Amino Acid Metabolism Overview
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Questions and Answers

Which compound acts as a nitrogen donor for most amino acids?

  • Glutamate (correct)
  • ATP
  • Ammonia
  • Glucose

    • Higher organisms cannot synthesize amino acids from fixed nitrogen.

    False (B)

    What is the process of reducing atmospheric nitrogen to ammonia called?

    nitrogen fixation

    Proteins to be degraded are tagged with __________.

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

    Match the following metabolic pathways with their role in amino acid synthesis:

    <p>Glycolysis = Provides carbon skeletons Citric Acid Cycle = Intermediate for amino acid synthesis Pentose Phosphate Pathway = Generates ribose 5-phosphate Nitrogen Fixation = Reduces nitrogen to ammonia</p> Signup and view all the answers

    Which of the following amino acids is considered essential in the human diet?

    <p>Histidine (D)</p> Signup and view all the answers

    Humans can synthesize all amino acids necessary for their survival without the need for dietary sources.

    <p>False (B)</p> Signup and view all the answers

    Name two biosynthetic pathways from which amino acids obtain their carbon skeletons.

    <p>glycolysis and pentose phosphate pathway</p> Signup and view all the answers

    The amino acid _____ can be synthesized from phenylalanine in one step.

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

    Match the amino acids to their classification as either essential or nonessential:

    <p>Glutamate = Nonessential Leucine = Essential Serine = Nonessential Lysine = Essential</p> Signup and view all the answers

    Which amino acid is synthesized directly from pyruvate?

    <p>Alanine (A)</p> Signup and view all the answers

    The majority of amino acids obtain nitrogen only from glutamate.

    <p>True (A)</p> Signup and view all the answers

    Identify one reason why some amino acids are classified as essential.

    <p>They require many biosynthetic steps for their synthesis.</p> Signup and view all the answers

    What happens to excess amino acids that are not needed for biosynthesis?

    <p>They are oxidized or converted to glycogen or fat. (D)</p> Signup and view all the answers

    All human proteins contain only a select few amino acids.

    <p>False (B)</p> Signup and view all the answers

    What condition results from extreme forms of malnutrition related to protein intake?

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

    Ammonia serves as the source of ___________ in all amino acids.

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

    Match the following processes or components with their descriptions:

    <p>Nitrogen fixation = Process that converts N2 to NH3 Klebsiella = Type of soil bacteria that can fix nitrogen Muscle proteins = Functional proteins that can be destroyed for amino acid supply Albumin = A serum protein affected by malnutrition</p> Signup and view all the answers

    What is required for combining nitrogen with hydrogen to produce ammonia?

    <p>Very high temperatures and high pressure (A)</p> Signup and view all the answers

    Nitrogen comprises about 50% of the Earth's atmosphere.

    <p>False (B)</p> Signup and view all the answers

    Name one type of bacteria that can fix nitrogen.

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

    What is the primary function of the nitrogenase complex in higher organisms?

    <p>To reduce N2 to NH3 (C)</p> Signup and view all the answers

    Higher organisms can fix nitrogen on their own.

    <p>False (B)</p> Signup and view all the answers

    How many ATP molecules are hydrolyzed to form two molecules of NH3?

    <p>16</p> Signup and view all the answers

    Leguminous plants rely on an O2-binding protein known as ______ to maintain low oxygen concentration in root nodules.

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

    Match the following amino acids with their sources of nitrogen:

    <p>Glutamine = Incorporates nitrogen from two ammonium ions Glutamate = Donates α-amino group in amino acid synthesis Tryptophan = Nitrogen sourced from Glutamine Histidine = Nitrogen sourced from Glutamate</p> Signup and view all the answers

    What percentage of the Earth's newly fixed nitrogen is accounted for by diazotrophic microorganisms?

    <p>60% (D)</p> Signup and view all the answers

    Ammonia is directly assimilated into amino acids without any modifications.

    <p>False (B)</p> Signup and view all the answers

    The majority of amino acids other than Glu and Gln obtain their nitrogen from ______ or ______.

    <p>Glu, Gln</p> Signup and view all the answers

    Which amino acids must be obtained from the diet?

    <p>Essential amino acids (B)</p> Signup and view all the answers

    Ubiquitin is involved in the degradation of proteins in eukaryotic cells.

    <p>True (A)</p> Signup and view all the answers

    What is the significance of insulin's half-life?

