Gene Expression and Cell Specialization Practice Test

A researcher compares a red blood cell precursor and a pancreatic beta cell from the same individual. Both have identical nuclear DNA. The precursor contains abundant mRNA for hemoglobin, while the beta cell contains abundant mRNA for insulin; the other transcript is nearly absent in each cell type. The researcher finds no difference in ribosome number between the cells. Which explanation best accounts for the observed cell-type-specific protein production?

In a lab, a student compares two human cell types from the same individual: a skeletal muscle cell and a pancreatic beta cell. DNA sequencing shows the same alleles for several genes in both cells. However, RT-PCR detects abundant insulin mRNA in beta cells but not in muscle cells, while muscle cells show abundant myosin heavy-chain mRNA that is low in beta cells. Both cell types contain nuclei and are maintained under the same culture conditions for 24 hours. Which explanation best accounts for the different proteins produced by the two cell types?