Amino Acids and Peptides Overview
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Questions and Answers

Which functional group in cysteine is responsible for its unique chemical reactivity?

  • Amino group
  • Sulfhydryl group (correct)
  • Hydroxyl group
  • Carboxyl group

    • What type of bond is formed between two cysteine residues to create cystine?

  • Peptide bond
  • Covalent disulfide bond (correct)
  • Ionic bond
  • Hydrogen bond

    • Which of the following describes a dipeptide?

  • A single amino acid
  • A branched chain of amino acids
  • A compound containing two amino acids (correct)
  • A polymer of 10 to 20 amino acids

    • What is the correct sequence of reaction in peptide bond formation?

    <p>Amino group of one amino acid bonds with the carboxyl group of another (C)</p> Signup and view all the answers

    Which of the following is NOT a type of peptide?

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

    Under what condition can amino acids bond to form a peptide chain?

    <p>Under proper conditions (C)</p> Signup and view all the answers

    What is a polypeptide?

    <p>A long unbranched chain of amino acids (A)</p> Signup and view all the answers

    Which of the following functional groups is NOT involved in the structure of cysteine?

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

    What defines the primary structure of a protein?

    <p>The sequence of amino acids linked by peptide bonds (B)</p> Signup and view all the answers

    Which of the following is true about the primary structure of proteins across different species?

    <p>They show some similarities but are not identical across species. (D)</p> Signup and view all the answers

    What maintains the alpha-helix structure of proteins?

    <p>Hydrogen bonds between the backbone portions of the protein (C)</p> Signup and view all the answers

    The twisting of the alpha-helix in proteins forms what type of spiral?

    <p>Right-handed spiral (D)</p> Signup and view all the answers

    Which type of structure does not define the order of amino acids in a protein?

    <p>Secondary structure (A), Quaternary structure (B), Tertiary structure (C)</p> Signup and view all the answers

    What are the three-letter abbreviations based on?

    <p>The first three letters of the amino acid's name (B)</p> Signup and view all the answers

    Which of the following is an exception to the three-letter abbreviation rule?

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

    What is the purpose of one-letter symbols for amino acids?

    <p>To simplify the representation of amino acid sequences (A)</p> Signup and view all the answers

    Why is one letter chosen for amino acids that have duplicate letters?

    <p>The most abundant amino acid gets the letter (C)</p> Signup and view all the answers

    Which amino acid corresponds to the one-letter symbol 'W'?

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

    Which of the following options correctly describes the naming of amino acids?

    <p>All amino acids have unique three-letter and one-letter symbols (B)</p> Signup and view all the answers

    How is the classification of amino acids important in biochemistry?

    <p>It influences the structure and functionality of proteins (D)</p> Signup and view all the answers

    What role do R-groups play in amino acids?

    <p>They influence the polarity and function of the amino acid (C)</p> Signup and view all the answers

    What is a defining characteristic of a protein?

    <p>It is a naturally-occurring polymer made of amino acids. (B)</p> Signup and view all the answers

    Which type of protein contains two or more polypeptide chains?

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

    What is the range of amino acid residues present in common proteins?

    <p>400–500 residues (B)</p> Signup and view all the answers

    How are simple proteins characterized?

    <p>They consist solely of amino acid residues. (D)</p> Signup and view all the answers

    What distinguishes conjugated proteins from simple proteins?

    <p>Conjugated proteins include non-amino-acid entities. (B)</p> Signup and view all the answers

    What is the minimum number of amino acid residues that must be present for a peptide to be classified as a protein?

    <p>40 residues (A)</p> Signup and view all the answers

    Which of the following describes a monomeric protein?

    <p>It consists of a single polypeptide chain. (D)</p> Signup and view all the answers

    Which term refers to a protein with non-amino-acid components?

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

    What is the primary role of catalytic proteins?

    <p>They act as catalysts in chemical reactions. (C)</p> Signup and view all the answers

    Which type of protein is primarily involved in the body's immune response?

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

    What is the function of transport proteins?

    <p>To bind and transport small biomolecules. (B)</p> Signup and view all the answers

    Which example is classified as a messenger protein?

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

    What characteristic defines structural proteins?

    <p>They confer stiffness and rigidity to biological structures. (C)</p> Signup and view all the answers

    Which type of proteins are critical for muscle movement?

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

    What function do transmembrane proteins serve?

