Protein Structure and Function Quiz
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Questions and Answers

What stabilizes the a-helix structure in proteins?

  • Van der Waals forces between nonpolar residues
  • Ionic bonds between side chains
  • Disulfide bridges between cysteine residues
  • Hydrogen bonding along the main chain (correct)

    • How many amino acids typically comprise one turn of the a-helix?

  • 4-5 amino acids (correct)
  • 3-4 amino acids
  • 6-7 amino acids
  • 5-6 amino acids

    • What does tertiary structure in proteins primarily refer to?

  • The sequence of amino acids in the polypeptide chain
  • The interaction of multiple protein subunits
  • The three-dimensional configuration of folded protein regions (correct)
  • The arrangement of nucleotide bases in nucleic acids

    • What role do the A, B, and C domains play in the protein structure discussed?

    <p>They bind specific cofactors necessary for enzymatic reactions</p> Signup and view all the answers

    What is a common evolutionary process applied to protein domains?

    <p>Shuffling and recombination of domains</p> Signup and view all the answers

    Which component of proteins is directly composed of amino acids?

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

    What is the common core structure of all natural amino acids?

    <p>NH2-CHR-COOH</p> Signup and view all the answers

    Which configuration is predominantly found in natural amino acids?

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

    How many naturally occurring amino acids are there?

    <p>20</p> Signup and view all the answers

    What process involves the unzipping of DNA to generate an RNA strand?

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

    Which of the following amino acids has a unique structure that distinguishes it from others?

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

    Which of the following describes the role of tRNA during protein synthesis?

    <p>It carries amino acids to the ribosome.</p> Signup and view all the answers

    Which characteristic defines aliphatic amino acid side chains?

    <p>They are generally hydrophobic.</p> Signup and view all the answers

    Which pair of bases is correctly matched in DNA base pairing?

    <p>A=T</p> Signup and view all the answers

    What is the process that forms zwitterions in amino acids?

    <p>Deprotonation of the acid group and protonation of the amine group</p> Signup and view all the answers

    During which stage does an RNA polymerase add bases to the 3' end of the growing RNA strand?

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

    What does the 'R' in the amino acid structure represent?

    <p>A specific side chain or residue</p> Signup and view all the answers

    What type of chemical reaction can nucleic acids undergo?

    <p>Hydrolysis by strong base or acid</p> Signup and view all the answers

    How many RNA bases make up a single codon?

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

    What is the role of the ribosome during translation?

    <p>To synthesize proteins by moving along mRNA.</p> Signup and view all the answers

    What amino acid does the codon UUC specify?

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

    What is the role of selenocysteine in protein synthesis?

    <p>It is the 21st amino acid with a unique codon.</p> Signup and view all the answers

    Which of the following amino acids is NOT considered essential for humans?

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

    What role do hydrophobic sidechains play in protein folding?

    <p>They help proteins to span membranes.</p> Signup and view all the answers

    Which amino acids are known for their extreme structural properties that contribute to flexibility and rigidity?

    <p>Gly and Pro</p> Signup and view all the answers

    What structural feature defines a peptide bond?

    <p>It creates an amide linkage between two amino acids.</p> Signup and view all the answers

    What happens to acidic sidechains in a normal cellular environment at pH 7?

    <p>They become negatively charged.</p> Signup and view all the answers

    Why are peptide bonds resistant to degradation?

    <p>They replace ionic groups of amino acids.</p> Signup and view all the answers

    What type of interactions do acidic and basic sidechains primarily form to help proteins attract each other?

    <p>Electrostatic interactions</p> Signup and view all the answers

    Which of the following is NOT an essential amino acid?

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

    What is required to synthesize essential amino acids?

    <p>Dietary protein</p> Signup and view all the answers

    Where are Gly and Pro typically found in protein structures?

    <p>At the ends of secondary structural features and in hinge/loop regions</p> Signup and view all the answers

    What type of protein interactions are commonly influenced by electrostatic interactions?

    <p>Protein-protein recognition</p> Signup and view all the answers

    What is the primary function of proteases in protein synthesis?

    <p>To help break down peptide bonds.</p> Signup and view all the answers

    Which of the following proteins is an example of one that is resistant to degradation?

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

    What is the charge of basic sidechains when protonated?

    <p>Positively charged</p> Signup and view all the answers

    Which of the following pairs of amino acids are primarily involved in forming salt bridges?

    <p>Arg and Lys</p> Signup and view all the answers

    What is the role of disulfide bonds in proteins?

    <p>They covalently link strands of proteins together.</p> Signup and view all the answers

    What chemical process leads to the formation of disulfide bonds?

