Questions and Answers
Which statements are true of inducible operons?
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?
Place the following events in transcription in the correct order.
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A(n) ______ is a regulatory protein that blocks transcription, while a(n) ______ is a regulatory protein that facilitates transcription.
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RNA polymerase can only add to an existing nucleotide sequence.
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If a 75 base-pair fragment of DNA has 25 cytosines in it, how many adenines would you expect it to have?
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RNA interference (RNAi) is a mechanism by which?
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Arrange the following proteins in the correct order in which they participate in DNA replication.
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What do RNA polymerases do?
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Organize the steps that are involved in the mechanism of RNA interference (RNAi).
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Genes for constitutive enzymes can be turned on and off as necessary.
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What is a constitutive enzyme?
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What is an inducible enzyme?
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What is a repressible enzyme?
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If an organism lost the ability to make primase, what would it be unable to do?
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Why are two different mechanisms for copying the DNA strands used?
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What component of RNA is different from one person (or one bacterium) to the next?
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The purpose of RNA synthesis is to provide a new copy of DNA as the original strand deteriorates over time.
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Which nucleotide is not found in RNA?
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Transcription begins when RNA polymerase binds to the?
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What role does the sigma factor of RNA polymerase have in transcription?
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If one strand of DNA contains the bases ACAGT, what would be the complementary bases on the mRNA strand?
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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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Description
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.
