Can someone make sense of this for me plz I don't understand A mutation is a permanent change of the nucleotide sequence of the genome of an organism, virus, or extra chromosomal
DNA or other genetic elements. Only gamete cells (sperm & eggs) will pass on mutations. Mutations are a common
natural process occurring in DNA sequences.
Think of mutations as "typos” in the DNA code. These typos happen about every 100,000 nucleotides. When a human
cell is copied and transmitted the exact same sequence of 3 billion nucleotides to its daughter cells. This means there are
about 120,000 errors in an average human cell each time it divides.
Three ways DNA can be altered when a mutation (change in DNA sequence) occurs.
1. Point Mutation or Substitution - mutation causing replacement of a single base nucleotide with another nucleotide
of the genetic material, DNA or RNA. In other words, one base-pair is replace by
another.
. If a substitution changes the amino acid, it's called a missense mutation
• If a substitution does not change the amino acid, it's called a SILENT mutation
• If a substitution changes the amino acid to a "stop." it's called a NONSENSE mutation.
G → Cor A→G CGTC
2. Insertion - One or more base pairs is added to a sequence.
DNA: CGA TGG → CGA ATG G
mRNA: GCT ACC → GCT TACC
3. Deletion - one or more base pairs is lost from a sequence
DNA: CGA TGG → CAT GG
mRNA: GCT ACC → GTA CC
There are five possible results
1. Silent mutations - When a base pair is substituted but the change still codes for the same amino acid in the se-
quence.
TCT and TCC both code for the same amino acid, Serine
2. Substitution - When a base is substituted and the new codon codes for a different amino acid.
TCT codes for Serine and CCT codes for Proline
3. Premature Stop - When a substitution results in the formation of a STOP codon before all of the
codons have been read and translated by the ribosome.
DNA: GTG GTC CGA AAC ACC → GTG GTC TGA AAC ACC
mRNA: GUG GUC CGA AAC ACC → GUG GUC UGA AAC ACC
Val-Val-Pro-Asn-Thr
Val-Val-STOP
4. Codon Deletion or Insertion - When a whole new amino acid is added or one is missing from the mutant protein.
DNA: GTG GTC CGA AAC ACC → GTG GTC TGC CGA AAC ACC
mRNA: GUG GUC CGA AAC ACC → GUG GUC UGC CGA AAC ACC
Val-Val-Pro-Ans-Thr → Val-Val-Cys-Pro-Asn-Thr
5. Frame Shift - When a deletion or insertion results in a different base pair being the beginning of the next codon,
shifting it over, changing the whole sequence of amino acids. Meaning the reading "frame" changes,
changing the amino acid sequence.
DNA: GTG GTC CGA AAC ACC → GTG GTC GAA ACA CCT
mRNA: GUG GUC CGA AAC ACC → GUG GUC GAA ACA CCT
Val Val-Pro-Ans-Thr Val Val-Glu-Thr Pro