Amino Acid Structure and Properties Quiz
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Questions and Answers

Which of the following is NOT a component of an α-amino acid?

  • Carboxylic acid group
  • R group
  • Amino group
  • Hydrogen atom (correct)

    • At neutral pH, amino acids in solution exist predominantly as:

  • Unionized molecules
  • Dipolar ions (correct)
  • Cations
  • Anions

    • Which of the following is true about the optical activity of amino acids?

  • All amino acids are optically active
  • Only α-amino acids are optically active
  • Glycine is the only optically active amino acid
  • Only amino acids with four different groups connected to the α-carbon are optically active (correct)

    • Why are cells able to specifically synthesize the L isomers of amino acids?

    <p>Because L-isomers are more stable than D-isomers</p> Signup and view all the answers

    What is the role of proline in peptide chains?

    <p>Proline stabilizes the 3-dimensional shape of peptide chains</p> Signup and view all the answers

    What is the significance of the hydroxyl groups in serine and threonine?

    <p>The hydroxyl groups make serine and threonine more reactive</p> Signup and view all the answers

    What is the function of glycine in proteins?

    <p>Glycine is particularly abundant in structural proteins</p> Signup and view all the answers

    Which of the following statements about amino acids is NOT true?

    <p>Amino acids are the monomeric subunits of proteins.</p> Signup and view all the answers

    Which of the following amino acids is NOT commonly found in proteins?

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

    Which of the following amino acids is optically active?

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

    Which of the following amino acids is NOT hydrophilic?

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

    Which of the following amino acids is an essential amino acid?

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

    Which of the following amino acids is commonly found in collagen and gelatin?

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

    Which of the following amino acids has a cyclic structure in its side chain?

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

    Which of the following amino acids has a hydroxyl group in its side chain?

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

    Which of the following amino acids can engage in H-bonding and ester formation?

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

    Which of the following amino acids is an important component of the active site of many enzymes?

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

    Which of the following is true about the structure of an α-amino acid?

    <p>It consists of a central carbon atom, an amino group, and a carboxylic acid group</p> Signup and view all the answers

    Which of the following is true about the R group of an α-amino acid?

    <p>It is often referred to as the side chain</p> Signup and view all the answers

    What is the predominant form of amino acids in solution at neutral pH?

    <p>Dipolar ions</p> Signup and view all the answers

    What is the isoelectric point (IEP) of an amino acid?

    <p>The pH at which the net ionic charges are balanced</p> Signup and view all the answers

    Which of the following is true about the optical activity of amino acids?

    <p>Only L isomers of α-amino acids are optically active</p> Signup and view all the answers

    Why are cells able to specifically synthesize the L isomers of amino acids?

    <p>L isomers have a higher stability</p> Signup and view all the answers

    What is the significance of the hydroxyl groups in serine and threonine?

    <p>They can undergo post-translational modifications</p> Signup and view all the answers

    Which of the following is true about the structure of glycine?

    <p>It is not an α-amino acid</p> Signup and view all the answers

    What is the role of proline in peptide chains?

    <p>It disrupts the secondary structure of proteins</p> Signup and view all the answers

    What is the function of glycine in proteins?

    <p>It is a non-essential amino acid</p> Signup and view all the answers

    all amino acids of animal proteins are ______ isomers

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

    D-amino acid residues have been found only in ______ and a few, generally small peptides, including some peptides of bacterial cell walls

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

    D-alanine and D-glutamic acid occur in ______ cell wall

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

    some antibiotics contain D-______ acids

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

    D-alanine, D-glutamic acid and D-ornithine are present in bacitracin-an active agent against a variety of ______ positive and a few ______ negative bacteria (in vitro)

    <p>Gram, Gram</p> Signup and view all the answers

    polymyxins contain D-______

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

    why are cells able to specifically synthesize the L ______ of amino acids

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

    the remarkable range of functions exhibited by proteins result from the diversity and versatility of the 20 kinds of building ______-amino acids

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

    glycine (Greek glykos, “sweet”) was so named because of its ______ taste

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

    alanine has ______ group as its side chain

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

    An α-amino acid consists of a central carbon atom, called the α carbon, an amino group, a carboxylic acid group, a hydrogen atom, and a distinctive ______.

    <p>R group</p> Signup and view all the answers

    The R group is often referred to as the ______.

    <p>side chain</p> Signup and view all the answers

    Amino acids in solution at neutral pH are predominantly dipolar ions (Zwitterions) rather than ______ molecules.

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

    In the dipolar state, the amino group is ______ and the carbonyl group is ______.

    <p>protonated, dissociated</p> Signup and view all the answers

    The pH at which the net ionic charges are balanced is the ______.

    <p>isoelectric point (IEP)</p> Signup and view all the answers

    Amino acids are ______.

