1. Mutations Can Change the Meaning of Genes CH 11 Section 6

2. How Mutations Affect Genes Mutation: any change in the nucleotide sequence of DNA Types of Mutations: Base substitutions: replacement of one nucleotide w/ another. May or may not affect protein Base deletions & Base insertions: May be more harmful b/c all subsequent codons will be altered

3. There are two general categories of gene mutation: base substitution and base insertion (or deletion). The effect on the resulting polypeptide is shown here, following substitution (a) and deletion (b).

4. What Causes Mutations? Errors during DNA replication Errors during chromosome crossovers Mutagens: physical or chemical agents that cause mutations X-rays Ultraviolet light

5. Examples The sickle-shaped cells clog tiny blood vessels, dangerously blocking the normal flow of blood. The molecular basis for the disease lies in the difference of only one DNA nucleotide out of a 438-base sequence.

6. Reviewing Concepts - Multiple Choice 1. The work of several scientists helped to show that the hereditary material is a. DNA. b. proteins. c. ribosomes. d. codons. 2. The backbone of nucleic acid polymers is composed of a. nitrogenous bases and phosphates. b. polypeptides. c. sugars and phosphates. d. nucleotides. 3. Excluding the stop sequence, how many nucleotides are necessary to code for a polypeptide that is 100 amino acids long? a. 33 b. 66 c. 100 d. 300 4. Which of the following occurs first during the process of transcription? a. Introns are removed and exons are joined together. b. Two DNA strands start to separate. c. DNA polymerases join together complementary base pairs. d. tRNA translates codons. 6. Which of the following does not directly participate in translation? a. ribosomes b. tRNA c. mRNA d. DNA 7. A geneticist found that a certain mutagen had no effect on the polypeptide coded by a particular gene. This mutagen most likely caused a. a silent mutation. b. loss of one nucleotide. c. addition of one nucleotide. d. deletion of a gene.