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Concept
Telomere
Summary
A telomere (ˈtɛləmɪər,_ˈtiːlə-; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Telomeres are a widespread genetic feature most commonly found in eukaryotes. In most, if not all species possessing them, they protect the terminal regions of chromosomal DNA from progressive degradation and ensure the integrity of linear chromosomes by preventing DNA repair systems from mistaking the very ends of the DNA strand for a double-strand break.
In 1938, when the young North American geneticist Hermann J. Müller used to work with flies of the species Drosophila melanogaster, exposed to X rays at the Edinburgh Animal Genetics Institute (United Kingdom), he did not foresee the implications that his findings would have in the molecular biology and genetics in the following 70 years. He had just observed that the ends of the irradiated chromosomes, different from the other genome, did not present alterations such as deletions or inversions, thanks to the presence of a protective cap that he called «terminal gene» and afterwards «telomere», from the greek terms «telos» (end) and «meros» (part) (Müller HJ. The remaking of chromosomes. Collecting Net 1938; 13:181-198)
In the early 1970s, Soviet theorist Alexei Olovnikov first recognized that chromosomes could not completely replicate their ends; this is known as the "end replication problem". Building on this, and accommodating Leonard Hayflick's idea of limited somatic cell division, Olovnikov suggested that DNA sequences are lost every time a cell replicates until the loss reaches a critical level, at which point cell division ends. According to his theory of marginotomy DNA sequences at the ends of telomeres are represented by tandem repeats, which create a buffer that determines the number of divisions that a certain cell clone can undergo. Furthermore, it was predicted that a specialized DNA polymerase (originally called a tandem-DNA-polymerase) could extend telomeres in immortal tissues such as germ line, cancer cells and stem cells.
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Related concepts (77)
Gene
In biology, the word gene (from γένος, génos; meaning generation or birth or gender) can have several different meanings. The Mendelian gene is a basic unit of heredity and the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and noncoding genes. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function.
DNA repair
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA damage, resulting in tens of thousands of individual molecular lesions per cell per day. Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe the gene that the affected DNA encodes.
Telomere
A telomere (ˈtɛləmɪər,_ˈtiːlə-; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Telomeres are a widespread genetic feature most commonly found in eukaryotes. In most, if not all species possessing them, they protect the terminal regions of chromosomal DNA from progressive degradation and ensure the integrity of linear chromosomes by preventing DNA repair systems from mistaking the very ends of the DNA strand for a double-strand break.
Related courses (4)
BIO-622: Practical - Lingner Lab
Telomere biology.
The students will obtain theoretical and practical insight into telomere biology and the roles of telomeres during cellular senescence and for genome stability.
BIO-471: Cancer biology I
The course covers in detail molecular mechanisms of cancer development with emphasis on cell cycle control, genome stability, oncogenes and tumor suppressor genes.
BIO-392: Oncology
This course provides a comprehensive overview of the biology of cancer, illustrating the mechanisms that cancer cells use to grow and disseminate at the expense of normal tissues and organs.