chapter 6
A mutation prevents primase from functioning during DNA replication. Why would DNA polymerase be unable to initiate synthesis of a new DNA strand?
DNA polymerase requires an existing primer with a free 3′-OH group. Primase normally creates short RNA primers that provide this starting point.
A mutation prevents the sigma factor from recognizing bacterial promoter sequences. Which stage of transcription would be directly disrupted, and why?
What is initiation, because sigma factor recognizes the promoter and helps RNA polymerase bind DNA?
Describe 3 types of DNA-binding motifs in proteins
Helix-Turn-Helix,Zinc Finger, Leucine Zipper
Scientists compare two species and discover that several genes remain in the same order and orientation on corresponding chromosomes. What is this conserved genomic arrangement called, and what does it suggest about their evolutionary history?
What is synteny, which provides evidence of conserved chromosome organization and common ancestry?
A mutation causes DNA ligase to become nonfunctional. DNA polymerase continues synthesizing Okazaki fragments normally. What problem will occur?
The Okazaki fragments will remain disconnected because DNA ligase normally seals the gaps between fragments by joining the 5′ phosphate and 3′ hydroxyl ends.
DNA replication is described as semiconservative. What does this mean about the composition of each newly formed DNA molecule?
Each new DNA molecule contains one original parental strand and one newly synthesized complementary strand.
A mutation changes the third nucleotide of an mRNA codon, but the amino acid remains unchanged. What property of the genetic code explains this outcome?
What is codon redundancy, also called degeneracy, associated with third-position wobble?
A bacterial cell has high glucose and high lactose concentrations. The lac repressor is inactive, but CAP cannot bind DNA. What level of lac operon transcription would you expect, and why?
Low transcription. Lactose inactivates the lac repressor, allowing transcription, but high glucose decreases cAMP, preventing CAP from binding and activating transcription.
A scientist discovers that an organism has multiple copies of nearly every chromosome rather than the typical two sets. This phenomenon is common in many crop plants and can contribute to evolutionary diversity. What is this phenomenon called?
What is polyploidy, or whole-genome duplication?
Two genes within the same gene family have highly similar DNA sequences, while a third copy contains numerous mutations and no longer produces a functional protein. What most likely happened to the third gene?
What is the formation of a pseudogene following gene duplication and subsequent mutation accumulation?
Unlike homologous recombination, another type of recombination can occur without matching DNA sequences. Identify this mechanism and describe one possible outcome.
Nonhomologous recombination, also called site-specific recombination in the slides. It does not require sequence homology and commonly involves DNA insertion or deletion.
A bacterial cell is exposed to tetracycline, an antibiotic that targets bacterial ribosomes. Which cellular process is inhibited, and why can this drug selectively affect bacteria?
What is translation, because bacterial and mammalian ribosomes have structural differences that allow selective targeting?
A mutation prevents TFIID from recognizing the TATA box. Predict the effect on RNA polymerase II recruitment and explain why this differs from bacterial transcription initiation.
RNA polymerase II recruitment and transcription initiation would be impaired because TFIID, which contains the TATA-binding protein, is important for promoter recognition. Unlike bacterial RNA polymerase, eukaryotic RNA polymerase II requires general transcription factors.
A bacterial population becomes resistant to an antibiotic after receiving a plasmid containing an antibiotic-resistance gene from another bacterial cell. What evolutionary mechanism explains this change, and why is it particularly significant in prokaryotes?
What is horizontal gene transfer through conjugation, which allows bacteria to acquire new genetic information without inheriting it from a parent cell?
Two different cell types in the same organism contain identical DNA but produce different proteins. What explains this difference, and what cellular process is primarily responsible?
Different cell types express different sets of genes despite having the same DNA. This is caused by differential gene expression, primarily through regulation of transcription.
A mobile genetic element contains sequences recognized by transposase. What is the function of this enzyme, and what are these mobile genetic elements commonly called?
Transposase recognizes the ends of transposons and facilitates their movement within DNA. Transposons are commonly called jumping genes.
A mutation prevents charged tRNAs from entering the A site of a ribosome. Which major step of translation elongation will be disrupted?
What is the delivery of the next amino acid, preventing continued polypeptide elongation?
A scientist introduces a transcription factor that activates its own gene's expression. Once activated by an external signal, the gene continues expressing itself even after the original signal disappears. Identify the regulatory mechanism and explain how it creates cellular memory.
A positive feedback loop, also called a gene latch. The transcription factor activates its own expression, maintaining production after the initial signal disappears and allowing stable gene expression patterns to persist through cell divisions.
A mutation occurs in a somatic cell of an adult organism rather than a germ-line cell. Explain why this mutation can affect the individual but generally will not be passed to offspring.
What is a somatic mutation that is not inherited because somatic cells do not produce gametes?
A DNA coding strand reads 5′-ATGCCATGA-3′. What RNA sequence will be produced, assuming this is the coding region?
What is 5′-AUGCCAUGA-3′?
A genetic element moves through an RNA intermediate rather than directly moving as DNA. What type of mobile genetic element is this, and what distinguishes its movement from ordinary DNA transposition?
A retrotransposon. It moves through an RNA intermediate that is used to generate a new DNA copy.
A cell needs to rapidly eliminate a damaged protein without exposing other cellular proteins to destructive proteases. Explain how ubiquitin and proteasomes accomplish this.
What is ubiquitin tagging, which directs the protein into the proteasome for controlled degradation into amino acids?
A mutation prevents the trp repressor from binding tryptophan. Even when intracellular tryptophan concentrations are high, what happens to transcription of the trp operon?
The trp operon remains transcriptionally active because the repressor cannot undergo the allosteric change required to bind the operator, even when tryptophan is abundant.
During meiosis, homologous chromosomes misalign and undergo unequal crossing-over. One chromosome gains an additional copy of a gene while the other loses it. What evolutionary process has occurred, and how can the extra copy contribute to evolutionary innovation?
What is gene duplication, which provides an extra copy that can accumulate mutations and potentially evolve a new function?
DNA polymerase has both polymerization and proofreading activities. What are the directions of these two activities, and how does proofreading improve replication accuracy?
Polymerization occurs 5′ to 3′, while proofreading occurs 3′ to 5′ through exonuclease activity. Proofreading removes incorrectly incorporated nucleotides.