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MCB Lecture 9 – Mitchondria – Van Oost
The mitochondrial DNA has a heavy strand and a light strand. What is the
o H-Strand: Coding strand except for the D-Loop
o L-Strand: Codes for 1 mRNA and several tRNA’s
Where is the origin of replication located in the H-Strand?
o In the D-Loop
How many genes does the Mitochondrial DNA code for?
o 13 Protein Coding Genes
What are the proteins used for that are coded by the Mitochondrial DNA?
o Oxidative Phosphorylation in the ETC
Where do the rest of the proteins come from that are necessary for the
function of the mitochondria?
o Nucleus
How many mitochondrial genomes are there per cell?
o 2-10
What is the name of the Mitochondrial DNA Polymerase?
o POL-G (DNA Polymerase y)
What is the name of the DNA Helicase?
What is Progessive External Ophtalmoplegia (PEO)? Include Mode of
o Autosomal Dominant
o Caused by deletions in mtDNA, leading to a mutation in DNA
Polymerase y or mutations in TWINKLE
o Symptoms:
 Bilateral Ptosis
 Muscle weakness, wasting
 Exercise Intolerance
Answer the following questions regarding HIV:
o What is the drug that is given to HIV patients? What is the medical
 3’ azido-2’3’ dideoxythymidine, Zidovudine
o How does the drug work?
 It is phosphorylated so that it can compete with dTTP so that
reverse transcriptase is terminated.
o How does this affect DNA Polymerase?
 It does not affect DNA Polymerase δ in the nucleus.
 It inhibits DNA y in the mitochondria.
o What is the symptom/side effect?
 Myopathy (muscle weakness)
What is a difference in the post-transcriptional modification of
mtDNA and Nuclear DNA?
o The mtDNA is polyadenylated, but not capped.
What is the first amino acid added during translation?
o N-Formyl Methionine
How many tRNAs are needed for mitochondrial protein synthesis?
o 22 tRNAs (30+ for nuclear translation)
Do mutations occur more often or less often than in nuclear DNA?
What is the difference?
o 10-fold faster in mtDNA than in Nuclear DNA
How do you know that a pedigree is representing Mitochondrial
o Men NEVER pass down the disease.
What are the three major types of mutations in Mitochondrial DNA?
o Rearrangements that generate deletions
o Point mutations
o Missense mutations
When mutations happen in Mitochondrial DNA, what types of tissues are
affected first? What do those tissues do as a result?
o Tissues with high-energy demand are affected first.
o They start producing lactic acid.
What is Heteroplasmy?
o A single cell can harbor some molecules that have a mutation and
others that do not. The ratio of these determines if the individual
presents the disease or not.
What is Homoplasmy?
o When all of the mtDNA is identical. Homoplasmic mtDNA that is
diseased is usually fatal.
What are three diseases caused by giant deletions in mtDNA?
o Kearns-Sayre Syndrome (KSS)
o Pearson Syndrome
What is Kearns-Sayre Syndrome (KSS)?
o mtDNA Deletion in muscle, not blood.
o Causes cerebellar ataxia and heart block
What is Pearson Syndrome?
o mtDNA with muscle AND bone marrow involvement
o Pancytopenia, Sideroblastic Anemia (all tissues have mtDNA with
What are the two pathologies that are caused by mutations in tRNA genes?
What is MELAS
o Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-Like
o Mutation in tRNA(Leu)
o Always heteroplasmic
What is MERRF?
o Myoclonus Epilepsy Ragged Red Fibers
o Mutation in tRNA(Lys)
o Always heteroplasmic
What is LHON?
o Leber’s Heredity Optic Neuropathy
o Missense mutation in Complex I (NADH Dehydrogenase)
What is NARP?
o Neurogenic Muscle Weakness, Ataxia, and Retinitis Pigmentosa
o Mutation in ATPase 6 gene
o Always heteroplasmic
What is a maternally inherited form of NARP that is more severe than NARP?
o Leigh Syndrome