DNA carries the hereditary information for an organism. Since it is a double helix, when the two strands unwind during DNA replication, either one can serve as a template for DNA replication. The bases are added to the copied strand according to base-pairing rules with adenine pairing to thymine and cytosine pairing to guanine.
The replicated DNA will have one strand from the original template and one newly synthesized complementary strand.
Mistakes can occur during...
DNA carries the hereditary information for an organism. Since it is a double helix, when the two strands unwind during DNA replication, either one can serve as a template for DNA replication. The bases are added to the copied strand according to base-pairing rules with adenine pairing to thymine and cytosine pairing to guanine.
The replicated DNA will have one strand from the original template and one newly synthesized complementary strand.
Mistakes can occur during the pairing of complementary nucleotides to the original template strand. However, the cells have an enzyme called DNA polymerase which can remove the wrong nucleotide by enzymatic action and continue synthesizing the complementary strand. Due to the action of this important enzyme, by the time DNA replication is complete, there is only 1 error per 10 billion nucleotides. This amount is an estimate based on many different sources and I have included two excellent links regarding DNA errors and repair mechanisms.
Even after DNA replication is complete, errors between mismatched base pairs can still be corrected. DNA can be exposed to harmful agents such as X-rays, chemicals in the environment, and UV radiation among others, which can cause damage. Sometimes DNA can spontaneously change. If the cell's repair mechanisms cannot correct a mistake, the change is permanent and is called a mutation.
There are multiple repair enzymes in cells to continuously fix errors in DNA. Examples include nucleases which are able to cut out segments of DNA with damage and the original template strand can be used to guide the correction in the complementary strand.
UV radiation can cause thymine dimers to occur which causes the DNA double helix to buckle. This occurs between adjacent thymine bases. This type of damage which is uncorrected may lead to skin cancer.
It is important to note that errors are not that common, however, some mutations do persist. If DNA never mutated, life could never have new genes. Although many mutations are harmful, some could actually be beneficial in the right environment.
I have included a link to show DNA polymerase and its action on DNA replication and repair.
No comments:
Post a Comment