    <p>optically active</p> Signup and view all the answers

    With four different groups connected to the tetrahedral α-carbon atom, α-amino acids are chiral – they are ______.

    <p>optically active</p> Signup and view all the answers

    The α-carbon of all amino acids are asymmetric, so there are two ______ of each except glycine.

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

    The two mirror-image forms are called the ______ and ______ isomers.

    <p>L, D</p> Signup and view all the answers

    By convention, if the α-NH3+ is projected to the left, the α-amino acid has an absolute ______ configuration.

    <p>L configuration</p> Signup and view all the answers

    Phenylalanine, tyrosine & tryptophan have ______ side chains

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

    The aromatic side chains make them relatively ______ (hydrophobic)

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

    All can participate in ______ interactions

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

    Tyrosine and tryptophan are significantly more ______ than phenylalanine

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

    because of the tyrosine ______ group and the nitrogen of the tryptophan ______ ring

    <p>hydroxyl, indole</p> Signup and view all the answers

    Aromatic amino acids are exploited in the ______ of proteins

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

    Tyrosine was first isolated from ______ (its name is derived from the Greek tyros, “cheese”)

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

    Phenylalanine & tyrosine are important constituents of ______

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

    Are precursors for the synthesis of important regulatory proteins as neurotransmitters and ______

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

    Which of the following is true about the aromatic side chains of phenylalanine, tyrosine, and tryptophan?

    <p>They are nonpolar (hydrophobic)</p> Signup and view all the answers

    Which of the following amino acids is significantly more polar than phenylalanine?

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

    Which amino acid can be converted to tyrosine by the enzyme phenylalanine Hydroxylase?

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

    Which of the following amino acids are important constituents of proteins?

    <p>Phenylalanine, tyrosine, and tryptophan</p> Signup and view all the answers

    Which amino acids are precursors for the synthesis of important regulatory proteins such as neurotransmitters and hormones?

    <p>Phenylalanine, tyrosine, and tryptophan</p> Signup and view all the answers

    Which amino acids are the starting point for the synthesis of catecholamines?

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

    Which enzyme is absent in the congenital disease phenylketonuria?

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

    Which amino acid was first isolated from cheese?

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

    Which amino acids can participate in hydrophobic interactions?

    <p>Phenylalanine, tyrosine, and tryptophan</p> Signup and view all the answers

    Which of the following statements about amino acids is true?

    <p>D-alanine and D-glutamic acid occur in bacterial cell walls</p> Signup and view all the answers

    Which amino acid is commonly found in collagen and gelatin?

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

    What is the role of serine and threonine in proteins?

    <p>They can serve as attachment sites for oligosaccharide chains in glycoproteins</p> Signup and view all the answers

    Which of the following amino acids is NOT hydrophilic?

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

    Which amino acid is an important reactive amino acid in proteins because the pka of the nitrogen in the imidazole ring of histidyl residues in proteins is in the range of pH of the tissues?

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

    Which amino acid is an important component of proteins due to the reactivity of the amino group on the side chain?

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

    Which amino acid is the precursor of nitric oxide?

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

    Which amino acid has a nonpolar thioether group in its side chain and acts as a methyl donor in biochemical processes?

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

    Which of the following amino acids contains a sulfhydryl group in its side chain?

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

    Which amino acid can form a covalent cross-link called a disulfide bond?

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

    Which amino acid is a constituent of myosin?

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

    Which of the following uncommon amino acids is found in prothrombin (factor II)?

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

    Which of the following is NOT a type of protein mentioned in the text?

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

    Which of the following is the correct formula for haemoglobin mentioned in the text?

    <p>C2952H4664O832N812S8Fe4</p> Signup and view all the answers

    What is the function of albumin in the body?

    <p>Regulation of water balance</p> Signup and view all the answers

    What does the sedimentation of a protein containing solution indicate?

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

    Which of the following best describes the structure of an α-amino acid?

    <p>A central carbon atom, an amino group, a carboxylic acid group, and an R group</p> Signup and view all the answers

    Which of the following is true about the optical activity of amino acids?

    <p>All α-amino acids are optically active</p> Signup and view all the answers

    Which of the following best describes the predominant form of amino acids in solution at neutral pH?

    <p>Dipolar ions (Zwitterions)</p> Signup and view all the answers

    By convention, if the α-NH3+ is projected to the left, the α-amino acid has an absolute ______ configuration.

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

    Which of the following is NOT a general function of proteins?

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

    Which of the following is a dynamic function of proteins?

    <p>Metabolic control</p> Signup and view all the answers

    Which proteins are involved in enzymatic catalysis?

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

    Which proteins are involved in transport of molecules?

    <p>Transferrin and albumin</p> Signup and view all the answers

    Which proteins provide structural strength and elasticity to organs?

