Molecular Biology of the Gene - Part 2
44 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

In prokaryotic cells, translation of mRNA can begin before transcription is complete.

True (A)

What separates transcription and translation in eukaryotic cells?

  • Golgi apparatus
  • Ribosomes
  • Nuclear envelope (correct)
  • Cytoplasm

    • The initial RNA transcript from a gene, before processing, is called a ______.

    primary transcript

    Describe the central dogma of molecular biology.

    <p>The central dogma states that genetic information flows from DNA to RNA to protein.</p> Signup and view all the answers

    Match the following terms with their corresponding descriptions:

    <p>Template strand = The DNA strand used as a template for RNA synthesis Coding strand = The DNA strand with the same sequence as the mRNA, except with T instead of U Codon = A three-nucleotide sequence in mRNA that specifies an amino acid RNA processing = Modifications made to eukaryotic RNA transcripts to produce mature mRNA</p> Signup and view all the answers

    How many nucleotides are typically required to code for a single amino acid?

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

    The template strand for a gene is always the same strand, regardless of the gene's location on the chromosome.

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

    What is the direction of codon reading during translation?

    <p>The codons are read in the 5' to 3' direction.</p> Signup and view all the answers

    What is the primary function of the three 'stop' codons in the genetic code?

    <p>To signal the end of translation (C)</p> Signup and view all the answers

    The genetic code is ambiguous, meaning a single codon can code for multiple amino acids.

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

    What is the name of the enzyme responsible for catalyzing RNA synthesis during transcription?

    <p>RNA polymerase</p> Signup and view all the answers

    The DNA sequence where RNA polymerase attaches is called the ______

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

    What are the noncoding segments of a gene called?

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

    Exons are the segments of a gene that are not expressed.

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

    What is the primary function of spliceosomes?

    <p>To remove introns from RNA transcripts.</p> Signup and view all the answers

    Ribozymes are catalytic RNA molecules that function as __________.

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

    Match the following terms with their descriptions:

    <p>Introns = Noncoding segments of genes Exons = Coding regions of genes Spliceosome = RNA-protein complex that removes introns Alternative RNA splicing = Produces different proteins from the same gene</p> Signup and view all the answers

    What does alternative RNA splicing allow for in a gene?

    <p>The production of different proteins (C)</p> Signup and view all the answers

    Ribozymes can only catalyze splicing reactions.

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

    How does exon shuffling contribute to protein evolution?

    <p>It mixes and matches exons between different genes to create new proteins.</p> Signup and view all the answers

    What does the P site of the ribosome hold?

    <p>The tRNA carrying the growing polypeptide chain (D)</p> Signup and view all the answers

    The three stages of translation are initiation, elongation, and cessation.

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

    What amino acid does the initiator tRNA carry?

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

    During translation, the ribosome moves along the mRNA in a ________ direction.

    <p>5′ → 3′</p> Signup and view all the answers

    Which of these steps occur during the elongation phase of translation?

    <p>Addition of amino acids to the growing chain (C)</p> Signup and view all the answers

    Match the following binding sites with their functions:

    <p>P site = Holds growing polypeptide chain A site = Binds next amino acid tRNA E site = Exit site for discharged tRNA</p> Signup and view all the answers

    Energy is required for all steps of the translation process.

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

    What happens when a stop codon reaches the A site during translation?

    <p>A release factor activates and releases the polypeptide.</p> Signup and view all the answers

    What is the function of transcription factors in the initiation of transcription?

    <p>To guide the binding of RNA polymerase (C)</p> Signup and view all the answers

    The TATA box is a promoter that is crucial for forming the initiation complex in prokaryotic cells.

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

    What do the 5′ cap and the poly-A tail do for the mRNA molecule?

    <p>They facilitate export to the cytoplasm, protect from hydrolytic enzymes, and help ribosomes attach.</p> Signup and view all the answers

    In eukaryotes, RNA polymerase II transcribes the _____ signal sequence during termination.

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

    Match the processes or components involved in transcription with their descriptions:

    <p>Promoters = Signal the transcription start point RNA polymerase = Synthesizes the RNA strand Transcription initiation complex = Assembly of RNA polymerase and transcription factors RNA processing = Modifying pre-mRNA in the nucleus</p> Signup and view all the answers

    What happens to RNA nucleotides during elongation?

    <p>They are added to the 3′ end of the growing RNA molecule (B)</p> Signup and view all the answers

    Transcription can occur simultaneously on multiple RNA polymerases at a single gene.

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

    What is the significance of the poly-A tail in mRNA?

