Question

how cell is able to perform different functions?

Answer 1

All the cells in a person's body have the same DNA and the same genes. However, the difference between cells in different tissues and organs is that the "expression" of the genes differs between cells. ... For example, liver cells have different proteins than skin cells, even though their DNA is the same.

Answer 2

Great question! All cells of your body started off as a cluster of cells that contained all the DNA and genes necessary to grow, specialize into different cell types and tissues, and organize into organs and organ systems capable of communicating with one another and fulfilling the functions of the organism. Cells at the very early stages of development are pluripotent, meaning they can replicate and differentiate into most cell types of the body. The different cell types of the body all contain the same genetic code (DNA) that was present at the earliest stages of development, but specialized cell types of the body turn on or off the genes that are important for their function. These genes are repressed or made available by modifications to the histones (proteins that help to pack the DNA into tiny bundles so they fit inside the cell and are protected from degradation  

Thereby, cells in the liver can perform a totally different function than cells of the lungs and pancreas. Their genetic codes are identical, but the genes (fragments of DNA that encode for proteins) that are active or inactive in each cell type are completely different. The only similar genes that are expressed by all cell types are those responsible for basic cellular functions like metabolism and maintaining the structural integrity of the cell.

I hope this very brief answer is helpful. I recommend reading up on molecular biology and genetics to learn more!