Mitochondrial DNA Structure and Function
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Questions and Answers

Mitochondrial DNA has no ______ and is not found in the nucleus.

introns

Mitochondrial DNA encodes proteins involved in the ______ chain.

electron transport

The heavy chain of mitochondrial DNA is guanine rich, while the light chain is ______ rich.

cytosine

Homoplasmy means that all copies of mtDNA are ______.

<p>identical</p> Signup and view all the answers

Most mtDNA mutations are ______, occurring in only some copies of mtDNA.

<p>heteroplasmic</p> Signup and view all the answers

MtDNA can be useful in population studies due to its lack of ______.

<p>recombination</p> Signup and view all the answers

The ______ Eve represents the most recent common matrilineal ancestor of all living humans.

<p>Mitochondrial</p> Signup and view all the answers

The mutation rate of mtDNA is ______ compared to nuclear DNA.

<p>higher</p> Signup and view all the answers

Mitochondrial DNA is carried in the sperm ______.

<p>midpiece</p> Signup and view all the answers

Replication of mitochondrial DNA occurs ______ for the heavy chain.

<p>clockwise</p> Signup and view all the answers

Mitochondrial DNA begins replicating until it has enough copies to form ______ cells.

<p>two</p> Signup and view all the answers

Mitochondrial DNA polymerase is encoded by ______ in nuclear DNA.

<p>POLG</p> Signup and view all the answers

Heteroplasmic mutations occur in only some copies of ______.

<p>mtDNA</p> Signup and view all the answers

The fraction of mutant mtDNA in offspring will be variable due to the mitochondrial genetic ______ during oogenesis.

<p>bottleneck</p> Signup and view all the answers

Unlike nuclear DNA, mtDNA does not undergo ______, allowing it to be passed unchanged to all offspring.

<p>recombination</p> Signup and view all the answers

Mitochondrial DNA is beneficial for studies due to its high ______ number per cell.

<p>copy</p> Signup and view all the answers

What is the consequence of the mitochondrial genetic bottleneck during oogenesis?

<p>The fraction of mutant mtDNA in the offspring will be inconsistent.</p> Signup and view all the answers

How does mtDNA accumulate mutations compared to nuclear DNA?

<p>mtDNA accumulates mutations more rapidly.</p> Signup and view all the answers

Which statement correctly describes the inheritance of mtDNA?

<p>It follows a maternal inheritance pattern.</p> Signup and view all the answers

What is the estimated age of the oldest mtDNA cluster that does not include African members?

<p>90,000 to 180,000 years old.</p> Signup and view all the answers

Why is mtDNA particularly useful for studying evolutionary processes?

<p>It has a high mutation rate and lacks recombination.</p> Signup and view all the answers

What was concluded about the mutation rate of mtDNA from Cann et al. in 1989?

<p>One mutation takes approximately 1,000 years to arise.</p> Signup and view all the answers

What does 'Mitochondrial Eve' represent in the context of human ancestry?

<p>The most recent common matrilineal ancestor</p> Signup and view all the answers

Which part of mtDNA is most prone to mutations?

<p>The D loop region.</p> Signup and view all the answers

What event significantly reduced the human population approximately 70,000 years ago?

<p>The eruption of Mount Toba</p> Signup and view all the answers

What does the concept of 'Mitochondrial Eve' refer to?

<p>The most recent common matrilineal ancestor of all living humans.</p> Signup and view all the answers

What factor prevents certain matrilineal lines of descent from passing on mitochondrial DNA?

<p>Extinction of male descendants</p> Signup and view all the answers

What is the estimated range of years during which Mitochondrial Eve likely lived?

<p>200,000 to 500,000 years ago</p> Signup and view all the answers

Which component of mitochondrial DNA accumulates mutations at a higher rate than others?

<p>Hypervariable regions (HVR1 &amp; HVR2)</p> Signup and view all the answers

How many primary haplogroups are identified in mitochondrial DNA?

<p>38</p> Signup and view all the answers

What is a characteristic trait of haplotypes within haplogroups?

<p>Defined by mitochondrial mutations</p> Signup and view all the answers

What does the term 'Evolutionary Bottleneck' refer to in the context of human history?

<p>A significant reduction in population size</p> Signup and view all the answers

What is the approximate penetrance rate among male LHON mutation carriers?

<p>50%</p> Signup and view all the answers

Which of the following is a factor that influences the phenotypic expression of LHON?

<p>Mutant mtDNA in optic nerves</p> Signup and view all the answers

What is a key characteristic of mitochondrial DNA (mtDNA) compared to nuclear DNA?

<p>mtDNA is circular in shape.</p> Signup and view all the answers

What allele is associated with a significant increase in vision loss risk in LHON?

<p>High-risk allele at Xp21</p> Signup and view all the answers

How many genes are encoded in mitochondrial DNA?

