# Cell biology/Introduction
## Why Bother?

Cells are at an intermediate level of the structural hierarchy of living things. All organisms except viruses have cells as fundamental components, and even viruses depend on the machinery of a cell to reproduce. Cells are composed of molecules and multicellular organisms such as humans are composed of many types of cells that cooperate to form tissues and organs. A student learning about cell biology should also consider studying the chemistry of living organisms, although cell biology can be understood without deep analysis of chemical details. You can use the Wikiversity Biochemistry resources to provide the basic information you should have about the chemistry of living organisms. For more extensive online information about Biochemistry, there is an online textbook available through the PubMed system.

## What is Cell Biology?

A large part of Cell Biology is the study of how biological molecules (mainly proteins and nucleic acids like DNA) account for the structure and function of cells. Cell Biologists also work to account for the structure and function of multicellular organisms in terms of their cellular components. The human body has many specialized cell types that cooperate to provide all of the functions of the human body. Cell biologists are very much concerned with the hormonal and other chemical signals that pass between cells and coordinate the activities of the trillions of cells in a human body.

## Basic Cell Structure

Cell Biology is concerned with the structure and function of cells. "Structure" and "function" are two different ways of looking at the same thing; structures exist to accomplish certain functions and we account for biological function in terms of the structural components of living organisms. Microscopy is an important technique in Cell Biology that reveals cell structure and guides us towards an understanding of how cells function. Most cells are too small to be seen by the naked eye and the spatial distributions of molecular components in cells can only be revealed by microscopy. (Cell Microscopy Art Gallery.)
The structural integrity of cells depends on proteins that form the cytoskeleton. One of the major types of cytoskeletal proteins is keratin. Panel B (Figure 1) shows the cellular location of a type of keratin protein inside these dog kidney epithelial cells. In panels A and B, the green color shows the location of DNA inside the cell nuclei.

## Basic Cell Function

Microscopy of dog (A and B) or mouse (C) cells. In Panels A and B, green shows the location of DNA in cell nuclei. Red shows the position of a cell surface protein (A) or a cytoskeletal protein (B). Panel C shows a mitotic cell with condensed chromosomes.]] The functions of cells are mostly made possible by the protein molecules of cells. The images shown to the right (Figure 1) illustrate microscopy of the cellular locations of two specific proteins. The human genome project has found that humans have genes that provide instructions for about 20,000 different proteins. In Panel A, the red color shows the location of a protein called beta-catenin. Much of the beta-catenin of cells is located at the cell surface where it functions to promote normal cell adhesion. Most cells of the body are part of solid tissues. Many cells of solid tissues have special cell surface proteins that allow adjacent cells to adhere tightly to each other.
DNA is the genetic molecule of cells that carries the molecular instructions used by cells to make protein molecules. Cells, as the basic functional components of living organisms, have the capacity to reproduce and divide into daughter cells. During cell reproduction, the cell nucleus disintegrates and the DNA molecules are packaged as condensed mitotic chromosomes. Panel C (Figure 1) shows two sets of mouse chromosomes ready to be packaged into the two daughter cells of a dividing parental cell.

## Cell Biology and Medicine

Microscopy of dog (A and B) or mouse (C) cells. In Panels A and B, green shows the location of DNA in cell nuclei. Red shows the position of a cell surface protein (A) or a cytoskeletal protein (B). Panel C shows a mitotic cell with condensed chromosomes.]] Many diseases can be understood and treated at the cellular level. For example, cancers are diseases caused by abnormal cell growth or other forms of abnormal "antisocial" behavior by cells. The protein beta-catenin (Figure 1A) is a proto-oncogene that when mutated or abnormally regulated inside cells can contribute to cancers such as colon cancer. Mutated keratin (Figure 1B) genes can cause skin blistering diseases. Abnormal keratins and abnormal autoimmune attacks on proteins that cooperate with keratins to hold skin cells together can cause diseases in humans such as Pemphigus.
Many common medical diagnosis methods such as the Pap smear use microscopy of cells to identify cancerous and pre-cancerous cells.
An area of medical research that has been in the news lately (2005) is the study of stem cells. The cells shown in Figure 1C are embryonic stem cells that have the capacity to differentiate into neurons. There is much interest in the idea that diseases such as Parkinson's disease can be treated by transplantation of stem cells.

## Biology Background Information

The online Cell Biology textbook has great background information that would be covered in an introductory Biology class. Make sure you are familiar with this information before diving into more advanced lectures.
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