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BMS2042 Genetics > Mitochondrial DNA Disorders > Flashcards

Mitochondrial DNA Disorders Flashcards

1
Q

What is the respiratory chain, in reference to mitochondria?

A

A series of 5 membrane-bound protein complexes collectively responsible for oxidative phosphorylation.

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2
Q

Are most mitochondrial genes encoded by nuclear or mitochondrial DNA?

A

Nuclear.

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3
Q

What is the diameter of mitochondria?

A

1 micrometer.

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4
Q

What is the size of one mitochondrial chromosome?

A

16.6 kb

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5
Q

How many DNA molecules are there per mitochondria?

A

2-10

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6
Q

What percentage of mitochondria DNA is GC?

A

44%

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7
Q

What nucleotide is the heavy strand of mitochondria rich in?

A

Guanine

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8
Q

What nucleotide is the light strand of mitochondria rich in?

A

Cytosine

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9
Q

What is the D loop in mitochondrial DNA?

A

Small section of triple-stranded DNA due to repeat synthesis of a short segment of the H stand DNA. It is a regulatory region and contain hypervariable regions.

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10
Q

How many genes are the on a mitochondrial chromosome?

A

37

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11
Q

How many mitochondrial genes specify RNA products?

A

24

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12
Q

How many mitochondrial genes encode proteins?

A

13

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13
Q

What percentage of mitochondrial DNA is coding?

A

93%

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14
Q

What percentage of mitochondrial DNA is non-coding?

A

7%

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15
Q

What region of mitochondrial DNA is non-coding?

A

D-loop

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16
Q

Does mitochondrial DN contain introns?

A

No

17
Q

Describe the positioning of mitochondrial genes in relation to each other.

A

Continuous, separated by 1-2 non-coding bases or overlapping.

18
Q

Explain how the bottleneck effect affects inheritance of mitochondrial genes.

A

If the mother has heteroplasmy, her primordial germ cells will all contain different mitochondria. As they contain very few mitochondria they will have different numbers of different mitochondria.

19
Q

What are the four reasons for higher functional mutation rates in mitochondrial compared to nuclear DNA?

A

93% is coding- higher chance of functional mutation
More rounds of replication- more chance for errors
No histone protection of DNA- oxidative damage (+ mitochondrial function)
Lack of adequate repair mechanisms.

20
Q

How can heteroplasmy in an individual hinder diagnosis of a mitochondrial disease?

A

Heteroplasmy may be tissue specific. E.g. analysing blood will not diagnose affected muscle.

21
Q

Can nuclear DNA cause of modify the mitochondrial genotype?

A

Yes

22
Q

What are some symptoms of mitochondrial disease?

A

Neurological signs, encephalopathy, dementia, ataxia, dystonia, neuropathy, seizures, myopathy, hypotonia, weakness, cardiomyopathy. Also deafness, diabetes, retinal pigmentation, acidosis.

23
Q

Do all mitochondrial diseases follow an all-or-nothing principle?

A

No, some are of quantitative measure and appear at a threshold.

24
Q

What mitochondrial mutations cause leber hereditary optic neuropathy (LHON)?

A

NADH dehydrogenase subunits 1, 2, 6 (ND1, ND24, ND6) and m11778G-A.

25
Q

A mutation in what mitochondrial gene causes NARP/ Leigh syndrome?

A

Subunit 6 of ATPase (m1624C-T).

26
Q

Give examples of two homoplasmic mitochondrial disorders?

A

Leber hereditary optic neuropathy (LHON) and NARP/Leigh syndrome.

27
Q

Give two examples of heteroplasmic mitochondrial diseases.

A

MELAS and MERFF.

28
Q

What mitochondrial mutation causes MELAS?

A

Mutation in leucine in tRNA (m3243A-G).

29
Q

What mitochondrial mutation causes MERFF?

A

Mutation in lysine in tRNA (m8344G-A; m8356T-C).

30
Q

Why does mitochondrial DNA’s high mutation rate benefit forensics and evolutionary studies.

A

Easy to efficiently assay diversity in many samples.

Polymorphisms are easier to find than in nuclear DNA.

31
Q

Compare the mutation rate in mitochondrial DNA to nuclear DNA.

A

50-100 times higher

32
Q

What regions of mitochondrial DNA are particularly useful for forensic and evolutionary studies?

A

HV1 and HV2.

33
Q

What are the advantages of HV1 and HV2?

A

High variety, small (250-350bp) so easy to amplify using PCR.

34
Q

How is an individual’s mitochondrial DNA sequence interpreted?

A

It is compared to the standard reference sequence (Cambridge/Oxford). Relative’s mtDNA can then be compared.

35
Q

What is a major advantage of mitochondrial DNA over nuclear DNA in forensic and evolutionary studies.

A

Its high quantity.

BMS2042 Genetics (10 decks)

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