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Molecular Exam 3 > Mitochondrial Genetics and Disease > Flashcards

Mitochondrial Genetics and Disease Flashcards

1
Q

What is the function of mitochondria?

A

To provide cellular energy in form of ATP

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2
Q

How does the mitochondria provide cellular energy?

A

Oxidative Phosphorylation and Electron Transport Chain

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3
Q

Explain the general pathway of ETC from lecture

A
  1. Electrons flow down ETC
  2. Pumps Hydrogen into space between inner mitochondria and outer mitochondria
  3. Forms H+ gradient
  4. When H+ go down gradient, energy is captured in form of ATP
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4
Q

Mitochondria have their own DNA and their own genome. ___ genes code for ___ proteins. There are 24 parts to make proteins, __ tRNA and ___ rRNA.

A

37
13
22
2

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5
Q

What are some characteristics of mitochondria?

A

Powerhouse of cell

Self- replicate

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6
Q

What are some characteristics of mitochondrial DNA?

A 
Rate of mtDNA mutation is higher than in nuclear DNA 
Maternally inherited
16,569 bp
Most cells have 1,000 mtDNA molecules
No DNA repair mechanism 
No DNA recombination
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7
Q

What is heteroplasmy?

A

Mixture of normal and mutant (abnormal) mitochondria that occurs in 1 cell when there is a mutation in mtDNA

Segregation of mitochondria during cell division occurs by chance

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8
Q

T/F: You need a certain level of aberrant mitochondria and normal mitochondria in order for disease to occur.

A

True

Threshold effect of mutant mitochondria are required for disease manifestation

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9
Q

What is the threshold effect?

A

If cells carry too many mutant mitochondria, disease occurs

Need a certain amount of mutant mitochondria for disease to occur

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10
Q

What 2 things are needed for a disease to result with respect to mitochondria?

A

Need mutation to occur and a certain percentage of mitochondria to be aberrant

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11
Q

What is the inheritance pattern of mitochondrial DNA?

A

Maternal

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12
Q

How many complexes are there for mitochondrial respiration?

A

5

ETC Complexes I - IV
- oxidizes NADH and FADH2

Complex V = ATP synthase
- uses H+ gradient to alter ADP to ATP

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13
Q

Define mitochondrial myopathy

A

Muscle disease caused by mitochondrial dysfunction

The degeneration of muscle fibers caused by the accumulation of abnormal mitochondria

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14
Q

What are the 2 general characteristics of mitochondrial myopathies?

A

Clinical variability

Age related progression of disease

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15
Q

What are the clinical characteristics of mitochondrial myopathies?

A 
Muscle weakness
Exercise intolerance 
Lactic acidosis 
Neurological signs (mitochondrial encephalopathy) 
Vomiting
Seizures
Dementia
Stroke- like episodes
Ptosis
Opthalomeglia 
Blindness
Cardiomyopathy
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16
Q

Aggregates of abnormal mitochondria form red sarcolemmal blotches called _____?

A

Ragged Red Fibers

17
Q

What are the 2 mitochondrial mutations?

A
  1. Point mutations in mtDNA tRNA genes
    • MELAS and MERRF
  2. mtDNA genoma deletions and rearrangements
    • KSS and CPEO
18
Q

Myoclonus Epilepsy with Ragged Red Fibers (MERRF) Clinical Features

A

Myoclonus

  • involuntary jerking of muscle
  • usually the 1st symptom

Myoclonic Epilepsy

Ataxia
- lack of coordinated muscle movements

Ragged Red Fibers
- muscle tissue

Seizures

Dementia

19
Q

Myoclonus Epilepsy with Ragged Red Fibers (MERRF) Mutations

A

90% of cases are caused by 2 mutations of tRNA lysine

85% of cases due to A to G mutation (single nucleotide change) in mtDNA tRNA lysine gene

5% of cases sue to G to C mutations in mtDNA tRNA lysine gene

20
Q

Myoclonus Epilepsy with Ragged Red Fibers (MERRF) Genotype/ Phenotype correlation

A

25 year old with 95% mutant tRNA-lysine = severe clinical presentation

25 year old with 85% tRNA-lysine = normal and healthy

Age related presentation (patient 2 develops disease later)

21
Q

Mitochondrial Encephalopathy, Lactic Acidosis with Stroke- like episodes (MELAS) Clinical Presentation

A

Seizures
- Stroke- like episodes of hemiparesis (weakness of 1 side of body)

Blindness

Headaches

Anorexia

Recurrent vomiting

Lactic acidosis

Ragged red fibers

22
Q

Mitochondrial Encephalopathy, Lactic Acidosis with Stroke- like episodes (MELAS) age of onset

A

2 - 10 years old

23
Q

Mitochondrial Encephalopathy, Lactic Acidosis with Stroke- like episodes (MELAS) mutation

A

mutation in tRNA leucine

24
Q

Kearns- Sayre Syndrome (KSS) age of onset

A

onset before 20 years old

25
Q

Kearns- Sayre Syndrome (KSS) clinical presentations

A

Retinitis Pigmentosa
- degenerative eye disease leading to blindness

At least one of the following:

  • cardiac conduction abnormality
  • cerebellar ataxia
  • cerebral spinal protein level above 100 mg/dL

Optic Atrophy

Hearing loss

Dementia

Seizures

Cardiomyopathy

Lactic Acidosis

26
Q

Kearns- Sayre Syndrome (KSS) mutation

A

85% due to mtDNA rearrangements

  • duplicated mtDNA
  • deleted mtDNA
  • insertions

200 different deletions

Ragged red fibers seen in skeletal muscle

27
Q

Chronic Progressive External Ophthalmoplegia (CPEO) General features

A

Mild to moderate mitochondrial myopathy

Ragged red fibers observed in skeletal muscle

28
Q

Chronic Progressive External Ophthalmoplegia (CPEO) mutation

A

mtDNA rearrangements

29
Q

Chronic Progressive External Ophthalmoplegia (CPEO) Clinical Presentation

A

Ptosis (drooping of eyelids)

30
Q

Which of the mitochondrial myopathies affect muscles?

A

MERRF
MELAS
KSS
CPEO

31
Q

Leber Hereditary Optic Neuropathy (LHON) clinical presentation

A

Mitochondrial mutation that only affects optic nerve
- does not affect muscle

Acute/ subacute bilateral central vision loss
- blindness in late adolescence

Degeneration of retinal ganglion cell layer and optic nerve

Rapid onset and progression
- initially affects 1 eye but eventually both at the same time

32
Q

Leber Hereditary Optic Neuropathy (LHON) age of onset

A

20s - 30s

33
Q

Leber Hereditary Optic Neuropathy (LHON) mutation

A

mtDNA mutation in coding genes of complex I proteins

No tRNA or rRNA rearrangements

Single base pair substitutions in complex I proteins

Molecular Exam 3 (2 decks)

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