Amino Acids and Protein Structure
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Questions and Answers

Which of the following amino acids is considered highly hydrophilic?

  • Arginine (correct)
  • Leucine
  • Phenylalanine
  • Isoleucine

    • What characteristic differentiates the N-terminal from the C-terminal of a peptide?

  • The C-terminal has a side chain.
  • The C-terminal is the first amino acid in the sequence.
  • The N-terminal contains a carboxyl group.
  • The N-terminal has an amino group. (correct)

    • Which of the following statements about peptide bonds is incorrect?

  • Peptide bonds result in the formation of a polypeptide chain.
  • Peptide bonds connect amino acids in proteins.
  • Peptide bonds can be broken by hydrogen bonding. (correct)
  • Peptide bonds are formed by dehydration reactions.

    • Which property of amino acids is influenced by the functional groups in their side chains?

    <p>Solubility in water (B)</p> Signup and view all the answers

    Which of the following statements about the molecular weight of amino acids is accurate?

    <p>Tryptophan is heavier than Glycine in terms of molecular weight. (B)</p> Signup and view all the answers

    Which characteristic distinguishes α-amino acids from other types of amino acids?

    <p>They are found in proteins. (D)</p> Signup and view all the answers

    How many different combinations can be made with 3 amino acids?

    <p>8,000 (C)</p> Signup and view all the answers

    Which of the following is true about the stereoisomers of amino acids?

    <p>Chiral amino acids have four different substituents. (D)</p> Signup and view all the answers

    Which class of biomolecules is NOT categorized with amino acids?

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

    What role do proteins serve in biological systems?

    <p>They can act as enzymes and antibodies. (C)</p> Signup and view all the answers

    What is the significance of the R group in the structure of amino acids?

    <p>It determines the identity and characteristics of the amino acid. (D)</p> Signup and view all the answers

    Which statement about amino acids is incorrect?

    <p>Only β-amino acids are used in protein synthesis. (D)</p> Signup and view all the answers

    What type of amino acid is GABA?

    <p>γ-amino acid (B)</p> Signup and view all the answers

    Which of the following characteristics is true about amino acids in the nonpolar, aliphatic group?

    <p>They do not contain a benzene ring. (B)</p> Signup and view all the answers

    How does electronegativity influence bond polarity in amino acids?

    <p>A larger difference in electronegativity increases bond polarity. (D)</p> Signup and view all the answers

    What does it mean when a compound is described as hydrophobic?

    <p>It repels water molecules. (A)</p> Signup and view all the answers

    Which factor differentiates glutamate from glutamic acid?

    <p>Glutamate is the ionized form of glutamic acid. (B)</p> Signup and view all the answers

    Which of the following correctly describes the role of water in relation to charged compounds?

    <p>Charged compounds are soluble in water due to its polarity. (A)</p> Signup and view all the answers

    Which statement about glycine is true?

    <p>Glycine is the only amino acid that does not have an isomer. (D)</p> Signup and view all the answers

    How can aromatic compounds in amino acids be identified?

    <p>They contain a benzene ring or derivatives. (D)</p> Signup and view all the answers

    What is a characteristic feature of polar, uncharged amino acids?

    <p>They are soluble in water due to the presence of polar bonds. (C)</p> Signup and view all the answers

    Flashcards

    Amino Acids

    Organic molecules that serve as the building blocks of proteins. They contain an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a unique side chain (R group) attached to a central carbon atom (alpha carbon).

    Isomers

    Molecules that have the same chemical formula but different structural arrangements. They cannot be superimposed on each other.

    Enantiomers

    A specific type of isomer where the molecules are mirror images of each other and cannot be superimposed.

    Chiral Carbon Atom

    A carbon atom that is bonded to four different groups or atoms. It is the center of chirality, meaning it can exist in two non-superimposable mirror image forms.

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    L-Amino Acids

    The configuration of amino acids found in proteins. It is typically represented as L-amino acids, with the amino group on the left side of a Fischer projection.

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    Peptide Bond

    The bond formed between two amino acids during protein synthesis. It involves a reaction between the carboxyl group of one amino acid and the amino group of another, releasing a water molecule.

