3.8: Mutation Causes

Learning Objectives

• Discuss causes of mutation.
• Explain spontaneous mutation.

Figure \(\PageIndex{1}\): What does radiation contamination do? It mutates DNA. The Chernobyl disaster was a nuclear accident that occurred on April 26, 1986. It is considered the worst nuclear power plant accident in history. A Russian publication concludes that 985,000 excess cancers occurred between 1986 and 2004 as a result of radioactive contamination. The 2011 report of the European Committee on Radiation Risk calculates a total of 1.4 million excess cancers occurred as a result of this contamination. (Copyright: 4.8: Mutation Types by CK-12 Foundation, is licensed CK-12)

Causes of Mutation

Mutations have many possible causes. Some mutations seem to happen spontaneously without any outside influence. They can occur when mistakes are made during DNA replication or transcription. Other mutations are caused by environmental factors. Anything in the environment that can cause a mutation is known as a mutagen.

Types of mutagens include radiation, chemicals, and infectious agents. Examples of mutagens are listed in the table below (Table \(\PageIndex{1}\)).. Do you know of other examples of each type of mutagen shown here?

Mutagen	Type	Examples
Radiation	UV Radiation	Natural sunlight, tanning beds
Radiation	X-rays	Medical, dental, airport security screening
Chemical	Cigarette smoke	Active and passive smoke
Chemical	Nitrate and nitrate preservatives	Hot dogs and other processed meats
Chemical	Benzoyl peroxide	Common ingredient of acne products
Infectious agents	Pathogens	HPV and Helicobacter pylori

Spontaneous Mutations

Mutations are random changes in the sequence of bases in DNA. There are five common types of spontaneous mutations. These are described in the table below (Table \(\PageIndex{2C}\))..

Mutation	Description
Tautomerism	a base is changed by the repositioning of a hydrogen atom
Depurination	loss of a purine base (A or G)
Deamination	spontaneous deamination of 5-methycytosine
Transition	a purine to purine (A to G, G to A), or a pyrimidine to pyrimidine (C to T, T to C) change
Transversion	a purine becomes a pyrimidine, or vice versa

The Chernobyl Disaster: Follow-up

Though the area immediately around the Chernobyl disaster may not be safe for human life for thousands of years, the Exclusion Zone around the Chernobyl nuclear power station has become a haven for wildlife. As humans were evacuated from the area 25 years ago, existing animal populations multiplied and rare species not seen for centuries have returned or have been reintroduced, for example lynx, wild boar, wolf, Eurasian brown bear, European bison, Przewalski's horse, and eagle owl. The Exclusion Zone is so lush with wildlife and greenery that in 2007 the Ukrainian government designated it a wildlife sanctuary. It is now one of the largest wildlife sanctuaries in Europe.

Chapter Summary

• Mutations are caused by environmental factors known as mutagens.
• Types of mutagens include radiation, chemicals, and infectious agents.
• Mutations may be spontaneous in nature.

Review Questions

Use this resource to answer the questions that follow.

Q. What is mutation?

A. Mutations are all the chemical process in the cells.

B. Mutations are random changes in the sequence of bases in DNA.

C. Mutation is a process of cell death.

D. Mutation is a process of protein synthesis.

Answer:

B

Critical Thinking Questions

1. Define mutation and mutagen.
2. List three examples of mutagens.
3. Distinguish between a transition and a transversion.
4. What happens to most of the mutations that develop naturally?
5. Where in the genome do most mutations occur?
6. Are most mutations bad? Explain your answer.
7. What is meant by DNA repair?

Glossary

Mutation

Mutations are random changes in the sequence of bases in DNA

Mutagen

Anything in the environment that can cause a mutation is known as a mutagen.