Amino Acids and Their Functions
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Questions and Answers

What distinguishes essential amino acids from non-essential amino acids?

  • Essential amino acids can be synthesized in the body.
  • Non-essential amino acids are always present in high amounts in foods.
  • Essential amino acids cannot be synthesized in the body. (correct)
  • Non-essential amino acids must be obtained from the diet.

    • Which of the following describes glucogenic amino acids?

  • They can be converted into glucose. (correct)
  • They are primarily used for protein synthesis.
  • They can only be converted into ketone bodies.
  • They are only found in plant-based sources.

    • What is a common consequence of methionine breakdown in the body?

  • It produces a risk factor for heart disease due to homocysteine. (correct)
  • It is the primary source of energy during fasting.
  • It generates ammonia as a metabolic byproduct.
  • It leads to an increase in essential amino acids.

    • What role do amino acids primarily play in energy metabolism?

    <p>They can be completely metabolized for energy or converted to glucose.</p> Signup and view all the answers

    What is phenylketonuria (PKU) primarily caused by?

    <p>A genetic defect in amino acid metabolism.</p> Signup and view all the answers

    Which type of amino acids can lead to the formation of glucose?

    <p>Glucogenic amino acids</p> Signup and view all the answers

    What is a characteristic of ketogenic amino acids?

    <p>They lead to the formation of ketone bodies.</p> Signup and view all the answers

    Which of the following amino acids is an example of a glucogenic amino acid?

    <p>Alanine</p> Signup and view all the answers

    What metabolic intermediate is NOT associated with glucogenic amino acids?

    <p>Acetyl-CoA</p> Signup and view all the answers

    Which condition is associated with a genetic defect in amino acid metabolism?

    <p>Phenylketonuria (PKU)</p> Signup and view all the answers

    What is a potential risk associated with methionine breakdown?

    <p>Increase in homocysteine levels</p> Signup and view all the answers

    What is the significance of sufficient amino acids in nutrition?

    <p>They are essential for health and disease management.</p> Signup and view all the answers

    What does the breakdown of amino acids generate that can lead to toxicity?

    <p>Urea</p> Signup and view all the answers

    What condition is characterized by the deposition of dark pigment on vertebrae?

    <p>Alkaptonuria</p> Signup and view all the answers

    Which vitamin deficiency can lead to elevated homocysteine levels?

    <p>Vitamin B6</p> Signup and view all the answers

    What is a potential consequence of elevated levels of homocysteine?

    <p>Development of ectopic lentis</p> Signup and view all the answers

    Which genetic defect is associated with the metabolism of methionine?

    <p>Homocystinuria</p> Signup and view all the answers

    What amino acid is a direct precursor to homocysteine?

    <p>Methionine</p> Signup and view all the answers

    Which of the following is NOT a consequence of high homocysteine levels?

    <p>Liver cancer</p> Signup and view all the answers

    What is the role of Vitamins B12 and folate in homocysteine metabolism?

    <p>They promote the synthesis of methionine</p> Signup and view all the answers

    Which of the following statements is true regarding elevated homocysteine levels?

    <p>They are linked to oxidative damage.</p> Signup and view all the answers

    What is the primary enzyme that is defective in Phenylketonuria (PKU)?

    <p>Phenylalanine hydroxylase</p> Signup and view all the answers

    Which symptom is commonly associated with untreated PKU?

    <p>Shortened life expectancy</p> Signup and view all the answers

    What change occurs in the diet of patients with Phenylketonuria?

    <p>Low phenylalanine diet</p> Signup and view all the answers

    What genetic mutation is involved in Phenylketonuria?

    <p>Mutation in the phenylalanine hydroxylase gene</p> Signup and view all the answers

    What is the result of a defective homogentisate oxidase?

    <p>Symptoms of alkaptonuria</p> Signup and view all the answers

    What happens to IQ scores if a low phenylalanine diet is discontinued in PKU patients?

    <p>They decrease with age</p> Signup and view all the answers

    What is the primary clinical symptom of alkaptonuria?

    <p>Dark urine color</p> Signup and view all the answers

    What is a notable feature of the new drug Palynziq for PKU patients?

    <p>It includes phenylalanine ammonia lyase</p> Signup and view all the answers

    Under what condition are amino acids predominantly used as fuel during starvation?

    <p>Cellular proteins are used as fuel</p> Signup and view all the answers

    What is the main purpose of transaminase enzymes in amino acid metabolism?

    <p>Transfer amino groups between amino acids and α-ketoglutarate</p> Signup and view all the answers

    What does the carbon skeleton of the amino acid alanine produce after transamination?

    <p>Pyruvate</p> Signup and view all the answers

    Which vitamin derivative acts as a cofactor for transaminases?

    <p>Pyridoxal phosphate</p> Signup and view all the answers

    What is the percentage of energy needs that typically comes from amino acids?

    <p>~15%</p> Signup and view all the answers

    What is a potential consequence of measuring transaminase activity in serum?

    <p>Diagnosing liver damage</p> Signup and view all the answers

    Which of the following metabolites produced from amino acids does NOT enter the TCA cycle?

