Term
| What is the Genetic Bottleneck? How this may affect genetic transmission of mtDNA variants? |
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Definition
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Term
| Where do majority of the proteins used in the mito come from? |
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Definition
| Majority of proteins used in the mito come from DNA genome in nucleus |
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Term
| What is the structure of MitDNA? |
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Definition
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Term
| What are the two strands of MitDNA? |
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Definition
H and L
(H: G-rich, L: C-rich) |
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Term
What is the only noncoding region?
Where is found?
What is also there in that region? |
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Definition
displacement loop, aka control region
On the H strand
Promotors for transcription of both the H-strand and the L-strand |
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Term
The H is call coding except .... ?
The L strand codes for what? |
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Definition
The H-strand is all coding (except for the D-loop)
The L-strand codes for 1 mRNA and several tRNA’s |
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Term
| How many proteins in the MitDNA are produced which function in oxidative phosphorylation? |
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Definition
| Only 13 (!) proteins produced which function in oxidative phosphorylation |
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Term
| How many copies of mitDNA are there per organelle? Per cell? |
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Definition
| 2-10 mitochondrial DNA genomes per organelle, so a cell may contain thousands of mtDNA genomes |
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Term
| Replication of mtDNA is dependent on nuclear DNA replication. TRUE or FALSE? |
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Definition
FALSE
Replication of mtDNA independent of nuclear DNA replication
NOTE: Dedicated DNA polymerase involved |
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Term
| DNA polymerase Gamma does what functions? |
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Definition
| The only DNA polymerase present in mitochondria, so it has to function in DNA replication and DNA repair also. It HAS proofreading capability. |
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Term
| Mutations in the DNA polymerase Gamma gene POLG2 will cause? |
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Definition
| reduced levels of mitochondrial DNA and/or multiple mutations in the mitochondrial DNA (in particular large deletions) |
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Term
| Progressive external ophtalmoplegia (PEO) |
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Definition
(autosomal dominant): mutation in POLG2 (Pol Gamma) or TWINKLE (mt helicase) → bilateral ptosis, weak eye muscles
deficiencies of the mitochondrial polymerase lead to reduced levels of mtDNA causing mitochondrial dysfunction |
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Term
| Explain the myopathy side of AZT (zidovudine) myopathy. |
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Definition
HIV viral RNA is inhibited by AZT competing with dTTP. Once AZT is added to a growing strand by RTase, reverse transcription is terminated.
unfortunately, DNA polymerase γis also inhibited by the AZT derivative, explaining the myopathy as a side effect of AZT therapy
deficiencies of the mitochondrial polymerase lead to reduced levels of mtDNA causing mitochondrial dysfunction |
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Term
| What recognizes MitDNA tRNA region? |
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Definition
| RNA endo nuclease recognizes the secondary structure adopted by the RNA regions coding for the tRNA’s |
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Term
Where are the promoters?
Are both strands (H and L) completely transcribed at the same rate
What does the RNA endonuclease give? |
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Definition
in the control region.
YES
Both giant transcripts are processed by a RNA endo nuclease to give the separate transfer RNAs, ribosomal RNAs and the polyadenylated messenger RNAs (note: capping does not occur in mitochondria) |
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Term
| How many tRNA are needed for mitochondrial protein synthesis? |
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Definition
Relaxed codon usage: only 22 tRNAs needed for mitochondrial protein synthesis
whereas for cytosolic protein synthesis 30 or more tRNAs are needed. |
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Term
| What is the variant genetic code of mitDNA? |
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Definition
| 4 of the 64 codons have a different meaning |
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Term
| How does mit protein synthesis resemble that of bacteria? |
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Definition
| for example translation starts with N-formyl methionine |
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Term
| Mitochondrial genome versus normal genome Numbers |
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Definition
Genome: 16569 bp
Number of genes: 37
% coding: 93%
No recombination
Exclu maternal inherit.
1 circular type of DNA molecule with several thousand per cell. |
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Term
| MitDNA codes most and least of which two complexes? |
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Definition
Most for complex 1: 7
Least for complex 2: 1 |
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Term
| Explain Mitochondrial mode of inheritance |
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Definition
A vertical pedigree pattern
Children of affected men are never affected
All children of an affected woman may be affected, but mitochondrial conditions are typically extremely variable, even within a family
Please note: mitochondrial inheritance is a misnomer: it should be mitochondrial DNA inheritance and many mitochondrial diseases follow typical Mendelian inheritance patterns (remember: mitochondrial function is determined by 37 mitochondrial DNA genes and 900 nuclear DNA genes) |
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Term
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Definition
| Homoplasmy is the presence of a mutation affecting all of the mitochondrial DNA (mtDNA) copies in a mammalian cell or |
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Term
| Mitochondrial DNA is surprisingly variable between normal individuals. Where do these variations come from? |
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Definition
SNP's and small deletions/insertions
Oxygen radicals formed as by-product of the oxidative phosphorylation are the likely cause of the high mutation rate of mtDNA |
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Term
| What are the 3 major types of mitDNA mutations? |
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Definition
Rearrangements that generate deletions or duplications in the mtDNA
Point mutations in tRNA genes that impair mitochondrial protein synthesis
Missense mutations in the coding regions of genes that alter oxidative phosphorylation activity |
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Term
| What is heteroplamic? What role does it play in the disease state? |
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Definition
A single cell can harbor some molecules that have a mutation and others that do not. This heterogeneity in mtDNA composition is called heteroplasmy.
