Final answer:
All genes in human cells have the potential to be 'on' or 'off', but only a subset is expressed in each cell. Gene regulation involves transcription factors which control gene expression conserving energy and space. This selective expression gives cells their specialized functions.
Step-by-step explanation:
Regarding the capability of genes to be 'switched on' or 'off', this aspect is crucial for energy conservation, especially in single-celled organisms like bacteria. In humans, with approximately 22,000 genes in every cell, the same genes are present, but not all are 'turned on' or expressed. This selective expression leads to the presence of different proteins in different cell types, thus granting them specific functions.
Gene regulation is a highly controlled process in eukaryotic cells. It can involve numerous proteins that bind to one another or the DNA, influencing gene expression rates and resulting polypeptide levels. Usually, gene expression is controlled at one or a few steps, with transcription initiation being a common point of control.
Transcription factors play a significant role in determining whether a gene is 'on' or 'off'. These factors are proteins that attach to specific DNA sequences to promote or inhibit gene transcription. The regulation of gene expression is not just an energy saver; it also conserves space within the cell since only a subset of genes needs to be unwound from the DNA structure to be transcribed and translated.
Thus, while all genes have the ability to be 'on' or 'off', in any given cell type, only a subset of genes is actually turned on to produce the necessary proteins. The rest remain inactivated due to the meticulous process of gene regulation, which is vital for the cell's specialization and efficient functioning.