Amino Acid Metabolism - Flashcards
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Assertion: At physiological pH, amino acids exist predominantly as zwitterions. Reason: Their amino groups are protonated and carboxyl groups deprotonated.
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2
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Assertion: Glycine is the only non‐chiral amino acid. Reason: Its side chain is a hydrogen atom, which makes its alpha carbon achiral.
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3
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Assertion: The basic structure of an amino acid consists of a central alpha carbon attached to an amino group, a carboxyl group, a hydrogen atom, and an R group. Reason: This tetrahedral arrangement is necessary for protein formation.
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4
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Assertion: Amino acids polymerize to form proteins. Reason: Peptide bonds are formed via condensation reactions between the carboxyl group of one amino acid and the amino group of another.
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5
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Assertion: The twenty common amino acids are encoded by the genetic code. Reason: Although 22 alpha‐amino acids exist, only 20 are routinely used in proteins.
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6
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Assertion: The alpha carbon in amino acids (except glycine) is chiral. Reason: It is bonded to four distinct groups.
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7
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Assertion: Amino acids are classified based on the nature of their side chains. Reason: The R groups determine properties such as polarity, charge, and size.
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8
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Assertion: Non‐polar amino acids are hydrophobic. Reason: Their side chains consist mainly of aliphatic or aromatic groups that do not interact with water.
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9
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Assertion: Aromatic amino acids absorb UV light at 280 nm. Reason: Their aromatic rings enable this absorption.
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10
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Assertion: Polar uncharged amino acids can form hydrogen bonds. Reason: Their side chains contain electronegative atoms such as oxygen which facilitate bonding.
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11
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Assertion: Acidic amino acids are negatively charged at physiological pH. Reason: Their side chains contain carboxyl groups that are deprotonated in neutral conditions.
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12
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Assertion: Basic amino acids are positively charged at physiological pH. Reason: Their side chains have groups that accept protons.
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13
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Assertion: Essential amino acids cannot be synthesized by the body. Reason: They must be obtained from the diet due to the lack of endogenous synthesis pathways.
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14
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Assertion: Non‐essential amino acids can be synthesized by the human body. Reason: The enzymes and pathways exist to produce these amino acids from precursor molecules.
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15
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Assertion: Conditionally essential amino acids become essential under certain circumstances. Reason: Under stress or illness the body’s production of these amino acids may be insufficient.
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16
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Assertion: Branched‐chain amino acids include leucine, isoleucine, and valine. Reason: Their side chains have a branched aliphatic structure.
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17
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Assertion: Hydroxyl‐containing amino acids such as serine and threonine contain –OH groups. Reason: These groups enable them to participate in hydrogen bonding and phosphorylation.
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18
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Assertion: Sulfur‐containing amino acids include cysteine and methionine. Reason: Their side chains contain sulfur atoms which are important for redox reactions and disulfide bond formation.
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19
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Assertion: Aromatic amino acids include phenylalanine, tyrosine, and tryptophan. Reason: They contain aromatic rings that are key to their chemical properties.
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20
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Assertion: In amino acids, the R group largely determines water solubility. Reason: The chemical nature of the side chain (polar vs. non-polar) governs interactions with water molecules.
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21
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Assertion: Both D and L forms of amino acids exist. Reason: They are stereoisomers (enantiomers) resulting from the chiral nature of the alpha carbon.
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22
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Assertion: Zwitterions contribute to protein stability. Reason: The internal ionic bonds within zwitterionic molecules enable stable folding patterns.
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23
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Assertion: The protonation states of amino acids are influenced by pH. Reason: pH affects the ionization of the amino and carboxyl groups.
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24
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Assertion: Glycine’s simple structure confers flexibility in proteins. Reason: Its minimal side chain (a single hydrogen) allows tighter packing in protein structures.
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25
Assertion: Amino acids in peptides are linked by peptide bonds. Reason: A condensation reaction between the carboxyl and amino groups forms these bonds.
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Assertion: The tetrahedral geometry of the alpha carbon is crucial for protein folding. Reason: It ensures a specific three-dimensional arrangement necessary for biological function.
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27
Assertion: Amino acids exhibit diverse chemical functionalities. Reason: The variety in their R groups enables them to participate in a range of biochemical reactions.
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Assertion: The chirality of amino acids (except glycine) contributes to protein stereochemistry. Reason: Proteins are composed predominantly of L–amino acids which affect folding and function.
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29
Assertion: The structure of amino acids is central to their role in metabolism. Reason: Their functional groups are involved in reactions such as transamination and decarboxylation.
