The mitochondrial genome Flashcards
How is ATP generated in the mitochondria?
Generation of ATP by oxidative phosphorylation
What are mitochondrial functions?
- Haem synthesis
- Neurotransmitter synthesis
- Nucleotide synthesis
What is the structure of the mitochondrial genome?
Double stranded circular molecule
What does the mitochondrial genome consist of and not have?
Consists of heavy and light strands and has no introns
How many genes does the mitochondrial genome have?
Has 37 genes
What are the genes present in the mitochondrial genome and the amount present?
- 13 Oxidative phosphorylation protein subunits
- 22 tRNAs
- 2 rRNAs
What is the D loop in the mitochondrial genome?
The D loop is a non-coding region where replication and transcription are initiated
How is the mitochondrial genome inherited?
Maternally inherited, no recombination
What does the mitochondrial genome encode?
Encodes proteins of oxidative phosphorylation
What does the non-coding region contain?
Contains regulatory sequences for replication and transcription
Where does mtDNA replication start?
mtDNA replication starts in the origin of heavy strand (OH)
Where does transcription of mtDNA start?
Transcription starts at the heavy strand promoter(HSP) and the light strand promoter(LSP)
What is mtDNA packaged into?
Packaged into nucleotides
How many copies of mtDNA are there per nucleotide?
One or two copies of mtDNA per nucleoid
What does transcription factor A(TFAM) act as when mtDNA is packaged?
Acts as a histone protein
Genetic code in vertebrate mitochondria DNA vs nuclear DNA
- AUA and AUG code for methionine in mitochondria; whereas in nuclear DNA, AUA codes for isoleucine
- UGA codes for tryptophan in mitochondria; whereas in nuclear DNA, it’s a stop codon
- AGA and AGG are stop codons in mitochondria; whereas in nuclear DNA, it’s arginine
What is the endosymbiotic theory of the origin of the mitochondria?
-Mitochondria and chloroplasts originated as bacterial cells that came to live inside larger cells
What does the mitochondria require both of?
Requires both nuclear and mtDNA encoded proteins
How many proteins does oxidative phosphorylation require?
Oxidative phosphorylation requires >100 proteins but mtDNA only encodes 13 of those proteins
What must happen in order to make the 13 proteins for oxidative phosphorylation?
In order to make the 13 proteins for oxidative phosphorylation, protein mtDNA must be:
- Replicated
- Transcribed
- Translated
What are all the proteins involved in replication, transcription and translation of mtDNA encoded by?
All proteins involved in replication, transcription and translation of mtDNA are encoded by nuclear genes and imported into mitochondria
What are all the other proteins involved in oxidative phosphorylation made by?
All other proteins involved in oxidative phosphorylation are made by nuclear genes
What is the structure of the mtDNA polymerase(polymerase gamma)?
- Heterotrimer protein
- One catalytic subunit (POLA)
- Two accessory subunits (POLB)
What does POLgammaA contain?
Contains 3’-5’ exonuclease domain to proofread newly synthesized DNA
What does POLgammaB enhance?
Enhances interactions with DNA template and increases activity and processability of POLgammaA
What is the structure of mtDNA helicase(TWINKLE)?
TWINKLE:
-Six TWINKLE subunits
What does mtDNA helicase, TWINKLE, do?
It unwinds double stranded mtDNA template to allow replication by POLgamma
What does the mitochondrial single stranded binding protein bind to and what does it do?
Binds to single stranded DNA
- Protects against nucleases
- Prevents secondary structure formation
- Enhances mtDNA synthesis by stimulating TWINKLE helicase activity
Steps involved in the replication of mtDNA
- Replication of heavy strand
- Replication of light strand
- Replication of both strands complete and segregation of daughter molecules occurs
Replication of heavy strand
- Parental heavy strand displaced and coated with mtSSBP
- TWINKLE helicase unwinds mtDNA
- Mitochondrial polymerase (POLRMT) synthesizes RNA primer using light strand as template
- POLgamma uses RNA primer to replicate DNA at OH
Replication of light strand
- Heavy strand replication passes OL
- Stem loop structure is formed preventing mtSSBP binding
- Mitochondrial polymerase (POLRMT) synthesizes RNA primer using heavy strand as a template
- POLgamma uses RNA primer to replicate light strand DNA at OL
Completion of both strands
- Synthesis proceeds until both strands are fully replicated
- After replication, daughter molecules are segregated
Heavy strands
Heavy strands have a high composition of A and G (heavy bases)
Light strands
Light strands have a high composition of C and T(light bases)
Mitochondrial diseases
- Rare monogenic diseases
- Affect highly metabolic organs
- Can affect one or several organ systems
- Genetically heterogeneous
What causes mitochondrial disease?
Mutation in >300 nuclear genes cause mitochondrial disease, not just mtDNA
What determines mitochondrial disease manifestation?
Heteroplasmy levels determine mitochondrial disease manifestation
How is mtDNA inherited and mutation load?
mtDNA is maternally inherited and inheritance of mutation load is random
What way can be used to identify mtDNA mutations
mtDNA mutations can be identified by next generation sequencing
