Cells form the basic structural and functional units of an organism.1 All cells contain a cell membrane, cytoplasm and nucleus.1 Situated in the nucleus is the genetic material or deoxyribonucleic acid (DNA), which is the fundamental building block for life. DNA is made up of subunits called genes. Each gene is coded for a specific product such as a protein or enzyme.2
Genes are contained in chromosomes and only the genes required are switched on.2 Some important genes in the context of cellular proliferation include:
- proto-oncogenes: a gene involved in normal cell growth. Mutations (changes) in a proto-oncogene may cause it to become an oncogene, in which it becomes overactive and can cause the growth of cancer cells3
- tumour suppressor genes: a type of gene that makes a protein called a tumour suppressor protein that helps control cell growth. Mutations (changes in DNA) in tumour suppressor genes may lead to cancer.3
Each tissue and organ in the body is composed of vast populations of cells, totaling more than 1014 (100 000 000 000 000). An astonishing 1012 (1 000 000 000 000) cells die or are shed in the normal course of each day and must be replaced to sustain life.
The process by which cells grow and divide to replenish lost cells is termed cell proliferation. This is a highly regulated activity in normal, healthy tissue. The synthesis of new cells is balanced against cell loss so that the total number of cells composing all tissues and organs in the body remains essentially unchanged.4-7
Cell growth, the replication of genetic material and cell division are all governed by the cell cycle, a highly-ordered series of events that culminates in mitosis (the division of a cell, giving rise to two daughter cells). Progression through the cell cycle depends on successful passage through a number of critical phases, known as checkpoints, which function to ensure the synthesis of fully functioning daughter cells.6-9
Define normal cell proliferation and differentiation.
Outline the phases of the cell cycle and the cellular activities that occur in each of these phases.
Explain the roles of each of the cell cycle control checkpoints.
Access nobelprize.org and complete the Control of the Cell Cycle game.