Amino Acids and Proteins - Practice Questions
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Questions and Answers

Aspartame, an artificial dipeptide sweetener containing phenylalanine, carries a warning for phenylketonurics. Which characteristic BEST describes phenylalanine?

  • Contains a sulfhydryl group
  • An aromatic amino acid (correct)
  • A dietary nonessential amino acid
  • Contains a hydroxyl group

    • GABA, a neurotransmitter, is formed by decarboxylation of an amino acid's alpha-carboxyl group. Which amino acid is MOST likely the precursor to GABA?

  • Tryptophan
  • Glycine
  • Glutamate (correct)
  • Aspartate

    • An enzyme involved in intermediary metabolism contains alpha-helices. Which statement BEST describes the alpha-helical secondary structure?

  • A structure favored by a high amount of proline residues
  • Stabilized by phosphodiester linkages
  • Stabilized by peptide bonds alone
  • Contains amino acids with their side chains towards the outside of the helix (correct)

    • A research group studies covalent bonds in the tertiary structure of proteins. Which bond are they MOST likely studying?

    <p>Disulfide bonds between two cysteine residues (B)</p> Signup and view all the answers

    In E. coli, glucose is converted to chorismate, an intermediate in the synthesis of histidine, phenylalanine, tyrosine, and tryptophan. Which of the following statements BEST describes gene expression for tryptophan synthesis in these bacteria?

    <p>Tryptophan acts as a co-repressor to attenuate transcription of the <em>trp</em> operon (B)</p> Signup and view all the answers

    During translation, a tRNA molecule interacts with mRNA. If the positions of nucleotides in the tRNA and mRNA are numbered sequentially, which position on the tRNA best indicates the location of the first nucleotide of the anticodon?

    <p>1 (B)</p> Signup and view all the answers

    A research laboratory studies a disease-causing gene leading to loss of enzyme function. Karyotyping and DNA microarray show no chromosomal changes. Northern blot analysis shows normal mRNA transcript levels. Western blot shows a smaller protein. Which mutation is most consistent with these findings?

    <p>One base pair insertion in an exon (C)</p> Signup and view all the answers

    Insulin undergoes modification after synthesis. The primary insulin translation product is modified to produce the mature hormone. Which modification is most likely observed during this process?

    <p>Hydrolytic cleavage of specific peptide bonds (C)</p> Signup and view all the answers

    A bacterial strain has reduced translation rates due to decreased activity in peptide bond formation; this inhibits ribosomal protein synthesis. A mutation in which of the following is most consistent with these findings?

    <p>One of the ribosomal RNAs (B)</p> Signup and view all the answers

    A mutation in the gene encoding aminoacyl-tRNA synthetase would directly affect which of the following processes?

    <p>Elongation during translation (B)</p> Signup and view all the answers

    A researcher introduces a mutation into the gene for a prokaryotic ribosomal protein. This mutation specifically impairs the ability of the ribosome to bind mRNA. Where is the most likely location of this mutation?

    <p>In the rRNA component that interacts with the Shine-Dalgarno sequence (B)</p> Signup and view all the answers

    Which of the following is NOT a typical modification that occurs to eukaryotic proteins after translation?

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

    When the anticodon of a tRNA base pairs with the codon of an mRNA, what is the orientation of their directionality?

    <p>Antiparallel, ensuring proper alignment and hybridization. (D)</p> Signup and view all the answers

    A lab observes a disease-causing gene exhibiting a loss of enzyme function. Karyotyping and DNA microarray reveal an unchanged chromosome structure. Northern blot analysis shows no change in mRNA transcript levels, but Western blot analysis indicates a smaller than normal protein. Which mutation is most likely responsible?

    <p>A single base pair insertion in an exon. (B)</p> Signup and view all the answers

    An insertion of 'GCG' into an exon of a gene will most likely result in which outcome?

    <p>The addition of one more amino acid into the polypeptide. (D)</p> Signup and view all the answers

    If the codon 'CCC' is mutated to 'CCG', what is the most likely consequence?

    <p>A silent mutation, with no change in the amino acid sequence. (D)</p> Signup and view all the answers

    What is the most likely outcome of a splice site mutation?