    <p>It protects the mRNA from degradation and aids in its export from the nucleus.</p> Signup and view all the answers

    What is the role of tRNA during translation?

    <p>To transfer amino acids to a growing polypeptide (D)</p> Signup and view all the answers

    The size of eukaryotic ribosomes is smaller than that of bacterial ribosomes.

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

    What does the term 'wobble' refer to in translation?

    <p>The flexible pairing at the third base of a codon.</p> Signup and view all the answers

    The __________ end of a tRNA molecule serves as the attachment site for an amino acid.

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

    Match the following components with their functions in translation:

    <p>tRNA = Transfers amino acids to ribosomes Ribosomes = Facilitate coupling of tRNA and mRNA Aminoacyl-tRNA synthetase = Catalyzes tRNA and amino acid matching mRNA = Carries genetic information from DNA</p> Signup and view all the answers

    Which of the following accurately describes the structure of a tRNA molecule?

    <p>It has cloverleaf structure in its two-dimensional representation. (D)</p> Signup and view all the answers

    Accurate translation requires only the proper match between tRNA and an amino acid.

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

    During translation, mRNA is translated into __________.

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

    Flashcards

    Codons

    Triplet sequences of nucleotides that specify amino acids or stop signals.

    Redundancy of the genetic code

    More than one codon can specify the same amino acid.

    Transcription

    The process of copying a segment of DNA into RNA.

    RNA polymerase

    Enzyme that catalyzes the synthesis of RNA from a DNA template.

    Signup and view all the flashcards

    Transcription stages

    Includes initiation, elongation, and termination of RNA synthesis.

    Signup and view all the flashcards

    Introns

    Noncoding segments of a gene that are removed during RNA splicing.

    Signup and view all the flashcards

    Exons

    Coding regions of a gene that are expressed and translated into proteins.

    Signup and view all the flashcards

    RNA Splicing

    The process of removing introns and connecting exons in RNA transcripts.

    Signup and view all the flashcards

    Spliceosomes

    Complexes of proteins and small RNAs that carry out RNA splicing.

    Signup and view all the flashcards

    Ribozymes

    Catalytic RNA molecules that can splice RNA and function like enzymes.

    Signup and view all the flashcards

    Alternative RNA Splicing

    A process that allows a gene to produce multiple polypeptides by varying the exons used.

    Signup and view all the flashcards

    Exon Shuffling

    The process by which exons from different genes are mixed to create new proteins.

    Signup and view all the flashcards

    Protein Domains

    Discrete regions in a protein that perform specific functions, often coded by exons.

    Signup and view all the flashcards

    Ribosome Binding Sites

    Three sites where tRNA binds: A site, P site, E site.

    Signup and view all the flashcards

    P site Function

    Holds tRNA with the growing polypeptide chain.

    Signup and view all the flashcards

    A site Function

    Holds tRNA carrying the next amino acid.

    Signup and view all the flashcards

    E site Function

    Exit site for discharged tRNAs.

    Signup and view all the flashcards

    Stages of Translation

    Three main stages: Initiation, Elongation, Termination.

    Signup and view all the flashcards

    Initiation of Translation

    Small subunit binds mRNA and initiator tRNA carrying methionine.

    Signup and view all the flashcards

    Elongation Process

    Amino acids are added to the polypeptide chain in three steps.

    Signup and view all the flashcards

    Termination of Translation

    Ends when a stop codon reaches A site; polypeptide is released.

    Signup and view all the flashcards

    Promoters

    Sequences that signal the start point of transcription and extend upstream.

    Signup and view all the flashcards

    Transcription initiation complex

    The assembly of transcription factors and RNA polymerase II bound to a promoter.

    Signup and view all the flashcards

    TATA box

    A specific promoter sequence crucial for forming the initiation complex in eukaryotes.

    Signup and view all the flashcards

    Transcription elongation

    The phase where RNA polymerase adds nucleotides to the growing RNA strand.

    Signup and view all the flashcards

    Termination of transcription

    The process where RNA polymerase stops transcription, differing in bacteria and eukaryotes.

    Signup and view all the flashcards

    RNA processing

    Modification of pre-mRNA in eukaryotes before it exits the nucleus.

    Signup and view all the flashcards

    mRNA cap and tail

    Modifications at the 5′ end (cap) and 3′ end (poly-A tail) of mRNA.

    Signup and view all the flashcards

    Translation

    The process of converting mRNA into protein in cells.

    Signup and view all the flashcards

    tRNA

    Transfer RNA; carries amino acids to the ribosome during translation.

