Summary
Highlights
Gene expression is the process where a gene is utilized to create a functional product, most commonly a protein. This involves transcribing DNA into mRNA and then translating mRNA into a polypeptide chain which forms the protein. However, not all genes are expressed, necessitating gene regulation to control which genes are active.
Prokaryotic cells have their DNA in the cytoplasm, allowing transcription and translation to occur simultaneously. Their gene regulation largely focuses on controlling transcription. Eukaryotic cells, with a nucleus, have more complex gene regulation points, including transcription, post-transcription, translation, and post-translation.
Transcription factors are regulatory proteins that can either increase or decrease transcription. In eukaryotes, they bind to promoters to help RNA polymerase initiate transcription or to repress it. Some also bind to enhancer sequences, which can be distant from the gene, to boost transcription. Environmental factors can also influence transcription factors, affecting gene expression.
Prokaryotic operons, like the Lac Operon, exemplify gene regulation during transcription. A repressor can block RNA polymerase from transcribing genes by binding to the operator. When lactose is present, an isomer of lactose binds to the repressor, moving it out of the way, allowing RNA polymerase to transcribe the genes that produce enzymes to break down lactose.
Epigenetic marks, such as chemical groups like methyl, can influence how tightly DNA is packed around histones in eukaryotic cells. Tightly packed DNA prevents transcription factors from binding, thereby inhibiting transcription. Removing these marks can allow DNA to be transcribed and expressed. This mechanism also occurs in prokaryotes, albeit with differences in DNA packing.
Eukaryotic cells exhibit regulation at multiple stages. Post-transcription, mRNA can be processed by removing introns, influencing the final protein. During translation, proteins like eIF-2 facilitate its initiation. If eIF-2 is phosphorylated, it changes shape and cannot initiate translation, preventing protein synthesis. Post-translation, chemical modifications or the attachment of ubiquitin can alter protein function or lead to degradation, impacting expression.
Understanding gene expression and regulation is crucial for comprehending normal bodily functions and identifying causes of diseases like cancer. Cancer cells often have abnormal gene expression, with genes either over-expressed or under-expressed. For instance, increased transcription factor activity boosting cell division genes can contribute to cancer. This knowledge is vital for developing new treatments.