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30
Assertion: The carboxyl group in amino acids imparts acidic properties. Reason: It can donate a proton in solution.
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31
Assertion: The amino group in amino acids gives them basic properties. Reason: It can accept a proton in solution.
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Assertion: Amino acids are the building blocks of proteins. Reason: They link together via peptide bonds to form polypeptide chains.
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Assertion: Variations in the R groups of amino acids influence enzyme activity. Reason: Different side chains interact uniquely with enzyme active sites.
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Assertion: Amino acid solubility in water is determined by the nature of their side chains. Reason: Hydrophilic side chains enhance water solubility while hydrophobic ones reduce it.
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Assertion: Certain amino acids can function as neurotransmitters. Reason: Some amino acids or their derivatives, like glycine, have direct roles in cell signaling.
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Assertion: Glycine serves as an inhibitory neurotransmitter in the central nervous system. Reason: It binds to receptors that cause hyperpolarization in neurons.
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Assertion: The 280 nm UV absorption property of aromatic amino acids is useful for quantifying protein concentration. Reason: Their aromatic rings absorb UV light, serving as a basis for spectrophotometric assays.
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Assertion: The common structure of amino acids underlies their ability to form proteins. Reason: A uniform backbone enables repetitive peptide bond formation.
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Assertion: The existence of D– and L–amino acids contributes to biological specificity. Reason: Proteins are almost exclusively synthesized from L–amino acids.
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40
Assertion: Zwitterions are overall electrically neutral molecules. Reason: The positive and negative charges on amino acids cancel each other out.
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41
Assertion: The uniqueness of each amino acid is determined by its side chain. Reason: Variations in the R group affect physical and chemical properties.
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Assertion: Amino acids can engage in hydrogen bonding, ionic interactions, and hydrophobic contacts. Reason: Their diverse side chains allow multiple types of molecular interactions.
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Assertion: The structure of amino acids is highly conserved across different organisms. Reason: The universal genetic code specifies the same 20 standard amino acids.
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Assertion: Amino acids play key roles in enzyme structure and function. Reason: They form active sites and structural frameworks within enzymes.
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Assertion: Peptide bond formation is a dehydration synthesis reaction. Reason: Water is eliminated when the carboxyl group of one amino acid binds to the amino group of another.
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Assertion: The chiral nature of amino acids (except glycine) influences protein secondary structure. Reason: Chirality affects the folding patterns of polypeptide chains.
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Assertion: Amino acid metabolism contributes to energy production. Reason: Catabolic breakdown products enter the citric acid cycle for ATP generation.
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Assertion: The R group in amino acids can influence enzyme specificity. Reason: Variations in side chain structure affect substrate binding to enzymes.
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Assertion: Amino acids participate in cell signaling processes. Reason: Some amino acid derivatives, such as neurotransmitters, act as signaling molecules.
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Assertion: The ability of amino acids to form hydrogen bonds is critical for establishing protein tertiary structure. Reason: Hydrogen bonds stabilize the three-dimensional conformation of proteins.
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Assertion: Amino acids are classified into groups based on their side chain functional groups. Reason: Functional group variations dictate properties such as polarity and charge.
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Assertion: Aliphatic amino acids are generally non–polar. Reason: Their side chains contain only carbon and hydrogen atoms.
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Assertion: Aromatic amino acids are hydrophobic in nature. Reason: Their aromatic rings limit interactions with water.
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Assertion: Polar uncharged amino acids are hydrophilic. Reason: Their side chains contain electronegative atoms that facilitate hydrogen bonding.
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Assertion: Acidic amino acids carry a negative charge at physiological pH. Reason: Their side chains possess carboxyl groups that are deprotonated.
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Assertion: Basic amino acids are positively charged at physiological pH. Reason: Their side chains have groups capable of accepting protons.
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Assertion: Phenylalanine is classified as a purely non–polar amino acid. Reason: Its benzene ring does not favor interactions with water.
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Assertion: Tyrosine is categorized as an aromatic amino acid despite having a hydroxyl group. Reason: The aromatic ring predominantly determines its chemical behavior.
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Assertion: Tryptophan has a complex bicyclic structure. Reason: Its indole group contributes to its hydrophobic character and unique UV absorption.
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Assertion: Asparagine is classified as a polar uncharged amino acid. Reason: Its side chain contains an amide group that does not ionize at physiological pH.
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Assertion: Glutamine is similar to asparagine with regard to functional groups. Reason: Both contain amide side chains derived from their corresponding acidic amino acids.