    <p>Collagen and elastin</p> Signup and view all the answers

    Which proteins are involved in the control and regulation of gene transcription and translation?

    <p>Histone proteins</p> Signup and view all the answers

    Which category do nonpolar, aliphatic amino acids belong to?

    <p>Nonpolar, aliphatic</p> Signup and view all the answers

    What is the general configuration of the peptide bond?

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

    What are the charged groups present in polypeptides?

    <p>N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids</p> Signup and view all the answers

    What are proteins classified based on?

    <p>Composition, molecular weight, molecular shape, function, source, and physicochemical properties</p> Signup and view all the answers

    Which amino acid is an important precursor of the pharmacologically active substance histamine?

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

    Which amino acid has a lipotropic action and prevents fatty infiltration of the liver?

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

    What is the most abundant excitatory neurotransmitter in the vertebrate nervous system?

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

    Which amino acid is involved in the synthesis of urea and stimulates the secretion of insulin and growth hormone?

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

    What is the general structure of an α-amino acid?

    <p>An α-amino acid consists of a central carbon atom, called the α carbon, an amino group, a carboxylic acid group, a hydrogen atom, and a distinctive R group.</p> Signup and view all the answers

    What are the two mirror-image forms of amino acids called?

    <p>The two mirror-image forms are called the L isomer and D isomer.</p> Signup and view all the answers

    What is the predominant form of amino acids in solution at neutral pH?

    <p>Amino acids in solution at neutral pH are predominantly dipolar ions (Zwitterions) rather than unionised molecules.</p> Signup and view all the answers

    What is the pH at which the net ionic charges are balanced called?

    <p>The pH at which the net ionic charges are balanced is the isoelectric point (IEP).</p> Signup and view all the answers

    What are the different categories in which amino acids are classified?

    <p>nonpolar, aliphatic; aromatic; polar, uncharged; and charged</p> Signup and view all the answers

    What is the function of a peptide bond?

    <p>covalently joining amino acids in proteins</p> Signup and view all the answers

    What is the naming convention for a polypeptide?

    <p>changing the suffixes of amino acid residues</p> Signup and view all the answers

    What are the charged groups present in polypeptides?

    <p>N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids</p> Signup and view all the answers

    What is the significance of the hydroxyl groups in serine and threonine?

    <p>The hydroxyl groups in serine and threonine make them much more hydrophilic (water loving) and reactive than alanine and valine.</p> Signup and view all the answers

    What is the role of proline in peptide chains?

    <p>Proline is an important determinant of the 3-dimensional shape of peptide chains.</p> Signup and view all the answers

    Which amino acids are commonly found in collagen and gelatin?

    <p>Hydroxy derivatives of proline are found only in collagen and gelatin.</p> Signup and view all the answers

    What are the aromatic amino acids and what makes them different from each other?

    <p>The aromatic amino acids are phenylalanine, tyrosine, and tryptophan. Tyrosine and tryptophan are significantly more polar than phenylalanine due to the hydroxyl group in tyrosine and the nitrogen of the tryptophan indole ring.</p> Signup and view all the answers

    What is the role of cysteine in proteins?

    <p>Cysteine plays a role in determining the tertiary structure of proteins and can form disulfide bonds.</p> Signup and view all the answers

    What is the difference between cysteine and cystine?

    <p>Cysteine is the monomeric form with a sulfhydryl group, while cystine is the dimeric form with a disulfide bond.</p> Signup and view all the answers

    What are some examples of uncommon amino acids?

    <p>Some examples of uncommon amino acids are 4-hydroxyproline, 5-hydroxylysine, 6-N methyllysine, carboxyglutamate, desmosine, and selenocysteine.</p> Signup and view all the answers

    What is the role of methionine and acetylcysteine in the liver?

    <p>Methionine increases conjugation reaction in the liver, while acetylcysteine increases GSH formation in the liver.</p> Signup and view all the answers

    What are the properties and functions of proteins?

    <p>Proteins are extremely large natural polymers with molecular weights reaching several million. They are too large to pass through cell membranes and remain trapped in the cells where they are made. Proteins can interact with one another and with other biological macromolecules to form complex assemblies. They contain a wide range of functional groups, which accounts for the broad spectrum of protein function. The function of a protein is directly dependent on its three-dimensional structure.</p> Signup and view all the answers

    How do proteins fold into three-dimensional structures?

    <p>Proteins spontaneously fold up into three-dimensional structures that are determined by the sequence of amino acids in the protein polymer.</p> Signup and view all the answers

    What is the significance of sedimentation in protein analysis?

    <p>Sedimentation is a process in which a protein-containing solution is centrifuged at a high speed to separate the molecules based on their molecular weight.</p> Signup and view all the answers

    What is the role of pH in determining protein properties?

