Cancer Genetics and Epigenetics 2024, Vol.12, No.3, 157-165 http://medscipublisher.com/index.php/cge 158 1 Classification and Characteristics of Cancer Mutations 1.1 Types of gene mutations 1.1.1 Point mutations The classification and characteristics of cancer mutations are key topics in cancer research. Understanding these mutations helps to better comprehend tumor development and design relevant treatment methods. Point mutations are one of the most common types of gene mutations. They refer to changes in a single nucleotide within a gene (Parhami et al., 2020) and can be categorized into subtypes such as missense mutations, nonsense mutations, nucleotide insertions or deletions, and silent mutations. Missense mutations are point mutations that result in the replacement of one amino acid with another (Figure 1). This type of mutation may alter the structure and function of proteins, thereby affecting normal cellular biological activities. Some missense mutations are considered oncogenic because they can activate or enhance the function of oncogenes. Nonsense mutations refer to a codon encoding an amino acid being replaced with a stop codon, leading to premature termination of protein synthesis. This usually results in the loss or defect of the protein, affecting cellular function. Figure 1 missense mutation amino acid replacement Nucleotide insertions or deletions involve the insertion or deletion of one or more nucleotides in a gene. This can cause a frameshift mutation, altering the amino acid sequence of the protein. Silent mutations refer to mutations that do not change the amino acid sequence because multiple codons encode the same amino acid. Although they do not alter the chemical properties of amino acids, they may still impact protein structure and function. 1.1.2 Deletion and insertion mutations Deletion and insertion mutations are common types of gene mutations in cancer research that can significantly impact the normal biological functions of cells. Deletion mutations refer to the loss of some bases in the gene sequence, leading to changes in the DNA sequence. This may cause a frameshift mutation, altering the amino acid sequence of the protein. Deletion mutations often result in highly unstable proteins because they may generate new codons after the deleted region, potentially causing abnormal protein synthesis. In cancer, this type of mutation typically leads to the abnormal expression of key regulatory proteins in cancer cells, thereby promoting tumor growth and spread. Insertion mutations involve the addition of extra bases into the gene sequence, resulting in changes to the DNA sequence. These extra bases can cause a frameshift mutation, altering the way proteins are synthesized. Similar to deletion mutations, insertion mutations can also lead to the production of abnormal proteins. These abnormal proteins may lose normal function or have enhanced oncogenic properties. Insertion mutations play a crucial role in some cancers, particularly in DNA repair genes, as these mutations can disrupt DNA damage repair mechanisms, increasing the susceptibility of cancer cells. 1.1.3 Structural variations Structural variations play a key role in the occurrence and development of cancer because they can alter genetic information and gene expression patterns in cells. Structural variations involve large-scale changes in the DNA sequence, including gene rearrangements, chromosomal deletions, chromosomal duplications, and inversions. These variations can significantly impact genomic stability and normal cellular functions, thereby promoting tumor development. Understanding these variations helps researchers gain better insights into the molecular mechanisms of cancer. Gene rearrangements refer to the reorganization of two different parts of a gene at the DNA level, typically involving chromosomal breaks and reattachments. This variation may produce fusion proteins, which can have oncogenic properties because they may lose normal regulation and promote uncontrolled cell growth. Chromosomal deletions involve the loss of a part or entire chromosome, which can lead to the inactivation of
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