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Assertion: The grouping of amino acids as essential and non–essential is based on biosynthetic capability. Reason: Essential amino acids cannot be synthesized by the organism and must come from the diet.
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Assertion: Arginine is considered a conditionally essential amino acid under certain physiological conditions. Reason: Though it can be synthesized, increased demand during stress may exceed synthesis.
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Assertion: Branched–chain amino acids play a vital role in muscle metabolism. Reason: They serve as important energy sources during prolonged exercise.
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Assertion: Hydroxyl–containing amino acids such as serine and threonine are targets for phosphorylation. Reason: Their hydroxyl groups serve as sites for kinase activity.
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Assertion: Sulfur–containing amino acids (methionine and cysteine) participate in redox reactions. Reason: The sulfur atom in their side chains is prone to oxidation and reduction.
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Assertion: The classification of amino acids into glucogenic and ketogenic is based on their catabolic products. Reason: Some amino acids are broken down into intermediates for gluconeogenesis while others yield ketone bodies.
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Assertion: Leucine is considered a purely ketogenic amino acid. Reason: Its catabolism produces acetyl–CoA exclusively, without gluconeogenic precursors.
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Assertion: Lysine is classified as a purely ketogenic amino acid. Reason: Its degradation pathway results solely in acetyl–CoA formation.
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Assertion: Isoleucine is both glucogenic and ketogenic. Reason: Its breakdown produces intermediates that contribute to both glucose production and ketone body formation.
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Assertion: Phenylalanine is both glucogenic and ketogenic. Reason: Its catabolism yields intermediates that can feed into both gluconeogenesis and ketogenesis.
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Assertion: Tryptophan is both glucogenic and ketogenic. Reason: It is degraded into intermediates contributing to both glucose and ketone body synthesis.
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Assertion: Threonine is primarily glucogenic. Reason: Its catabolic pathway yields intermediates that lead to glucose production.
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Assertion: Aspartate is classified as a glucogenic amino acid. Reason: It is converted into oxaloacetate during metabolism.
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Assertion: Glutamate plays a central role in amino acid metabolism. Reason: It serves as a key amino group donor in transamination reactions.
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Assertion: AST is an aminotransferase enzyme. Reason: It catalyzes the reversible transfer of an amino group from aspartate to alpha–ketoglutarate.
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Assertion: ALT is used as a biomarker for liver function. Reason: Elevated ALT levels indicate hepatocellular injury.
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Assertion: Proline cannot undergo standard transamination reactions. Reason: Its secondary amino group interferes with PLP binding.
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Assertion: The classification of amino acids into essential and non–essential also depends on dietary intake. Reason: The body synthesizes non–essential amino acids to compensate for dietary insufficiencies.
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Assertion: Under stress, some non–essential amino acids become conditionally essential. Reason: Their synthesis may not meet the increased metabolic demand.
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Assertion: The aromatic ring in amino acids enhances UV absorbance. Reason: Aromatic groups strongly absorb UV light, aiding in spectrophotometric protein assays.
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Assertion: The amide side chains of asparagine and glutamine contribute to protein stability. Reason: They are capable of forming multiple hydrogen bonds.
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Assertion: The hydrophobic nature of aliphatic amino acids drives protein folding. Reason: They tend to be buried in the interior of proteins away from water.
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Assertion: Carboxyl groups in acidic amino acids serve as nucleophiles in enzyme active sites. Reason: Their negative charge attracts electrophilic substrates.
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Assertion: The cationic side chains of basic amino acids facilitate binding to nucleic acids. Reason: Positive charges interact with the negatively charged phosphate backbone of DNA and RNA.
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Assertion: Vitamin B6 in its PLP form is essential for transamination reactions. Reason: PLP acts as an intermediate carrier of amino groups during these reactions.
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Assertion: Transamination reactions are reversible. Reason: The equilibrium between amino acids and their corresponding keto acids allows metabolic flexibility.
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Assertion: The genetic code restricts protein synthesis to 20 standard amino acids. Reason: Although more than 20 exist, only 20 are incorporated into proteins under normal conditions.
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Assertion: Variations in amino acid side chains affect the overall charge and isoelectric point of proteins. Reason: The mix of acidic, basic, and neutral amino acids determines protein charge properties.
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Assertion: The classification of amino acids has nutritional and metabolic implications. Reason: Dietary requirements depend on the availability of essential versus non–essential amino acids.
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Assertion: Amino acids with branched side chains can regulate metabolic signaling pathways. Reason: They modulate signal transduction through their catabolic intermediates.
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Assertion: The presence of specific amino acids at enzyme active sites is critical for substrate specificity. Reason: Side chains directly interact with substrates to facilitate catalysis.
