Final answer:
The statement that 'Promoter methylation is narrow in tumours' is false. In cancer, promoter regions of tumour suppressor genes are often broadly hypermethylated, leading to their silencing and contributing to uncontrolled cell proliferation.
Step-by-step explanation:
The statement 'Promoter methylation is narrow in tumours' is false. Promoter methylation refers to the addition of methyl groups to the DNA segment at the promoter region of a gene, which typically acts to repress transcription. In many tumours, a common epigenetic alteration is the broad hypermethylation of promoters for tumour suppressor genes, which in effect silences these genes and can contribute to uncontrolled cell growth that defines cancer. This hypermethylation is the opposite of narrow; it often involves a large genomic region and affects multiple genes.
Gene expression is regulated at multiple stages, not just the transcriptional stage, including post-transcriptional, translational, and post-translational modifications. Moreover, the ability of RNA polymerase to bind to a promoter is essential for the transcription of a gene into mRNA. If a promoter is heavily methylated, as is often found in cancer cells, this binding can be inhibited, thereby preventing the transcription of the gene associated with the promoter.
It is also important to note that mutations in genes that normally either promote or suppress cell division can both cause cancer. Such mutations can result in either the unregulated activity of genes promoting cell division or the inactivation of tumour suppressor genes.