Amino Acids and Their Functions
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Questions and Answers

Which of the following features is common to all amino acids?

  • A cyclic structure
  • A polar side chain
  • An R group specific to each amino acid (correct)
  • A positively charged side chain

    • What is the primary function of proteins as biological catalysts?

  • To facilitate chemical reactions without being consumed (correct)
  • To encode genetic information
  • To provide structural support to cells
  • To transport molecules across membranes

    • Which classification of amino acids contains the fewest members?

  • Nonpolar, aliphatic
  • Positively charged (correct)
  • Aromatic
  • Polar, uncharged

    • In the context of amino acid stereoisomers, which statement is correct?

    <p>L stereoisomers are the only forms found in natural proteins</p> Signup and view all the answers

    Which of the following correctly identifies the function of the amino group in amino acids?

    <p>It contributes to the molecule's overall charge</p> Signup and view all the answers

    At what pH level will the amino groups of all amino acids be protonated and carry a positive charge?

    <p>Below pH 8.8</p> Signup and view all the answers

    Which of the following statements about the isoelectric point (pI) of amino acids without ionizable side chains is true?

    <p>At pH equal to pI, the net charge of the amino acid is zero.</p> Signup and view all the answers

    What is the significance of the pKa values of ionizable side chains in amino acids?

    <p>They influence the charge of the amino acid at various pH levels.</p> Signup and view all the answers

    What role do buffers play in relation to amino acids and their pKa values?

    <p>They prevent changes in pH close to the pKa.</p> Signup and view all the answers

    What characterizes the primary structure of proteins?

    <p>The specific arrangement of amino acids linked by peptide bonds.</p> Signup and view all the answers

    What type of bond is formed between amino acids in a peptide?

    <p>Peptide bond</p> Signup and view all the answers

    How many peptide bonds are present in a tripeptide?

    <p>2</p> Signup and view all the answers

    Which of the following is the correct classification for a peptide made of 4 to 10 amino acids?

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

    In peptide naming, what does the 'N-terminal' refer to?

    <p>The first amino acid in the chain</p> Signup and view all the answers

    Which of the following describes a polypeptide?

    <p>A peptide with molecular weight above 10 kDa</p> Signup and view all the answers

    What type of groups within peptides primarily contribute to their ionization behavior?

    <p>α-amino and α-carboxyl groups</p> Signup and view all the answers

    What is suggested by the molecular weight of a protein being greater than 10 kDa?

    <p>It contains several hundred amino acids</p> Signup and view all the answers

    Which sequence represents the one-letter code abbreviation for the peptide consisting of serine, glycine, tyrosine, alanine, and leucine?

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

    What is the primary role of polar, uncharged R groups in protein structures?

    <p>To stabilize protein structure through hydrogen bonds.</p> Signup and view all the answers

    Which statement correctly describes the behavior of aromatic amino acids in relation to UV light?

    <p>They absorb UV light at 270–280 nm, aiding in concentration measurement.</p> Signup and view all the answers

    What is the process called when two cysteine molecules form a disulfide bond?

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

    At neutral pH, the predominant form of amino acids is the zwitterion. What characterizes this form?

    <p>It has both negatively and positively charged groups.</p> Signup and view all the answers

    Which statement regarding the isoelectric point (pI) of amino acids is accurate?

    <p>At pI, the amino acid carries no net electric charge.</p> Signup and view all the answers

    How do the pK1 and pK2 values relate to the behavior of amino acids at varying pH levels?

    <p>At pH higher than pK1, the carboxyl group's proton is removed, resulting in a negative charge.</p> Signup and view all the answers

    Which R group type contributes to the hydrophobic effect in proteins?

    <p>Aromatic R groups</p> Signup and view all the answers

    What occurs to the α-amino and α-carboxyl groups during the titration of amino acids?

    <p>The carboxyl group acts as a weak acid and the amino group as a weak base.</p> Signup and view all the answers

    What distinguishes uncommon amino acids in terms of their functions?

    <p>They can undergo modifications that impact protein functionality.</p> Signup and view all the answers

    What is the average molecular weight of an amino acid used for estimating the number of residues in a protein?

    <p>128</p> Signup and view all the answers

    Which type of protein contains lipids as a major component?

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

    What percentage of total residues in bovine chymotrypsinogen is accounted for by glycine?

    <p>9.4%</p> Signup and view all the answers

    Which prosthetic group is associated with hemoproteins?

    <p>Iron porphyrin</p> Signup and view all the answers

    In estimating the number of amino acid residues, what is subtracted from the average molecular weight of an amino acid?

