Harper's Biochemistry Chapter 27 - Biosynthesis of the Nutritionally Nonessential Amino Acids
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Questions and Answers

Which amino acid is primarily synthesized from homocysteine and is not considered nutritionally essential?

  • L-Serine
  • L-Tyrosine
  • L-Cysteine (correct)
  • L-Proline

    • What is the main precursor for the synthesis of glycine in mammals?

  • Serine (correct)
  • Choline
  • Alanine
  • Glutamate

    • Why is dietary tyrosine not able to replace phenylalanine in the diet?

  • Phenylalanine is nonessential and can be synthesized from other amino acids.
  • Tyrosine has no dietary significance.
  • The conversion of phenylalanine to tyrosine is irreversible. (correct)
  • Tyrosine can be converted to phenylalanine.

    • Which pathway accurately describes the initial step in proline biosynthesis?

    <p>Glutamate's γ-carboxy group is converted to an anhydride.</p> Signup and view all the answers

    Which reaction results in the formation of alanine through transamination?

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

    What additional routes exist for glycine formation in mammals?

    <p>From serine and choline</p> Signup and view all the answers

    In collagen biosynthesis, hydroxyproline and hydroxylysine are important. What is a key characteristic of these amino acids?

    <p>They are formed post-translationally.</p> Signup and view all the answers

    Which enzyme catalyzes the synthesis of asparagine from aspartate?

    <p>Asparagine synthetase</p> Signup and view all the answers

    What role does tetrahydrobiopterin play in the metabolism of phenylalanine?

    <p>It provides reducing power derived from NADPH.</p> Signup and view all the answers

    Which metabolic pathway is involved in producing glycine aside from transamination?

    <p>Serine biosynthesis</p> Signup and view all the answers

    The reaction dependent on Mg-ATP is characteristic of which amino acid synthesizing enzyme?

    <p>Asparagine synthetase</p> Signup and view all the answers

    Which of these amino acids is considered a nonessential amino acid due to its synthesis in the body?

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

    What is a significant feature of the transamination reaction between pyruvate and glutamate?

    <p>It results in alpha-ketoglutarate.</p> Signup and view all the answers

    What is the primary role of asparagine in amino acid metabolism?

    <p>To serve as a precursor for glutamate synthesis</p> Signup and view all the answers

    What is the intermediate formed during the conversion of glutamate to glutamine?

    <p>γ-glutamyl phosphate</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of 3-phosphoglycerate to serine?

    <p>3-phosphoglycerate dehydrogenase</p> Signup and view all the answers

    Which amino acid conversion process is characterized by the use of both ammonium ion and glutamine as nitrogen sources?

    <p>Aspartate to asparagine</p> Signup and view all the answers

    What is the consequence of the coupled hydrolysis of PPi to Pi in the asparagine synthesis reaction?

    <p>It strongly favors the synthesis of asparagine</p> Signup and view all the answers

    Which compound provides the nitrogen in the enzyme-catalyzed reaction converting aspartate to asparagine?

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

    Which factor directly influences the cytotoxic ammonium ion concentration during the synthesis of glutamate?

    <p>The reductive amidation of α-ketoglutarate</p> Signup and view all the answers

    What type of reaction is the conversion of glutamate to glutamine primarily categorized as?

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

    In what metabolic pathway is the 3-phosphoglycerate dehydrogenase involved?

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

    What is the fate of the γ-amino group of the tetrahedral intermediate during the glutamine synthesis process?

    <p>It is released as a proton</p> Signup and view all the answers

    Which statement about the synthesis of tyrosine is true?

    <p>Tyrosine is classified as nutritionally semiessential.</p> Signup and view all the answers

    What role do glutamate dehydrogenase and glutamine synthetase play in amino acid biosynthesis?

    <p>They help incorporate the ammonium ion into amino acids.</p> Signup and view all the answers

    In individuals suffering from Marasmus, which amino acid synthesis deficiency could contribute to their condition?

    <p>Inadequate synthesis of tyrosine.</p> Signup and view all the answers

    Which amino acid is derived from the posttranslational modifications seen in collagen biosynthesis?

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

    What distinguishes nonessential amino acids from essential amino acids?

    <p>Nonessential amino acids can be synthesized by the body, though not always efficiently.</p> Signup and view all the answers

    Which pathway is involved in the biosynthesis of amino acids that include potentially toxic ammonium ions?

    <p>Combined enzymatic actions of multiple amino acid biosynthesis pathways.</p> Signup and view all the answers

    What is a significant consequence of Menkes Syndrome on amino acid metabolism?

