DNA and Genomes Overview
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Questions and Answers

What is the primary function of the lac operon in E. coli?

  • To break down proteins
  • To synthesize fatty acids
  • To metabolize glucose
  • To metabolize lactose (correct)
  • Which of the following correctly describes an inducible operon?

  • It is turned on by the presence of a substrate. (correct)
  • It is always expressed regardless of conditions.
  • It is activated by the presence of a product.
  • It is repressed in the presence of a substrate.
  • How does the presence of glucose affect the lac operon?

  • It permanently disables the lac operon.
  • It activates transcription of the lac operon.
  • It represses transcription of the lac operon. (correct)
  • It has no effect on the lac operon.
  • Which component of the lac operon is responsible for breaking down lactose?

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

    What is the role of the regulatory gene lacI in the lac operon?

    <p>It encodes a repressor that binds to the operator. (C)</p> Signup and view all the answers

    In prokaryotic transcriptional regulation, what is a sigma factor?

    <p>A protein that assists RNAP in binding to specific promoters. (B)</p> Signup and view all the answers

    What happens when the trp operon is activated?

    <p>Transcription is inhibited when tryptophan is present. (C)</p> Signup and view all the answers

    Which of the following correctly describes the trp operon's mechanism?

    <p>Regulates genes needed for tryptophan synthesis. (C)</p> Signup and view all the answers

    What is the primary function of the lac operon in prokaryotic cells?

    <p>To regulate the metabolism of lactose (A)</p> Signup and view all the answers

    How does the trp operon differ from the lac operon in its regulation?

    <p>The trp operon is repressed in the presence of tryptophan (A)</p> Signup and view all the answers

    What role does the sigma factor play in transcription regulation in prokaryotes?

    <p>It aids in the initiation of transcription (A)</p> Signup and view all the answers

    Which of the following best describes the operon theory?

    <p>Operons ensure all genes in a pathway are regulated together (A)</p> Signup and view all the answers

    What is the mechanism of translational regulation in prokaryotes?

    <p>Controls the binding of tRNA to mRNA (A)</p> Signup and view all the answers

    Which component of the trp operon is responsible for sensing tryptophan levels?

    <p>The repressor protein (C)</p> Signup and view all the answers

    Why is alternative splicing significant for eukaryotic gene expression?

    <p>It allows multiple protein products from a single gene (D)</p> Signup and view all the answers

    How does the genetic code differ from the genome?

    <p>The genome includes regulatory sequences and non-coding regions (A)</p> Signup and view all the answers

    What is the primary function of the lac operon in prokaryotes?

    <p>To promote the uptake and metabolism of lactose (C)</p> Signup and view all the answers

    Which of the following best describes the trp operon?

    <p>It is an example of a repressible operon that controls tryptophan synthesis (A)</p> Signup and view all the answers

    What role do operators play in operon theory?

    <p>They are segments of DNA recognized by regulatory proteins to control transcription (A)</p> Signup and view all the answers

    In prokaryotic transcription regulation, what mechanism is primarily used to inhibit gene expression?

    <p>Binding of repressor proteins to operators (B)</p> Signup and view all the answers

    During translational regulation in prokaryotes, how does the ribosome recognize the start codon?

    <p>It interacts with the Shine-Dalgarno sequence on mRNA (D)</p> Signup and view all the answers

    Which feature is unique to prokaryotic gene structure compared to eukaryotic genes?

    <p>Lack of introns and a simpler regulatory region (B)</p> Signup and view all the answers

    What is a characteristic of transcription in prokaryotes?

    <p>It can occur simultaneously with translation (D)</p> Signup and view all the answers

    How does the presence of glucose affect the expression of the lac operon?

    <p>It leads to catabolite repression, reducing lac operon expression (A)</p> Signup and view all the answers

    Flashcards

    Inducible Operon

    A gene system where transcription is turned ON by the presence of a substrate.

    Repressible Operon

    A gene system where transcription is turned OFF by the presence of a product.

    Lac Operon

    A negative inducible operon in E. coli that allows the cell to metabolize lactose.

    Lac Operon's Regulation

    The lac operon is regulated by a repressor protein (LacI) and the presence of lactose; when lactose is present, the repressor detaches from the operator, allowing transcription.

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    Carbon Catabolite Repression

    A regulatory mechanism where bacteria prioritize using glucose over other sugars when glucose is available.