    <p>A splicing defect, potentially leading to an mRNA transcript of altered length. (D)</p> Signup and view all the answers

    A 99% reduction in promoter function will most likely lead to which of the following?

    <p>Reduced levels of mRNA expression and protein production. (D)</p> Signup and view all the answers

    If a western blot shows a smaller than normal protein, and a northern blot shows no change in mRNA transcript of the gene, what can you conclude?

    <p>The mutation most likely introduced a premature stop codon during translation. (A)</p> Signup and view all the answers

    In a scenario where a disease-causing gene shows no change in chromosome structure or mRNA transcript but produces a smaller protein, which mutation is least likely?

    <p>A large deletion spanning multiple exons, easily detectable via DNA microarray. (D)</p> Signup and view all the answers

    What event is crucial for ribosome function on a polycistronic mRNA during bacterial translation?

    <p>Recognition of some internal AUG sequences as start codons. (B)</p> Signup and view all the answers

    In the context of bacterial translation involving polycistronic mRNA, which statement accurately characterises the initiation process at AUG codons?

    <p>Only the initial AUG codon in the mRNA incorporates formyl-methionine (f-Met). (A)</p> Signup and view all the answers

    What type of post-translational modification is most likely observed during the maturation of insulin from its primary translation product?

    <p>Hydrolytic cleavage of specific peptide bonds (C)</p> Signup and view all the answers

    During translation, a researcher observes that multiple proteins are being produced from a single mRNA molecule in a bacterial cell. Which of the statements below is the likeliest explanation?

    <p>The mRNA is polycistronic, allowing for multiple start codons to initiate translation at different points. (C)</p> Signup and view all the answers

    A bacterial strain exhibits reduced rates of translation due to decreased activity in peptide bond formation. A mutation in which component is most consistent with these findings?

    <p>One of the ribosomal RNAs (C)</p> Signup and view all the answers

    Which modification does NOT occur post-translationally in eukaryotes?

    <p>Removal of formyl-methionine groups from the N-terminal end of the protein (D)</p> Signup and view all the answers

    Considering the structure and function of tRNA in translation, which position corresponds to the first nucleotide of the anticodon that interacts with the mRNA codon?

    <p>Position 5 (site of wobble in codon-anticodon interactions). (A)</p> Signup and view all the answers

    A researcher observes that a newly synthesized pre-proinsulin molecule is not being correctly processed into mature insulin. Which of the following is LEAST likely to be the cause?

    <p>A mutation in the gene encoding glucagon (D)</p> Signup and view all the answers

    A scientist mutates a bacterial gene, resulting in the production of a non-functional enzyme. Further analysis reveals that the mRNA transcribed from the mutated gene is polycistronic, but only the first protein in the cistron is produced. What is the most likely cause of this?

    <p>A mutation in the Shine-Dalgarno sequence of the downstream genes. (C)</p> Signup and view all the answers

    Which of the given options, is a direct participant in the recognition and alignment of mRNA on the ribosome during translation in prokaryotes?

    <p>The Shine-Dalgarno sequence of the mRNA (C)</p> Signup and view all the answers

    A researcher discovers a new bacterial species with a unique translation mechanism. The mRNA produced is polycistronic, but unlike other bacteria, each protein in the cistron is produced in equal amounts, regardless of its position in the mRNA. Which of the following would best explain this observation?

    <p>Each open reading frame has an equally efficient ribosome-binding site. (A)</p> Signup and view all the answers

    A researcher is studying a protein that requires glycosylation to be fully functional. Where would this process occur?

    <p>In the endoplasmic reticulum and Golgi apparatus (B)</p> Signup and view all the answers

    What is the function of the start codon AUG in eukaryotic protein synthesis?

    <p>It codes for the amino acid Methionine and initiates translation. (D)</p> Signup and view all the answers

    During translation, where does the amino acid bind to the tRNA?

    <p>The 3' end of the tRNA. (B)</p> Signup and view all the answers

    Which of the following antibiotics primarily inhibits the translocation step of translation in bacteria?

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

    During the nomenclature of a nucleic acid, how is the order in which it's named described?

    <p>5' to 3' direction. (B)</p> Signup and view all the answers

    Which of the given options is NOT required to achieve the elongation step in prokaryotic translation?

