Genetics: Codons and Ribosomes Quiz
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Questions and Answers

A set of 3 nucleotides that specifies a particular amino acid is called a ______.

codon

Which of the following is NOT a termination codon?

  • AUG (correct)
  • UGA
  • UAG
  • UAA

    • The genetic code is a set of rules that defines how DNA is translated into RNA.

    False (B)

    What is the significance of the AUG codon?

    <p>The AUG codon serves as the start codon, indicating where the ribosome should begin translation of the mRNA sequence.</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Codon = A set of three nucleotides that specifies a particular amino acid Reading frame = The series of nucleotides read in sets of 3 (codon) Start codon = The AUG codon that signals the beginning of translation Termination codon = A codon that signals the end of translation</p> Signup and view all the answers

    How many codons are present in the following mRNA sequence: A U A U A U G C C C G C ?

    <p>4 (D)</p> Signup and view all the answers

    The genetic code is degenerate, meaning that most amino acids are specified by only one codon.

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

    The synthesis of proteins is guided by information carried by ______ molecules.

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

    The growing carboxyl end of the polypeptide chain remains activated by its covalent attachment to a tRNA molecule.

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

    What is the primary function of the small subunit of a ribosome?

    <p>Provides a framework for tRNA matching to mRNA codons (B)</p> Signup and view all the answers

    What are the two main components of a ribosome?

    <p>A large subunit and a small subunit</p> Signup and view all the answers

    Ribosomes are complex catalytic machines made from ______ and several RNA molecules.

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

    Match the following components with their corresponding functions:

    <p>mRNA = Carries genetic information from DNA to ribosomes tRNA = Delivers amino acids to the ribosome Ribosomal proteins = Structural and catalytic components of ribosomes rRNA = Essential for ribosome structure and function</p> Signup and view all the answers

    Eukaryotic ribosomes are assembled in the cytoplasm.

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

    How does the mRNA move through the ribosome?

    <p>It is pulled through by a motor protein (C)</p> Signup and view all the answers

    What is the approximate rate of error in protein synthesis?

    <p>1 mistake per 10,000 amino acids</p> Signup and view all the answers

    Protein glycosylation is the most frequent type of covalent modification.

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

    What is the primary role of molecular chaperones?

    <p>To aid in the folding of proteins (C)</p> Signup and view all the answers

    Many molecular chaperones are called ______ proteins, as their synthesis increases significantly after exposure to elevated temperatures.

    <p>heat-shock</p> Signup and view all the answers

    Name two major families of eukaryotic molecular chaperones.

    <p>Hsp60 and Hsp70</p> Signup and view all the answers

    Match the following molecular chaperones with their respective locations:

    <p>Hsp60 = Mitochondria Hsp70 = Cytosol BIP = Endoplasmic reticulum</p> Signup and view all the answers

    In prokaryotes, the ______ sequence, also known as the Shine–Dalgarno sequence, is located upstream of the AUG start codon and helps position it in the ribosome.

    <p>ribosome binding site</p> Signup and view all the answers

    Eukaryotic mRNAs are typically polycistronic, meaning they encode for multiple proteins from a single mRNA molecule.

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

    What is the role of the Shine-Dalgarno sequence in bacterial translation?

    <p>It helps position the ribosome at the start codon. (D)</p> Signup and view all the answers

    What are the three stop codons that signal the termination of translation?

    <p>UAA, UAG, and UGA</p> Signup and view all the answers

    Which of the following is NOT a feature of translation initiation in eukaryotes?

    <p>Presence of a Shine-Dalgarno sequence (B)</p> Signup and view all the answers

    The small ribosomal subunit can bind to the mRNA independently of the large ribosomal subunit in eukaryotes.

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

    Explain why a bacterial ribosome can directly assemble on a start codon located in the interior of an mRNA molecule.

    <p>Bacterial mRNAs lack a 5' cap and rely on the Shine-Dalgarno sequence for ribosome binding. As a result, the ribosome can readily assemble on the start codon wherever it's located in the mRNA, as long as it's preceded by the appropriate ribosome-binding site.</p> Signup and view all the answers

    The initiator tRNA in prokaryotes is always charged with the amino acid ______.

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

    What is the primary difference between eukaryotic and prokaryotic translation initiation?

    <p>Eukaryotes use a 5' cap to initiate translation, while prokaryotes use a Shine-Dalgarno sequence. (A)</p> Signup and view all the answers

    The production of Pol gene products is a continuous process, with constant production occurring throughout the cell cycle.

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

    What is the primary reason for the limited production of Pol gene products?

    <p>The upstream translational frameshift only occurs occasionally. (A)</p> Signup and view all the answers

    The frameshift required for Pol gene product production occurs at a specific ______ in the mRNA.

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

    What is the significance of the structural feature of the RNA sequence downstream of the frameshift site in the production of Pol gene products?

