mutations & mitosis24 January 2012

recap

•Our genetic information is stored in DNA• Specific genetic sequences code for specific

polypeptides• DNA is semi-conservative• Given the sequence one side of the DNA

double helix, can determine the corresponding sequence on the other side• A – T ; C – G

for example

A T G C A C C G G T A C| | | | | | | | | | | |T A C G T G G C C A T G

recap

• specific gene sequences to produce a polypeptide are ‘read’ on a strand of DNA transcribed into mRNA• (DNA double stranded, RNA single)

• A – U (uracil)• C – G•G – C• T – A

for example

A T G C A C C G G T A C| | | | | | | | | | | |U A C G U G G C C A U G

| | | | | | | | | | | |T A C G T G G C C A T G

recap

•mRNA leaves nucleus, translated into polypeptide at ribosome• each 3-nucleotide sequence

corresponds to a specific amino acid• eg. AUG methionine

mutations & mitosis24 January 2012

question/discussion:

•A fish has a mutation in its genome that causes it to fluoresce bright green under certain wavelengths of light. Is this a positive, negative, or neutral mutation? Explain.

•How could the fish be ‘treated’ so it no longer fluoresces?

mutations

•deletion (base missing)• addition (extra base added)• substitution (base substituted for

another)

mutations

• Positive Mutations• When a gene mutation benefits the individual.• Negative Mutations• When a gene mutation harms the individual• Neutral Mutation• When a gene mutation has no effect on the

individual

• A litter of glowing kittens, produced at the Mayo Clinic, could provide scientists with new methods for studying AIDS. Eric Poeschla and collaborators developed a highly efficient method for genetically engineering cats. They inserted genes—including a gene that glows green—into the eggs of domestic cats prior to fertilization and showed these genes were expressed throughout the body of the resulting animals. The fluorescent cats passed these genes onto their offspring, who also glowed.

gene therapy

• Gene therapy is complicated and experimental:• A virus in engineered to carry a normal gene• The virus must somehow be targeted to the cells with

the defective gene• The normal gene must then replace the defective gene• The normal gene must then be “switched on” so that

the replacement normal gene produces the proper healthy proteins. It is also important that the normal gene make the correct amount of healthy protein.