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C H A P T E R 7  Introduction to cell physiology

C hemotherapeutic drugs are used to destroy both organ- isms that invade the body (e.g. bacteria, viruses, parasites, protozoa, fungi) and abnormal cells within the body (e.g. neoplasms, cancers). These drugs affect cells by altering cellular function or disrupting cellular integrity, causing cell death, or by preventing cellular reproduction, eventu- ally leading to cell death. Because most chemotherapeutic agents do not possess complete selective toxicity , they also, to some extent, affect the normal cells of people. To understand the actions and adverse effects caused by chemotherapeutic agents and to determine interventions that increase therapeutic effectiveness, it is important to understand the various properties and the basic structure and function of the cell. THE CELL The cell is the basic structural unit of the body. The cells that make up living organisms, which are arranged into tissues and organs, all have the same basic structure. Each cell has a nucleus, a cell membrane and cytoplasm, which contains a variety of organelles (Figure 7.1). Cell nucleus Each cell is “programmed” by the genes , or sequences of DNA, that allow for cell division, produce specific

proteins that allow the cell to carry out its functions and maintain cell homeostasis or stability. The nucleus is the part of a cell that contains all genetic material necessary for cell reproduction and for the regulation of cellular production of proteins. The nucleus is encapsulated in its own membrane and remains distinct from the rest of the cytoplasm. A small spherical mass, called the nucle- olus, is located within the nucleus. Within this mass are dense fibres and proteins that will eventually become ribosomes , the sites of protein synthesis within the cell. Genes are responsible for the formation of messenger RNA and transcription RNA, which are involved in production of the proteins unique to the cell. The DNA necessary for cell division is found on long strains called chromatin. These structures line up and enlarge during the process of cell division. Cell membrane The cell is surrounded by a thin barrier called the cell membrane , which separates intracellular fluid from extracellular fluid. The membrane is essential for cellular integrity and is equipped with many mechanisms for maintaining cell homeostasis. Lipoproteins The cell membrane is a lipoprotein structure, meaning that it is mainly composed of proteins and

Cilia with microtubules

Golgi apparatus

Peroxisomes

Lysosomes

Cell membrane

Nucleus: Nuclear membrane Nuclear pore Nucleolus

Centrioles

Microtubules

Polyribosomes

Mitochondria

Smooth endoplasmic reticulum

Rough endoplasmic reticulum

FIGURE 7.1  General structure of a cell and the location of its organelles.