Point mutation

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Point mutation

A point mutation, or single base substitution, is a type of mutation

Mutation

In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or virus , or can be induced by the organism, itself, by cellular processes such as s...
that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. One can categorize point mutations as follows:

Transition mutations are about an order of magnitude more common than transversions. Point mutations can also be categorized functionally:

For example, sickle-cell disease

Sickle-cell disease

Sickle-cell disease or sickle-cell anaemia is a life-long blood disorder characterized by red blood cells that assume an abnormal, rigid, sickle shape....
is caused by a single point mutation (a missense mutation) in the beta-hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
gene

Gene

A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cell and pass genetic trait to offspring....
that converts a GAG codon into GTG, which encodes the amino acid

Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
valine

Valine

Valine is an a-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteogenic amino acids....
rather than glutamic acid

Glutamic acid

Glutamic acid is one of the 20 proteinogenic amino acids and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salt of glutamic acid are known as glutamates....
.

Point mutations that occur in non-coding sequences are most often without consequences, although there are exceptions.

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Encyclopedia

A point mutation, or single base substitution, is a type of mutation

Mutation

transitions: replacement of a purine
Purine

Purine is a heterocyclic compound aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
base with another purine
Purine

Purine is a heterocyclic compound aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
or replacement of a pyrimidine
Pyrimidine

Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring....
with another pyrimidine
transversions: replacement of a purine with a pyrimidine or vice versa.

Transition mutations are about an order of magnitude more common than transversions. Point mutations can also be categorized functionally:

nonsense mutation
Nonsense mutation

In genetics, a nonsense mutation is a point mutation in a DNA sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcription mRNA, and in a truncation, incomplete, and usually nonfunctional protein product....
s: code for a stop, which can truncate the protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
missense mutation
Missense mutation

In genetics, a missense mutation is a point mutation in which a single nucleotide is changed, resulting in a codon that codes for a different amino acid....
s: code for a different amino acid
silent mutation
Silent mutation

Silent mutations are DNA mutations that do not result in a change to the amino acid sequence of a protein. They may occur in a noncoding DNA , or they may occur within an exon in a manner that does not alter the final amino acid sequence....
s: code for the same or a different amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
but without any functional change in the protein

For example, sickle-cell disease

Sickle-cell disease

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
gene

Gene

Amino acid

Valine

Valine is an a-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteogenic amino acids....
rather than glutamic acid

Glutamic acid

Promoter

In biology, a promoter is a region of DNA that facilitates the Transcription of a particular gene. Promoters are typically located near the genes they regulate, on the same strand and Upstream and downstream ....
sequence of a gene, then the expression of the gene may change. Also, if the mutation occurs in the splicing seat of an intron

Intron

Introns, derived from the term "intragenic regions" and also called intervening sequence , are DNA regions in a gene that are not translated into proteins....
, then this may interfere with correct splicing of the transcribed pre-mRNA.

Sometimes the term point mutation is also used to describe insertions

Insertion (genetics)

Genetic Insertion is the addition of one or more nucleotide base pairs into a genetic sequence. This can often happen in microsatellite regions due to the DNA polymerase slipping....
or deletions of a single base pair (which has more of an adverse effect on the synthesized protein due to the nucleotides' still being read in triplets, but in different frames: a mutation called a frameshift mutation

Frameshift mutation

A frameshift mutation genetics mutation caused by indels, ie. gene insertion or genetic deletion of a number of nucleotides that is not evenly divisible by three from a DNA sequence....
).

Causes

Point mutations may arise from spontaneous mutation

Mutation

DNA replication

DNA replication, the basis for heredity, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative replication" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand....
. The rate of mutation may be increased by mutagen

Mutagen

In biology, a mutagen is a physical or chemical agent that changes the genetic information of an organism and thus increases the frequency of mutations above the natural background level....
s. Mutagens can be physical, such as radiation from UV rays, X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequency in the range 30 Hertz to 30 Hertz and energies in the range 120 Electron volt to 120 keV....
s or extreme heat, or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA). Mutagens associated with cancers are often studied to learn about cancer and its prevention.

Point mutation

Causes

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