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11.3. Causes of mutations

Causes of genetic mutations

Mutations can be spontaneous, caused by errors in replication or fortuitous DNA damage, or induced, artificially produced by mutagenic agents.

The DNA is subjected to repeated attacks of chemical or physical environment of the cell agents substances can cause natural mutations.

But in addition to nature, there are also attacks produced by unhealthy social (alcohol, tobacco,...) and eating habits that have increased the number of mutagenic agents. These mutagenic agents can be classified into:

  • Chemical mutagens: they are chemical compounds capable of abruptly altering DNA structures, such as:
    • Alkylating agents, such as mustard gas, which alter replication by introducing radicals methyl, ethyl, ...
    • Intercalating agents, such as acridine orange and benzopyrene. Benzopyrene that binds to DNA preventing base pairing.
    • Deaminating agents.
    • Analogs of puric and pyrimidine bases.
    • Nitrous acid that accelerates the transformation of cytosine into uracil.
    • Dioxins that are carcinogens.
  • Physical mutagens: these are radiations that can alter the sequence and structure of DNA.
    • Non-ionizing radiation: For example, ultraviolet radiation that originates dimers of pyrimidine (generally thymine), which distort the double helix of DNA and prevent its replication and cell division or form free radicals.

By derivative work: Mouagip (talk)DNA_UV_mutation.gif: NASA/David HerringThis vector graphics image was created with Adobe Illustrator. (DNA_UV_mutation.gif) [Public domain], via Wikimedia Commons

Vídeo: Radiación UV y mutación del ADN.

  • Ionizing radiation (X-rays, gamma), break the phosphodiester bonds, altering the DNA chains. For example, gamma and alpha radiation. The ultrasound also produce structural chromosomal variations.
      • Biological mutagens: are those "living" organisms that can alter the sequences of the genetic material of their host, such as: viruses, bacteria and fungi. Examples are transposons (autonomous DNA fragments).

      • Factors that are not mutagenic agents but that determine whether or not a mutation will take place: temperature, oxygen pressure, aging.

      The 37 ºC of temperature causes, for example, that the human cells lose every day about 5000 puric bases (adenine and guanine) and the transformation of cytosine into uracil and adenine into hypoxanthine.

      • Mutagens that result from metabolized non-carcinogenic substances, for example benzopyrene is the substance resulting from liver metabolism.

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Aragon. September 2018, option A, question 4. September 2014, option B, question 1.

Mutations (2.5 points)

c) Mutagens. (0.5 points)

Aragon. June 2016, option B, question 4.

Mutations: (2 points)

b) List two mutagenic agents. (0.5 points)

Andalusia, June 2017, option B, question 5.

In the radiology services of the health centers there are posters that warn of the risks of x-ray examinations to pregnant women or those who may be pregnant. What is this warning based on? Give reasons for the answer [1].

Murcia, September 2018, option B, question 5.

Answer the following questions:

a) What are mutations? (0.6 pts)

b) What is a mutagenic agent? (0.6 pts). Give an example of a physical mutagenic agent and another of a chemical agent (0.3 pts).

Extremadura, July 2020, question 6

Mutations and mutagenic agents:

A. Concept of mutation. (0.5 points)
B. Classification of mutagenic agents. Give two examples of each type. (1.5 points)

Extremadura, June 2021, question 6

6.-Regarding mutations:

A. Concept of mutation. (0.5 points)
B. Differentiate between gene and chromosomal mutation. (0.5 points)
C. List two types of mutagenic agents and give two examples for each of them. (1 point)

Navarra, June 2021, question 13

a) Cite 3 examples of mutagenic agents.

b) A person is continuously exposed to mutagenic agents in such a way that he suffers a mutation in his genome. What has happened if that mutation is hereditary?

c) What if that mutation is not hereditary?

Asturias, July 2021, question 4b

Define the concept of mutation. Name a physical and chemical mutagenic agent, indicating their action. (Maximum score 1 point)

Fundamental ideas about the causes of mutations

The causes of mutations can be:

  • Spontaneous, produced by errors in replication or by fortuitous DNA damage.
  • Induced, artificially produced by mutagenic agents.

Mutagens or mutagenic agents are chemical, physical or biological agents that alter the genetic information of an organism and this increases the frequency of mutations above the natural level. 


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