Abali - Mitochondrial Genome Flashcards
mtDNA transcription
Similar to prokaryotic transcription in that it has 1 RNA pol that makes tRNA rRNA and mRNA. It is controlled by TFAM, a transcription activator. Also involved is mitochondrial transcription factor B1 or B2.
Important things to know about mitochondrial transcription
- the universal code that one would find on a codon chart is not the same for mtDNA. Some things that code for one AA will not code for that same AA in mitochondria.
- The third base is in the wobble position. mt-tRNA aren’t that specific and generally it doesn’t really care about the third position.
- there is no or very few bases in 5’ UTR.
- Poly(A) tail is either part of the stop codon or immediately after.
- mRNA is not capped
- proving that mito is like prokaryotes, it has prokaryotic orthologs: IF2, IF3, mtEFTu, mtEFTs, mtEFG
How many peptides made by mitochondria? And what are some distint features?
13 - all involved in oxidative phosphorylation. Any other protein is made by the nuclear genome and imported into the cell.
- very high mutation rate in mtDNA.
- MATERNAL INHERITANCE OF mtDNA.
- bottleneck
- random segregation
- threshold effect
- changes with age
distinctive features: very high mutation rate
close to source of reactive oxygen species.
- DNA PolGamma is prone to mistakes even with it’s proofreading capabilities.
- no introns so mutations are mostly in coding region.
distinctive features: maternal injeritence
parental mtDNA is destroyed in the embryo by ubuiqination. Affected males can’t pass on the affected mtDNA to their children.
Bottleneck effect
The number of mitochondrial DNA molecules within the developing oocyte is reduced before being amplified to a large total seen in a mature oocyte. The reduction of mito DNA redistributes the mito DNA. So some may have a lot of mutated mito DNA and some a little, which is completely random.
replicative (random) segregation of mitochondrial DNA
mitochondrial DNA replicate and sort independently into the offspring. Disease state depends on the ratio of abnormal to normal mitochondria in the cell. Once above a certain threshold ratio you will have the disease.
homoplasmy vs. heteroplasmy
homo = all mtDNA are the same hetero = mix of normal and mutant mtDNA
threshold effect
your body needs a certain amount of ATP so if you have a high ratio of mutated to normal mito you will not make enough ATP. This is especially apparent in the very metabolically active parts of your body like cardiac muscle, skeletal muscle, and CNS.
distinctive features: changes with age
the number of mtDNA mutations increases with age because of the prevalence of radical O2 species. Also PolGamma will be more likely to be defective. Because of this, levels of oxidative phosphorylation begin to decline. If ATP production drops below a certain level then pathological problems can result.
Describe the slide that discussed Kearns-Sayre syndrome and what the absence/presence of certain things means
So as we can see in the slide, the mutated mitochondria are larger, will see large clusters of red deposits in muscle, structurally abnormal, weird cristae.
- Rugged red fibers do not occur in any disease other than mitochondrial disases. So if you have them, you have a mito disease. If you don’t have them it doesn’t necessarily rule out mito disease.
- Regarding the stains, we stained with succinate dehydrogenase, encoded by the nuclear DNA, and cytochrome c oxidase, which is encoded by mito and nuclear DNA. We can see that in the same cells the ones stained with succinyl dehydrogenase will stain blue because of the high proliferation of the mito within the cell. The ones stained with cytochrome c oxidase will not stain because of the mitochondrial mutation in this patient and lack of proliferation.
characteristics of DNA mutation
Tissues with a high metabolic demand are particularly affected. Any progressive multi-system disease should raise a potential concern regarding mitochondrial mutations. A clear maternal inheritance without male transmission indicates mito DNA defect. An autosomal inheritance pattern is indicative of nuclear DNA interaction such as DNA pol Gamma.
Most common mitochondrial diseases and do they have RRF or no RRF?
NO RRF: Leigh, LHON
RRF: CPEO, Kearns-Sayre, MELAS, MERRF
Leigh Syndrome
NO RRF
- progressive childhood encephalophaty
- death at age 5
- Can be AR, XL, or maternally inherited
Leber Hereditary Optic Neuropathy (LHON)
NO RRF
- painless and progressive loss of vision
- maternally inherited: mutation in subunit that encodes for ETC complex I.
- loss of retinal ganglion cells in the perifoveal region, and degeration of the papillomacular bundle
