Genes are not expressed equally in every cell of an organism. While essential genes needed for survival are continually expressed, other genes are regulated so that they are only expressed in specific cells, at specific times to produce specific amounts of protein.
Suggest why the regulation of gene expression is beneficial for an organism.
Scientists have calculated that roughly 1.3% of a mouse genome is made up of coding sequences. Non-coding DNA sequences can produce functional RNA molecules called transfer RNA. Other non-coding sequences act as specific regions that interact with transcription factors to regulate gene expression.
i)
Define the term "coding sequence".
[1 mark]
ii)
Name the type of non-coding region that decreases or blocks transcription when a repressor protein binds.
Over 20,000 people died during the Dutch famine of 1944-1945. The "Dutch Hunger Winter" was unusual in that it started and ended very abruptly, allowing it to be analysed like an experiment to understand the effects of starvation and malnutrition on human health.
When investigating the short-term and long-term effects of the famine scientists found that pregnant women were particularly vulnerable. The children they gave birth to suffered from long-term health issues. As these children became adults they experienced significantly higher rates of obesity, diabetes and schizophrenia. Scientists also found that the Dutch Hunger Winter cohort had a 10% higher mortality rate after reaching 68 years old compared to those born before or after the famine. One study suggested that the conditions of the Dutch Hunger Winter silenced specific genes in unborn children and that they remained silenced through methylation.
i)
Define the term methylation.
[1 mark]
ii)
Explain how methylation suppresses the transcription of a gene.
Gene expression can be regulated after an mRNA transcript has been produced through post-transcriptional modification. There are several advantages of post-transcriptional modification, one of them being that it helps prevent the degradation of mRNA.
i)
Explain why mRNA is an inherently unstable molecule.
[1 mark]
ii)
Suggest two other advantages of post-transcriptional modification in eukaryotic organisms.
