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Beschreibung
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Gene mutations
- Gene mutations are changes in the nucleotide base sequence in a cistron, the section
of DNA that constitutes a gene. Gene mutations produce different alleles of a gene
- Mutations are random and rare events which might arise a spontaneously as a result of errors
during the replication od DNA. If the errors results in a change of a single nucleotde base, it is
called a point mutation. If a point mutation occurs in cells that give rise to gametes, or in a gamete
itslef, it might be inherited by offspring and passed on to successive generations. Point mutations
can be divided into two general types; basepair deletions or insertions, and base-pair substitutions
- Deletions and insertions are losses or additions of nucleotide base pairs.
Unless they occur in multiple of threes, they lead to an alteration in all the
codons downstream from the deletion or insertion. such mutations are
called frame-shift mutations. Unless a frame-shift mutation is near the
end of a gene, it will almost certainly produce a non-funstional protein
- A substituition is the replacement of one nucleotide pair with another, resulting in the
alteration of just one base in one triplet of the DNA template strand. Some substitutions have
no effect on the encoded protein becuase of the degenerate nature of the gentic code.
- That is, there are more codons than amino acids, therefore some amino acids have more than
one codon. a change in one base in the coding strand may change one codon into another that
is translated into the same amino acid. Such substitutions are smetimes called silent mutations
- Other substitutions may result in a change in a single amino acid in a polypeptide chain but have little effect on the action of the protein. The new
protein may have almost the same shape as the original protein, or the change may occur in a part of the protein where the exact sequence of amino
acids is not improtant
- However, substitutions can have a significant effect on protein
structure and function. One example is sickle cell anamia
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