Many diseases caused by mutated mitochondrial DNA show a positive relation with the proportion of mutated mtDNA molecules
Severe mutations in mtDNA are seen only in the heteroplasmic state, because they would be lethal in the homoplasmic state |
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Term
| What are the common findings in disorders caused by mutations in mitochondrial DNA? |
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Definition
Tissues with a high energy demand are preferentially affected
Lactic acidosis is a very common biochemical finding
Ragged red muscle fibers is a very common histological finding |
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Term
| What is the genetic bottleneck? |
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Definition
When the fertilized egg divides, each cell gets an even number of MIT but those that it gets may or may nor be affected with the mutation. The division is not equal and so you end up with different levels heteroplasmy. Can have 10 bad and 1 good in some cells, or 1 bad and 10 good in other cells.
When talking about giant deletions that are always found in the heteroplasmic state. Easy to detect with target has high copy number! |
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Term
| Explain Kearns-Sayre syndrome (KSS). |
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Definition
-Caused by giant deletions in mitochondrial DNA
- typical ragged red muscle fibers (contain > 80% mutated mtDNA)
- Late onset
- Progressive external ophtalmoplegia, retinopathy, cerebellar ataxia, heart block |
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Term
| Explain Disease: Pearson syndrome. |
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Definition
with bone marrow involvement
Pediatric disease
pancytopenia, is a reduction in the number of red and white blood cells, as well as platelets, in all tissues have mtDNA with deletions
Sideroblastic anemia, exocrine pancreatic failure |
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Term
What would we see on a Southern blot of genomic DNA
hybridized with a mtDNA probe |
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Definition
DNA isolated from muscle
of a patient with Kearns-Sayre
Syndrome is shorter and so travels down further on the gel compared to the control. |
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Term
| What disease is caused by mutations in tRNA genes in mtDNA-1? |
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Definition
Disease :MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes)
mutated tRNA-Leu → can’t make proper mitochondrial proteins.
LEUCINE!!!
always heteroplasmic |
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Term
| What disease is caused by Mutations in tRNA genes in mtDNA-2? |
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Definition
Disease :MERRF (Myoclonus Epilepsy and Ragged Red Fibers)
progressive myoclonic epilepsy and seizures
maternally transmitted
Mutated gene: tRNALys (A8344G; T8356C)
always heteroplasmic
Lysine!!! |
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Term
| What disease is caused by Mutations in protein coding genes in mtDNA-1? |
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Definition
LHON (Leber’s Hereditary Optic Neuropathy): missense mutation of Complex I in optic nerve → blindness, occur more in males (because only have one X chrom).
may be homoplasmic (but still the optic nerve is the only affected tissue !)
Maybe Mild |
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Term
| What disease is caused by Mutations in protein coding genes in mtDNA - 2? |
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Definition
NARP (Neurogenic Muscle Weakness, Ataxia (lack of muscle coordination), Retinitis Pigmentosa): mutated ATPase 6 gene → retinitis pigmentosa
maternally inherited Leigh Syndrome is a more severe form with more mutated mtDNA
always heteroplasmic |
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Term
| What are the most important mutations in miTDNA? |
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Definition
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Term
| A normal person carries how many variations of MtDNA? |
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Definition
| MtDNA is highly variable between individuals but a normal individual carries only one haplotype |
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Term
| Explain the bottleneck effect. |
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Definition
| The extent of heteroplasmy from one generation to the next may change dramatically due to the genetic bottleneck effect |
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Term
| What are the 3 types of Mutations in mtDNA ? |
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Definition
| Mutations in mtDNA are deletions affecting multiple genes, base substitutions in transfer RNA genes and missense mutations in protein coding genes |
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Term
| What are typical mtDNA deletion syndromes? |
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Definition
| Typical mtDNA deletion syndromes are Progressive External Ophtalmoplegia, Kearns-Sayre and Pearson syndrome and are sporadic |
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Term
| Mutations in the tRNA for leucine |
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Definition
| result in MELAS Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes |
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Term
| Mutations in the tRNA for lysine |
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Definition
| result in MERFF Myoclonus Epilepsy and Ragged Red Fibers |
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Term
| Missense mutations in in several different complex I subunit genes |
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Definition
| result in LHON Leber's Hereditary Optic Neuropathy |
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Term
| Missense mutations in one of the two complex V subunits result in |
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Definition
| result in NARP (Neurogenic muscle weakness, Ataxia, and Retinitis Pigmentosa)/Leigh |
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Term
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Definition
| has no reactive OH on end. |
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