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    Lac Operon's Enzymes

    lacZ (beta-galactosidase), lacY (permease), and lacA (galactosidase acetyltransferase) participate in lactose digestion.

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    Transcriptional Regulation

    The process of controlling how genes are expressed within prokaryotes.

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    Transcription Factors

    Proteins that bind to specific DNA sequences to control the initiation of transcription.

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    Elongation (Transcription)

    The phase of transcription where RNA polymerase extends the RNA transcript, starting from the initiation site.

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    Sigma Factor

    A protein that helps RNA polymerase bind to the promoter region of DNA, initiating transcription.

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    Intrinsic Termination (Transcription)

    A mechanism that stops transcription when an RNA sequence with a hairpin loop and a GC-rich region is formed.

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    Rho-dependent Termination (Transcription)

    A mechanism that involves the Rho protein, which binds to the RNA transcript and pulls it away from RNA polymerase.

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    Primary Transcript (Eukaryotic mRNA)

    The initial RNA molecule produced after transcription, before any processing.

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    Mature mRNA (Eukaryotic)

    The processed RNA molecule ready for translation, containing a 5' cap, poly-A tail, and introns removed.

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    Alternative Splicing

    A process where different combinations of exons from a single gene can be spliced together, creating multiple protein isoforms.

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    Genetic Code

    The set of rules that translates nucleotide sequences in mRNA into amino acid sequences in proteins.

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    Replication in Prokaryotes

    The process of DNA replication in prokaryotes involves a single origin of replication (OriC) where the DNA double helix is unwound, and the process occurs simultaneously on both strands, creating two identical DNA molecules.

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    Replisome

    A complex of proteins involved in DNA replication in prokaryotes. It includes DNA polymerase, helicase, and other enzymes.

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    Difference in Replication: Prokaryotes vs. Eukaryotes

    Prokaryotes have a smaller, simpler replisome with fewer proteins, while eukaryotes have a larger, more complex replisome with additional proteins and machinery. Prokaryotes have one replisome, while eukaryotes have multiple replisomes.

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    Transcription Unit or Gene

    A segment of DNA that encodes a functional RNA molecule, such as mRNA, tRNA, or rRNA.

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    Prokaryotic Gene Structure

    A prokaryotic gene typically consists of a promoter region, a coding region (ORF), and a terminator region. The promoter contains the -35 and -10 boxes for the binding of RNA polymerase.

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    Eukaryotic Gene Structure

    A eukaryotic gene is more complex, with a distal promoter, proximal promoter, core promoter, exons, introns, and a polyadenylation signal.

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    Transcription Initiation in Prokaryotes

    RNA polymerase binds to the promoter region of a gene, unwinds the DNA double helix, and initiates the synthesis of RNA.

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    Transcription Elongation & Termination

    RNA polymerase moves along the DNA template strand, adding nucleotides to the growing RNA molecule. Transcription terminates when RNA polymerase reaches a specific terminator sequence.

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    Study Notes

    DNA and Genomes

    • DNA is a double helix with two antiparallel strands held together by hydrogen bonds.
    • Nucleotides are connected by phosphodiester bonds.
    • Sugars and phosphate groups form the backbone, while nitrogenous bases are inside.

    Genetic Material Characteristics

    • Genomes must store genetic information and be expressed.
    • Genomes must be stable but capable of mutation.
    • Genomes must replicate accurately and be inherited to progeny cells.

    Genomic Organization Comparison

    Feature Viruses Bacteria Eukaryotes
    Genome Type ssDNA, dsDNA, ssRNA, dsRNA dsDNA, circular Linear DNA in chromosomes
    Size Very small Medium size Largest in size
    Structure Compact with overlapping genes, few NC regions Dense with few non-coding regions, minimal introns Extensive non-coding regions, introns, repetitive DNA
    Packaging Encapsulated within a protein capsid DNA supercoiled and associated with proteins, but no defined nucleus DNA wrapped around histones, organized into chromatin within defined nucleus
    Key Features Dependent on host machinery for replication, high mutation rates, especially in RNA viruses Efficient use of genetic material, capable of horizontal gene transfer Complex, diverse cell function & development, genes transcribed individually, mitochondria and chloroplasts, extensive post-transcriptional and post-translational regulation

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