In: Biology
1. Eukaryotic transcription factors control gene expression in a combinatorial manner. a) With the aid of a diagram, briefly discuss this statement. b) Provide an example of how combinatorial regulation of gene expression is involved in the development of higher organisms.
Answer: Combination of proteins are responsible for the regulation of gene expression and development in higher organisms. There are both activators and repressors in the cell that control gene expressions. The genome (DNA) is common in all types of cell, while the expression is different in different cells. This makes cell of diverse structure and function. For example, the nerve cells have the same genome as that of blood cell, but their structure and function are a lot different. The differential gene expression is controlled by transcription factors (TFs). But the number of TFs is lesser than the genes they control for expression. That means a different combination of factors regulates gene expression. These combinations can activate or repress genes.
Figure 1 Combination of transcrition factors (TFs; activator) and repressor controlling gene expression in eukaryotes.
Figure (1) shows the three conditions for control of gene expression in eukaryotes. In cell type 1, there is a higher level of gene expression due to the presence of two different TF that binds to different operator present in the upstream region of the mRNA. While the binding of only one of the two TFs in cell type 2 causes a low level of transcription. In cell type 3, the binding of repressor protein leads to no transcription of the given gene. So, the control of gene expression is combinational. These differential levels of gene expression provide different phenotypes to cells.
For the development of a eukaryotic organism, the gene expression is different in both place and time. Specific development occurs at a specific time of growth. The development could be in a specific tissue or organ. Combination of factors secreted in paracrine signalling pathways determines the gene expression in eukaryotes.