Introduction to Cell Biology
University of California, San Diego, USA
The earth is filled with an extraordinary variety of organisms occupying environmental niches from the depths of the oceans to the highest mountain peaks. Some of these organisms are microscopic and are just a single cell, while others are complex multicellular organisms that can weigh several tons. Every living organism... read moreis made of a cell or cells, the fundamental units that carry out the processes associated with life. Different cells carry out vastly different functions and yet many unifying themes do exist, for all cells, in all environments.
What is a cell? How do different cell types carry out completely different functions while at the same time sharing many of the same intracellular molecules and mechanisms? How do cells communicate with one another? How does cell growth go awry and eventually lead to cancer? These, and many other key questions in cell biology, will be answered in this series.
Cells are filled with molecules and molecules have structure; that structure is intimately connected to function. To understand the connection between structure and function at both molecular and cellular levels, one must start with some basics: the nature of chemical bonds/interactions, the behaviour of molecules in the aqueous environment of a cell, and how the shape and chemical properties of molecules will determine their activity. Ultimately, biological macromolecules come together to form cells and carry out cellular functions.
All cells are surrounded by a membrane barrier, and many cells also have internal membrane bound compartments; these membranes separate the inside from the outside, thus isolating important functions to specific locations. But cells are by no means static “sacs”. To carry out cellular functions, material must travel across these membranes in both directions and all cells have mechanisms to facilitate and control this transport.
The inside of a cell is teeming with activity. Proteins are made and delivered to specific cellular locations. The cytoskeleton, a network of intracellular fibers, is critical for many cellular functions, including cell motility, mitosis and cell division. Energy is required for all cellular processes; the main source of cellular energy, ATP, is generated in mitochondria.
Intracellular and Intercellular information exchange is crucial to life and a variety of signalling molecules are responsible for communication both within and between cells. Extracellular signalling molecules trigger specific intracellular responses via complex pathways. When signalling pathways involved in cell growth don’t function as they should, the result can be out-of-control growth, or cancer. Normal cellular processes can also be disrupted when foreign “invaders” attack organisms. To combat these attacks, a diverse array of protective mechanisms has evolved, both at the cellular and organismal levels.