    <p>Insulin has a short half-life of approximately 1 hour, indicating its role in regulating blood sugar levels quickly.</p> Signup and view all the answers

    Ubiquitin attaches to the target protein at the ______ group of lysine residues.

    <p>ε-amino</p> Signup and view all the answers

    Match the enzymes involved in ubiquitin conjugation to their functions:

    <p>E1 = Ubiquitin-activating enzyme that adenylates ubiquitin E2 = Ubiquitin-conjugating enzyme that transfers ubiquitin E3 = Ubiquitin–protein ligase that facilitates ubiquitin transfer to target protein ATP = Required for the activity of E1 and E3</p> Signup and view all the answers

    What condition is associated with a defect in E3 proteins?

    <p>Angelman syndrome (C)</p> Signup and view all the answers

    Protein turnover is a constant process that only happens during cell division.

    <p>False (B)</p> Signup and view all the answers

    What role does ubiquitin play in the degradation of proteins?

    <p>Ubiquitin tags proteins for degradation, signaling that they should be broken down by the proteasome.</p> Signup and view all the answers

    Which enzymes are primarily involved in the interconversion of amino acids?

    <p>Aspartate aminotransferase and alanine aminotransferase (A)</p> Signup and view all the answers

    Glutamate is not involved in aminotransferase reactions.

    <p>False (B)</p> Signup and view all the answers

    What role does aminotransferase play in the metabolism of amino acids?

    <p>It transfers amino groups to alpha-keto acids.</p> Signup and view all the answers

    Alanine is formed by the reaction of __________ and glutamate.

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

    Match the following compounds with their corresponding roles.

    <p>Aspartate = Product of oxaloacetate and glutamate reaction Alanine = Product of pyruvate and glutamate reaction α-ketoglutarate = A common reactant in transamination Oxaloacetate = Intermediate in citric acid cycle</p> Signup and view all the answers

    What is the main clinical significance of measuring serum AST and ALT levels?

    <p>To detect liver disease (A)</p> Signup and view all the answers

    Hepatic cell injury results in decreased serum aminotransferase activity.

    <p>False (B)</p> Signup and view all the answers

    What cofactor is required for the activity of aminotransferases?

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

    Flashcards

    Protein Synthesis

    The process of creating proteins using genetic information encoded in DNA and RNA. It involves two main steps: transcription (DNA to RNA) and translation (RNA to protein).

    Amino Acids

    A group of 20 different amino acids that are the building blocks of proteins. Each amino acid has a unique structure and properties.

    Nitrogen Fixation

    The process of converting atmospheric nitrogen gas into ammonia (NH3). This is a crucial step for living organisms as they cannot directly use nitrogen gas.

    Ubiquitin

    A molecule that acts as a tag for proteins that need to be broken down. This tag signals the cell's machinery to degrade the protein.

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    Protein Degradation

    The process of breaking down proteins into smaller amino acids. This occurs at variable rates depending on the protein and the cell's needs.

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    Essential Amino Acids

    Amino acids that cannot be synthesized by the body and must be obtained through diet.

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    Protein Turnover

    The process of breaking down and resynthesizing proteins within cells.

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    Protein Half-Life

    The amount of time it takes for half of a protein to be degraded.

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    Ubiquitin-Activating Enzyme (E1)

    An enzyme that activates ubiquitin by attaching it to a cysteine residue.

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    Ubiquitin-Conjugating Enzyme (E2)

    An enzyme that transfers ubiquitin to its own cysteine residue.

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    Ubiquitin-Protein Ligase (E3)

    An enzyme that brings E2 and the target protein together to attach ubiquitin.

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    Ubiquitin Chain (4+)

    A chain of four or more ubiquitin molecules that strongly signals for protein degradation.

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    Amino Acid Excess

    Excess amino acids are not stored for later use, but are either oxidized for energy or converted into glycogen or fat.

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    Kwashiorkor

    A condition caused by severe protein deficiency, characterized by muscle wasting, growth retardation, and fluid buildup (edema).

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    Amino Acid Biosynthesis

    A process that uses ammonia (NH3) derived from nitrogen fixation as a source of nitrogen to synthesize amino acids.

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    Protein Digestion & Degradation

    The breakdown of ingested dietary proteins and the degradation of proteins within cells, yielding amino acids.

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    Nitrogen Excretion

    The process of removing excess nitrogen from the body, primarily in the form of urea.