    <p>Impaired copper transport affecting collagen formation.</p> Signup and view all the answers

    Which amino acid is not derived from the amino acids typically classified as nutritionally semiessential?

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

    Which statement is true regarding posttranslational modifications in amino acids?

    <p>They may lead to the formation of unique structural features in proteins.</p> Signup and view all the answers

    In the context of amino acid synthesis, what is a key reason why young children might experience growth issues?

    <p>Insufficient production of nutritionally semiessential amino acids.</p> Signup and view all the answers

    Which amino acids are classified as nutritionally essential according to their roles in tissue aminotransferase reactions?

    <p>Valine, Leucine, Isoleucine</p> Signup and view all the answers

    What is the enzymatic activity associated with the conversion of phenylalanine to tyrosine?

    <p>Hydroxylation that involves a co-factor deficiency</p> Signup and view all the answers

    Which of the following elements is NOT necessary for the hydroxylation of proline and lysine during collagen synthesis?

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

    In Menkes Syndrome, which bioelement is particularly deficient, impacting copper utilization?

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

    Which term describes amino acids that must be obtained from the diet due to the body's inability to synthesize them?

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

    What is the outcome when there is a deficiency of vitamin C in collagen biosynthesis?

    <p>Impaired stability of collagen and scurvy development</p> Signup and view all the answers

    Which amino acid is derived from the decarboxylation of α-ketoglutarate during metabolism?

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

    In the context of metabolic pathways, what is the primary role of aminotransferases regarding essential amino acids?

    <p>Interconverting amino acids and their corresponding α-keto acids</p> Signup and view all the answers

    Which of the following conditions is NOT associated with a deficiency in protein energy intake?

    <p>Diabetes mellitus</p> Signup and view all the answers

    Which of the following vitamins is essential for the reduction of dihydrobiopterin during amino acid metabolism?

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

    What condition is characterized by a dietary deficiency of vitamin C leading to bleeding gums and poor wound healing?

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

    Which disorder results from a lack of copper, affecting collagen biosynthesis and leading to symptoms like kinky hair and growth retardation?

    <p>Menkes syndrome</p> Signup and view all the answers

    Which disorder is caused by an impaired ability of connective tissue to form peptidy 4-hydroxyproline and 5-hydroxylysine due to nutritional deficiencies?

    <p>Ehlers-Danlos syndrome</p> Signup and view all the answers

    What condition might develop in a child weaned onto a starchy diet that lacks sufficient protein and calories?

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

    Which amino acid deficiencies can result in unstable collagen structure and lead to connective tissue disorders?

    <p>Proline and hydroxyproline</p> Signup and view all the answers

    Which genetic disorder is characterized by fragile bones and a deficiency in collagen synthesis?

    <p>Osteogenesis imperfecta</p> Signup and view all the answers

    What is a potential outcome of both caloric intake and specific amino acid deficiencies in patients with short bowel syndrome?

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

    What is the condition that results from a child being weaned onto a starchy diet lacking in protein?

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

    Which amino acid requires the most enzymatic steps for its synthesis according to the provided data?

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

    What type of dietary deficiency is predominantly associated with both kwashiorkor and marasmus?

    <p>Protein deficiency</p> Signup and view all the answers

    How many total enzymes are required for the synthesis of nutritionally nonessential amino acids as listed?

    <p>17</p> Signup and view all the answers

    Which of the following amino acids is NOT classified as nutritionally essential?

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

    In the context of amino acid metabolism, what is a significant characteristic of marasmus?

    <p>Overall caloric deficiency</p> Signup and view all the answers

    Which nutritionally essential amino acid requires both shared and non-shared enzymatic steps for its synthesis?

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

    Which of the following disorders is linked to specific amino acid metabolism due to deficiency?

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

    What dietary component is specifically mentioned as poor sources leading to amino acid deficiency in certain regions?

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

    Which specific elongation factor is involved in recognizing selenocysteyl-tRNASec for incorporation into proteins?

    <p>Selenocysteine insertion sequence binding protein</p> Signup and view all the answers

    What role do both procollagen-proline 4-hydroxylase and procollagen-lysine 5-hydroxylase play in collagen biosynthesis?

    <p>They catalyze mixed-function oxidase reactions that incorporate molecular oxygen.</p> Signup and view all the answers

    Which compound serves as a substrate for the production of cysteine in the body?

