Bio 241 Lec 32
Mitochondrial DNA in Humans
- Circular DNA approximately 17 kb pairs long and codes for 37 genes. Most of the genes are for mitochondrial protein synthesis.
3 Types of Yeast mitochondrial mutations
1. Segregational - A petite mutant and a wildtype mate to form a wildtype diploid. After sporylating daughter diploid there will be a 1:1 ratio of normal to petite. (Mendelian) 2. Neutral - A petite mutant and a wildtype mate to form a wildtype diploid. After sporylating the daughter diploid all offspring will be wildtype. 3. Suppressive - A petite mutant and a wildtype mate to form a petite diploid. After sporylating the daughter diploid all offspring will be petite.
Mitochondrial Mutations in Yeast
A colony will appear as petite. (Much smaller than a typical colony) Remember yeast can exist in haploid a or alpha type as well as diploid states.
Maternal Effect Genes
A gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the genotype. The 1st generation mutant female will appear phenotypically normal. The mutation is expressed in her egg cells which come into effect upon reproduction.
What is a prion?
A misfolded, infectious protein. It has the ability to interact with normal proteins and unfold them.
Prion model of transmission
A mouse with PrP^C is infected successfully. A mouse without PrP^C resists infection. This shows that prion can only infect if the healthy version of the protein is present, if not it has no effect.
Reproduction effect on homoplasmy vs heteroplasmy
A parent mitochondria could start heteroplasmy. After many generations and random division of mitochondria, some offspring may become homoplasmic for mutant mitochondria, while some may be homoplasmic for wildtype mitochondria, while others will have varying degrees of heteroplasmy.
How can you tell offspring phenotype in a maternal effect cross?
All offspring will either be wildtype or mutant. Look at mother genotype to determine offspring phenotype. Example: Snail Shell Coiling
Homoplasmy vs Heteroplasmy
Homoplasmy - All mitochondria have identical genes Heteroplasmy - Mitochondria have varied genes
How is mitochondrial DNA inherited in humans?
Mitochondrial DNA is maternally inherited. example (Myoclonic Epilepsy and Ragged Red Fiber Disease)
General Mitochondrion Function
Oxidative Phosphorylation -Mitochondrial mutations can lead to loss in dopaminergic neurons (Parkinson's)
What is the prion protein and its healthy counterpart?
Prion Protein denoted as - PrP^SC Normal Counterpart denoted as - PrP^C These proteins have same sequence but the prion is incorrectly folded.
How was prion identity determined?
The prion was not sensitive to UV Light or nucleases (DNA). It was sensitive to proteases however.
Explain the reasoning behind segregational mutation in yeast mitochondria.
There is a mutation in a nuclear gene involved in mitochondrial function.
Explain the reasoning behind suppressive mutation in yeast mitochondria.
This results from a deletion that prevents proper mitochondrial function, but also gives the mutant a reproductive advantage.
Explain the reasoning behind neutral mutation in yeast mitochondria.
This results from a mutation in the mitochondrial gene that affects mitochondria function.