Biology Chapter 7 Flashcards
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Questions and Answers

Which statements are true of inducible operons?

  • Inducible operons are usually in the 'off' state.
  • The inducer is often the product of the enzyme that is encoded. (correct)
  • Inducible operons are turned off when not needed. (correct)
  • Inducible operons are not regulated at all.

    • Why do cells require mechanisms to regulate the expression of genes that code for proteins?

    Not all proteins are needed at all times, or in equal amounts. Regulating their expression saves energy and time.

    Which statements about translation are correct?

  • All codons code for the same amino acid.
  • The three potential reading frames usually code for the same amino acid. (correct)
  • One codon can code for two different amino acids.
  • The three potential reading frames on mRNA code for different amino acids.

    • Place the following events in transcription in the correct order.

    <p>1 = RNA polymerase binds to the promoter region just upstream of the gene. 2 = RNA polymerase unwinds the DNA at the promoter site and begins to transcribe the template strand of DNA. 3 = RNA polymerase moves along the template strand of DNA adding complementary RNA nucleotides, extending the mRNA. 4 = Transcription continues until a terminator site in the DNA is reached. 5 = The mRNA transcript is released.</p> Signup and view all the answers

    A(n) ______ is a regulatory protein that blocks transcription, while a(n) ______ is a regulatory protein that facilitates transcription.

    <p>repressor, activator</p> Signup and view all the answers

    RNA polymerase can only add to an existing nucleotide sequence.

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

    If a 75 base-pair fragment of DNA has 25 cytosines in it, how many adenines would you expect it to have?

    <p>50</p> Signup and view all the answers

    RNA interference (RNAi) is a mechanism by which?

    <p>eukaryotic cells destroy RNA transcripts in a selective and specific manner to control gene expression.</p> Signup and view all the answers

    Arrange the following proteins in the correct order in which they participate in DNA replication.

    <p>1 = Primase 2 = Helicase 3 = DNA ligase 4 = DNA polymerase</p> Signup and view all the answers

    What do RNA polymerases do?

    <p>Synthesize chains of ribonucleotides, synthesize molecules shorter than the chromosome.</p> Signup and view all the answers

    Organize the steps that are involved in the mechanism of RNA interference (RNAi).

    <p>1 = Cell produces short single-stranded RNA 2 = An RNA-induced silencing complex (RISC) assembles 3 = Binding of the RNA in the RISC to mRNA tags the mRNA for destruction 4 = Enzymes cut mRNA; RISC can then bind to another molecule</p> Signup and view all the answers

    Genes for constitutive enzymes can be turned on and off as necessary.

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

    What is a constitutive enzyme?

    <p>Synthesized constantly, these enzymes usually play a critical and indispensable role in central metabolic pathways.</p> Signup and view all the answers

    What is an inducible enzyme?

    <p>Not routinely produced at significant levels, but their synthesis can be turned on when needed.</p> Signup and view all the answers

    What is a repressible enzyme?

    <p>These are produced routinely, but their synthesis can be turned off when they are no longer required.</p> Signup and view all the answers

    If an organism lost the ability to make primase, what would it be unable to do?

    <p>Add a short sequence of complementary RNA to the existing DNA strand.</p> Signup and view all the answers

    Why are two different mechanisms for copying the DNA strands used?

    <p>The strands are oriented in opposite directions.</p> Signup and view all the answers

    What component of RNA is different from one person (or one bacterium) to the next?

    <p>The order of nitrogenous bases.</p> Signup and view all the answers

    The purpose of RNA synthesis is to provide a new copy of DNA as the original strand deteriorates over time.

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

    Which nucleotide is not found in RNA?

    <p>Thymine.</p> Signup and view all the answers

    Transcription begins when RNA polymerase binds to the?

    <p>Promoter on DNA.</p> Signup and view all the answers

    What role does the sigma factor of RNA polymerase have in transcription?

    <p>It recognizes and binds to the promoter region of the template DNA.</p> Signup and view all the answers

    If one strand of DNA contains the bases ACAGT, what would be the complementary bases on the mRNA strand?

    <p>UGUCA.</p> Signup and view all the answers

    Study Notes

    Inducible Operons

    • Inducible operons are typically "on" and deactivate when not needed.
    • The presence of the inducer, usually the product of the encoded enzyme, triggers the operon.

    Regulation of Gene Expression

    • Cells do not need all proteins at all times; regulated expression is essential.
    • Regulation conserves energy and time by matching protein availability to cellular demands.

    Translation

    • mRNA has three potential reading frames that generally code for the same amino acid.
    • One codon can represent two different amino acids, highlighting genetic variability.

    Transcription Process

    • Initiation: RNA polymerase binds to the promoter upstream of the gene.
    • RNA polymerase unwinds DNA at the promoter and starts transcribing the template strand.
    • The enzyme adds complementary RNA nucleotides to extend mRNA until a terminator site is encountered.
    • Completion: mRNA transcript is released.

    Role of Regulatory Proteins

    • Repressor proteins inhibit transcription.
    • Activator proteins enhance transcription.

    RNA Polymerase Functionality

    • RNA polymerase synthesizes RNA chains and does not require an existing nucleotide sequence to start.

    Base Pair Expectations

    • In a 75 base-pair DNA fragment with 25 cytosines, expect 50 adenines due to base pairing rules.

    RNA Interference (RNAi)

    • RNAi allows eukaryotic cells to selectively destroy RNA transcripts, managing gene expression control.

    DNA Replication Protein Order

    • Proteins act in the following order: Helicase, Primase, DNA Polymerase, DNA Ligase.

    RNA Polymerases

    • They synthesize shorter chains of ribonucleotides instead of full-length chromosomes.

    RNA Interference Mechanism

    • Steps include the production of short single-stranded RNA, assembly of RNA-induced silencing complex (RISC), tagging mRNA for destruction, and enzymatic cutting of mRNA.

    Bacterial Gene Control

    • Constitutive enzymes cannot be turned on or off; they are always active.

    Types of Enzymes

    • Constitutive Enzymes: Continuously synthesized, vital for central metabolic pathways.
    • Inducible Enzymes: Not produced unless needed, facilitate breakdown of specific energy sources.
    • Repressible Enzymes: Regularly produced but turned off when unnecessary, primarily used in anabolic pathways.

    Primase’s Role

    • Loss of primase functionality means the organism cannot add RNA sequences to existing DNA during replication.

    DNA Strand Orientation

    • Two mechanisms for DNA replication are necessary because DNA strands are antiparallel.

    Genetic Variability

    • Variations in the order of nitrogenous bases define the uniqueness of RNA among individuals and species.

    RNA Synthesis Misconceptions

    • RNA synthesis is not meant to provide a backup for deteriorating DNA but serves distinct functions in gene expression.

    Nucleotide Composition

    • Thymine is absent in RNA, replaced by uracil.

    Promoter Binding

    • Transcription is initiated when RNA polymerase binds to the promoter on the DNA.

    Sigma Factor Function

    • The sigma factor of RNA polymerase plays a crucial role in recognizing and binding to the promoter region of template DNA.

    Complementary Base Pairing

    • For a DNA sequence of ACAGT, the complementary mRNA sequence will be UGUCA.

    Synthesis of mRNA

    • This process involves the transcription of genetic information from DNA into RNA, which is crucial for protein synthesis.

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    Test your knowledge of inducible operons and protein regulation with these flashcards from Chapter 7. Understand the differences between inducible and repressible operons and the importance of regulatory mechanisms in cells.

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