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MCB 250 Final Exam 2025 With 100%
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In 1985, Helen Blau and coworkers fused human liver cells to the (much larger) skeletal muscle cells of mice. Within hours, these hybrid cells began to stain with antibodies specific for human muscle proteins. Which of the following do you think is the most likely explanation of this observation? โ Answer โ๏ธ Mouse muscle proteins activated transcription of human genes One important feature attributed to signal transduction pathways is that they amplify the signal as it moves through the cell. What do you think this means? โ Answer โ๏ธ The number of molecules representing the signal increases at successive steps in the pathway.
Why did Spradling and Rubin elect to use two different Plasmids in order to introduce P elements into their Transgenic flies? โ Answer โ๏ธ If the P element contains a transposase gene, After integration it would undergo uncontrolled Transposition in subsequent generations. In a different experiment, the researchers simply deleted That portion of the cloned oskar cDNA which normally Yields the 3โ-UTR. This partially deleted cDNA was then transcribed into RNA, and the RNA injected into fertilized fly eggs. Where Would you expect this RNA to become localized? โ Answer โ๏ธ uniform throughout the embryo When mutated, all of the genes in this pathway affect
Phenotype in a subset of tissues. Sometimes the transgene causes insertional Mutagenesis, yielding phenotypes associated with A loss of some endogenous gene function. Which of the following statements about insertional Mutagenesis is false? โ Answer โ๏ธ Insertion must occur within the protein (or RNA) coding region of a gene in order to Produce a mutant phenotype. The initiation of translation requires the mutual binding Of the mRNA, the 30S and 70S subunits of the Ribosome, three initiation factors, a charged initiator tRNA, and a molecule of GTP. This takes time. What will happen to the trp operon mRNA if RNA Polymerase transcribes the entire leader sequence Before a ribosome can initiate translation of the leader
Peptide? โ Answer โ๏ธ Sequences 3 and 4 will anneal to form the Terminator hairpin; transcription will terminate At the end of the leader. What is the main function of the conserved โhandleโ Sequences in crRNA-mediated degradation of foreign DNAs? โ Answer โ๏ธ Interact with the cas proteins When Argonaute cleaves an mRNA, that mRNA can no Longer be translated. This is true even when the RNA is Cleaved outside the protein-coding region, e.g. in the 3โ UTR. Why is this the case? โ Answer โ๏ธ Eukaryotic ribosomes only translate mRNAs that Have both a 5โ methyl-G cap and a 3โ poly(A) tail.
Be true of flies homozygous for this mutant allele? โ Answer โ๏ธ Both XX and XY embryos would develop as Females. In a single maturing B cell, gene rearrangement occurs Abnormally and leads to a premature stop codon in the Exon encoding the C chain. What effect is this likely to Have on the organism? โ Answer โ๏ธ Unlikely to have any effect on health or Survival. The IgG light chain genes normally undergo VJ recombination, While heavy chain genes normally undergo V(D)J Recombination. Why doesnโt the heavy chain also recombine a V segment to a J segment? โ Answer โ๏ธ The V and J segments of heavy chain genes both
Have 23-mer signal sequences, and recombination Requires a 23-mer and a 12-mer. Why do different domains within a protein evolve at Different rates? โ Answer โ๏ธ Protein domains whose structure is essential to Protein function are under greater selection Pressure and their amino acid sequences tend to Evolve more slowly. What role does the subcellular localization of mRNAs play in the process of differential gene expression? โ Answer โ๏ธ Permits genetically identical daughters of a single cell division to contain different regulatory proteins. What is the most common molecular mechanism for passing information along a signal transduction pathway? โ Answer โ๏ธ phosphorylation
poles of the embryo respectively. This localization depends upon nucleotide sequences located in which part of the RNA molecule? โ Answer โ๏ธ 3โ-UTR In the Drosophila embryo, the twist, rhomboid, and sog genes are transcribed in response to different intranuclear concentrations of Dorsal transcription factor. How do these genes detect differences in Dorsal concentration? โ Answer โ๏ธ These genes have Dorsal-binding sites of varying affinity In the Drosophila embryo, cells that inherit the pole granules develop into โ Answer โ๏ธ germ line During DNA transposition by the cut-and-paste mechanism, the transposase cuts the two strands of the target site DNA several nucleotides apart. Cellular repair enzymes fill in these overhangs, resulting in the formation of โ Answer โ๏ธ target site direct repeats.