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    Amino Acid Sequence

    The unique sequence of amino acids that makes up a protein. This sequence dictates the protein's shape, function, and properties.

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    Protein Sequence Representation

    Amino acid sequence is represented using three-letter or one-letter abbreviations to denote each amino acid. For example, Met-Tyr-Ala-Gly-Gly-Trp-Leu represents a sequence of amino acids.

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    Hydrophobic interactions

    The attraction of molecules to each other caused by non-covalent interactions like Van Der Waals forces, hydrogen bonding, or dipole-dipole attraction.

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    Solubility

    The amount of solute that can dissolve in a given amount of solvent at a specific temperature.

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    N-terminal

    The end of a polypeptide chain with a free amino group (-NH2).

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    C-terminal

    The end of a polypeptide chain with a free carboxyl group (-COOH).

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    Nonpolar, aliphatic R groups

    Amino acids with nonpolar side chains that lack functional groups like hydroxyl or amine groups. These side chains are primarily composed of hydrocarbons, making them hydrophobic and less reactive.

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    Electronegativity

    A measure of an atom's ability to attract electrons within a chemical bond. More electronegative atoms pull electrons closer, creating polarity.

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    Aromatic compounds

    Organic compounds that contain the benzene ring structure. They often have different properties than compounds without the ring.

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    Aliphatic Compounds

    Organic compounds that lack the benzene ring structure and are typically composed of straight chains or branched chains of carbon atoms.

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    Positively Charged R groups

    Amino acids with positively charged side chains due to the presence of protonated amino groups in their R groups. They are usually hydrophilic.

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    Negatively charged R groups

    Amino acids with negatively charged side chains due to the presence of deprotonated carboxyl groups in their R groups. They are usually hydrophilic.

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    Polar uncharged R groups

    Amino acids with polar but uncharged side chains. They contain functional groups like hydroxyl or amide groups, making them hydrophilic but not charged.

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    Glutamic Acid

    The carboxylic acid form of an amino acid. It has a free carboxyl group at the end of its side chain.

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    Study Notes

    Amino Acids

    • Amino acids are the building blocks of proteins
    • Proteins are composed of 20 different amino acids
    • Each amino acid contains a central carbon atom (α-carbon) bonded to four groups:
      • An amino group (NH2)
      • A carboxyl group (COOH)
      • A hydrogen atom (H)
      • A variable side chain (R group), which differentiates the 20 amino acids
    • Proteins are typically 50-2,000 amino acids long
    • Possible combinations of 20 amino acids in a protein are massive: 20^2 = 400, 20^3 =8,000, 20^100 ≈ 10130, 201000 ≈ ?
    • Proteins have diverse functions including hormones, antibodies, muscle fibers, oxygen transport, ion channels, and enzymes
    • The α-carbon is tetrahedral with bond angles of 109.5°
    • Amino acids in proteins are L-amino acids
    • Amino acids have both positive and negative charges (e.g., H3N+ - C - COO-)
    • Proteins contain various amino acids having different R-groups, defining different classes
    • Classification of amino acids bases on their R groups:

      • Nonpolar, aliphatic

      • Aromatic

      • Polar, uncharged

      • Positively charged

      • Negatively charged

    • Abbreviations are used to represent amino acids (e.g., Ala for alanine)
    • Peptide bonds link amino acids to create polypeptide chains
    • The ends of a peptide chain are different (amino-terminal and carboxyl-terminal ends).
    • Peptides are smaller than proteins and are made from amino acids, using peptide bonds
    • Size of peptides and proteins varies, as shown by examples such as cytochrome c(12,400 MW, 104 residues) and titin (2,993,000 MW, 26,926 residues).
    • Amino acids are important for the structure and function of biomolecules

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    Amino Acids - PDF

    Description

    This quiz delves into the fundamental concepts of amino acids and their role as the building blocks of proteins. You will explore the structure of amino acids, the diversity of protein functions, and the significance of the α-carbon and R groups. Perfect for biology students looking to deepen their understanding of protein biochemistry.

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