Which of the following is a level of gene regulation that exists in eukaryotes but NOT in prokaryotes?
ATranscriptional repression by a DNA-binding repressor
BChromatin remodeling via histone modification
CRegulation of RNA polymerase binding
DPost-translational protein degradation
Chromatin remodeling is unique to eukaryotes because prokaryotes lack histones and nucleosome packaging. Prokaryotes do use repressors, RNA polymerase regulation, and protein degradation — all of these occur in both kingdoms. Histone acetylation, methylation, and DNA methylation are distinctly eukaryotic mechanisms that control whether DNA is physically accessible to the transcription machinery.
Question 2 True / False
An enhancer sequence should be located immediately upstream of the promoter it regulates in order to function.
TTrue
FFalse
Answer: False
Enhancers can be thousands of base pairs away from the promoter — upstream, downstream, or even within introns — and can act on either strand. DNA looping brings the enhancer into physical contact with the promoter by forming a loop in three-dimensional space. This is one of the most important distinctions between eukaryotic and prokaryotic gene regulation.
Question 3 Short Answer
A liver cell and a neuron contain the same genome but express very different sets of proteins. What accounts for this difference?
Think about your answer, then reveal below.
Model answer: Differential gene expression: each cell type expresses a distinct set of transcription factors that activate or repress different genes, and chromatin structure (histone modifications, DNA methylation) locks genes open or closed in a cell-type-specific pattern.
Cell identity is determined not by which genes are present but by which genes are expressed. Transcription factors bind to enhancers and promoters and either recruit or block the transcription machinery. Chromatin state — whether a region is accessible or compacted — is inherited through cell divisions and maintains cell-type identity. This is the fundamental mechanism by which a single genome produces over 200 distinct cell types.