Difference Between DNA Damage and Mutation

Key Difference – DNA Damage vs Mutation
 

DNA bears the genetic information of each cell. It is stored with the heredity information which is supposed to be passed from one generation to the next generation. The genetic information is hidden within the DNA molecules in the form of precise nucleotide sequences. There are billions of nucleotides, and they are arranged in groups called genes. Genes are encoded with instructions to make all the proteins and other materials essential for organism’s growth, development, and metabolism. The number and accurate order of the nucleotides in DNA determine the properties of each organism. Therefore, maintaining the integrity and stability of DNA are vital for life. However, DNA are constantly being subjected to changes due to various factors including internal and environmental origin. DNA damages and mutations are such changes that occur in DNA. DNA damage is referred to as a breakage or an alteration of the physical or chemical structure of DNA. Mutation is defined as base changes in the DNA sequence. The key difference between DNA damage and mutation is that DNA damages can be correctly repaired by enzymes whereas mutations cannot be recognized and repaired by enzymes.

CONTENTS
1. Overview and Key Difference
2. What is DNA Damage
3. What is Mutation
4. Side by Side Comparison – DNA Damage vs Mutation
5. Summary

What is DNA Damage?

DNA damage is an abnormality of physical and/or chemical structure of the DNA. Due to DNA damage, its structure deviates from the normal structure. DNA damages mostly occur during DNA replication. Adding a wrong nucleotide during the replication happens in every 10⁸ base pairs. However, 99% of the errors are corrected during the proofreading activity of DNA polymerase enzymes. The remaining 1% will not be repaired and will be passed to the next generation as a mutation.

DNA damages can happen due to the introduction of illegitimate bases during replication, deamination or other modification of bases, loss of a base from the DNA backbone resulting in abasic sites, single strand breaks, double strand breaks, formation of pyrimidine dimers, intra and interstrand crosslinking, etc. These DNA damages are constantly repaired by the several DNA repairing mechanisms in the cells. They include base excision repair, nucleotide excision repair, mismatch repair, homologous end joining or non-homologous end joining, etc.

There are several reasons for DNA damages. DNA replication errors result in DNA damages. DNA can be damaged due to exposure to UV light, toxic chemicals, ionizing radiation, X-rays, anti tumor drugs and harmful cellular by-products (oxygen radicals, alkylating agents).

Figure 01: DNA Damage by UV Radiation

What is Mutation?

Mutation is a change in the base sequence of the DNA. Enzymes fail to recognize DNA errors when they occur in both strands. If the base changes happen in both strands in the form of mutation, they cannot be repaired by the enzymes. Therefore, mutations are transmitted to the duplicating genomes and passed to the succeeding generations, producing different phenotypes. Mutated genes result in different amino acid sequences which produce wrong proteins products.

Mutations can be generated due to endogenous or exogenous sources such as failure of repairing mechanisms, errors of DNA recombination and replication, oxidative stress, toxic chemicals, X ray, UV light etc. During replication, mutations occur at a rate of one mutation in every 10 billion base pairs that are replicated.

The outcomes of the mutations can be positive (beneficial), negative (detrimental) and neutral.  Mutations are in different types such as point mutations, frameshift mutations, missense mutation, silent mutations and nonsense mutations.

Figure 02: Mutation by UV

What is the difference between DNA Damage and Mutation?

Summary – DNA Damage vs Mutation

DNA damage and mutation are two types of errors occurred in the DNA structure. DNA damage is any modification in the chemical or physical structure of DNA converting it into an altered DNA molecule than the original DNA molecule. These modifications are quickly traced by the enzymes and corrected before converting into a heritable change called mutation. Mutation is a heritable change in the base sequence of the DNA. They are not normally recognized by the enzymes and subjected to repairing. Mutations lead to unwanted protein products and different phenotypes. This is the difference between DNA damage and mutation.
Reference:
1. Suzanne Clancy. “DNA Damage & Repair: Mechanisms for Maintaining DNA Integrity.” Nature News. Nature Publishing Group, 2008. Web. 11 Mar. 2017
2. Lodish, Harvey. “DNA Damage and Repair and Their Role in Carcinogenesis.”Molecular Cell Biology. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 12 Mar. 2017
3. Chakarov, Stoyan, Rumena Petkova, George Ch Russev, and Nikolai Zhelev. “DNA damage and mutation. Types of DNA damage.” BioDiscovery. Dundee Science Press, 23 Feb. 2014. Web. 13 Mar. 2017

Image Courtesy:
1. “Direct DNA damage” De Gerriet41 – Trabajo propio (Dominio público) via Commons Wikimedia 
2. “DNA UV mutation” By NASA/David Herring – NASA,  (Public Domain) via Commons Wikimedia

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