, which is necessary for converting phenylalanine into tyrosine. Individuals with PKU accumulate high levels of phenylalanine, which can lead to neurological issues if not managed through diet. Understanding PKU is crucial to grasp why individuals with this condition do not exhibit a deficiency of tyrosine despite the inability to convert phenylalanine.

Tyrosine Synthesis

Tyrosine is classified as a non-essential amino acid because it can be synthesized in the body from phenylalanine. In individuals with PKU, while the conversion process is impaired, tyrosine can still be obtained from dietary sources or through alternative metabolic pathways. This explains why individuals with PKU do not typically exhibit a deficiency of tyrosine despite the metabolic block.

Dietary Management

Dietary management is a critical aspect of living with PKU, as individuals must adhere to a low-phenylalanine diet to prevent toxic accumulation. This diet often includes special medical foods that provide adequate tyrosine and other essential nutrients. By carefully managing their diet, individuals with PKU can maintain normal levels of tyrosine, mitigating the risk of deficiency despite their metabolic limitations.

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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?

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Textbook Question

How do we know that the structure of a protein is intimately related to the function of that protein?

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Textbook Question

Describe the gene and protein defects in phenylketonuria (PKU). How are these defects connected to disease symptoms?

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Discuss the potential difficulties of designing a diet to alleviate the symptoms of phenylketonuria.

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Textbook Question

Early detection and adherence to a strict dietary regimen have prevented much of the intellectual disability that used to occur in those with phenylketonuria (PKU). Affected individuals now often lead normal lives and have families. For various reasons, such individuals tend to adhere less rigorously to their diet as they get older. Predict the effect that mothers with PKU who neglect their diets might have on newborns.

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Textbook Question

The study of biochemical mutants in organisms such as Neurospora has demonstrated that some pathways are branched. The data shown in the following table illustrate the branched nature of the pathway resulting in the synthesis of thiamine:

Why don't the data support a linear pathway? Can you postulate a pathway for the synthesis of thiamine in Neurospora?

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Textbook Question

Why is an alteration of electrophoretic mobility interpreted as a change in the primary structure of the protein under study?

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Textbook Question

Define and describe the differences in the primary, secondary, and tertiary structures of a protein.

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