mutation

• Mutation is what gives rise to new alleles
• Mutation is important and helpful in the process of evolution
• Mutation results in variation
• Mutation is a random change in nucleotide sequence of a gene
• Mutation could affect the phenotype of an organism
• There are two major types of mutations: chromosomal and gene mutations
• Chromosomal mutations affect the structure or number of chromosomes
• Gene mutations are random changes in the sequence of bases in a gene
• Gene mutations cause altered codons in the RNA sequence
• Gene mutations result in new alleles
• Alleles are different forms of one gene
• Base substitution is when one nucleotide is replaced by another
• Base substitution can result in three types of mutations
• Types of point mutations

  1. Base substitution

  2. Insertion

  3. Deletion
• Mutation


  Substitution at a single base where one nucleotide is replaced by another, resulting in three types of mutations: silent mutation, nonsense mutation, missense mutation
• Silent mutation


  Occurs when changing a base by substitution still codes for the same amino acid due to the degeneracy of the DNA triplet code, not affecting the amino acid sequence
• Nonsense mutation


  Occurs when a stop codon is introduced due to base substitution, resulting in premature chain termination and an incomplete, non-functional protein
• Missense mutation


  Refers to a mutation where the triplet code codes for a different amino acid, affecting the amino acid sequence and potentially the protein's function
• Silent mutation


  Does not affect the amino acid sequence
• Nonsense mutation


  Results in premature chain termination and an incomplete, non-functional protein
• Missense mutation


  Affects one amino acid in the polypeptide sequence, potentially altering the protein's function depending on the location and the property of the changed amino acid
• Missense mutation


  If the changed amino acid has a different property, the tertiary structure of the protein will be more affected, potentially resulting in a faulty protein
• Missense mutation in an enzyme

  If an essential amino acid at the active site is changed, the faulty protein will likely not be functional
• Base substitution


  It can result in a silent mutation, a non-sense mutation, or a missense mutation, depending on the location of the mutation
• Base insertion and base deletion both result in frame shift mutation
• Frame shift mutation


  When the reading frame shifts, affecting all subsequent codons and amino acids after the mutation
• Reading frame


  How three bases are read together to form codons
• Frame shift mutation can result in a non-functional polypeptide and affect all subsequent amino acids after the mutation
• Deletion or insertion of one nucleotide can cause a frame shift, potentially leading to a nonsense mutation
• If three nucleotides are deleted or inserted at once, the damage may be more localized and may not affect all subsequent amino acids
• Sickle cell anemia is an example of a base substitution mutation affecting the beta globin gene in hemoglobin
• In sickle cell anemia, the mutation changes CTT to CAT at the DNA level, resulting in a change from GAA to GUA in the mRNA codon, leading to a different amino acid in the polypeptide chain
• The mutation in sickle cell anemia changes glutamic acid to valine, altering the primary structure of the protein
• Translation


  Each trna brings a different amino acid to the ribosome, leading to a change of amino acid in the polypeptide chain, altering its primary structure
• Glutamic acid


  Supposed to be polar
• Valine


  Non-polar
• Glutamic acid changing to valine

  Changes the secondary, tertiary, and quaternary structure of hemoglobin, resulting in problematic effects
• Mutated beta globin causes hemoglobin molecules to be less soluble, leading to clumping together and forming fibers within the red blood cell
• Clumping of hemoglobin within the red blood cell leads to reduced ability to bind oxygen, formation of sickle-shaped red cells, increased risk of rupture, and blockage of blood vessels
• To experience symptoms of sickle cell anemia, a person must inherit two mutated beta globin alleles, one from each parent