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

    Which enzyme is crucial for the redox reactions involving selenocysteine in the human body?

    <p>Thioredoxin reductase</p> Signup and view all the answers

    What is the likely impact of a deficiency in vitamin C on collagen synthesis?

    <p>It would lead to improper cross-linking of collagen fibers.</p> Signup and view all the answers

    What is the primary reaction that converts glutamate to proline in biosynthesis?

    <p>Reduction following cyclization of glutamate γ-semialdehyde</p> Signup and view all the answers

    Which enzyme is responsible for the hydrolytic removal of the phosphoryl group from phosphoserine?

    <p>Phosphoserine hydrolase</p> Signup and view all the answers

    What is a significant characteristic of the reaction converting phenylalanine to tyrosine?

    <p>It requires tetrahydrobiopterin as a cofactor.</p> Signup and view all the answers

    What is the ultimate precursor for cysteine synthesis in terms of nutritional importance?

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

    Which of the following statements about hydroxylated amino acids is true?

    <p>They do not have specific tRNAs for incorporation during translation.</p> Signup and view all the answers

    In the metabolic pathway of phenylalanine to tyrosine, what is the fate of the oxygen atoms involved in the reaction?

    <p>Both atoms are reduced to form water.</p> Signup and view all the answers

    What distinguishes the transformation of 3-phosphoglycerate to serine in amino acid metabolism?

    <p>It requires the action of a dehydrogenase enzyme.</p> Signup and view all the answers

    Which amino acid is derived from the hydrolysis of cystathionine?

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

    In collagen biosynthesis, what role do hydroxyproline and hydroxylysine play?

    <p>They enhance protein stability through cross-linking.</p> Signup and view all the answers

    What is the significance of the reaction catalyzed by cystathionine β-synthase in amino acid metabolism?

    <p>It links homocysteine and serine to form cystathionine.</p> Signup and view all the answers

    What is the key product formed from the amidation of glutamate catalyzed by glutamine synthetase?

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

    Which intermediate is formed during the conversion of glutamate to glutamine?

    <p>γ-Glutamyl phosphate</p> Signup and view all the answers

    What role does the hydrolysis of PPi to Pi play in the synthesis of asparagine?

    <p>It strongly favors the reaction.</p> Signup and view all the answers

    Which enzyme catalyzes the reaction that produces serine from 3-phosphoglycerate?

    <p>3-Phosphoglycerate dehydrogenase</p> Signup and view all the answers

    Which amino acid synthesis utilizes both ammonium ion and glutamine as nitrogen sources?

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

    During the synthesis of glutamate, what is the primary effect of reducing ammonium ion concentration?

    <p>It promotes more glutamate synthesis.</p> Signup and view all the answers

    What is the function of NH4+ in bacterial asparagine synthetases?

    <p>It provides a nitrogen source.</p> Signup and view all the answers

    Which reaction type does the conversion of aspartate to asparagine primarily represent?

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

    In terms of enzymatic activity, what initiates the reaction for the formation of γ-glutamyl phosphate during glutamine synthesis?

    <p>Binding of glutamate</p> Signup and view all the answers

    What is the final product released after the dephosphorylation step in the formation of serine from 3-phosphoglycerate?

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

    Match the following terms related to amino acids with their correct definitions:

    <p>Essential amino acids = Must be obtained from the diet Nutritionally nonessential amino acids = Can be synthesized by the body Transaminases = Enzymes that facilitate amino acid metabolism Scurvy = Disorder caused by vitamin C deficiency</p> Signup and view all the answers

    Match the following amino acids with their associated biosynthesis precursors:

    <p>Aspartate = Oxaloacetate Glutamate = α-Ketoglutarate Serine = 3-Phosphoglycerate Glycine = Threonine</p> Signup and view all the answers

    Match the vitamin with its role in amino acid metabolism:

    <p>Vitamin C = Prevents scurvy by aiding collagen synthesis Folate = Involved in amino acid metabolism Vitamin B6 = Coenzyme in transamination reactions Vitamin E = Antioxidant that protects cellular membranes</p> Signup and view all the answers

    Match the following amino acids with their nutritional classification:

    <p>Phenylalanine = Essential Glycine = Nutritionally nonessential Valine = Essential Glutamine = Nutritionally nonessential</p> Signup and view all the answers

    Match the following amino acids with their role in collagen biosynthesis:

    <p>Hydroxyproline = Stabilizes collagen structure Hydroxylysine = Involved in cross-linking of collagen Proline = Precursor for hydroxyproline Lysine = Precursor for hydroxylysine</p> Signup and view all the answers

