Point mutation

Mutagens can be physical, such as radiation from UV rays, X-rays or extreme heat, or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA).

Reactive oxygen molecules with free radicals, which are a byproduct of cellular metabolism, can also be very harmful to DNA.

In 1959 Ernst Freese coined the terms "transitions" or "transversions" to categorize different types of point mutations.

Stop-gain is a mutation that results in a premature termination codon (a stop was gained), which signals the end of translation.

[4] Stop-loss is a mutation in the original termination codon (a stop was lost), resulting in abnormal extension of a protein's carboxyl terminus.

Start-loss is a point mutation in a transcript's AUG start codon, resulting in the reduction or elimination of protein production.

Non-conservative mutations result in an amino acid change that has different properties than the wild type.

A single nucleotide can change, but the new codon specifies the same amino acid, resulting in an unmutated protein.

On the other hand, harmful mutations cause the organism to die or be less likely to reproduce in a phenomenon known as natural selection.

Because the mutations can affect the DNA and thus the chromatin, it can prohibit mitosis from occurring due to the lack of a complete chromosome.

If the mutation occurs in the region of the gene that is responsible for coding for the protein, the amino acid may be altered.

A mutation in this region may alter these sequences and, thus, change the way the transcription factors bind to the protein.

[9] A novel assay, Fast parallel proteolysis (FASTpp), might help swift screening of specific stability defects in individual cancer patients.

Under low-oxygen conditions (being at high altitude, for example), the absence of a polar amino acid at position six of the β-globin chain promotes the non-covalent polymerisation (aggregation) of hemoglobin, which distorts red blood cells into a sickle shape and decreases their elasticity.

[14] Hemoglobin is a protein found in red blood cells, and is responsible for the transportation of oxygen through the body.

[16] Beta-hemoglobin is created from the genetic information on the HBB, or "hemoglobin, beta" gene found on chromosome 11p15.5.

[17] A single point mutation in this polypeptide chain, which is 147 amino acids long, results in the disease known as Sickle Cell Anemia.

The single nucleotide change in the beta-globin means that even the smallest of exertions on the part of the carrier results in severe pain and even heart attack.

Below is a chart depicting the first thirteen amino acids in the normal and abnormal sickle cell polypeptide chain.

The HEXA gene makes part of an enzyme called beta-hexosaminidase A, which plays a critical role in the nervous system.

Mutations in the HEXA gene disrupt the activity of beta-hexosaminidase A, preventing the breakdown of the fatty substances.

[21] RIP occurs during the sexual stage in haploid nuclei after fertilization but prior to meiotic DNA replication.

Indeed, for example, in the phytopathogenic fungus L. maculans, RIP mutations are found in single copy regions, adjacent to the repeated elements.

[27] Rep and Kistler have speculated that the presence of highly repetitive regions containing transposons, may promote mutation of resident effector genes.

[28] So the presence of effector genes within such regions is suggested to promote their adaptation and diversification when exposed to strong selection pressure.

[32] Deletion of the rid homolog in Aspergillus nidulans, dmtA, results in loss of fertility[33] while deletion of the rid homolog in Ascobolus immersens, masc1, results in fertility defects and loss of methylation induced premeiotically (MIP).

[34] RIP is believed to have evolved as a defense mechanism against transposable elements, which resemble parasites by invading and multiplying within the genome.

Hertwig studied sea urchins, and noticed that each egg contained one nucleus prior to fertilization and two nuclei after.

Hermann Fol continued Hertwig's research by testing the effects of injecting several spermatozoa into an egg, and found that the process did not work with more than one spermatozoon.

People considered all possible methods of determining the replication process of DNA, but none were successful until Meselson and Stahl.