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    Nonessential amino acids

    Amino acids that can be synthesized by the body from other molecules, given sufficient dietary intake.

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    Transamination

    The process of adding an amino group to an alpha-keto acid, forming an amino acid. It is a key step in amino acid biosynthesis.

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    Aminotransferases

    A family of enzymes that catalyze transamination reactions, involving the transfer of an amino group from an amino acid to an alpha-keto acid.

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    Glutamate and glutamine

    The primary source of nitrogen for the synthesis of many amino acids in the body.

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    Metabolic pathways providing carbon skeletons

    Glycolysis, pentose phosphate pathway, and the citric acid cycle are all metabolic pathways that provide carbon skeletons for the synthesis of amino acids.

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    Biosynthesis of amino acids

    The synthesis of amino acids that involves multiple steps and enzymes. These amino acids are often essential because the body has lost some of the enzymes needed for their synthesis over evolution.

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    Nitrogenase Complex

    The enzyme responsible for nitrogen fixation, it uses electrons to convert nitrogen gas into ammonia.

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    Leghemoglobin

    A protein found in root nodules, it binds oxygen and prevents it from inhibiting the nitrogenase complex, allowing nitrogen fixation to occur alongside energy production.

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    Ammonium Assimilation

    The process of incorporating ammonia (NH3) into amino acids, primarily glutamate and glutamine. This process is essential for the synthesis of other amino acids

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    Glutamate Dehydrogenase

    An enzyme that catalyzes the reductive amination of α-ketoglutarate to glutamate, using NADPH as a reducing agent.

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    Glutamine Synthetase

    An enzyme that catalyzes the incorporation of ammonia into glutamate to form glutamine, using ATP as energy.

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    Amino Acid Synthesis

    The process of synthesizing amino acids from intermediates of major metabolic pathways - glycolysis, the citric acid cycle, and the pentose phosphate pathway

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    Carbon Skeletons for Amino Acid Synthesis

    The process of providing carbon skeletons for the synthesis of amino acids, primarily from intermediates of glycolysis, the citric acid cycle, and the pentose phosphate pathway.

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    What are aminotransferases?

    Enzymes that catalyze the transfer of an amino group from one molecule to another, often involving an alpha-keto acid and an amino acid.

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    What does alanine aminotransferase (ALT) do?

    The interconversion of pyruvate and glutamate to alanine and α-ketoglutarate.

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    What does aspartate aminotransferase (AST) do?

    The interconversion of oxaloacetate and glutamate to aspartate and α-ketoglutarate.

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    What's the role of glutamate in aminotransferases?

    A central component of the urea cycle, a process for removing excess nitrogen from the body. It acts as a 'gateway' for nitrogen from almost all amino acids, transferring it to α-ketoglutarate.

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    What role do aminotransferases play in clinical diagnosis?

    Elevated serum aminotransferase activity, often due to liver damage, can indicate potential liver disease. This is measured clinically to diagnose health problems.

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    Why do proteins get degraded?

    Protein degradation provides amino acids from both dietary intake and cellular breakdown. This is needed for various functions, including energy production.

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    What happens to extra amino acids?

    Excess amino acids, beyond what the body needs for synthesis and essential functions, are processed for energy production or converted into other molecules like glycogen or fat.

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    How are amino acids acquired from food?

    Dietary proteins are broken down into amino acids in the digestive system, then absorbed and transported in the bloodstream.