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

    Which of the following mutations is MOST likely to result in a protein that is produced in normal amounts but fails to be secreted from the cell?

    <p>A mutation affecting the signal sequence of a secreted protein . (C)</p> Signup and view all the answers

    Which of the following drugs inhibits bacterial DNA replication?

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

    What is the target of rifamycin?

    <p>Prokaryotic RNA polymerase (C)</p> Signup and view all the answers

    Which eukaryotic translation inhibitor targets peptidyl transferase activity?

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

    Which of the following drugs is classified as a nucleoside analog and inhibits DNA replication?

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

    Which of the following drugs inhibits eukaryotic RNA polymerase II?

    <p>Alpha-amanitin (B)</p> Signup and view all the answers

    Which of the following antibiotics inhibits the aminoacyl tRNA entry into the A site of the ribosome?

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

    Flashcards

    Aspartame

    An artificial dipeptide sweetener that includes phenylalanine.

    Phenylalanine

    An aromatic amino acid found in aspartame.

    GABA precursor

    Glutamate is the amino acid that forms GABA through decarboxylation.

    Alpha-helix

    A common secondary structure of proteins stabilized by hydrogen bonds.

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    Covalent bonds in proteins

    Bonds formed by side chains of amino acids, crucial for tertiary structure.

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    Disulfide bonds

    Covalent bonds between two cysteine residues that stabilize protein structure.

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    Chorismate

    An intermediate in the synthesis pathways for several amino acids.

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    Gene expression in E.coli

    Utilization of mRNA for enzyme production in tryptophan synthesis.

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    mRNA and enzyme production

    Five mRNA molecules lead to five enzymes through translation.

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    Post-translational processing

    A single polypeptide is modified to yield multiple functional enzymes.

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    Start codon recognition

    Some internal AUG sequences act as start codons during translation.

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    Formyl-methionine in translation

    Formyl-methionine is incorporated when the AUG codon is recognized by the ribosome.

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    Anticodon first nucleotide

    Position indicating the first nucleotide of the tRNA anticodon corresponds to the second position of the mRNA.

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    Mutation impact on enzyme function

    A specific mutation can lead to a smaller-than-normal protein lacking function.

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    Insulin modification after synthesis

    The primary insulin translation product undergoes specific modifications to mature into functional insulin.

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    Peptide bond formation mutation

    A mutation affecting the ribosome leads to decreased peptide bond formation during translation.

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    Antiparallel arrangement

    The orientation where tRNA anticodon pairs with mRNA codon in opposite directions.

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    Mutation types

    Alterations in DNA sequence which can affect protein function or structure.

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    Insertion mutation

    A mutation where one or more nucleotide pairs are added to the DNA sequence.

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    Frameshift mutation

    An insertion or deletion that alters the reading frame of the gene.

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    Silent mutation

    A mutation that does not change the amino acid sequence of the protein.

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    Splice site mutation

    A mutation that affects the splicing of pre-mRNA, potentially altering mRNA length.

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    Promoter function reduction

    Decrease in promoter activity resulting in lower mRNA transcription levels.

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    Western blot analysis

    A method used to detect specific proteins in a sample based on size.

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    Polycistronic mRNA

    A type of mRNA that encodes multiple proteins under one regulatory mechanism.

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    Internal AUG codons

    AUG sequences within a polycistronic mRNA that can initiate protein synthesis.

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    Formyl-methionine

    The modified form of methionine used as the first amino acid in bacterial protein synthesis.

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    Introns

    Non-coding segments of mRNA that are spliced out in eukaryotes.

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    Anticodon

    A set of three nucleotides on tRNA that pair with the corresponding codon on mRNA.

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    Wobble position

    The third nucleotide position in anticodon-codon pairing that allows non-traditional base pairing.

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    Nucleic acid naming convention

    Nucleic acids are always named from the 5’ to 3’ direction.

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    Mature insulin formation

    The process of converting pre-proinsulin to mature insulin through modifications.

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    Post-translational modification

    Changes made to a protein after translation, affecting its function and activity.

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    Hydrolytic cleavage

    The process of breaking peptide bonds in proteins, essential for insulin maturation.

