Spark
Loading...

Mutation Types and Protein Effects

In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Mutations result from errors during replication, mitosis, meiosis, or damage to DNA, which then may trigger error-prone repair or cause an error during replication (translesion synthesis). Mutations may also result from substitution, insertion or deletion of segments of DNA due to mobile genetic elements. Mutations may or may not produce detectable changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution, cancer, and the development of the immune system, including junctional diversity.

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.

Key Points

  • A point mutation can be reversed by another point mutation, in which the nucleotide is changed back to its original state (true reversion) or by second-site reversion (a complementary mutation elsewhere that results in regained gene functionality).
  • A missense mutation means the nucleotide mutation alters the overall codon triplet such that a different amino acid is paired with the new codon.
  • 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.
  • The earlier in the sequence the deletion or insertion occurs, the more altered the protein produced is.
  • Substitution mutations, often caused by chemicals or malfunction of DNA replication, exchange a single nucleotide for another.
  • The resulting amino acid (or stop codon) probabilities for each codon are displayed in a genetic code logo.

Terms

Tap a term for a plain-language explanation.

Sources & licensing(4)