Protein Structure and Function Quiz
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Questions and Answers

What term describes the linear sequence of amino acids in a protein?

  • Secondary structure
  • Primary structure (correct)
  • Tertiary structure
  • Quaternary structure

    • Which structural level follows the primary structure of a protein?

  • Tertiary structure
  • Quaternary structure
  • Secondary structure (correct)
  • None of the above

    • How do functional groups impact protein functionality?

  • They stabilize quaternary structures.
  • They determine the amino acid sequence.
  • They contribute to enzymatic catalysis. (correct)
  • They limit protein folding.

    • What type of change can alter a protein’s functionality?

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

    Which structures can proteins form at the quaternary level?

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

    What is the unique feature of amino acids in relation to chirality?

    <p>They can exist as L or D isomers. (D)</p> Signup and view all the answers

    What process do nucleic acids use to code for proteins?

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

    Which of the following statements is true regarding amino acids?

    <p>They contain variable R groups that define their properties. (B)</p> Signup and view all the answers

    What is chirality as defined by Lord Kelvin?

    <p>A property of a figure that cannot coincide with its image through rotation and translation (B)</p> Signup and view all the answers

    What is a racemic mixture?

    <p>A mixture containing equal parts of L and R amino acids (D)</p> Signup and view all the answers

    What are zwitterions in the context of amino acids?

    <p>Molecules that contain both positively and negatively charged groups, remaining electrically neutral (D)</p> Signup and view all the answers

    What effect does the pH level have on amino acids in solution?

    <p>At low pH, amino acids become protonated, while high pH leads to deprotonation (A)</p> Signup and view all the answers

    Why can Asx (B) and Glx (Z) amino acids create ambiguity in protein sequences?

    <p>Because they differ only by terminal amide groups, which can be lost (A)</p> Signup and view all the answers

    What is one potential future application of synthetic systems using R-amino acids?

    <p>To create entire 'mirror image' lifeforms with distinct properties (A)</p> Signup and view all the answers

    What commonly affects the properties of synthetic biomolecules using R-amino acids?

    <p>The resilience to degradation compared to standard biomolecules (A)</p> Signup and view all the answers

    What specific aspect about amino acid sequences is important for protein function?

    <p>The linear sequence of amino acids (A)</p> Signup and view all the answers

    Which amino acid is known for its ability to readily gain and lose H+ ions at physiological pH?

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

    What is the importance of the sequence of a protein?

    <p>It specifies the protein's structure, which in turn defines its function. (B)</p> Signup and view all the answers

    At physiological pH, what form does the side chain of aspartate normally take?

    <p>Negatively charged form (A)</p> Signup and view all the answers

    What characteristic is shared by aspartate and glutamate in proteins?

    <p>Both are ionizable amino acids. (C)</p> Signup and view all the answers

    Which protein was the first to be fully sequenced, earning James D. Watson a Nobel prize?

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

    What is the pKa of a terminal amino group in amino acids?

    <p>8.0 (D)</p> Signup and view all the answers

    What role does methionine typically play in protein synthesis?

    <p>It is often the first amino acid due to the start codon ATG. (A)</p> Signup and view all the answers

    What flavor is glutamate known to provide in certain foods?

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

    Which amino acid is unique for not being chiral?

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

    What type of bonds can cysteine residues form?

    <p>Covalent disulfide bridges that stabilize protein conformation. (B)</p> Signup and view all the answers

    How many hydrophobic amino acids are listed in the content?

    <p>9 (A)</p> Signup and view all the answers

    What non-standard amino acid can be encoded by the UGA stop codon?

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

    In terms of polarity, which statement is true about polar amino acids?

    <p>They attract water molecules due to uneven electron distribution. (C)</p> Signup and view all the answers

    Which amino acid contains a pyrrolidine ring structure due to its unique properties?

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

    Which amino acid has a side chain that is considered polar and ionizable?

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

    What distinguishes hydrophobic amino acids from others?

    <p>They possess alkane chains that are pushed away from water. (A)</p> Signup and view all the answers

    What defines an amino acid as essential for an organism?

    <p>It must be obtained through the organism's diet due to insufficient synthesis. (A)</p> Signup and view all the answers

    Which amino acid is known to modulate the mTORC1 complex?

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

    What is the implication of ample leucine levels in an organism?

    <p>It negatively inhibits mTOR, signaling adequate growth resources. (A)</p> Signup and view all the answers

    How can exercise influence appetite according to the functions of phenylalanine?

    <p>By modulating appetite in response to lactic acid levels. (D)</p> Signup and view all the answers

    What role does SOD1 play in cellular function?

    <p>It regulates the buildup of free radicals. (C)</p> Signup and view all the answers

    What kind of mutations can precipitate severe consequences related to ALS?

