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Mutation Types and Protein Effects

← Builds on Transcription, RNA Processing, and Translation

Terms you will need

  • point mutationA point mutation is a change in a single building block (nucleotide) in DNA. It can cause no change, a different amino acid in a protein, or a stop to protein production.
  • silent mutationA silent mutation is a change in DNA that does not change the amino acid in a protein, so it usually has no effect on the organism.
  • missense mutationA missense mutation is a change in DNA that results in a different amino acid in a protein, which can make the protein not work properly.
  • nonsense mutationA nonsense mutation is a change in DNA that creates a stop signal in the middle of a protein, making the protein incomplete and often not working.
  • frameshift mutationA frameshift mutation is a change in DNA where adding or removing nucleotides shifts the reading frame, causing a completely different protein to be made.
  • insertionAn insertion is when extra nucleotides are added to DNA, which can change the reading frame and the protein made.

How this topic runs

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Mutations are changes in the DNA sequence of an organism's genome and can arise from errors during DNA replication, damage to DNA, or exposure to mutagens. These changes may or may not affect the organism's observable traits, but they are the ultimate source of genetic variation, which is essential for evolution and adaptation. Mutations can lead to no change, altered protein function, or loss of function, and they play a key role in both normal biological processes and diseases. Understanding mutation types and their effects on proteins is crucial for grasping how genetic changes influence an organism's biology and evolution.

Figures (10)

DNA replication: The double helix is 'unzipped' and unwound, then each separated strand (turquoise) acts as a template for replicating a new partner strand (green). Nucleotides (bases) are matched to synthesize the new partner strands into two new double helices.
DNA polymerases adds nucleotides to the 3′ end of a strand of DNA.[21] If a mismatch is accidentally incorporated, the polymerase is inhibited from further extension. Proofreading removes the mismatched nucleotide and extension continues.
Scheme of the replication fork.a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: Okazaki fragments
Many enzymes are involved in the DNA replication fork.
The cell cycle of eukaryotic cells
Dam methylates adenine of GATC sites after replication
Three major single-chromosome mutations: deletion (1), duplication (2) and inversion (3).
Five types of chromosomal mutations
Types of small-scale mutations
The structure of a eukaryotic protein-coding gene. A mutation in the protein coding region (red) can result in a change in the amino acid sequence. Mutations in other areas of the gene can have diverse effects. Changes within regulatory sequences (yellow and blue) can effect transcriptional and translational regulation of gene expression.

These changes come in different types and can lead to no change, a slightly different protein, or a broken protein. One type is a frameshift mutation. This happens when DNA has extra or missing nucleotides that aren't a multiple of three.

Since DNA is read in groups of three (codons), this shifts the whole reading pattern. This often leads to a completely different protein or a stop signal that cuts the protein short. Another type is a substitution mutation.

Sometimes this doesn't change the protein at all (synonymous) because the genetic code allows for some flexibility. Other times, it changes the protein (nonsynonymous). Nonsynonymous can be missense (a different amino acid) or nonsense (a stop signal where there wasn't one before).

Mutations can also be classified by their effect. Harmful mutations lower survival or reproduction. Beneficial ones help an organism survive better.

These effects depend on the environment and how the mutation changes the protein's function.

Key Points

  • A point mutation is a modification of single base pairs of DNA or other small base pairs within a gene.
  • A missense mutation changes a nucleotide to cause substitution of a different amino acid.
  • A nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and possibly a truncated, and often nonfunctional protein product.
  • A frameshift mutation is caused by insertion or deletion of a number of nucleotides that is not evenly divisible by three from a DNA sequence.
  • Insertions add one or more extra nucleotides into the DNA.

Terms

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