    Signup and view all the flashcards

    Aminoacyl-tRNA synthetase

    Enzyme that matches tRNA with its specific amino acid.

    Signup and view all the flashcards

    Anticodon

    A set of three nucleotides in tRNA that pairs with mRNA codon.

    Signup and view all the flashcards

    Wobble pairing

    Flexible base pairing at the third position of a codon.

    Signup and view all the flashcards

    Ribosome

    Cellular structure that facilitates the coupling of tRNA and mRNA during protein synthesis.

    Signup and view all the flashcards

    Eukaryotic Ribosomes vs. Bacterial Ribosomes

    Eukaryotic ribosomes are larger and differ in composition compared to bacterial ribosomes.

    Signup and view all the flashcards

    tRNA Structure

    tRNA has a cloverleaf shape that folds into an L-shape, with one end for amino acid attachment.

    Signup and view all the flashcards

    Prokaryotic Translation

    In prokaryotes, translation of mRNA starts before transcription completes.

    Signup and view all the flashcards

    Eukaryotic Translation

    Eukaryotic cells have transcription occurring in the nucleus and translation occurs in the cytoplasm, separated by the nuclear envelope.

    Signup and view all the flashcards

    Primary Transcript

    The original RNA transcript from any gene before any processing occurs.

    Signup and view all the flashcards

    Central Dogma

    The process where DNA is transcribed to RNA, which is then translated into protein: DNA → RNA → Protein.

    Signup and view all the flashcards

    Template Strand

    The DNA strand used as a template to create complementary RNA during transcription.

    Signup and view all the flashcards

    Coding Strand

    The non-template strand of DNA that has the same sequence as the mRNA (except for U instead of T).

    Signup and view all the flashcards

    Study Notes

    Chapter 12: Molecular Biology of the Gene - Part 2

    • The DNA within an organism dictates the synthesis of proteins which lead to specific traits.
    • Proteins link genotype and phenotype.
    • Gene expression directs protein synthesis through two stages: transcription and translation.
    • The study of metabolic defects revealed the connection between genes and enzymes.
    • In 1902, Archibald Garrod suggested that genes dictated phenotypes via enzymes catalyzing specific chemical reactions.
    • Symptoms of inherited diseases reflect an inability to synthesize specific enzymes.
    • Cells synthesize and break down molecules in a series of steps forming metabolic pathways.
    • Nutritional mutants in Neurospora provided support for the one gene-one enzyme hypothesis.
    • Beadle and Tatum exposed bread mold to X-rays, creating mutants unable to survive on minimal media.
    • Colleagues Adrian Srb and Norman Horowitz identified three classes of arginine-deficient mutants, each lacking a different enzyme necessary for arginine synthesis.
    • The one gene-one enzyme hypothesis suggests a gene's role in dictating the production of a specific enzyme.

    RNA and the Genetic Code

    • RNA serves as a bridge between genes and protein synthesis.
    • Transcription synthesizes RNA using DNA information.
    • Transcription produces messenger RNA (mRNA).
    • Translation synthesizes a polypeptide using mRNA information.
    • Ribosomes are the sites of translation.
    • Prokaryotic translation can begin before transcription ends, but eukaryotic transcription is separated from translation by the nuclear envelope.
    • Eukaryotic RNA transcripts undergo modifications (RNA processing) to form finished mRNA.

    Transcription and Translation

    • DNA has two strands, the template strand provides a template for RNA synthesis.
    • mRNA produced is complementary to the template strand.
    • mRNA base triplets (codons) are read in the 5' to 3' direction.
    • The nontemplate strand is the coding strand, identical to mRNA codons except T replaces U.
    • The genetic code has 64 codons, 61 specifying amino acids, and 3 are stop signals.
    • The code is redundant (more than one codon for some amino acids), and unambiguous (each codon specifies only one amino acid).
    • Codons must be read in the correct reading frame for proper polypeptide production.

    Transcription

    • Transcription, the first stage of gene expression, is catalyzed by RNA polymerase.
    • RNA polymerase unwinds and separates DNA strands to synthesize RNA.
    • RNA polymerase doesn't need a primer.
    • RNA synthesis follows base-pairing rules (A with U and G with C), with uracil replacing thymine.
    • Transcription has three stages: initiation, elongation, and termination.

    Transcription Initiation

    • Promoters signal the start point of transcription and generally extend upstream of the start point.
    • Transcription factors help RNA polymerase bind to and initiate transcription.
    • The completed assembly of transcription factors and RNA polymerase is the transcription initiation complex.
    • A promoter region called a TATA box is crucial for forming the initiation complex in eukaryotes.

