The Mitochondrial Genome Flashcards
What are the features of the mitochondrial genome?
Double stranded circular molecule Heavy and light strand Multi copy gene 37 genes No introns D loops is a non-coding region where replication and transcription are initiated Maternally inherited so no recombination
What numbers and types of genes make up the 37 mitochondrial genes?
13 OXPHOS protein subunits
22 transfer RNAs
2 ribosomal RNAs
What do the OXPHOS proteins consist of?
5 enzyme complexes (CI-CV)
What is special about the OXPHOS complex II?
It’s the only entirely nuclear coded subunit
What does the non-coding mtDNA region contain?
Regulatory sequences for replication and transcription
Where does mtDNA replication start?
The origin of the heavy strand
Where does mtDNA transcription start?
Heavy strand and light strand promoters
What is mtDNA packaged into?
Nucleoids
How many copies of mtDNA do you get per nucleoid?
One or two copies
What does transcription factor A act as in mtDNA?
A histone protein
What are the exceptions to the universal genetic code?
AUA codes for methionine in mtDNA and isoleucine in nuclear DNA
UGA codes for tryptophan in mtDNA and is a stop codon in nuclear DNA
AGA and AGG are stop codons in mtDNA not argenine
What are mtDNA variants called?
Haplogroups
Why is the human mtDNA genotype specifically split into haplogroups?
MtDNA is maternally inherited so no recombination occurs
Does the mitochondria need both mtDNA and nuclear DNA to function?
Yes
How many OXPHOS proteins does the mtDNA encode?
13
What is the mtDNA polymerase called?
Polymerase gamma
What are the subunits of Polymerase gamma?
One catalytic subunit (A) and two accessory subunits (B)
What does the Polymerase gamma catalytic subunit contain and what does it do?
Contains 3’-5’ exonucelase domains to proofread newly synthesised DNA
What do the Polymerase gamma accessory subunits contain and what do they do?
Enhance interactions with the DNA template and increases activity and processing of the polymerase gamma A
What is the mtDNA helicase called?
TWINKLE
How many subunits is TWINKLE made up of?
Six
What does the mitochondrial single stranded binding protein do?
Binds to single stranded DNA
Why does mitochondrial single stranded binding protein bind to single stranded DNA?
Protects against nucleuses, prevents secondary structure formation and enhances mtDNA synthesis by stimulating TWINKLE helicase activity
What is the strand displacement model of mtDNA replication?
Parental heavy strand displaced and coated with MtSSBP
TWINKLE helicase unwinds MtDNA
Mitochondrial RNA polymerase synthesise RNA primer using the light strand as a template
Polymerase gamma uses RNA primer to replicate DNA at the OH
What are the steps in mtDNA light strand replication?
Stem loop structure formed
MtRNA polymerase synthesises RNA primer using the heavy strand as a template
Polymerase gamma uses RNA primer to replicate the light strand DNA
What does segregation of mtDNA daughter molecules need?
Topoisomerase IIIa
What is the most common form of mitochondrial disease?
OXPHOS disorders
What does LHON stand for?
Leber’s hereditary optic neuroretinopathy
What does KSS stand for?
Kearns-Sayre syndrome
What does MELAS stand for?
Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes
What does MERRF stand for?
Myoclonus epilepsy red ragged fibres
What does NARP stand for?
Neurogenic muscle weakness, ataxia, and retinitis pigmentosa
What does MINGIE stand for?
Mitochondrial myopathy neuropathy gastrointestinal disease encephalopathy
What are the hallmarks of mitochondrial disease?
Abnormal bilateral leisions in the basal ganglia of the brain Gamori staining Hypertrophic cardiomyopathy Pseudo-intestinal obstruction Sideroblast anaemia Enlargement of eye vessels
What is gamori staining?
Clusters of red signal in the muscle fibres
How do you diagnose a mitochondrial disease?
Clinical signs
Blood and tissue histochemical and analyse measurements
Neuro imaging
Enzymatic assays of OXPHOS in tissue samples and cultured cells
DNA analysis
What are some clinical features of mitochondrial disease?
Most have a neurological component and are progressive
What types of muscle histology studies are there?
Haematoxylon and eosin Gomori trichrome SDH Cox Combined cox/SDH
What is homoplasmy?
One type of mtDNA in a cell
What is heteroplasmy?
One or more mutant mtDNAs in a cell
What do heteroplasmy levels determine?
Disease manifestation
What % heteroplasmy causes disease manifestation?
80%
What do heteroplasmic mutations mean for the inheritance of mutant load?
Random
What do homoplasmic mutations mean for the inheritance of mutant load?
Cause the female carriers to transmit to all children
How can you identify mtDNA mutations?
Off target reads using WES
What do mutations in the mtDNA replication machinery cause?
Secondary mutations in mtDNA
What do dominant mutations in TWINKLE cause?
MtDNA deletions and late-onset mitochondrial myopathy
What are your options for embryos with mtDNA mutations?
Oocyte donation
Prenatal diagnosis
Preimplantation genetic diagnosis
Mitochondrial replacement therapy
What is the most common form of mitochondrial disease?
OXPHOS disorders
