Sickle cell anemia presentation



The Molecular Biology of Mutations and Muscular Dystrophy

By Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania, 2011[1]

1. The table shows five different mutations of a small section of a gene.

• Use the base-pairing rules to complete the second column. For each mutation, write in any mRNA codons that will be changed as a result of the mutation and use check marks to indicate codons that will not be changed.

• Using the genetic code chart, identify and circle any stop codons in the mRNA molecules.

• For each mutation, write any amino acids that will be changed in the last column. Use dashes to indicate any amino acids that will be missing as a result of stop codons and use check marks to indicate any amino acids that will not be changed.

|DNA (Template Strand) |mRNA codon |Polypeptide |

|Original DNA = | | |

|GCAAGTACCTGA |CGU UCA UGG ACU |arg – ser – trp – thr |

|Mutation = | | |

|GCCAGTACCTGA |____ ____ ____ ____ |___ ___ ___ ___ |

|(nucleotide change underlined) | | |

|Mutation = | | |

|GCACGTACCTGA |____ ____ ____ ____ |___ ___ ___ ___ |

|(nucleotide change underlined) | | |

|Mutation = | | |

|GCAAGTACTTGA |____ ____ ____ ____ |___ ___ ___ ___ |

|(nucleotide change underlined) | | |

|Mutation = | | |

|GAAGTACCTGA |____ ____ ____ ____ |___ ___ ___ ___ |

|(first C deleted) | | |

|Mutation = | | |

|GCAAGTACTGA |____ ____ ____ ____ |___ ___ ___ ___ |

|(second C deleted) | | |

Genetic Code Chart for Translating Codons in mRNA to Amino Acids in a Polypeptide

[pic]

2. Explain why deletion of a single nucleotide in a gene generally results in more severe defects in the polypeptide than a point mutation that changes a single nucleotide.

3. Muscular dystrophy includes several genetic diseases which cause increasing weakness of a person's muscles. Two different types of muscular dystrophy are caused by different types of mutations in the gene for a protein that helps to prevent muscle cells from dying prematurely.

Duchenne muscular dystrophy is more severe. A child with Duchenne muscular dystrophy begins to show symptoms of loss of muscle function by about age 3 and needs to use a wheelchair by about age 10. A person with Duchenne muscular dystrophy typically dies as a young adult, due to failure of the muscles in the internal organs.

Becker muscular dystrophy is milder. Symptoms do not begin until age 12 or later, and the person can live into their 40s or 50s.

The table shows the main kinds of mutations that are responsible for these two types of muscular dystrophy. Complete the second column to indicate which type of muscular dystrophy you think would be caused by each type of mutation.

|Type of Mutation |Type of Muscular Dystrophy |

|Deletion Mutation ( | |

|# nucleotides deleted from mRNA is a multiple of 3 | |

|Deletion Mutation ( | |

|# nucleotides deleted from mRNA is not a multiple of 3 | |

| | |

|Point Mutation ( stop codon | |

Explain your reasoning.

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[1] Teachers are encouraged to copy this student handout for classroom use. A Word file (which can be used to prepare a modified version if desired), teacher notes, and links to additional activities are available at .

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