Questions and Answers
What is the term used to describe the conception of a baby with genetic contributions from three individuals?
What is the origin of mitochondria according to the Endosymbiosis Theory?
What benefit did the cyanobacteria or purple bacteria receive from the endosymbiotic relationship?
What is the characteristic that mitochondria gave to cells?
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What is the origin of chloroplasts according to the Endosymbiosis Theory?
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What is the term used to describe the evolutionary origin of mitochondria and chloroplasts?
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What is the primary function of chloroplasts?
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Approximately how large is the cpDNA of a tobacco plant in base pairs?
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What type of genes are carried by cpDNA?
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What is the term for the inheritance pattern of pigmentation in Mirabilis jalapa?
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How many genes does the cpDNA of a tobacco plant carry?
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Where are many chloroplast proteins coded?
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What happens to paternal mitochondria that enter the egg during fertilization?
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What is the pattern of transmission of human mitochondrial diseases?
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Why are mitochondria susceptible to DNA damage?
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What is heteroplasmy in the context of mitochondrial disease?
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What is the result of heteroplasmy in mitochondrial disease?
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What is the purpose of the 'Three Parent Babies' technology?
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What is the result of a high ratio of mutant to normal mitochondria in a cell?
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What is the significance of the ATPase6 gene in mitochondrial disease?
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What is the impact of mitochondrial mutations on the cell?
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What is the inheritance pattern of human mtDNA?
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Study Notes
Destruction of Sperm Mitochondria After Fertilization
- Paternal mitochondria are modified by ubiquitin, a small regulatory protein, which targets organelle destruction.
- This process occurs in most mammals, including humans.
Human Mitochondrial Diseases
- Human mtDNA is transmitted from the female parent to offspring via the cytoplasm of the egg, resulting in a strict maternal inheritance pattern.
- Mitochondrial mutations may occur in somatic cells and accumulate with age, making mitochondria susceptible to DNA damage due to high oxygen consumption and limited repair abilities.
- Over 200 human mitochondrial diseases have been identified, which are typically chronic degenerative disorders affecting cells requiring high levels of ATP, such as nerve and muscle cells.
Examples of Human Mitochondrial Diseases
- Leber hereditary optic neuropathy: a mutation in one of several mitochondrial genes encoding respiratory chain proteins.
- Neurogenic muscle weakness: a mutation in the ATPase6 gene encoding a subunit of the mitochondrial ATP-synthase.
- Mitochondrial myopathy: a mutation in a gene encoding a tRNA for leucine.
- Maternal myopathy and cardiomyopathy: a mutation in a gene encoding a tRNA for leucine.
Heteroplasmy in Mitochondrial Disease
- Heteroplasmy is an important factor in mitochondrial disease, where cells can contain a mixed population of mitochondria with disease-causing mutations.
- Disease may occur when the ratio of mutant to normal mitochondria exceeds a threshold value, with symptoms varying widely within a family.
Three Parent Babies
- A new reproductive technology involves using a third parent's mitochondria to prevent the transmission of mitochondrial diseases from the mother.
- This method was pioneered by John Zhang and colleagues in 2016.
The Endosymbiosis Theory
- The endosymbiosis theory describes the evolutionary origin of mitochondria and chloroplasts, which originated from bacteria that took up residence within primordial eukaryotic cells.
- Chloroplasts originated from cyanobacteria, while mitochondria originated from Gram-negative nonsulfur purple bacteria.
The Endosymbiotic Relationship
- The endosymbiotic relationship provided eukaryotic cells with useful characteristics, including the ability to carry out photosynthesis and synthesize more ATP.
- It is unclear how the cyanobacteria or purple bacteria benefitted from the relationship, possibly through a stable environment with adequate nutrients within the eukaryotic cell.
Chloroplast DNA
- The main function of chloroplasts is photosynthesis.
- Chloroplast DNA (cpDNA) is typically 10 times larger than the mitochondrial genome of animal cells.
- The cpDNA of tobacco plants consists of 156,000 bp and carries between 110 and 120 different genes, including rRNA and tRNA genes and many polypeptides required for photosynthesis.
Maternal Inheritance
- Carl Correns discovered that pigmentation in Mirabilis jalapa (the four o'clock plant) shows a non-Mendelian pattern of inheritance, which is termed maternal inheritance.
- The pigmentation of offspring depends solely on the maternal parent and not at all on the paternal parent.
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Description
This quiz covers the destruction of sperm mitochondria after fertilization and the mechanisms of maternal inheritance of mitochondria in animals.