    <p>They control the movement of molecules across cell membranes. (D)</p> Signup and view all the answers

    Which of the following is NOT a function of proteins classified by their role?

    <p>Storage of genetic information. (C)</p> Signup and view all the answers

    Study Notes

    Amino Acid Nomenclature

    • Three-letter abbreviations are used to name standard amino acids
      • Abbreviation is the first three letters of the amino acid name
      • Exceptions: Isoleucine (Ile), Tryptophan (Trp), Asparagine (Asn), and Glutamine (Gln)
    • One-letter symbols are used for comparing amino acid sequences of proteins
      • Usually the first letter of the name
      • When more than one amino acid has the same letter, the most abundant amino acid gets the first letter

    Cysteine: A Chemically Unique Amino Acid

    • Standard amino acid that contains a sulfhydryl group (-SH group)
      • Sulfhydryl group imparts cysteine a unique chemical property
    • Cysteine dimerizes to form a cystine molecule in the presence of mild oxidizing agents
      • Cystine contains two cysteine residues linked via a covalent disulfide bond

    Peptides

    • Amino acids can bond together to produce a peptide chain under proper conditions
      • Peptide: Unbranched chain of amino acids
      • Dipeptide: Compound containing two amino acids
      • Oligopeptide: Peptide with 10 to 20 amino acid residues
      • Polypeptide: Long unbranched chain of amino acids
    • Reaction occurs between the amino group of one amino acid and the carboxyl group of another amino acid

    General Structural Characteristics of Proteins

    • Protein: Naturally-occurring, unbranched polymer in which the monomer units are amino acids
    • Peptide: At least 40 amino acid residues are present
      • The terms polypeptide and protein are often used interchangeably
      • Some proteins have >10,000 amino acid residues
      • Common proteins contain 400–500 amino acid residues
      • Small proteins contain 40–100 amino acid residues
    • More than one polypeptide chain may be present in a protein
      • Monomeric: Protein which contains one polypeptide chain
      • Multimeric: Protein which contains two or more polypeptide chains

    Protein Classification Based on Chemical Composition

    • Simple protein: Protein in which only amino acid residues are present
      • More than one protein subunit may be present
    • Conjugated protein: Protein that has one or more non-amino-acid entities (prosthetic groups) present in its structure
      • One or more polypeptide chains may be present
      • Non-amino-acid components may be organic or inorganic

    Primary Structure of Proteins

    • Specific protein's primary structure is the same within the organism
      • Structures of some proteins are similar among different species of animals
        • Example: Insulin from pigs, cows, sheep, and humans are similar but not identical
    • Amino acids are linked to one another by peptide linkages

    Secondary Structure of Proteins

    • Arrangement in space adopted by the backbone portion of a protein
    • Types: Alpha-helix (α helix) and beta-pleated sheet (β pleated sheet)
    • Alpha-helix structure: A single protein chain adopts a shape that resembles a coiled spring (helix)
      • Coil configuration maintained by hydrogen bonds
      • Twist of the helix forms a right-handed, or clockwise, spiral

    Protein Classification Based on Function

    • Catalytic proteins are known for their role as catalysts
      • Almost every chemical reaction in the body is driven by an enzyme
    • Defense proteins are central to functioning of the body’s immune system
      • Known as immunoglobulins or antibodies
    • Transport proteins bind to small biomolecules, transport them to other locations in the body, and release them as needed
    • Messenger proteins transmit signals to coordinate biochemical processes between different cells, tissues, and organs
      • Examples: Insulin, glucagon, and human growth hormone
    • Contractile proteins are necessary for all forms of movement
      • Examples: Actin and myosin
      • Human reproduction depends on the movement of sperm, which is possible because of contractile proteins
    • Structural proteins confer stiffness and rigidity
      • Collagen is a component of cartilage
      • α-keratin gives mechanical strength and protective covering to hair, nails, feathers, and hooves
    • Transmembrane proteins control the movement of small molecules and ions through the cell membrane
      • Have channels to help molecules enter and exit the cell
      • Selective, allow passage of only one type of molecule or ion

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    LESSON 5 - AMINO ACIDS PDF

    Description

    This quiz covers the nomenclature and chemical properties of amino acids, focusing on standard amino acids and their abbreviations. It also discusses the unique characteristics of cysteine and the formation of peptide chains from amino acids. Test your knowledge on these essential biomolecules!

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