Expression of genes
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Questions and Answers

What describes the process by which proteins attain their biologically active form?

  • Folding (correct)
  • Denaturation
  • Condensation
  • Hydrolysis

    • Which level of protein structure involves the linear order of amino acids?

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

    • What type of bond links amino acids together in a polypeptide chain?

  • Disulfide bond
  • Peptide bond (correct)
  • Hydrogen bond
  • Ionic bond

    • Which statement about hemoglobin is true?

    <p>It binds iron to transport oxygen.</p> Signup and view all the answers

    What is the main consequence of a protein becoming denatured?

    <p>It loses its biological activity.</p> Signup and view all the answers

    How many types of amino acids do proteins consist of?

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

    What determines the unique properties of each amino acid?

    <p>Sidechain, R</p> Signup and view all the answers

    Which level of protein structure involves the association of multiple polypeptide chains?

    <p>Quaternary structure</p> Signup and view all the answers

    Which of the following describes a characteristic of enzymes?

    <p>They speed up chemical reactions.</p> Signup and view all the answers

    What type of interaction stabilizes tertiary structure in proteins?

    <p>Hydrogen bonding between sidechains</p> Signup and view all the answers

    What is the primary function of the polyA tail in mRNA?

    <p>Stabilizes the mRNA molecule</p> Signup and view all the answers

    What process occurs during splicing of mRNA?

    <p>Concatenation of exons to form mature mRNA</p> Signup and view all the answers

    What role does tRNA play in the translation process?

    <p>Brings amino acids to the ribosome matching the mRNA codons</p> Signup and view all the answers

    In the ribosome, which sites are involved in the elongation of the polypeptide chain?

    <p>A, P, E sites</p> Signup and view all the answers

    What characterizes wild type mutations?

    <p>Normal nucleotide sequence</p> Signup and view all the answers

    Which of the following describes a missense mutation?

    <p>Changes one amino acid for another</p> Signup and view all the answers

    What is a common effect of frameshift mutations?

    <p>Premature stop codons introduced soon after</p> Signup and view all the answers

    Which statement accurately describes the redundancy in the genetic code?

    <p>Many amino acids are specified by multiple codons.</p> Signup and view all the answers

    How does tRNA become charged with the appropriate amino acid?

    <p>Through the action of tRNA synthetase enzymes</p> Signup and view all the answers

    In the process of transcription, at which stage does RNA polymerase bind to the DNA?

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

    Which component of protein synthesis acts as the enzyme linking amino acids together?

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

    What is the function of the A site in the ribosome during translation?

    <p>Binds incoming tRNA with the corresponding amino acid</p> Signup and view all the answers

    What is the primary function of mRNA capping in eukaryotes?

    <p>To protect the mRNA from degradation.</p> Signup and view all the answers

    Which of the following statements about the genetic code is false?

    <p>A codon consists of two nucleotides.</p> Signup and view all the answers

    Which characteristic is true for RNA polymerase during transcription?

    <p>It detaches from the DNA strand at the termination stage.</p> Signup and view all the answers

    Which statement correctly explains the directional flow of genetic information?

    <p>Information flows from DNA to RNA to protein.</p> Signup and view all the answers

    How many stop codons are present in the genetic code?

    <p>3</p> Signup and view all the answers

    What is the role of transcription factors (TFs) in the initiation of transcription?

    <p>To assist RNA polymerase in binding to the promoter.</p> Signup and view all the answers

    During transcription, which nucleobase pairs with adenine in the RNA strand?

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

    Which of the following is not a stage of transcription?

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

    What is the primary consequence of a single mutation in the DNA that affects hemoglobin?

    <p>Clumping of hemoglobin and reduced oxygen transport</p> Signup and view all the answers

    Which of the following accurately lists the levels of protein structure?

    <p>Primary, secondary, tertiary, and quaternary</p> Signup and view all the answers

    What phenomenon occurs if a frameshift mutation is a multiple of 3?

    <p>No significant effect on protein structure</p> Signup and view all the answers

    What role does RNA polymerase play in gene expression?

    <p>Facilitates the transcription of DNA into mRNA</p> Signup and view all the answers

    In the context of mutations, what is primarily affected in protein coding genes?

    <p>The sequence of amino acids in proteins</p> Signup and view all the answers

    Which process involves the translation of mRNA into proteins?

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

    What is a result of sickle cell hemoglobin in red blood cells?

    <p>Results in stretched, sickle-shaped red blood cells</p> Signup and view all the answers

    What is the correct flow of genetic information as per the central dogma?

    <p>DNA – RNA – Protein</p> Signup and view all the answers

    What occurs in post-transcriptional processing?

