Mitochondrial DNA Structure and Function

Mitochondria and Mitochondrial Disease

• Mitochondria have 37 genes, encoding 13 proteins, 22 transfer RNAs, and 2 ribosomal RNAs, essential for normal mitochondrial function.
• 13 mt genes encode proteins responsible for or involved in oxidative phosphorylation to create ATP for the cell's source of energy.
• Mitochondrial proteins are derived from both nDNA and mtDNA encoded genes.
• mtDNA is more prone to mutation than nDNA, leading to mitochondrial disease.

Characteristics of Mitochondrial Disease

• Mitochondrial disease refers to disorders caused by a reduction in ATP production.
• Symptoms include muscle weakness, problems with movement, diabetes, kidney failure, heart disease, dementia, loss of hearing, and abnormalities involving the eyes and vision.
• Visual component is often present, with features such as ptosis, external ophthalmoplegia, and retinitis pigmentosa.
• Leber's hereditary optic neuropathy is a result of mutations in four mitochondrial genes, affecting the enzyme complex I necessary for oxidative phosphorylation.

Inheritance of Mitochondrial Disease

• Mitochondrial disease is maternally inherited, as the mitochondria in the male sperm are lost during fertilization.
• Each cell has 1000s of copies of mtDNA, which are the same at birth (homoplasmy).
• Individuals with mutated mtDNA have a mixture of mutated and non-mutated mtDNA within a particular cell (heteroplasmy).
• The level of mutation in mtDNA affects the severity of disease in offspring, with high levels of mutation leading to severe disease.

Other Genetic Disorders

• Familial Hypercholesteremia is an autosomal dominant disorder due to a defect in the LDL receptor, leading to acceleration of atherosclerosis.
• Phenylketonuria is an autosomal recessive disorder due to a defect in the enzyme phenylalanine hydroxylase, leading to mental retardation if left untreated.
• Lysosomal storage disease is an autosomal recessive disorder resulting from a mutation in one of the genes encoding lysosomal hydrolases, leading to an accumulation of substrate within the lysosomes.
• Neurofibromatosis is an autosomal dominant disorder resulting from a defect in the neurofibromin 1 or 2 genes, leading to growths in the nervous system and skin.
• Haemophilia is an X-linked recessive disorder resulting from deficiencies in Factor VIII or IX, leading to impaired blood clotting and a risk of haemorrhaging.

This quiz covers the structure and function of mitochondrial DNA, including the genes it encodes, the proteins involved in oxidative phosphorylation, and the differences between mtDNA and nDNA. Learn about the importance of mitochondrial function and the implications of mitochondrial disease.