    <p>Weight of water molecules</p> Signup and view all the answers

    Which of the following amino acids contributes 14 residues per molecule in bovine cytochrome c?

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

    What type of protein contains carbohydrates as a major component?

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

    How many residues does aspartic acid represent in bovine chymotrypsinogen?

    <p>3</p> Signup and view all the answers

    Which protein class includes enzymes that require metal ions for activity?

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

    What is the number of residues per molecule of alanine in bovine cytochrome c?

    <p>6</p> Signup and view all the answers

    Which amino acid has the lowest percentage of total residues in bovine chymotrypsinogen?

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

    What is the percentage of Leucine residues in bovine chymotrypsinogen?

    <p>7.8%</p> Signup and view all the answers

    Which of the following is NOT a type of conjugated protein?

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

    In the estimation formula for residues, what is the divisor used after adjusting for peptide bonding?

    <p>110</p> Signup and view all the answers

    Study Notes

    Amino Acids

    • Proteins are made from a common set of 20 amino acids, each with unique side chains.
    • Amino acids serve as the building blocks of protein, akin to an alphabet in written language.
    • Key functions of proteins include catalysis, transport, structural support, immune response, and regulation.

    Structural Features of Amino Acids

    • Each amino acid contains a chiral α carbon with four substituents: a carboxyl group, an amino group, a hydrogen atom, and a unique R group (side chain).
    • Glycine is unique as it has a second hydrogen atom instead of an R group.

    Stereoisomers

    • Amino acids exist as L (levorotatory) stereoisomers, with two enantiomers being optically active.

    Classification of Amino Acids

    • Amino acids are classified into five main groups based on R groups:
      • Nonpolar, aliphatic (7)
      • Aromatic (3)
      • Polar, uncharged (5)
      • Positively charged (3)
      • Negatively charged (2)

    Properties of R Groups

    • Nonpolar, aliphatic R groups enhance protein stability due to the hydrophobic effect.
    • Aromatic R groups absorb UV light at 270–280 nm; this property can be used to measure concentration.
    • Polar, uncharged R groups can form hydrogen bonds; cysteine can form disulfide bonds which are reversible.

    Disulfide Bonds

    • Disulfide bonds can be intramolecular or intermolecular, playing key roles in protein structure.

    Uncommon Amino Acids

    • Some uncommon amino acids have notable functions, being modified during or after protein synthesis (e.g., 4-hydroxyproline in collagen, pyrrolysine).

    Amino Acid Abbreviations

    • Standard amino acids have three-letter abbreviations (e.g., Gly for Glycine) or one-letter symbols.

    Acid-Base Properties of Amino Acids

    • Amino acids can act as acids or bases due to the presence of ionizable groups.
    • At neutral pH, amino acids exist predominantly in zwitterionic form, where they carry both positive and negative charges.

    Titration and pKa Values

    • The pKa values indicate the strength of the acidic or basic nature of the amino acids' functional groups.
    • pK1 (carboxyl group) ranges between 1.8-2.4; pK2 (amino group) ranges between 8.8-11.0.
    • The isoelectric point (pI) is where the net charge is zero, influencing solubility and migration in an electric field.

    Buffering Capacity of Amino Acids

    • Amino acids can serve as buffers, maintaining pH around their pKa values.

    Peptides and Proteins

    • Peptides are chains of amino acids connected by peptide bonds, which are covalent linkages formed via condensation and broken through hydrolysis.
    • Peptide types classified by number of amino acids include:
      • Dipeptides (2)
      • Tripeptides (3)
      • Oligopeptides (few)
      • Polypeptides (many, < 10 kDa)
      • Proteins (thousands, > 10 kDa)

    Peptide Naming

    • Peptides are named starting from the N-terminal to C-terminal, using full names or abbreviations (three-letter or one-letter).

    Ionization Behavior of Peptides

    • Peptides have one free α-amino group and one free α-carboxyl group, influencing their ionization.

    Biologically Active Peptides

    • Naturally occurring peptides vary in size and composition, serving various biological functions, with molecular weights ranging widely.

    Amino Acid Composition in Proteins

    • Composition varies significantly across different proteins, impacting their structure and function.

    Estimating Amino Acid Residues

    • The number of amino acid residues can be estimated by dividing molecular weight by 110, accounting for the water lost during peptide bond formation.

    Conjugated Proteins

    • Conjugated proteins contain additional chemical groups beyond amino acids, which can include lipids, carbohydrates, phosphate groups, and specific metals, enhancing their functionality.

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    Description

    Explore the fascinating world of amino acids, the building blocks of proteins. This quiz covers their structural features, classification, and key functions in biological systems. Test your understanding of the unique properties and roles of various amino acids.

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