21 7 Genetic Mutations A peacock with albinism

21. 7 Genetic Mutations A peacock with albinism does not produce the melanin needed to make bright colors for its feathers. Learning Goal Identify the type of change in DNA for a point mutation, a deletion mutation, and an insertion mutation. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Genetic Mutation A mutation • is a change in the nucleotide sequence of DNA. • may result in changes to the sequence amino acids that affect the structure and function of cells. • results from mutagens, such as radiation and chemicals (possibly some viruses). When a mutation severely alters proteins or enzymes, the new cells may not survive or the person may exhibit a disease or condition that is a result of a genetic defect. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Normal DNA Sequence The normal DNA sequence produces an m. RNA that provides instructions for the correct series of amino acids in a protein. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Types of Mutations • A point mutation is the replacement of one base in the template strand of DNA with another; this may cause a different amino acid to be inserted into the polypeptide. • A silent mutation occurs when a point mutation does not change the amino acid. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Mutations, Deletion and Insertion • In a deletion mutation, a base is deleted from the normal order of bases in the template strand of DNA. All the codons that follow are changed, producing a different sequence of amino acids from that point. • In an insertion mutation, a base is inserted into the normal order of bases in the template strand of DNA. All the codons that follow are changed, producing a different sequence of amino acids from that point. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Mutations, Deletion and Insertion Deletion and insertion mutations change all the codons that follow. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Effects of Mutations • Some mutations do not cause significant changes in the primary structure of a protein. For drastic changes in the amino acid sequence, • the structure of the resulting protein may lose its biological activity. • proteins (enzymes) may no longer catalyze reactions and substances may accumulate in the cells until they are poisonous. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Genetic Diseases • Genetic diseases result from a defective enzyme caused by mutation in its genetic code. • If the enzyme that converts tyrosine to melanin is defective, no melanin is produced, resulting in the genetic disease known as albinism. • Tyrosine is needed for the formation of melanin (skin and hair pigment). General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Genetic Diseases General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check Identify each type of mutation as a point mutation (P), an insertion mutation (I), or a deletion mutation (D). A. Cytosine (C) enters the DNA sequence. B. One adenosine is removed from the DNA sequence. C. A base sequence of TGA in DNA changes to TAA. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Identify each type of mutation as a point mutation (P), an insertion mutation (I), or a deletion mutation (D). A. Cytosine (C) enters the DNA sequence. (I) B. One adenosine is removed from the DNA sequence. (D) C. A base sequence of TGA in DNA changes to TAA. (P) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.