    <p>The downstream RNA sequence provides a specific recoding signal that is necessary for the frameshift to occur.</p> Signup and view all the answers

    Why are inhibitors of prokaryotic protein synthesis useful as antibiotics?

    <p>All of the above (D)</p> Signup and view all the answers

    Match the following components of eukaryotic protein synthesis with their respective functions:

    <p>mRNA = Carries the genetic code specifying the amino acid sequence of a protein tRNA = Delivers specific amino acids to the ribosome tRNA synthetases = Attach the correct amino acid to its corresponding tRNA Ribosomes = Act as the site of protein synthesis, facilitating the interaction of mRNA and tRNA</p> Signup and view all the answers

    Ribosomes are stationary structures that remain in place during the entire translation process.

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

    What is the primary role of initiation factors in eukaryotic protein synthesis?

    <p>Initiation factors are crucial for the assembly of the translation initiation complex, ensuring the correct positioning of mRNA and the initiator tRNA on the ribosome.</p> Signup and view all the answers

    The process of ______ increases the efficiency of protein synthesis by allowing multiple ribosomes to translate a single mRNA molecule simultaneously.

    <p>polysome formation</p> Signup and view all the answers

    Which of the following factors does NOT contribute to rapid ribosome recycling after translation?

    <p>The presence of a specific termination codon at the 3' end of the mRNA (D)</p> Signup and view all the answers

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    Flashcards

    Codon

    A set of 3 nucleotides that specifies an amino acid.

    Reading frame

    The order in which codons are read in sets of 3 for translation.

    Genetic code

    Rules that define how DNA is translated into amino acids.

    Degeneracy of genetic code

    Most amino acids are specified by more than one codon.

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    AUG codon

    The start codon that signals the beginning of translation.

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    Stop codons

    Codons that signal the termination of protein translation.

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    Triplet code

    The system of reading codons in groups of three nucleotides.

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    Peptidyl-tRNA

    A covalently attached tRNA that holds growing polypeptide chains.

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    mRNA

    Molecule that carries genetic information for protein synthesis from DNA to ribosomes.

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    Ribosome

    A complex molecular machine that decodes mRNA to synthesize proteins.

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    Ribosomal subunits

    Ribosomes consist of a large and a small subunit that combine during protein synthesis.

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    Catalyze peptide bond formation

    The large ribosomal subunit's role in linking amino acids together into a polypeptide chain.

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    Transcription in nucleolus

    Process where ribosomal RNA (rRNA) is transcribed and assembled with proteins.

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    Ribosomal RNA (rRNA)

    RNA molecules that form core structural and functional components of ribosomes.

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    Amino acid sequence

    The specific order of amino acids that form a protein, determined by mRNA codons.

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    Pol gene products

    Small amounts produced due to translational frameshift in Gag protein.

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    Translational frameshift

    A shift in reading that allows skipping stop codons during translation.

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    Polysomes

    Clusters of ribosomes translating the same mRNA simultaneously.

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    Ribosome recycling

    The rapid disengagement and reuse of ribosomal subunits after translation.

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    tRNA synthetases

    Enzymes that charge tRNA with appropriate amino acids before translation.

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    Translation initiation factors

    Proteins that assist the beginning phase of translation process.

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    Elongation factors

    Proteins that assist in the elongation phase of protein synthesis.

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    Termination factors

    Proteins involved in ending the translation process at stop codons.

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    Methionine tRNAs

    Two types of tRNA for methionine, but only one initiates translation.

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    Peptidyl transferase activity

    Catalytic function of ribosomes that forms peptide bonds between amino acids.

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    Covalent modifications

    Chemical alterations to proteins that affect their function, such as glycosylation and phosphorylation.

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    Molecular chaperones

    Proteins that assist in the proper folding of other proteins during synthesis and post-synthesis.

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    Heat-shock proteins (Hsp)

    A class of molecular chaperones that increase in quantity during heat stress to protect proteins from misfolding.

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    Hsp60 and Hsp70

    Two major families of heat-shock proteins that assist in protein folding in different cellular environments.

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    ATP hydrolysis in chaperones

    The process by which molecular chaperones use energy from ATP to aid in the folding and release of substrates.

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    GTP hydrolysis in translation

    A process essential for protein synthesis where GTP is hydrolyzed to provide energy for ribosomal assembly.

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    Initiator tRNA

    The methionine-charged tRNA that can bind to the small ribosomal subunit to start translation.

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    Shine-Dalgarno sequence

    A specific ribosome binding site on bacterial mRNA that initiates translation.

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    16S rRNA

    A component of the small ribosomal subunit that pairs with the Shine-Dalgarno sequence.

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    Polycistronic mRNA

    Bacterial mRNA that encodes multiple proteins due to internal start codons.

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    Uncapped bacterial mRNA

    Bacterial mRNA lacks a 5’ cap, unlike eukaryotic mRNA.

