Exercise: Mutation




BIO372 : Evolution : Natural Selection & Adaptation : Exercise: Mutation

Exercise: Mutation

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1. Evolutionary changes in organisms resulted from genetic mutations. Genes are primarily sections of DNA which code for proteins. Since DNA is composed of a linear string of four nucleotides, one type of mutation is the substitution of one nucleotide for another. Sometimes such substitutions result in subsequent changes and sometimes these mutations are silent.

a) Why is a silent mutation called "silent?" Give an example of such a silent mutation.

b) What is an example of a substitution which is not silent?

2. DNA codes primarily for proteins, which are composed of a linear string of amino acids. The linear string of amino acids is the primary structure of the protein.

a) What is the secondary structure of a protein?

b) What is a hydrogen bond and what role does it play in protein secondary structure?

3. The actual function of a protein depends on its three dimensional structure, i.e., the final shape of the molecule that determines how it interacts with other molecules. Substitutions in specific amino acids (mutations) can significantly alter the final structure of an important protein, such as an enzyme.

a) What is the amino acid substitution in the ß hemoglobin chain that results in the mutation to sickle cell hemoglobin? What was the probable codon for the original amino acid and what was it after the mutation?

b) What physical properties of these amino acids are thought to be responsible for the difference in the functioning of normal and sickle cell hemoglobin?

c) How is the function of sickle cell hemoglobin altered from its normal counterpart in the blood stream?

It is interesting to note that, in those parts of the world where malaria caused by the Plasmodium parasite is common (Africa and adjacent areas), individuals with sickle cell trait (heterozygous for the sickle cell gene) are resistant to malaria while individuals with normal hemoglobin are not resistant.

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