    <p>Single amino acid substitutions. (A)</p> Signup and view all the answers

    In the context of gene mutations, what is the term used to describe the variability in disease onset and progression?

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

    What is the function of glutamate in the nervous system?

    <p>It is the principal excitatory neurotransmitter. (A)</p> Signup and view all the answers

    Study Notes

    Protein Structure and Function

    • Proteins are essential biomolecules involved in various biological processes like replication, homeostasis, structural support, cell signaling, and developmental coordination.
    • Nucleic acids code for proteins in a linear fashion, where each nucleotide triplet corresponds to one amino acid.
    • The linear sequence of amino acids, called the primary structure, folds into secondary structures like alpha helices and beta sheets.
    • These secondary structures interact and form the tertiary structure, the final folded form of the polypeptide.
    • Multiple proteins can assemble into larger complexes like homodimers, heterodimers, and tetramers, representing the quaternary structure.
    • The 3-dimensional structure of proteins can be determined using X-ray diffraction, providing insight into protein function and activity.
    • Functional groups within amino acids contribute to protein-driven enzymatic catalysis.
    • Major functional groups in amino acids include carboxyl (OH-C=O), amino (NH2), and the variable R group.
    • Proteins interact with other molecules like nucleic acids, lipids, and polysaccharides, shaping cellular processes.
    • Proteins can undergo conformational change, altering their functionality and interactions.

    Amino Acid Structure and Properties

    • There are 20 standard amino acids used in all living organisms.
    • Each amino acid is characterized by its unique R group, which defines its chemical properties.
    • Amino acids are chiral molecules, existing as L (Laevorotatory) or D (Dextrorotatory) isomers.
    • All life on Earth utilizes L-amino acids.
    • In aqueous solutions, amino acids exist as zwitterions, containing both positive and negative charges.
    • Outside the physiological pH range, amino acids can exist in non-dipolar forms, with both sides protonated in acidic conditions and deprotonated in basic conditions.
    • Amino acid abbreviations are crucial for avoiding ambiguity in peptide sequences.
    • The sequence of amino acids determines the structure and function of proteins.
    • The first protein to be fully sequenced was insulin.
    • Edman degradation was instrumental in sequencing numerous proteins.
    • Protein sequence knowledge facilitated the understanding of the Central Dogma (DNA -> RNA -> Protein).

    Amino Acid Groups and Properties

    • Hydrophobic Amino Acids:

      • Contain alkane chains
      • Repelled by water molecules
      • Important for protein folding and membrane interactions

    • Methionine:

      • Often the first amino acid in a protein
      • Corresponds to the start codon ATG
      • Found in both prokaryotes and eukaryotes

    • Proline:

      • Unique structural property connecting back to the amino group
      • Forms a pyrrolidine ring
      • Impacts protein flexibility and folding

    • Glycine:

      • Non-chiral
      • Provides flexibility in protein structures

    • Polar Amino Acids:

      • Uneven electron distribution
      • Partial charges attract water molecules
      • Often found on the surface of proteins

    • Cysteine:

      • Can form disulfide bridges, covalent bonds that stabilize protein structure
      • Highly reactive, often found inside proteins

    • Histidine:

      • Found near active sites of enzymes
      • Imidazole group facilitates protonation and deprotonation at physiological pH
      • Important for enzyme catalysis

    • Aspartate/Aspartic Acid:

      • Negatively charged at physiological pH
      • Typically found on the surface of proteins

    • Glutamate/Glutamic Acid:

      • Negatively charged at physiological pH
      • Contributes to umami flavor in food

    • pKa:

      • Represents the pH at which 50% of a substance is deprotonated
      • Helps predict the protonation state of amino acids at different pH values

    Essential Amino Acids

    • Essential amino acids cannot be synthesized by the organism fast enough and must be obtained from the diet.
    • The essentiality of an amino acid can vary depending on the organism.

    Additional Roles of Amino Acids

    • Amino acids play critical roles beyond protein synthesis.
    • They maintain nitrogen homeostasis.
    • They can be metabolized for energy.
    • They serve as signaling molecules and neurotransmitters.

    Example of Amino Acid Changes in Disease

    • SOD1 is an enzyme crucial for protecting against free radicals.
    • Mutations in SOD1 can lead to ALS (Amyotrophic Lateral Sclerosis) and motor neuron disease.
    • Single amino acid substitutions can have dramatic effects on protein function and lead to disease.
    • ALS highlights the complex relationship between genetics, disease phenotypes, and the variability in disease progression.

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    Biochem Exam 2 Lecture 1 PDF

    Description

    Test your knowledge on the intricate world of proteins! This quiz covers the essential roles of proteins, their structures from primary to quaternary, and the techniques used to determine their 3D shapes. Deepen your understanding of how proteins impact biological processes.

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