Final answer:
Gene expression in eukaryotic cells is controlled at multiple levels: epigenetic modifications affect chromosomal structure and gene accessibility, transcriptional regulation is directed by transcription factors and promoter sequences, post-transcriptional mechanisms, including miRNA, control mRNA stability, and translational/post-translational modifications influence protein function and abundance.
Step-by-step explanation:
Gene Expression Regulation
Gene expression in eukaryotic cells is regulated at various levels including epigenetic, transcriptional, post-transcriptional, translational, and post-translational processes. The epigenetic control is a critical aspect where changes do not alter the DNA sequence but involve chemical modifications that affect the gene expression by altering chromosomal structure. This control allows the genetic material to be accessed by transcription machinery or to be protected from it. DNA methylation and histone modifications are key epigenetic mechanisms that change the accessibility to DNA, influencing whether a gene is transcribed into mRNA.
During the transcriptional regulation phase, the gene expression is primarily controlled by the binding of transcription factors to DNA regulatory sequences. Enhancer regions and promoter sequences such as the TATA box play a significant role in this process by determining the binding of RNA polymerase and the initiation of transcription. Post-transcriptional regulation includes processes such as RNA splicing, nuclear shuttling, and RNA stability, which determine how long an mRNA molecule will be available for translation into protein. MicroRNAs (miRNAs) and RNA-binding proteins affect the stability of mRNA, thereby controlling protein synthesis levels. Lastly, translational and post-translational regulations involve changes to the RNA or protein that can affect protein function or abundance in the cell, including modifications like phosphorylation.