Mitochondrial Genetics

Question 1

mtDNA encodes 37 gene products: __ proteins, __ tRNAs, and __ rRNAs.

Answer 1

13, 22, 2.

Question 2

A mitochondrial ___ is a muscle disease caused by a mitochondrial dysfunction.

Answer 2

myopathy.

Question 3

What are 2 characteristics of mitochondrial disorders?

Answer 3

Clinical variability and age related progression of disease.

Question 4

What do these 4 mitochondrial myopathies, MERRF, MELAS, KSS, CPEO, stand for?

Answer 4

Myoclonus epilepsy with ragged red fibers.

Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes.

Kearns-Sayre Syndrome

Chronic Progressive External Ophthalmoplegia

Question 5

___ is when a mutation occurs in the mtDNA, resulting in a mixture of normal mitochondria and mutant mitochondria in one cell.

Answer 5

Heteroplasmy.

Question 6

In order for a mitochondrial disease to manifest, a ___ of aberrant vs. normal mitochondria must be met. This can result from random, mutant ___ of the mitochondria.

Answer 6

Threshold.

segregation.

Question 7

T/F: The rate of mtDNA mutation is higher than nuclear genes.

Answer 7

True.

Question 8

What two types of tissues are mostly affected in mitochondrial genetic diseases? Why?

Answer 8

nervous and muscle, because they require more energy than others.

Question 9

Most cells contain about ___ mitochondrial DNA molecules.

T/F: mitochondria have a DNA repair mechanism.

Answer 9

1,000.

False, unlike nuclear DNA, mitochondrial DNA does not have a DNA repair mechanism.

Question 10

T/F: mtDNA has a 10x higher rate of mutation than nuclear DNA.

Answer 10

True.

Question 11

Point mutations in mtDNA tRNA genes lead to __ and __.

mtDNA genome deletions and rearrangements lead to __ and __.

Answer 11

MELAS and MERRF.

KSS and CPEO.

Question 12

85% of ___ cases due to A to G mutation in the mtDNA tRNA-lys gene at nucleotide position 8344.

5% of cases result from G to C mutation at position 8356.

Answer 12

MERFF.

Question 13

Why does one 25 year old with 95% mutant tRNA-lys show severe clinical presentation of MERFF while another 25 year old with 85% mutant tRNA-lys presents as clinically normal and healthy?

Answer 13

The second patient will develop disease later because of the age related progression of mitochondrial disorders.

Question 14

What are some characteristics of Kearns-Sayre Syndrome?

Answer 14

Onset before age 20.
Retinitis pigmentosa (degenerative eye disease leading to blindness).
CSF protein above 100 mg/dL.
Cerebellar ataxia.
Cardiac conduction abnormality.
Dementia.
Optic Atrophy.
Red Ragged Fibers.

Question 15

What are some characteristics of Chronic Progressive External Ophthalmoplegia (CPEO)?

Answer 15

Can be mild to moderate.
Ragged Red Fibers.
Ptosis occurs over many years.

Question 16

What are some characteristics of Leber Hereditary Optic Neuropathy (LHON)

Answer 16

Age of onset = 20s to 30s.
Rapid onset and progression.
Initially affects one eye, then both.
Only affects optic nerve.
No muscle involvement.
Degeneration of retinal ganglion cell layer and optic nerve.
mtDNA mutations in coding genes of complex I proteins.

Question 17

Complex I has how many subunits?

How many complexes are there for mitochondrial respiration?

The electron transport chain, which oxidizes __ and __, has how many enzyme complexes?

Answer 17

7.

5.

NADH and FADH2. 4.