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

    Which amino acid is primarily responsible for forming disulfide bonds?

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

    What occurs to disulfide bonds during reduction?

    <p>They are broken.</p> Signup and view all the answers

    Why do harder versions of keratin have more disulfide links?

    <p>More disulfide links provide greater structural strength.</p> Signup and view all the answers

    What is a key characteristic of disulfide bonds in relation to protein structure?

    <p>They are strong covalent bonds that stabilize protein structure.</p> Signup and view all the answers

    Where are thiol groups found that allow the formation of disulfide bonds?

    <p>In the R side chains of certain amino acids.</p> Signup and view all the answers

    What is the effect of oxidation on thiol groups in proteins?

    <p>It allows them to bond with other thiol groups to form disulfide bonds.</p> Signup and view all the answers

    Study Notes

    Amino Acids

    • Amino acids are the building blocks of proteins and peptides.
    • Some amino acids can be produced by the body, while others must be obtained from the diet.
    • Amino acids are crucial because proteins carry out enzymatic reactions in cells.
    • There are 20 naturally occurring amino acids.
    • All amino acids share a common core structure (NH2-CHR-COOH).
    • They differ based on their side chains (R groups).
    • In solution, amino acids exist as zwitterions (dipoles).
    • Most natural amino acids have an L configuration.

    Types of Amino Acid Side Chains

    • Aliphatic side chains (6) are generally hydrophobic and vary in steric bulk; Proline is an exception.
    • Aromatic side chains (4) include Histidine (weakly basic), Tyrosine (weakly acidic), Phenylalanine, and Tryptophan (bulky and hydrophobic).
    • Alcohols (2): Serine and Threonine.
    • Sulfur-containing groups (2): Cysteine (thiol), Methionine (thioether), and Selenocysteine (rare case).

    Classifying Amino Acids

    • Amino acids can be classified as acids, amides, and bases based on their side chains.
    • There are 2 carboxylic acids, 2 amides, a guanidine and an amine (strongly basic).

    Essential Amino Acids

    • Essential amino acids cannot be synthesized by the body and need to be obtained from the diet.
    • Humans require nine essential amino acids.
    • Consuming protein meets these dietary requirements.

    Peptide Bonds

    • Peptide bonds form amides between amino acids, replacing the charged groups of amino acids.
    • Peptide bonds create a resistant protein chain capable of hydrogen bonding.
    • Strong bases or acids can hydrolyze peptide bonds.

    Nucleic Acids

    • Three RNA bases form a codon, specifying an amino acid to be added to a protein chain.
    • Example: UUC = phenylalanine.
    • This process occurs within ribosomes.
    • DNA is transcribed into mRNA, acting as a template to code for proteins. During transcription, DNA must unzip and RNA polymerase generates an RNA strand on the template strand, with bases added only to the 3' end.

    tRNA (Transfer RNA)

    • tRNA carries specific amino acids to ribosomes during protein synthesis.
    • Anticodons on tRNA match the mRNA codons to attach the amino acids in the correct sequence.
    • Ribosomes move along the mRNA to catalyze protein synthesis (amino acid chain elongation).

    Protein Structure

    • Primary Structure: The amino acid sequence.
    • Secondary Structure: Folding of the amino acid chain, including a-helices and b-sheets due to hydrogen bonding patterns.
    • Tertiary Structure: Further folding of the protein chain, determining the 3D shape (e.g., domains).
    • Quaternary Structure: Arrangement of multiple polypeptide chains in a protein complex (e.g., hemoglobin).

    Protein Side-Chain Properties

    • Sidechains affect how proteins fold (e.g., hydrophobic interactions) and provide chemical functionality (e.g., ligand binding) in proteins.
    • Sidechains with lone pair functionalities can bind to metal ions (e.g. His, Met, Asp, Glu and Cys).

    Protein Interactions

    • Acidic and basic sidechains (e.g., Arg, Lys) form electrostatic interactions.
    • Weak interactions such as hydrogen bonding and van der Waals attractions contribute.

    Disulfide Bonds

    • Thiol groups (in cysteine) can form strong S-S bonds (disulfide bonds) to covalently link protein chains.
    • These bonds are used to stabilize protein structure.
    • An example of a protein with disulfide bonds is insulin.

    Tertiary Structure/Domains

    • Proteins may have tertiary structural elements and folded domains that create specific enzymatic reactions.
    • Subunits (parts) with separate functions may combine through evolution (e.g., cytochromes).

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    Description

    Test your knowledge on the essential concepts of protein structure, including alpha helices, amino acids, and their roles in biological processes. This quiz covers topics like tertiary structure, protein domains, and the fundamentals of tRNA in protein synthesis.

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