In many organisms, transposition is the major source of โ Answer โ๏ธ spontaneous mutation Which of the following is found in autonomous DNA transposons but not in non-autonomous DNA transposons? โ Answer โ๏ธ transposase gene In Drosophila, P element transformation is used to introduce transgenes into the flyโs genome. What phenotype does the experimenter use to distinguish flies that have been successfully transformed? โ Answer โ๏ธ red eyes Both mouse (Mus musculus) and human (Homo sapiens) genomes have been sequenced in full. What percentage of protein-coding genes show a one-to- one correspondence between these two species? โ Answer โ๏ธ 85% Which portion of the early mouse embryo will form all of the tissues of the adult mouse? โ Answer โ๏ธ inner cell mass
removed from the body for experimental manipulation, then successfully reintroduced. Which was the first human disease condition successfully treated by gene therapy? โ Answer โ๏ธ severe combined immunodeficiency (SCID) Clinical trials have used the targeted knockout of the CCR5 gene in an attempt to treat which human disease? โ Answer โ๏ธ acquired immunodeficiency syndrome (AIDS) Which of the following is a limiting or potentially negative factor in the use of gene therapies to ameliorate human disease? โ Answer โ๏ธ Introduction of foreign gene products into the body has the potential of eliciting an immune reaction. Random DNA insertions can mutate endogenous genes and thereby produce new disease conditions. It is difficult to target genetic modifications to specific tissues within the body.
It is difficult to treat disease conditions that depend upon multiple genes. In Drosophila, the Sex-lethal (Sxl) gene has how many different core promoters? โ Answer โ๏ธ 2 In the fruitfly Drosophila, females are normally XX and males are normally XY. What feature of a fruitflyโs genotype determines its sex? โ Answer โ๏ธ The ratio of X chromosomes to autosomes determines whether a fly is female (= 1.0) or male (= 0.5). In female fruitflies, the Sex-lethal (Sxl) gene autoregulates its own expression. At what level in gene expression does this autoregulation occur? โ Answer โ๏ธ pre-mRNA splicing Which of the following statements is not true of the Drosophila gene Sex-lethal (Sxl)? โ Answer โ๏ธ Sxl encodes a splicing repressor protein. Sxl pre-mRNA undergoes alternative splicing in males and females.
Unlike other insects, flies (= dipteran insects) have a unique organ called the โhaltereโ located on the right and left sides of their metathoracic segment. This pair of halteres evolved from what ancestral organ? โ Answer โ๏ธ wings After the homeotic genes were discovered in fruitflies, mammalian geneticists discovered a set of homologous genes โ called Hox genes โ mice. However, the mammalian Hox genes differed from the fruitfly in what regard? โ Answer โ๏ธ The mouse genome has four separate clusters of Hox genes, each of which corresponds to one complete set of homeotic genes in the fruitfly. The so-called homeotic or Hox genes display a phenomenon called colinearity. What is colinearity? โ Answer โ๏ธ A linear correspondence between the order of genes on the chromosome and their patterns of expression along the anteroposterior axis of the embryo.
A typical vertebrate animal has about 25,000 protein- coding genes, whereas a typical invertebrate animal has only 15,000. What is the principal reason for this difference? โ Answer โ๏ธ Duplication of preexisting genes in the vertebrate ancestry. Both siRNAs and miRNAs are generated by the cleavage of longer RNAs. What enzyme performs the final step in this cleavage? โ Answer โ๏ธ Dicer The proteins Dicer and Argonaut both have a PAZ domain. What is its function? โ Answer โ๏ธ To hold the 3โ end of a short regulatory RNA. What is the primary function of piwi-interaction RNAs (piRNAs)? โ Answer โ๏ธ Protect the germline of animals from transposons In the yeast Saccharomyces pombe, the RNAi machinery is required for transcriptional silencing of
- Answer โ๏ธ centromeres
