Mitochondrial Genome Flashcards
1
Q
Two membranes of the mitochondria:
A
- inner membrane
- outer membrane
- together, form two major compartments:
- intermembrane space
- mitochondrial matrix
- together, form two major compartments:
2
Q
Role of mitochondria:
A
- generate ATP
- control intracellular calcium concentrations
- regulate apoptotic cell death
- major source of endogenous reactive oxygen species
3
Q
The electron transport chain is located where in the mitochondria?
A
the inner mitochondrial membrane
- rich in proteins involved in ETC and ox/phos
4
Q
Cristae:
A
- the convolutions of the intermembrane space
- greatly increase surface area of the membrane
- higher the energy requirement, the more cristae present in a mitochondria
5
Q
Mitochondrial matrix:
A
- gel-like solution; 50% protein
- contains mitochondrial RNA and DNA
- proteins for:
- TCA
- lipid oxidation
- transamination
6
Q
Outer mitochondrial matrix:
A
- permeable to small molecules
- impermeable to large molecules
- contains signalling receptors for apoptosis
7
Q
Inner mitochondrial membrane contains:
A
- transporter proteins
- ETC
- ATP synthesizing complex
- impermeable to large and small molecules
8
Q
Endosymbiotic theory:
A
- mitochondria most likely evolved into eukaryotic cells through endocytosis of a prokaryote by an anaerobic eukaryotic cell
- created the two genomes in a eukaryotic cell: mitochondrial and nuclear
- mitochondria provides ATP; host cell does everything else
9
Q
Proteins for mitochondrial replication are created where:
A
- transcribed from both nuclear DNA and mitochondrial DNA.
- RNA transcribed/translated from nuclear DNA then imported into the mitochondria
10
Q
What is the only situation when proteins are exported from the mitochondria to the eukaryotic cell cytosol?
A
- during apoptosis
11
Q
How do mitochondria divide:
A
- via both fission and fusion
- fission is similar to bacterial division process
12
Q
Structure of mitochondrial DNA:
A
- circular DNA
- roughly 16,000 base pairs encodes for:
- 2 rRNA
- 22 tRNA
- 13 protein-encoding sequences
13
Q
Does mitochondrial DNA have introns?
A
No
14
Q
What part of the mitochondrial genome is the site where most of transcription and translation of the mitochondrial genome is controlled?
A
- D-Loop
- “D” = displacement
- the only non-coding region of mtDNA
15
Q
What cell cycle dos mitochondrial DNA replicate?
A
- any cell cycle
- mtDNA is replicated independently of nuclear DNA
16
Q
What part of the mitochondrial genome is where mtDNA replication is initiated?
A
the D-Loop
17
Q
mtDNA replisome:
A
- replicates mtDNA
- controlled by nuclear DNA
- a protein complex with a polymerase subunit and two accessory subunits
- also contains mtSSB
18
Q
Three activities carried out by mtDNA replisome:
A
- DNA polymerase activity
- exonuclease/proofreading activity
- lyase activity for enzymatic DNA repair
19
Q
Twinkle is:
A
- the mtDNA helicase
20
Q
What polymerase carries out mtDNA replication?
A
- DNA polymerase gamma
- encoded for by nuclear DNA
21
Q
Mitochondrial replication is intiated from:
A
- promoters encoding polycistronic transcripts that produce mRNA, tRNA, and rRNA
22
Q
What does the process of mtDNA transcription require?
A
- a mitochondrial RNA polymerase
- a transcription activator (TFAM)
- a transcription factor (B1 or B2)
23
Q
The two translation initiation factors in mtDNA:
A
IF2 and IF3
24
Q
Two elongation factors in mtRNA translation:
A
mtEFTu and mtEFTs
25
The translation termination factor in mtRNA translation:
mtRF1A
26
The two stop codons in mitochondrial translation:
AGA and AGG
27
General differences between mtRNA and nuclear RNA translation:
* two ribosomes for mitochondrial translation encoded by nuclear DNA
* all tRNAs for mitochondrial translation encoded by mtDNA
* codon usage in mitochondrial translation is relaxed
28
The 13 proteins encoded by mtDNA function where?
* they all function in oxidative phosphorylation
* all embedded in inner mitochondrial membrane
29
The six distinctive features of mtDNA genetics:
1. Very high mtDNA mutation rate
2. Maternal inheritance of mtDNA
3. Bottleneck effect
4. Replicative (random) segregation of mitochondria and mtDNA
5. Threshold effect
6. Changes with age
30
Why does mtDNA have a very high mtDNA mutation rate?
* Close to source of reactive O2 species, which cause damage.
* No introns, therefore mutations are mostly within the coding region.
* DNA polymerase gamma susceptible to mutations and defects
31
Process of mtDNA inheritance:
* solely inherited from mother
* if a mother has a mtDNA defect, some or all of the offspring's mitochondria may have the defect
* due to bottleneck effect and random replication
32
mtDNA bottleneck effect:
* Primordial germ cells harbor a heteroplasmic mtDNA mutation.
