Control of Gene Expression
• Many processes are common to all cells, so their genes are present in all the cells of the
body. These include the structural proteins of chromosomes, RNA and DNA polymerases
and many of the proteins that form the cytoskeleton such as actin.
• Some RNAs and proteins are found only in specialized cells in which they perform
specific function. For example, hemoglobin is expressed specifically in red blood cells.
• A typical human cell expresses 30–60% of its approximately 30,000 genes at some level
at a certain time.
• There are about 21,000 protein-coding genes and a about 9000 noncoding RNA genes in
• The level of expression of almost every gene is different from one cell type to another.
• Genes in different cell types respond very differently to the same extracellular signal.
• Cell regulate the expression of gene and control the production of protein at different
levels. They are:
Transcriptional control: to control when and how often a given gene is transcribed.
RNA processing control: to control the splicing and processing of RNA transcripts.
RNA transport and localization control: to select which completed mRNAs are exported
from the nucleus to the cytosol and determining where in the cytosol they are localized.
Translational control: to selecting which mRNAs in the cytoplasm are translated by
mRNA degradation control: to selectively destabilize certain mRNA molecules in the
Protein activity control: selectively activating, inactivating, degrading, or localizing
specific protein molecules after they have been made (Figure 7–5).
• The proteins which recognize specific sequences of DNA (typically 5–10 nucleotide pairs
in length) to regulate the function of gene are termed as transcription regulators.
• Transcription regulators are often called cis-regulatory sequences, because they bind on