Fundamentals of Cancer Detection, Treatment, and Prevention. Surya K. De. Читать онлайн. Newlib. NEWLIB.NET

Автор: Surya K. De
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Медицина
Год издания: 0
isbn: 9783527838578
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Chromosomes are found in all living cells and consist of a single molecule of DNA bound to various proteins (Figure 1.3). They carry the genes, which are the basic units determining inherited traits. Genes control cell function, particularly how cells grow and divide, and when they need to stop this growth [5–14].

Schematic illustration of cell structure showing DNA in the nucleus. The DNA molecule is a double helix. A gene is a length of DNA that codes for the manufacture of a specific protein.

      In the human body, there are 46 chromosomes, arranged in 2 sets of 23. We inherit one set from our mother and one from our father. Chromosomes contain all the information for the physical characteristics that make up an individual. One chromosome in each set determines whether a person is female or male. The other 22 chromosome pairs decide other physical characteristics in the human body. These chromosome pairs are also called autosomes.

Schematic illustration of information from DNA is used to make proteins from genes. Schematic illustration of cancer cells start as normal cells, which acquire mutations over time that change them to cancer cells.

      1.6.1 Acquired Mutations

      Mutations of this type are the most common cause of cancer, and when this occurs, it is called sporadic cancer. These mutations, initially affecting only a few cells in the body, damage the genes in these cells. Since these mutations are acquired, they do not pass from parents to children. Major factors contributing to acquired mutations include:

       Tobacco

       Ultraviolet (UV) radiation

       Viruses

       Age

      1.6.2 Germline Mutations

      Not as common as acquired mutations, germline mutations take place in reproductive cells, such as those in a female's egg or a male's sperm. Offspring resulting from the union of reproductive cells with germline mutation receive that mutation, which is copied into every cell in the body as it develops. Since these mutations are in the reproductive cells, they are carried from generation to generation and are known as inherited cancers. Germline cancers comprise between 5 and 20% of all cancers.

      Germline cancers should not be confused, however, with germ cell tumors, which start in the cells that give rise to sperm or eggs. These tumors can develop almost anywhere in the body, and they can be either benign or malignant.

      Certain types of genes have been linked to the development of cancer in the human body. Scientists categorize these genes in broad groups:

      1.7.1 Tumor Suppressor Genes

      The genes have the protective feature of controlling cell growth by:

       Monitoring new cell divisions

       Correcting DNA sequences that have mutated

       Controlling cell death (apoptosis)

      Examples include TP53 (tumor protein 53 or cellular tumor antigen p53, or referred to as p53), PTEN, RB1, and APC. When tumor suppressor genes mutate, cell growth is unchecked and may result in tumor formation.

      In the case of germline mutations, if certain tumor suppressor genes – namely BRCA1 or BRCA2 – mutate, there is a higher chance of developing hereditary breast or ovarian cancer for women, and prostate cancer for men. These specific mutations also have been linked to an increased risk of pancreatic cancer and melanoma.

Schematic illustration of structure of p53 tumor suppressor protein. p53 prevents cancer formation and acts as a guardian of the genome. Mutations in the p53 gene contribute to about half of the cases of human cancer.

      Source: Juan Gärtner/Adobe Stock

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      1.7.2 Oncogenes

      1.7.3 DNA Repair Genes