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Assertion: Structural differences among amino acids contribute to the diversity of protein function. Reason: Variations in side chains affect protein folding and activity.
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Assertion: Amino acids may undergo post-translational modifications. Reason: Chemical modifications of side chains can regulate protein function and interactions.
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Assertion: The dietary quality of proteins is influenced by amino acid composition. Reason: A balanced mix of essential and non–essential amino acids is required for optimal nutrition.
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Assertion: The oxidative deamination of glutamate is catalyzed by glutamate dehydrogenase. Reason: This enzyme is a complex allosteric protein regulated by ADP, GDP, ATP, and GTP.
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Assertion: The coupling of transamination with oxidative deamination is termed transdeamination. Reason: This process channels amino groups from various amino acids into a common deamination pathway via glutamate.
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Assertion: Glutamate dehydrogenase links amino acid catabolism to the citric acid cycle. Reason: It converts glutamate into α–ketoglutarate, a citric acid cycle intermediate.
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Assertion: Elevated serum levels of glutamate dehydrogenase indicate liver damage. Reason: Hepatocyte injury releases this mitochondrial enzyme into the bloodstream.
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Assertion: In mammals, nearly all amino acids can undergo transamination except lysine and threonine. Reason: Their molecular structures are not conducive to PLP-dependent aminotransferase reactions.
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Assertion: Proline is excluded from PLP-dependent reactions. Reason: Its secondary amino group precludes the formation of a Schiff base with PLP.
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102
Assertion: Decarboxylation of amino acids results in the formation of biologically active amines. Reason: Removal of the carboxyl group as CO₂ produces compounds such as dopamine and serotonin.
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Assertion: Histamine is produced by the decarboxylation of histidine. Reason: The removal of the carboxyl group from histidine generates histamine, an important mediator of immune responses.
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Assertion: The decarboxylation of 5–hydroxytryptophan produces serotonin. Reason: By removing CO₂ from 5–hydroxytryptophan, serotonin—a neurotransmitter—is formed.
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Assertion: Transaminase activity is critical for amino acid turnover. Reason: These enzymes enable the reversible transfer of amino groups between amino acids and keto acids.
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Assertion: Formation of a Schiff base is a key step in the mechanism of aminotransferases. Reason: PLP forms a covalent intermediate with the amino acid substrate via a Schiff base linkage.
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Assertion: Transamination reactions are reversible. Reason: The equilibrium between amino acids and their corresponding keto acids allows bidirectional amino group transfer.
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Assertion: The conversion of phenylalanine to tyrosine is an anabolic process. Reason: It requires phenylalanine hydroxylase and the cofactor tetrahydrobiopterin for the hydroxylation reaction.
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Assertion: In phenylketonuria (PKU), tyrosine becomes essential. Reason: A deficiency in phenylalanine hydroxylase prevents the conversion of phenylalanine to tyrosine.
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110
Assertion: The oxidative deamination of glutamate produces ammonia. Reason: Removal of the amino group via glutamate dehydrogenase releases ammonia, which is processed by the urea cycle.
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Assertion: Glutamate dehydrogenase is allosterically inhibited by ATP. Reason: High cellular energy levels (reflected by ATP and GTP) downregulate oxidative deamination.
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112
Assertion: GDP and ADP act as allosteric activators of glutamate dehydrogenase. Reason: Their presence signals low cellular energy, thereby promoting amino acid oxidation.
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113
Assertion: Transdeamination involves both transamination and oxidative deamination. Reason: This coupled process efficiently disposes of amino groups from various amino acids via glutamate.
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114
Assertion: The integration of amino acid catabolism with the citric acid cycle is a key metabolic adaptation. Reason: Carbon skeletons from amino acids are converted into intermediates for ATP production.
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115
Assertion: Regulation of transamination and deamination reactions is critical for nitrogen balance. Reason: These processes prevent toxic ammonia accumulation while providing energy.
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Assertion: Aminotransferases such as AST and ALT serve as biomarkers for liver disease. Reason: Damage to hepatocytes results in leakage of these enzymes into the serum.
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Assertion: The rate of amino acid decarboxylation influences neurotransmitter levels. Reason: Decarboxylation produces active amines, such as dopamine and serotonin, which act as neurotransmitters.
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Assertion: Decarboxylation of DOPA yields dopamine. Reason: Removal of the carboxyl group from DOPA produces dopamine, which functions as a neurotransmitter.
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119
Assertion: The PLP-dependent enzyme mechanism is highly conserved. Reason: It is essential for the metabolism of nearly all amino acids through transamination.