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    Study Notes

    Amino Acid Metabolism 1

    • Amino acid metabolism and protein turnover are connected and provide a steady supply of amino acids.
    • Cellular proteins are broken down and re-synthesised in response to metabolic demands.
    • Primary use of amino acids is for building blocks in protein synthesis and other nitrogenous compounds such as nucleotide bases, heme, and neurotransmitters.
    • Excess amino acids are not stored but used as metabolic fuel, oxidized, or converted to glycogen or fat.
    • Amino acid metabolism and protein turnover are linked to basic biochemistry and clinical medicine.
    • All 20 amino acids are found in virtually all human proteins. Deficiencies in even one can affect important proteins (e.g. muscle proteins and hemoglobin).
    • Malnutrition, in extreme cases like Kwashiorkor, leads to muscle wasting, apathy, impaired growth, brain damage, and reduced serum protein levels (like albumin), ultimately causing tissue edema.
    • Learning Objectives include how nitrogen is incorporated into amino acids/proteins, transported, controls protein turnover, manages excess nitrogen, and identifies metabolic errors.
    • Ammonia is the source of nitrogen in all amino acids.
    • Carbon backbones for amino acid synthesis come from glycolytic, pentose phosphate, or the citric acid cycle pathways.
    • Nitrogen fixation, a process reducing N2 to NH3 (ammonia), is crucial.
    • Microorganisms like soil bacteria (Klebsiella, Azotobacter, cyanobacteria) or symbiotic bacteria (Rhizobium) in root nodules can fix nitrogen; higher organisms cannot.
    • Nitrogen fixation needs a nitrogenase complex (a reductase and iron-molybdenum-containing nitrogenase) at specific conditions (10°C, 1atm or 100kPa)
    • At least 16 ATP molecules are hydrolysed to form two molecules of NH3 during nitrogen fixation.
    • Diazatrophic microorganisms fix 10¹¹ Kg of nitrogen per year, of which 60% is newly fixed nitrogen.
    • Ammonia can be obtained from the reduction of the nitrate ion (NO3⁻).
    • Low oxygen concentration in root nodules is crucial to support nitrogenase action as nitrogenase is extremely sensitive to inactivation by O2 (oxygen).
    • Leguminous plants maintain a low O2 concentration in their root nodules with an O2-binding protein (leghemoglobin).
    • Ammonium ion is assimilated into amino acids through glutamate and glutamine.
    • Glutamate and Glutamine act as nitrogen donors for most amino acids.
    • Glu contributes to the a-amino group while Gln contributes to the side-chain nitrogen atom for the synthesis of specific amino acids (e.g. Trp and His).
    • Glutamate dehydrogenase is the key enzyme that allows for this process.
    • A second ammonium ion is incorporated into glutamate to create glutamine.
    • The majority of amino acids that are produced from Glu or Gln obtain their nitrogen from.
    • Carbon skeletons for amino acid synthesis are obtained from intermediates of glycolysis, the citric acid cycle, and the pentose phosphate pathway.
    • Amino acids are categorised into biosynthetic families based on their precursors.
    • Some amino acids can be synthesized by humans; others must be obtained through the diet.
    • 9 amino acids are considered essential as they cannot be synthesized by humans and must be obtained from the diet.
    • Some amino acids such as tyrosine can sometimes be considered essential but can be synthesized in one step from phenylalanine.
    • 11 amino acids that are nonessential are those that can be synthesized by the body if dietary intake is sufficient.
    • Those amino acids needing many steps in synthesis are essential because some of the required enzymes were lost during evolution.
    • Glutamate, aspartate, and alanine are formed by adding an amino group to alpha-ketoacids.
    • Transamination reactions, catalysed by pyridoxal phosphate-dependent aminotransferases, are key for these syntheses.
    • Aminotransferases (or transaminases) catalyze interconversion of amino acids and alpha-keto acids via the transfer of amino groups.
    • Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are the two aminotransferases with significant clinical value in diagnosing liver disease.
    • Elevated serum aminotransferase activity indicates damage to liver cells prior to clinical symptoms.
    • Liver damage can result from viral hepatitis, excessive alcohol consumption, and reactions to certain drugs (such as acetaminophen).
    • Aminotransferases need the cofactor pyridoxal phosphate.
    • Protein turnover describes the degradation and resynthesis of proteins in cells.
    • Protein turnover is important in removing damaged proteins and for adjusting to metabolic demands.
    • Protein half-lives in cells vary widely; proteins have different turnover rates (from minutes to the life of the organism).
    • Proteins that are degraded use Ubiquitin which is a small protein (76 aa).
    • Ubiquitin tags proteins for destruction in all eukaryotic cells.
    • Ubiquitin attaches through Its Gly terminal to the target proteins amino groups.
    • ATP hydrolysis is required for this process.
    • Three enzymes (E1, E2, E3) are involved in the Attachment and transfer of ubiquitin to a protein.
    • Defective E3 enzymes can cause the accumulation of proteins and lead to diseases of protein aggregation.
    • Examples include Angelman Syndrome and a link to autism.
    • Protein turnover is important for normal cell function, and improper turnover can lead to diseases.

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    Amino Acid Metabolism 1 - Danny Zisterer PDF

    Description

    Explore the interconnected processes of amino acid metabolism and protein turnover. Understand how amino acids serve as building blocks for proteins and other essential compounds, as well as the consequences of deficiencies and malnutrition. This quiz covers essential concepts in biochemistry and clinical medicine.

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