* During early oogenesis, there is a substantial reduction in the amount of mtDNA present (the bottleneck).
* Some primary oocytes harbor higher levels of mutated mtDNA and others significantly less than the original primordial germ cell.
33
Replicative (random) segregation of mitochondria and mtDNA:
* mitochondrial fusion and fission leads to a random distribution of mitochondria and mtDNA in new daughter cells following mitosis and meiosis.
34
Homoplasmy:
* all mtDNA is the same in a cell
* can be all normal or all abnormal
35
Heteroplasmy:
* mixture of mutant and normal mtDNA in the same cell
36
Threshold effect:
* the threshold amount of ATP required for cell survival in a given tissue, with the threshold higher for tissues with high energy needs (cardiac muscle, skeletal muscle, CNS).
* means that cells can have defected mitochondrial cells with no phenotype so long as the threshold is met
37
Mitochondrial changes with age:
* mtDNA mutations increase (especially deletions) due to free radical damage and defective DNA polymerase gamma.
* levels of oxidative phosphorylation decline.
* If the levels of ATP synthesis in a cell drop below the threshold of that tissue, pathological problems can result.
38
Most mtDNA-related diseases share these two features:
* lactic acidosis
* massive mitochondrial proliferation in muscle
* results in "ragged red fibers"
39
Ragged Red Fibers (RRF):
* mutant mitochondrias preferentially accumulate in the ragged red fibers of muscle
* typically negative for cytochrome C oxidase activity
* present in 1/3 of mitochondrial diseases
40
What disease/sign is this?
* Kearns–Sayre Syndrome
* Increased mitochondrial activity in Ragged-Red Fibers
41
Succinate dehydrogenase:
* mitochondrial enzyme
* hyperactive in RRFs
* entirely coded by nuclear DNA
42
What two enzymes are hyperactive in Ragged Red Fibers?
1. succinate dehydrogenase
2. NADH
**BOTH IMPORTANT FOR OXIDATIVE PHOSPHORYLATION**
43
Cytochrome C oxidase:
* mitochondrial enzyme
* absent in RRFs
* encoded by both mtDNA and nuclear DNA
44
What tissues are most affected by mtDNA diseases?
* tissues with high metabolic demand
* i.e. nervous system, liver, cardiac, kidneys
* tissues may be affected to different degrees, which depends on the amount of mitochondrial activity with the defect and a tissue's ATP threshold
45
When should a diagnosis of mitochondrial disease be considered?
* with any progressive, multi-system disorder
46
The two most common mitochondrial diseases **_with no_** ragged red fibers:
**LL**
* Leigh Syndrome
* Leber Hereditary Optic Neuropathy (LHON)
47
The four most common mitochondrial diseases **_with_** ragged red fibers:
**MMCK**
* Chronic Progressive External Ophthalmoplegia (CPEO)
* Kearns-sayre Syndrome (Kss)
* Mitochondrial Encephalomyopathy With Lactic Acidosis And Strokelike Episodes (MELAS)
* Myoclonic Epilepsy With Ragged Red Fibers (MERRF)
48
Leigh Syndrome:
* A progressive childhood mitochondrial encephalopathy
* Mean age of death is 5 years
* mutations in genes encoding proteins involved in energy metabolism (mtDNA and nuclear DNA)
* **_NO RRFs_**
49
Leber Hereditary Optic Neuropathy (LHON):
* painless progressive loss of central vision
* loss of retinal ganglion cells
* mutations in ETC proteins (mtDNA only)
* maternally inherited with male prevalence
* **_NO RRFs_**
50
Leigh Syndrome can be caused by mutations in what types of DNA?
* mtDNA
* nuclear DNA
## Footnote
**mutations in energy metabolism proteins**
51
Leber Hereditary Optic Neuropathy (LHON) can be caused by mutations in what type of DNA?
* mtDNA only
## Footnote
**mutations in genes encoding subunits of ETC complex I.**
52
Kss and CPEO:
* eye, heart, and renal issues
* seizures and dementia
* short stature
* **_RRFs and spongy myelinopathy_**
53
Mitochondrial Encephalomyopathy With Lactic Acidosis And Strokelike Episodes (MELAS):
* encephalopathy (seizures, dementia)
* recurrent stroke-like episodes at a young age
* **_RRFs and brain degeneration_**
* **_infarcts and basal ganglia mineralization_**
54
Myoclonic Epilepsy With Ragged Red Fibers (MERRF):
* myoclonus, epilepsy, ataxia, and dementia.
* **RRFs and nervous system degeneration**
55
Leigh Syndrome Inheritance:
Most cases are autosomal recessive but X-linked and maternal inheritance is seen in some cases.
56
Leber Hereditary Ocular Neuropathy (LHON) Inheritance:
maternally inherited and shows a male prevalence.