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    Translation factors

    Proteins that assist in the initiation and assembly of ribosomes during translation.

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    Eukaryotic mRNA characteristics

    Typically encodes a single protein and has a 5’ cap for ribosome binding.

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    Study Notes

    Molecular Basis of Gene Mutations

    • Mutations are changes in DNA that impact genetic information.
    • They can occur at the molecular or chromosomal level.
    • Mutation effects vary greatly.
    • Mutations are essential for evolution.
    • A "mutant" refers to an organism with an unusual phenotype.

    Types of Mutations

    • Somatic Mutations: Occur in body cells (excluding germ cells).
      • Do not affect offspring.
    • Germ-line Mutations: Occur in germ cells.
      • Can be transmitted to offspring.

    Mutations in DNA Can Alter Proteins

    • Examples of disease-causing mutations:
      • Beta-globin gene mutations (e.g., sickle cell disease) result in a base pair change in the beta-globin gene, causing the amino acid glutamic acid to become valine. This change distorts the structure of red blood cells.
      • Collagen mutations (deletions, insertions, RNA splicing mutations, single-base substitutions) are linked to common disorders like osteoarthritis, osteoporosis, and aortic aneurysms.
      • Alzheimer's disease mutations: mutations in the genes encoding APP, APOE, PSEN1, and PSEN2.

    Mutations

    • May occur spontaneously or due to exposure to radiation or chemicals (mutagens).

    Spontaneous Mutation

    • Not caused by exposure to known mutagens.
    • Errors during DNA replication.
    • Mismatched base pairs or loss of nucleotides during replication.

    Induced Mutation

    • Caused by mutagens, some of which are also carcinogens (cancer-causing).
    • Radiations (e.g., UV light, X-rays).
    • Chemicals (both natural and synthetic).
    • Site-directed mutagenesis: a technique to create specific and intentional DNA sequence changes for research purposes.

    Types of Mutations (Point Mutations)

    • Point Mutation: A mistake changing a single base on a DNA molecule.
      • Transition: A pyrimidine replaces another pyrimidine (e.g., T to C) or a purine replaces another purine (e.g., A to G).
      • Transversion: A purine replaces a pyrimidine (e.g., A to T) or vice versa.
    • Silent Mutation: Does not alter the amino acid coded for.
    • Missense Mutation: Changes the codon, causing a substitution of an amino acid. This can alter or destroy protein function (e.g., sickle cell disease).
    • Nonsense Mutation: Changes a codon for an amino acid into a stop codon. Results in a truncated, often nonfunctional protein.
    • Insertion or Deletion Mutation: Addition or subtraction of a nucleotide not in multiples of 3 disrupts the reading frame of the gene.
      • Frameshift Mutation: Alters amino acids after the point of mutation, drastically changing the protein's structure and function.

    Not all Mutations Affect Protein Function

    • Silent Mutations: Do not affect the amino acid sequence, thus not impacting protein function.
    • Example: AAA to AAG both code for lysine (same amino acid) => no change in protein.

    Factors that can contribute to mutation rates:

    • The cell's DNA repair mechanisms.
    • The environment the cell is exposed to.
    • Spontaneous DNA damage such as depurination and deamination.

    DNA Repair Mechanisms

    • Excision Repair: Removes damaged DNA segments.

      • Nucleotide excision repair: Removes 20-30 base segments of damaged DNA.
      • Base excision repair: Removes 1-5 bases, often caused by oxidative damage or chemical reactions.

    • Mismatch Repair: Repairs errors introduced during DNA replication.

    • Double-strand breaks:

      • Nonhomologous End Joining: Quickly repairs double-strand breaks in DNA, but may introduce deletions.
      • Homologous Recombination: More accurate, using sister chromatids for repair, but is slow

    Co-Translational Protein Folding

    • Proteins may start folding as they are synthesized by ribosomes, which influences its final functionality.

    Molecular Chaperones

    • Assist in protein folding, helping to correct misfolded proteins or direct them to the correct compartments.
    • Types include HSP60, and HSP70- proteins
    • These chaperones are important for proper biological functioning.

    Protein synthesis by free and membrane-bound ribosomes

    • Proteins targeted to different locations use free or membrane-bound ribosomes.
    • Free ribosomes manufacture proteins intended for the cytoplasm.
    • Membrane-bound ribosomes synthesize proteins destined for the endomembrane system (ER, Golgi, lysosomes, etc).

    Protein Import

    • Proteins are transported to their designated locations by various mechanisms, often involving signal sequences.

    Summary

    • This covers many aspects of DNA structure, function, and expression, from the molecular level up to whole-organism implications, so it's quite a broad topic.

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    Description

    Test your knowledge on genetic codons and the structure of ribosomes in this comprehensive quiz. Explore concepts such as termination codons, translation, and the roles of various components involved in protein synthesis. Perfect for students studying genetics or molecular biology!

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