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    Peptidyl transferase activity

    Catalytic activity of ribosomal RNA facilitating peptide bond formation during translation.

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    Ribosomal RNA

    RNA component of ribosomes that aids in protein synthesis by catalyzing peptide bond formation.

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    Insulin glycosylation

    Addition of sugar residues to proteins, but does not occur in insulin.

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    Signal peptide removal

    The process of removing a signal peptide from pre-proinsulin to form mature insulin.

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    Shine-Dalgarno sequence

    A ribosomal binding site on mRNA crucial for the initiation of translation in prokaryotes.

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    Erythromycin mechanism

    Inhibits the translocation step in bacterial translation.

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    Bacterial translation inhibitors

    Include chloramphenicol, streptomycin, tetracycline, and erythromycin.

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    Chloramphenicol action

    Inhibits peptidyl transferase activity in bacteria.

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    Cycloheximide role

    Inhibits eukaryotic peptidyl transferase activity.

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    Streptomycin function

    Inhibits initiation of translation in bacteria.

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    Rifamycin function

    Inhibits prokaryotic RNA polymerase, stopping transcription.

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    Eukaryotic transcription inhibitors

    Include alpha-amanitin and actinomycin D.

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    Nucleoside analogs

    Inhibit DNA replication; examples include cytarabine and azidothymidine.

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    Study Notes

    Amino Acids and Proteins - Practice Questions

    • Aspartame and Phenylketonurics: Aspartame, an artificial dipeptide sweetener, contains phenylalanine. Phenylketonurics should avoid aspartame. Phenylalanine is characterized as an aromatic amino acid.
    • GABA Precursor: GABA (gamma-aminobutyric acid) is a neurotransmitter formed by the decarboxylation of glutamate's alpha-carboxyl group.
    • Enzyme Secondary Structure: Enzymes with alpha-helices in their secondary structure are stabilized by hydrogen bonds, with side chains projecting outward. Proline residues do not favor this structure.
    • Covalent Bonds in Tertiary Structure: Covalent bonds, specifically disulfide bonds formed between cysteine residues, are found in the tertiary structure of proteins.
    • E. coli Metabolism and Gene Expression: Glucose metabolism leads to chorismate, a precursor to histidine, phenylalanine, tyrosine, and tryptophan biosynthesis. If tryptophan is needed, a single mRNA containing instructions for all five enzymes is produced.
    • tRNA Anticodon Position: Position 5 on the tRNA diagram displayed, typically indicates the nucleotide that starts the anticodon.

    Translation and RNA - Practice Questions

    • AUG Start Codon: The AUG codon, found in mRNA, is generally the start site of protein synthesis, but not all AUG codons are start codons. Formyl-methionine is incorporated into the polypeptide at the AUG start codon.
    • Martian Genetic Code Differences: The code for the amino acids in Martian microorganisms' genetic code may vary from the terrestrial genetic code.
    • Mutations and Protein Size: Small insertion mutations into an exon may affect the chromosome, mRNA and ultimately protein, size. The protein products will likely be shorter than in the normal form.
    • Insulin Modifications: Insulin is modified after synthesis, including the cleavage of specific peptide bonds. This process is not glycosylation.
    • Ribosomal Protein Synthesis Inhibition: Mutations in ribosomal proteins, ribosomal RNA and EF-Tu protein can disrupt translation.

    Additional Practice Questions

    • Protein Synthesis: Concept maps in the biochemistry textbook for this topic are important study references. Specific questions on amino acids, protein structure and protein synthesis are recommended for studying.
    • Genetic Mutations and Proteins: Small gene mutations can have major effects on protein structure and function, resulting in shortened or lengthened proteins.
    • Gene Expression Mechanisms: The use of specific mRNA messages that combine proteins for a pathway, rather then producing many mRNA segments is important in bacterial gene expression to simplify the process.
    • Bacterial Translation Inhibitors: Erythromycin inhibits the translocation step in bacterial protein synthesis, while other inhibitors have different mechanisms.

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    Test your knowledge on amino acids and proteins with this quiz. Explore topics such as amino acid structures, neurotransmitter synthesis, and the role of enzymes. Perfect for students studying biochemistry or related fields.

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