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BMS2.04 Mitochondrial Genome (ABALI) > Mitochondrial Genome > Flashcards

Mitochondrial Genome Flashcards

1
Q

Two membranes of the mitochondria:

A
  • inner membrane
  • outer membrane
    • together, form two major compartments:
      • intermembrane space
      • mitochondrial matrix
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2
Q

Role of mitochondria:

A
  1. generate ATP
  2. control intracellular calcium concentrations
  3. regulate apoptotic cell death
    • major source of endogenous reactive oxygen species
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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
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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
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5
Q

Mitochondrial matrix:

A
  • gel-like solution; 50% protein
  • contains mitochondrial RNA and DNA
  • proteins for:
    • TCA
    • lipid oxidation
    • transamination
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6
Q

Outer mitochondrial matrix:

A
  • permeable to small molecules
  • impermeable to large molecules
  • contains signalling receptors for apoptosis
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7
Q

Inner mitochondrial membrane contains:

A
  • transporter proteins
  • ETC
  • ATP synthesizing complex
  • impermeable to large and small molecules
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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
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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
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10
Q

What is the only situation when proteins are exported from the mitochondria to the eukaryotic cell cytosol?

A
  • during apoptosis
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11
Q

How do mitochondria divide:

A
  • via both fission and fusion
    • fission is similar to bacterial division process
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12
Q

Structure of mitochondrial DNA:

A
  • circular DNA
  • roughly 16,000 base pairs encodes for:
    • 2 rRNA
    • 22 tRNA
    • 13 protein-encoding sequences
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13
Q

Does mitochondrial DNA have introns?

A

No

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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
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15
Q

What cell cycle dos mitochondrial DNA replicate?

A
  • any cell cycle
  • mtDNA is replicated independently of nuclear DNA
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16
Q

What part of the mitochondrial genome is where mtDNA replication is initiated?

A

the D-Loop

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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
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18
Q

Three activities carried out by mtDNA replisome:

A
  1. DNA polymerase activity
  2. exonuclease/proofreading activity
  3. lyase activity for enzymatic DNA repair
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19
Q

Twinkle is:

A
  • the mtDNA helicase
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20
Q

What polymerase carries out mtDNA replication?

A
  • DNA polymerase gamma
    • encoded for by nuclear DNA
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21
Q

Mitochondrial replication is intiated from:

A
  • promoters encoding polycistronic transcripts that produce mRNA, tRNA, and rRNA
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22
Q

What does the process of mtDNA transcription require?

A
  1. a mitochondrial RNA polymerase
  2. a transcription activator (TFAM)
  3. a transcription factor (B1 or B2)
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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
Q

The translation termination factor in mtRNA translation:

A

mtRF1A

26
Q

The two stop codons in mitochondrial translation:

A

AGA and AGG

27
Q

General differences between mtRNA and nuclear RNA translation:

A
  • 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
Q

The 13 proteins encoded by mtDNA function where?

A
  • they all function in oxidative phosphorylation
  • all embedded in inner mitochondrial membrane
29
Q

The six distinctive features of mtDNA genetics:

A
  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
Q

Why does mtDNA have a very high mtDNA mutation rate?

A
  • 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
Q

Process of mtDNA inheritance:

A
  • 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
Q

mtDNA bottleneck effect:

A
  • 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
Q

Replicative (random) segregation of mitochondria and mtDNA:

A
  • mitochondrial fusion and fission leads to a random distribution of mitochondria and mtDNA in new daughter cells following mitosis and meiosis.
34
Q

Homoplasmy:

A
  • all mtDNA is the same in a cell
  • can be all normal or all abnormal
35
Q

Heteroplasmy:

A
  • mixture of mutant and normal mtDNA in the same cell
36
Q

Threshold effect:

A
  • 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
Q

Mitochondrial changes with age:

A
  • 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
Q

Most mtDNA-related diseases share these two features:

A
  • lactic acidosis
  • massive mitochondrial proliferation in muscle
    • results in “ragged red fibers”
39
Q

Ragged Red Fibers (RRF):

A
  • 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
Q

What disease/sign is this?

A
  • Kearns–Sayre Syndrome
  • Increased mitochondrial activity in Ragged-Red Fibers
41
Q

Succinate dehydrogenase:

A
  • mitochondrial enzyme
  • hyperactive in RRFs
  • entirely coded by nuclear DNA
42
Q

What two enzymes are hyperactive in Ragged Red Fibers?

A
  1. succinate dehydrogenase
  2. NADH

BOTH IMPORTANT FOR OXIDATIVE PHOSPHORYLATION

43
Q

Cytochrome C oxidase:

A
  • mitochondrial enzyme
  • absent in RRFs
  • encoded by both mtDNA and nuclear DNA
44
Q

What tissues are most affected by mtDNA diseases?

A
  • 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
Q

When should a diagnosis of mitochondrial disease be considered?

A
  • with any progressive, multi-system disorder
46
Q

The two most common mitochondrial diseases with no ragged red fibers:

A

LL

  • Leigh Syndrome
  • Leber Hereditary Optic Neuropathy (LHON)
47
Q

The four most common mitochondrial diseases with ragged red fibers:

A

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
Q

Leigh Syndrome:

A
  • 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
Q

Leber Hereditary Optic Neuropathy (LHON):

A
  • 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
Q

Leigh Syndrome can be caused by mutations in what types of DNA?

A
  • mtDNA
  • nuclear DNA

mutations in energy metabolism proteins

51
Q

Leber Hereditary Optic Neuropathy (LHON) can be caused by mutations in what type of DNA?

A
  • mtDNA only

mutations in genes encoding subunits of ETC complex I.

52
Q

Kss and CPEO:

A
  • eye, heart, and renal issues
  • seizures and dementia
  • short stature
  • RRFs and spongy myelinopathy
53
Q

Mitochondrial Encephalomyopathy With Lactic Acidosis And Strokelike Episodes (MELAS):

A
  • encephalopathy (seizures, dementia)
  • recurrent stroke-like episodes at a young age
  • RRFs and brain degeneration
    • infarcts and basal ganglia mineralization
54
Q

Myoclonic Epilepsy With Ragged Red Fibers (MERRF):

A
  • myoclonus, epilepsy, ataxia, and dementia.
  • RRFs and nervous system degeneration
55
Q

Leigh Syndrome Inheritance:

A

Most cases are autosomal recessive but X-linked and maternal inheritance is seen in some cases.

56
Q

Leber Hereditary Ocular Neuropathy (LHON) Inheritance:

A

maternally inherited and shows a male prevalence.

BMS2.04 Mitochondrial Genome (ABALI) (1 decks)

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