    <p>Creatinine</p> Signup and view all the answers

    What is the end product of oxidative deamination during amino acid metabolism?

    <p>Urea</p> Signup and view all the answers

    Study Notes

    Amino Acid Metabolism

    • Amino acids are categorized as essential or non-essential
    • Essential amino acids must be obtained from the diet, while non-essential amino acids can be synthesized by the body.
    • Amino acids can be used as energy sources.
    • Some amino acids are glucogenic (converted to glucose), others are ketogenic (converted to ketone bodies).
    • Amino acid degradation (catabolism) involves transamination and oxidative deamination to remove the amino group.
    • The resulting nitrogen is converted to urea and excreted, while the carbon skeleton enters the TCA cycle.
    • Pyridoxal phosphate is an essential cofactor for transaminases which transfer amino groups.
    • Transaminases are enzymes involved in amino acid degradation and are useful clinical markers of tissue damage.
    • Genetic defects in amino acid metabolism can lead to serious diseases, with phenylketonuria (PKU) being a common example, particularly in Ireland.
    • Methionine breakdown can produce homocysteine, a risk factor for heart disease.
    • Amino acid breakdown generates ammonia and urea.
    • Adequate intake of amino acids is crucial for health, even more so in cases of disease.
    • Amino acids can't be stored long term in the body.

    Amino Acid Structure

    • Amino acids have a central carbon atom (α-carbon) bonded to an amino group (NH₃⁺), a carboxyl group (COO⁻), a hydrogen atom, and a variable R-group (side chain).
    • This R-group differentiates the various amino acids.
    • Examples of amino acids mentioned are Serine (Ser, S), Alanine (Ala, A), Phenylalanine (Phe, F) and Leucine (Leu, L).

    Essential and Nonessential Amino Acids

    • Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine are essential amino acids.
    • Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glutamine, Glycine, Proline, Serine, and Tyrosine are nonessential amino acids.
    • Beans are low in methionine, and many cereal crops are very low in lysine.

    Examples of Importance of Amino Acid Metabolism in Medicine

    • Genetic defects in amino acid metabolism lead to various medical conditions, e.g. phenylketonuria (PKU).
    • Elevated homocysteine levels are a risk factor for heart disease.
    • Amino acid degradation generates ammonia and urea; toxicity can result from a build-up.
    • Nutritional factors, and the need for adequate amino acids are important in health and in disease.

    Amino Acid Degradation (Catabolism)

    • Amino acids are degraded under three metabolic conditions following protein-rich meal ingestion, cellular protein turnover and starvation.
    • Amino acid degradation involves removing the amino group to generate energy or to convert to glucose or ketone bodies.
    • The carbon skeleton of amino acids enters the TCA cycle.
    • Transamination, and oxidative deamination are involved in removing the amino group.

    Classification of Amino Acids

    • Amino acids are classified as glucogenic or ketogenic based on their metabolic fate.
    • Glucogenic amino acids can be converted to glucose, while ketogenic amino acids lead to the formation of ketone bodies.
    • Examples of both glucogenic and ketogenic amino acids are given in a table.

    Inborn Errors of Amino Acid Metabolism

    • Genetic defects in amino acid metabolism can lead to deficiencies in enzyme function.
    • Inborn errors of metabolism can cause a build-up of toxic metabolites, and result in severe diseases such as PKU, Homocystinuria, and Alkaptonuria.
    • Disorders often cause mental retardation or other serious clinical problems.
    • Some disorders are more common in certain populations.

    Phenylketonuria (PKU)

    • PKU is caused by a genetic defect in phenylalanine hydroxylase, resulting in the inability to convert phenylalanine to tyrosine.
    • This leads to a buildup of phenylalanine and its by-products.
    • PKU is often treated with a low phenylalanine diet.
    • Untreated PKU can cause significant developmental problems, particularly intellectual disability.
    • All newborns are screened for PKU.

    Alkaptonuria

    • Alkaptonuria is caused by a deficiency in homogentisate oxidase.
    • This leads to accumulation of homogentisic acid.
    • Symptoms include dark urine and arthritis development.
    • The buildup of homogentisic acid in the body also results in the production of dark pigments in body tissue and bones.

    Homocystinuria

    • Homocystinuria is a genetic disorder involving elevated homocysteine levels.
    • It results from defects in the enzymes responsible for converting homocysteine to cysteine or methionine.
    • Deficiencies in vitamin B6, folate, or vitamin B12 can also contribute to homocysteine build-up.
    • Elevated homocysteine is a risk factor for premature arterial diseases, mental retardation, ectopic lentis (displacement of the lens of the eye) and skeletal abnormalities.

    Additional Notes

    • Many of the listed metabolic pathways are complex and require further in-depth study to fully understand all the nuances and details.
    • The use of diagrams and chemical structures to illustrate the metabolic steps is vital for understanding the process.

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    Amino Acid Metabolism Lecture Notes PDF

    Description

    This quiz explores the fundamental differences between essential and non-essential amino acids, as well as their roles in energy metabolism and amino acid breakdown. Test your knowledge on the characteristics and consequences of amino acids, including conditions like phenylketonuria (PKU).

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