    <p>Introns are removed and exons are spliced together</p> Signup and view all the answers

    Which of the following best defines a gene?

    <p>A sequence of nucleotides that codes for a protein</p> Signup and view all the answers

    Study Notes

    Protein Structure and Function

    • Proteins perform diverse functions based on their structures.
    • Protein structures enable a wide range of functions including digestion (enzymes), storage (ovalbumin), defense (antibodies), transport (hemoglobin), signaling (receptors), structural support (keratin), coordination (insulin), and movement (actin-myosin).
    • Protein function depends on biochemical properties determined by their structure.
    • Antibody protein surfaces match target antigens enabling recognition.
    • Hemoglobin protein pockets fit heme chemicals, enabling iron to transport oxygen.

    Protein Folding

    • Folded proteins have a final and stable structure and are active.
    • Denatured proteins are unfolded and inactive.
    • Proteins must fold to be biologically active.

    Protein Structure Levels

    • Primary structure: The linear order of amino acids in a polypeptide chain.
    • Secondary structure: Hydrogen bonding between nearby amino acids in the polypeptide backbone forming structures like alpha-helices and beta-sheets.
    • Tertiary structure: Interactions between side chains stabilize the protein into a 3D shape (often a globular shape) influencing the protein's function.
    • Quaternary structure: Close association of two or more polypeptide chains assembling into a larger functional unit.

    Proteins from Amino Acids

    • Proteins are polymers of amino acids.
    • Amino acids have a common structure:
      • An amino group
      • A carboxyl group
      • A central alpha carbon
      • A variable side chain (R group)
    • The unique side chains impart different properties to each amino acid type.

    Amino Acid Polymers

    • Amino acid polymers link via peptide bonds.
    • Peptide bonds form between amino acids in the backbone.
    • Proteins consist of 50-5000 amino acids.
    • Polypeptide chains have N-terminus and C-terminus.

    20 Amino Acid Types

    • Side chains confer unique properties to the different amino acid types
    • Proteins have a chemical toolkit of 20 amino acids.
    • Categorized into chemical types: hydrophobic, non-polar; nonpolar; polar; charged hydrophilic.

    Central Dogma of Molecular Biology

    • The central dogma describes the flow of genetic information, from DNA to RNA to protein.
    • "Once sequence information has passed into protein it cannot get out." - Crick, 1956
    • DNA -> RNA -> Protein

    Genetic Code: DNA Translates to Protein

    • Universal code: the genetic code is the same in all living organisms
    • Codons: 20 amino acids but 4 bases, so it takes multiple bases to encode each amino acid.
    • The code uses groups of three nucleotides, codons, each determining a specific amino acid.
    • Each codon has multiple possibilities in each of its three nucleotide positions meaning there are 64 possible amino acid codons.

    Genetic Code is Redundant

    • For most amino acids, there is more than one codon leading to redundancy.
    • There are 3 stop codons and 1 start codon which is shared.

    Transcription: Making mRNA

    • Initiation: RNA polymerase binds to a start point and transcription factors assist.
    • Elongation: RNA polymerase moves along the DNA template strand synthesizing RNA in the 5' to 3' direction. Uracil (U) in RNA pairs with adenine (A) in DNA;
    • Termination: RNA polymerase detaches from the DNA template completing the transcription process enabling it to restart another cycle.

    RNA Post-Transcriptional Processing

    • Occurs only in eukaryotes
    • Capping: A modified guanine nucleotide is added to the 5' end of the pre-mRNA in a protective role.
    • Polyadenylation: 50-250 adenine nucleotides are added to the 3' end of the pre-mRNA creating a poly(A) tail facilitating stabilization.
    • Splicing: Introns (non-coding segments) are removed and exons (coding segments) are joined forming mature mRNA containing only protein-coding sequences.

    Translation: mRNA to Protein

    • mRNA processed transcript acts as a blueprint of the sequence of codons.
    • tRNA adapter holds matching anticodon and complementary amino acids.
    • Ribosome enzymes chain amino acids into polypeptides.
    • tRNA synthetase enzymes charge tRNA.
    • Ribosomes bind mRNA and tRNAs to catalyze translation.

    Mutations and Protein Function

    • Mutations are changes in a gene's coding sequence.
    • Substitution mutations change nucleotides, leading to different outcomes: silent mutation (same amino acid), missense mutation (different amino acid), nonsense mutation (stop codon).
    • Frameshift mutations cause insertions/deletions, resulting in premature stop codons or many incorrect amino acids.
    • Mutations can cause genetic diseases; e.g., sickle cell anemia.

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