    Transcription Elongation

    • RNA polymerase moves along the DNA, unwinding the double helix.
    • Nucleotides are added to the 3' end of the growing RNA molecule.
    • Transcription progresses at a rate of approximately 40 nucleotides per second in eukaryotes.
    • A gene can be transcribed simultaneously by several RNA polymerases.

    Transcription Termination

    • Termination mechanisms differ in bacteria and eukaryotes.
    • In bacteria, RNA polymerase stops transcription at the terminator.
    • In eukaryotes, RNA polymerase II transcribes a polyadenylation signal sequence, and the RNA transcript is released 10-35 nucleotides downstream.

    Eukaryotic RNA Processing

    • Eukaryotic cells modify pre-mRNA (RNA processing) before it is dispatched to the cytoplasm.
    • Processing alters both ends of the primary transcript and often involves removing non-coding segments: introns.
    • Introns are non-coding regions of DNA and pre-mRNA.
    • Exons are coding regions of DNA and pre-mRNA that are eventually expressed.
    • A 5' cap and a poly-A tail are added to the pre-mRNA ends.
    • These modifications help with mRNA export, protection from enzymes, and ribosome attachment.
    • Spliceosomes catalyze the removal of introns.
    • Spliceosomes act by recognizing splice sites.

    Ribozymes

    • Ribozymes are catalytic RNA molecules that function as enzymes, including the ability to splice RNA.
    • RNA's ability to base-pair with itself allows three-dimensional folding.
    • Some RNA bases have functional groups that participate in catalysis.
    • RNA can hydrogen-bond with other nucleic acids.

    Intron Importance

    • Some introns contain sequences that regulate gene expression and modify gene products.
    • Many genes encode more than one kind of polypeptide (alternative RNA splicing).
    • This greatly increases the diversity of proteins that an organism can produce compared to its gene number.
    • Exon shuffling is the mixing and matching of exons between different genes, enabling protein evolution through diverse domains.

    Translation

    • Translation is the process of converting mRNA into protein.
    • tRNAs bring amino acids to the ribosomes.
    • Translation involves mRNA, tRNAs, and ribosomes, which pair complementary mRNA codons with tRNA anticodons.

    Transfer RNA

    • Each tRNA molecule matches a specific mRNA codon to a specific amino acid.
    • tRNAs have an anticodon that base-pairs with a complementary codon on mRNA.
    • A tRNA molecule is a single RNA strand (about 80 nucleotides long) that folds into a complex three-dimensional structure resembling a cloverleaf.
    • The 3' end of the tRNA molecule attaches to the specific amino acid.

    Translation Accuracy

    • Accurate translation depends on correct pairing between tRNA and amino acid (via aminoacyl-tRNA synthetase), and tRNA anticodon and mRNA codon.
    • Wobble allows some tRNAs to bind to more than one codon due to flexible pairing at the third base position.

    Ribosomes

    • Ribosomes are the sites of translation.
    • They catalyze polypeptide bond formation.
    • Eukaryotic ribosomes are larger than prokaryotic ribosomes.
    • Antibiotic drugs specifically target bacterial ribosomes without harming eukaryotic ones.
    • Ribosomes consist of two subunits (large and small) composed of proteins and rRNAs and have three binding sites for tRNA molecules (A site, P site, and E site).

    Polypeptide Building

    • Translation has three stages: initiation, elongation, and termination.
    • All three stages use protein factors and energy is required for some steps.

    Translation Initiation

    • Small ribosomal subunit binds to mRNA at the start codon (AUG) and an initiator tRNA carrying the amino acid methionine.
    • Large ribosomal subunit joins the assembly to form the translation initiation complex.

    Translation Elongation

    • Amino acids are added one by one to the C-terminus of the growing polypeptide chain.
    • Elongation involves codon recognition, peptide bond formation, and translocation steps.

    Translation Termination

    • Elongation continues until a stop codon reaches the A site.
    • A release factor accepts the stop codon and triggers hydrolysis of the polypeptide from the last tRNA.
    • Ribosomal subunits and other components separate.

    Completing the Protein

    • Polypeptides often require post-translational modifications to become functional proteins - like folding, adding or removing chemical groups, or targeting to specific compartments.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Molecular Biology of the Gene PDF

    Description

    Explore the principles of molecular biology as they relate to gene expression, protein synthesis, and metabolic pathways. This quiz covers key concepts, including the one gene-one enzyme hypothesis and historical experiments by Beadle and Tatum. Test your understanding of how genes influence traits through enzymes and metabolic processes.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser