A healthy human body maintains the appropriate types and numbers of cells needed to function efficiently through an elaborate system of checks and balances. When normal checks and balances fail, abnormal cell growth may lead to the development of cancer. Cancerous cells multiply in an unregulated fashion. This proliferation of abnormal cells often results in the formation of a tumor, or neoplasm. In the case of malignant tumors, the cells can develop the capability to invade surrounding tissue, migrate throughout the body, and grow in tissues distant from the original tumor.[i]

The body contains many different types of cells. Each type of cell has different functions and, therefore, different requirements for proliferation and differentiation.[ii]  Cancer develops when gene mutations disrupt these processes and lead to uncontrolled cell growth.1

Overview of Genetic Processes

Cells proliferate and perform their functions through genetic processes directed by deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).[iii]  

DNA

DNA is the molecule that carries the genetic information for all living organisms. It is a nucleic acid composed of linear chains of repeating units called nucleotides, arranged in two connected strands in the form of a double helix. DNA is composed of a unique sequence of building blocks known as adenine (A), guanine (G), cytosine (C), and thymine (T).3

DNA is located in the nucleus of the cell in the form of chromosomes. Each human cell, other than germ cells and mature red blood cells, contains 46 chromosomes arranged in pairs. A set of 23 chromosomes is inherited from each parent. The structure of DNA serves as the basis for the genetic code.3

DNA is duplicated prior to cell division through replication, transmitting an identical copy of its genetic information to each daughter cell. DNA replication takes place through the breaking down of the bonds between the bases, leaving a single DNA strand with each base unpaired. The unpaired bases attract free nucleotides with complementary bases, creating a new double-stranded DNA molecule identical to the sequence of the original. Each new DNA contains one old strand and one new strand. Each daughter cell of the dividing cell inherits one new DNA molecule.3

RNA

The RNA molecule is a single strand of nucleotides, similar to a single strand of DNA, except that the building blocks of RNA are A, G, C, and uracil (U).3  RNA is produced through the process of transcription, in which a single strand of RNA is synthesized from a DNA template strand in the nucleus. The primary function of RNA is protein synthesis. While DNA contains the master blueprint for protein synthesis, RNA is the working blueprint from which proteins are made.3

Figure 1 illustrates the structures of DNA and RNA.

 

[i] Fenton RG, Longo DL. Cancer cell biology and angiogenesis. In: Harrison’s Hematology and Oncology, 2nd ed. New York, NY; McGraw-Hill, 2013: Chapter 24.

[ii] Seely RR, Stephens TD, Tate, P. Cell structure and function. New York, NY; McGraw-Hill, 2013: Chapter 3.

[iii] Enger ED, Ross FC, Bailey DB. DNA and RNA: the molecular basis of heredity. In: Concepts in Biology, 18^th ed. New York, NY; McGraw-Hill, 2012: Chapter 8.