[Campbell Biology P.426] Based on Figure 18.12, which of the following best explains why the... | Practice Question

Based on Figure 18.12, which of the following best explains why the albumin gene is expressed in liver cells but not in lens cells, while the crystallin gene shows the opposite pattern?

  • A: Liver cells contain the albumin gene but not the crystallin gene, and vice versa for lens cells.
  • B: The specific combination of available activator proteins in each cell type determines which genes are expressed.
  • C: The enhancer for the albumin gene is structurally different in liver cells compared to lens cells.
  • D: Repressor proteins are present in liver cells to inhibit crystallin expression and in lens cells to inhibit albumin expression.

Explanation

Figure 18.12 and its accompanying text explicitly state that both liver and lens cells contain the genes for albumin and crystallin. The key difference in gene expression arises from the unique combination of available activator proteins in each cell type. Liver cells have activators for the albumin gene, leading to its expression, but lack activators for the crystallin gene. Conversely, lens cells have activators for the crystallin gene, allowing its expression, but lack activators for the albumin gene. This selective presence of activators determines the cell-type specific transcription.