    <p>The pH of the environment determines the solubility, viscosity, and enzymatic activity of a protein.</p> Signup and view all the answers

    What are the general functions of proteins in living systems?

    <p>Proteins serve crucial functions in essentially all biological processes such as catalysts, transport and storage of molecules, mechanical support and immune protection, generation of movement, transmission of nerve impulses, and control of growth and differentiation.</p> Signup and view all the answers

    What are the three dynamic functions of proteins?

    <p>The three dynamic functions of proteins are enzymatic catalysis, transport, and protective role.</p> Signup and view all the answers

    Give an example of a protein involved in enzymatic catalysis.

    <p>Enzymes are dynamic proteins and almost all biological reactions are enzyme catalyzed.</p> Signup and view all the answers

    Give an example of a protein involved in transport.

    <p>Haemoglobin and myoglobin transport oxygen in blood and in muscle respectively.</p> Signup and view all the answers

    Give an example of a protein involved in protective role.

    <p>Immunoglobulins and interferons act against bacterial or viral infection.</p> Signup and view all the answers

    What are the structural functions of proteins?

    <p>Proteins provide structural strength and elasticity to organs and play a 'brick-and-mortar' role in forming the matrix for bone, ligaments, connective tissue, and skin.</p> Signup and view all the answers

    Proteins are the most versatile macromolecules in living systems and serve crucial functions in all biological processes.

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

    Almost all biological reactions are enzyme catalyzed.

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

    Haemoglobin and myoglobin transport oxygen in blood and in muscle, respectively.

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

    Fibrin is formed where required to stop the loss of blood on injury to the vascular system.

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

    Many hormones are proteins, including insulin, thyrotropin, and somatotropin.

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

    Myosin and actin function in muscle contraction.

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

    Histone proteins are closely associated with DNA and control gene expression.

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

    Collagen and elastin form the matrix for bone, ligaments, connective tissue, and skin.

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

    Proteins provide structural strength and elasticity to organs.

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

    Keratin is the primary component of human hair, nails, skin, and tooth enamel.

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

    Study Notes

    Classification and Properties of Peptides and Proteins

    • Ornithine and citrulline are metabolites involved in the biosynthesis of arginine and the urea cycle.
    • Amino acids are classified into nonpolar, aliphatic; aromatic; polar, uncharged; and charged categories.
    • Peptide bonds covalently join amino acids in proteins, and can be hydrolyzed non-enzymatically under certain conditions.
    • A polypeptide is an unbranched chain of amino acids linked through peptide bonds, and its naming convention involves changing the suffixes of amino acid residues.
    • The peptide bond has a partial double-bond character, conferring rigidity and preventing free rotation.
    • The peptide bond is generally in the trans configuration.
    • The peptide bond is uncharged, and the charged groups present in polypeptides are the N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids.
    • Small peptides may contain D-amino acids or be linked by bonds other than the standard peptide bond.
    • Glutathione is a tripeptide with biochemical importance, acting as a coenzyme and undergoing oxidation under certain conditions.
    • Proteins are classified based on their composition, molecular weight, molecular shape, function, source, and physicochemical properties.
    • Proteins can be classified as simple (containing only amino acids) or conjugated (containing additional substances).
    • Albumins are a type of simple protein that are water soluble and precipitated with full saturation in ammonium sulfate.

    Classification and Properties of Peptides and Proteins

    • Ornithine and citrulline are metabolites involved in the biosynthesis of arginine and the urea cycle.
    • Amino acids are classified into nonpolar, aliphatic; aromatic; polar, uncharged; and charged categories.
    • Peptide bonds covalently join amino acids in proteins, and can be hydrolyzed non-enzymatically under certain conditions.
    • A polypeptide is an unbranched chain of amino acids linked through peptide bonds, and its naming convention involves changing the suffixes of amino acid residues.
    • The peptide bond has a partial double-bond character, conferring rigidity and preventing free rotation.
    • The peptide bond is generally in the trans configuration.
    • The peptide bond is uncharged, and the charged groups present in polypeptides are the N-terminal α-amino group, C-terminal α-carboxyl group, and ionized groups in the side chains of amino acids.
    • Small peptides may contain D-amino acids or be linked by bonds other than the standard peptide bond.
    • Glutathione is a tripeptide with biochemical importance, acting as a coenzyme and undergoing oxidation under certain conditions.
    • Proteins are classified based on their composition, molecular weight, molecular shape, function, source, and physicochemical properties.
    • Proteins can be classified as simple (containing only amino acids) or conjugated (containing additional substances).
    • Albumins are a type of simple protein that are water soluble and precipitated with full saturation in ammonium sulfate.

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    Test your knowledge of amino acid structure and physicochemical properties with this quiz! Learn about the building blocks of peptides and proteins, the composition of α-amino acids, and the unique R group. Challenge yourself and expand your understanding of amino acids.

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