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Assertion: Oxidative deamination predominantly occurs in liver mitochondria. Reason: The liver is the primary site for amino acid catabolism leading to urea production.
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Assertion: The activity of glutamate dehydrogenase is modulated by the cellular energy charge. Reason: High ATP and GTP levels inhibit its activity, conserving energy when cellular supplies are ample.
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Assertion: In transamination reactions, PLP acts as a carrier for amino groups. Reason: It forms reversible covalent bonds with substrates during amino group transfer.
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Assertion: The allosteric regulation of glutamate dehydrogenase is a key control point in amino acid metabolism. Reason: It balances amino acid oxidation with the cell's energy state.
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124
Assertion: The metabolic fate of an amino acid is dictated by its side chain structure. Reason: The chemical properties of the R group determine if an amino acid is glucogenic, ketogenic, or both.
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125
Assertion: In certain metabolic disorders, the inability to convert phenylalanine to tyrosine requires dietary intervention. Reason: In phenylketonuria (PKU), deficient phenylalanine hydroxylase forces tyrosine to become an essential amino acid.
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126
Assertion: The reversibility of Schiff base formation in aminotransferases is crucial for enzyme function. Reason: It enables the transfer of amino groups in both forward and reverse reactions.
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Assertion: Efficient amino acid catabolism contributes to overall energy homeostasis. Reason: Carbon skeletons from amino acids enter the citric acid cycle, providing substrates for ATP synthesis.
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128
Assertion: Enzymatic decarboxylation of amino acids produces compounds with significant physiological roles. Reason: Removal of the carboxyl group forms bioactive amines essential for neurotransmission.
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Assertion: The interconversion between amino acids and keto acids is a dynamic process. Reason: It allows organisms to adapt to varying nutritional and energetic demands.
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Assertion: Transamination reactions require essential cofactors for optimal activity. Reason: Vitamin B6, in the form of PLP, is indispensable for the aminotransferase mechanism.
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Assertion: Variations in amino acid catabolic pathways reflect evolutionary adaptations. Reason: Different tissues preferentially utilize specific amino acids based on metabolic needs.
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Assertion: Glutamate is the principal amino acid involved in nitrogen transport. Reason: It participates extensively in transamination reactions to redistribute nitrogen throughout the body.
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Assertion: The liver is central to amino acid metabolism. Reason: It contains the enzymes necessary for deamination, transamination, and urea synthesis.
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134
Assertion: The coupling of oxidative deamination with transamination (transdeamination) provides an efficient route for amino group disposal. Reason: It channels amino groups from diverse amino acids into a common pathway via glutamate.
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Assertion: Increased glutamate dehydrogenase activity is indicative of metabolic stress. Reason: It reflects an increased need for energy production from amino acid catabolism under stress conditions.
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136
Assertion: The coenzyme PLP is converted between an aldehyde and aminated form during transamination. Reason: This reversible transformation is essential for the dynamic transfer of amino groups.
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137
Assertion: The formation of neurotransmitters from amino acids involves decarboxylation. Reason: Removing the carboxyl group from amino acids such as DOPA and histidine yields dopamine and histamine, respectively.
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138
Assertion: The mechanisms of transamination are crucial for maintaining the amino acid pool within cells. Reason: They allow for the flexible redistribution of amino groups in response to metabolic needs.
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139
Assertion: The balance between anabolic and catabolic pathways in amino acid metabolism is tightly regulated. Reason: Coordinated control ensures that energy production and biosynthetic demands are met simultaneously.
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140
Assertion: A deficiency in PLP adversely affects multiple amino acid-dependent pathways. Reason: Vitamin B6 is essential for all PLP-dependent enzymes, including those in transamination.
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141
Assertion: Post-translational modification of amino acid residues can modulate enzyme activity. Reason: Chemical alterations of side chains can change protein conformation and function.
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142
Assertion: The integration of amino acid metabolism with glycolysis and the citric acid cycle is essential for metabolic homeostasis. Reason: It connects nitrogen disposal with energy production and biosynthetic pathways.
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143
Assertion: Increased transaminase activity is a compensatory response during starvation. Reason: It enables the mobilization of amino acids for energy production when other substrates are scarce.
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144
Assertion: The regulation of glutamate dehydrogenase reflects its central role in metabolism. Reason: Its allosteric modulation by cellular energy indicators finely tunes amino acid catabolism.
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Assertion: An imbalance in amino acid catabolism can lead to metabolic disorders. Reason: Disruption in these pathways may cause the accumulation of toxic intermediates.
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