Cell biology and gene expression

The body is made up of cells, which are composed of a membrane enveloping a nucleus and cytoplasm. The nucleus contains the genetic material of the body that controls its identity and determines the precise function of the cell. All cells have the potential to perform all functions, but in reality carry out only a limited number. The functions that a cell can perform are controlled by the genes. The cytoplasm contains a number of specialized organelles (many of which are common to all cells) which carry out many functions such as protein synthesis (ribosomes) protein breakdown (lysosomes) and the supply of energy (ATP in the mitochondrion). Protein synthesis is carried out in the ribosomes under the control of DNA.