Cell biology (formerly called cytology, from the Greek κυτος, kytos, "vessel") and otherwise known as molecular or cell biology, is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life. Cell biology explains the structure, organization of the organelles they contain, their physiological properties, metabolic processes, signaling pathways, life cycle, and interactions with their environment. This is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells. Knowing the components of cells and how cells work is fundamental to all biological sciences it is also essential for research in bio-medical fields such as cancer, and other diseases. Research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology. https://en.wikipedia.org/wiki/Cell_biology
Take a look inside a cell: http://learn.genetics.utah.edu/content/cells/insideacell/
What controls the development of more than 200 distinct cell types from this single source of genetic information? How are genes that serve special roles in the pancreas or brain prevented from being ‘switched on’ in other organs? And why does the activity of some important genes change in diseases such as cancer and diabetes?
We now know that these questions cannot be answered solely by understanding the DNA code. The exciting field of epigenetics is at the frontier of research into the essential processes that control genes and how these differ between cell types under normal and disease conditions.