    Match the following terms with their correct definitions:

    <p>Nutritionally essential amino acids = Amino acids that must be present in the human diet Nutritionally nonessential amino acids = Amino acids that do not need to be present in the diet Biosynthesis = The process of producing complex molecules from simpler ones ATP = A molecule that provides energy for biological processes</p> Signup and view all the answers

    Match the following classes of amino acids with their numbers:

    <p>Essential amino acids = 8 Nonessential amino acids = 12 Total common amino acids = 20 Enzymes for essential amino acids synthesis = Large relative to nonessential</p> Signup and view all the answers

    Match the following descriptions with the appropriate terms:

    <p>Plants and bacteria = Organisms that can synthesize certain amino acids Humans = Organisms that must obtain certain amino acids through diet Metabolically essential amino acids = Amino acids important for metabolism Reactions in biosynthesis = Chemical processes that produce amino acids</p> Signup and view all the answers

    Match the following historical aspects with their significance:

    <p>1930s = Period when the distinction of essential and nonessential amino acids was established Purified amino acids diet = Used to investigate amino acid requirements Neglect of certain biosynthesis pathways = Not discussed for humans in the context of amino acid Survival advantage = Benefit for retaining the ability to biosynthesize certain amino acids</p> Signup and view all the answers

    Match the following features to their correct descriptions:

    <p>Nutritionally essential = Must be ingested from food Nutritionally nonessential = Can be synthesized in the body Chemical reactions = Processes determining amino acid formation Dietary implications = Impact on amino acid availability for health</p> Signup and view all the answers

    Study Notes

    Amino Acid Metabolism

    • Certain amino acids are not essential for human health.
    • Essential vs Nutritionally essential amino acids are different.
      • 8 amino acids are nutritionally essential for humans.
      • 12 nutritionally non-essential amino acids can be synthesized metabolically.
    • The citric acid cycle and glycolysis intermediates are precursors for some amino acids (aspartate, asparagine, glutamate, glutamine, glycine, and serine).
    • Transaminases play a key role in amino acid metabolism.
    • 4-hydroxyproline and 5-hydroxylysine are formed in proteins like collagen.
    • Vitamin C deficiency (scurvy) impacts collagen formation.
    • Selenium, despite being toxic, is essential for selenocysteine, a component of some proteins.
    • A mixed-function oxidase is defined and its role in some reactions is outlined.
    • Tetrahydrobiopterin is a crucial component in tyrosine biosynthesis.
    • Modified tRNA is involved in selenocysteine insertion during protein synthesis.

    Biomedical Importance of Amino Acids

    • Amino acid deficiencies can arise from inadequate intake or absorption.
    • Kwashiorkor and marasmus are nutritional disorders caused by deficiencies.
    • Short bowel syndrome can lead to nutritional issues for patients.
    • Genetic disorders affect the formation of hydroxyproline and hydroxylysine in collagen.
    • Menkes syndrome, linked to a copper deficiency, affects collagen structure.

    Biosynthesis of Nonessential Amino Acids

    • Glutamate is derived from a-ketoglutarate via glutamate dehydrogenase.
    • Glutamine synthesis involves glutamine synthetase and y-glutamyl phosphate as intermediates.
    • Alanine and aspartate biosynthesis are via transamination of pyruvate and oxaloacetate, respectively.
    • Asparagine synthesizes via glutamines production.
    • Serine is formed by oxidation of 3-phosphoglycerate, via transamination and dephosphorylation
    • Glycine synthesis uses glyoxylate, glutamate, or alanine via aminotransferases.
    • Proline synthesis follows a pathway with glutamate y-semialdehyde as a crucial intermediate.
    • Cysteine is synthesized from methionine, with homocysteine and serine as intermediates.
    • Tyrosine production from phenylalanine requires phenylalanine hydroxylase.
    • Hydroxyproline and hydroxylysine's biosynthesis are specific to collagen.
    • The hydroxylases require vitamin C and molecular oxygen.
    • Valine, leucine, and isoleucine are interconverted by tissue aminotransferases.

    Selenocysteine

    • Selenocysteine (21st nonessential amino acid) is found in some proteins.
    • It's a crucial part of some enzymes involved in redox reactions.
    • Selenocysteine biosynthesis involves serine, selenate, ATP, specific tRNA (tRNASec), and multiple enzymes.
    • The selenocysteine insertion element (stem-loop in mRNA) guides correct incorporation.

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