<p>37 genes</p> Signup and view all the answers

In what year was mitochondrial replacement therapy (MRT) legalized in the United Kingdom?

<p>2015</p> Signup and view all the answers

What does homoplasmy in mtDNA indicate?

<p>All copies of mtDNA are identical.</p> Signup and view all the answers

Which type of RNA is not encoded by mitochondrial DNA?

<p>sRNA</p> Signup and view all the answers

What is the primary mode of inheritance for mitochondrial DNA?

<p>Maternal inheritance</p> Signup and view all the answers

What is the effect of exposure to aminoglycoside antibiotics on individuals with the m.A1555G mutation?

<p>Permanent hearing loss</p> Signup and view all the answers

What concept connects all humans through mitochondrial DNA?

<p>Mitochondrial Eve</p> Signup and view all the answers

What is a function of the mitochondrial electron transport chain?

<p>Production of ATP</p> Signup and view all the answers

What characterizes heteroplasmic mutations in mtDNA?

<p>They occur in only some copies of mtDNA.</p> Signup and view all the answers

What role does mitochondrial fission play in mtDNA?

<p>It allows for the distribution of mitochondria during cell division.</p> Signup and view all the answers

What is the predominant haplogroup found in around 40% of all maternal lineages in Europe?

<p>Haplogroup H</p> Signup and view all the answers

What is the most prevalent symptom of Leber Hereditary Optic Neuropathy (LHON)?

<p>Bilateral blindness</p> Signup and view all the answers

Which haplogroup is known to increase the penetrance of the Leber Hereditary Optic Neuropathy?

<p>Haplogroup J</p> Signup and view all the answers

How many haplogroups are identified in the European population?

<p>10 haplogroups</p> Signup and view all the answers

Which of the following conditions is characterized by myoclonic epilepsy and ragged red fiber disease?

<p>MERRF syndrome</p> Signup and view all the answers

What is a significant feature of mitochondrial DNA compared to nuclear DNA regarding inheritance?

<p>Mitochondrial DNA is exclusively matrilineal.</p> Signup and view all the answers

What does the term 'homoplasmy' in mitochondrial DNA imply?

<p>All copies of mtDNA are identical in a given cell.</p> Signup and view all the answers

Which statement accurately describes the structure of mitochondrial DNA?

<p>Mitochondrial DNA is circular and consists of approximately 16,600 base pairs.</p> Signup and view all the answers

Which statement about the function of mitochondrial DNA is true?

<p>It encodes proteins involved in the electron transport chain.</p> Signup and view all the answers

How does the process of mitochondrial fission relate to mtDNA?

<p>It facilitates the replication of mtDNA by creating multiple mitochondria.</p> Signup and view all the answers

What role does POLG play in mitochondrial DNA biology?

<p>It is a polymerase that encodes mitochondrial DNA replication.</p> Signup and view all the answers

Which characteristic distinguishes heteroplasmy from homoplasmy in mitochondrial DNA?

<p>Heteroplasmy involves varying forms of mtDNA within an individual.</p> Signup and view all the answers

What is the primary function of the mitochondrial electron transport chain?

<p>To generate ATP through oxidative phosphorylation.</p> Signup and view all the answers

Which haplogroup is primarily associated with increasing the penetrance of Leber Hereditary Optic Neuropathy?

<p>Haplogroup J</p> Signup and view all the answers

Which mutation accounts for the highest percentage of Leber Hereditary Optic Neuropathy cases?

<p>ND4 – m.G11778A</p> Signup and view all the answers

What is the estimated prevalence of Leber Hereditary Optic Neuropathy in the general population?

<p>1:50,000</p> Signup and view all the answers

Which mitochondrial disease is associated with lactic acidosis, stroke-like episodes, and can affect mitochondrial function?

<p>MELAS</p> Signup and view all the answers

What mechanism primarily influences the prognosis in individuals with Leber Hereditary Optic Neuropathy?

<p>DNA mutation type</p> Signup and view all the answers

Which group of haplogroups primarily represents the mitochondrial DNA diversity in the European population?

<p>H, J, K, N1, T, U4, U5, V, X, W</p> Signup and view all the answers

What symptom typically indicates the onset of Leber Hereditary Optic Neuropathy?

<p>Bilateral blindness starting between 18-35 years</p> Signup and view all the answers

What defines the haplogroups in mitochondrial DNA?

<p>Characteristic mtDNA mutations</p> Signup and view all the answers

What significant event approximately 70,000 years ago led to a decrease in the human population?

<p>The eruption of Mount Toba</p> Signup and view all the answers

What does the term 'Evolutionary Bottleneck' imply in human history?

<p>A significant reduction in population size</p> Signup and view all the answers

What is the estimated range of years during which Mitochondrial Eve lived?

<p>200,000 to 500,000 years ago</p> Signup and view all the answers

How many main population groups are identified in the context of mitochondrial lineage?

<p>5</p> Signup and view all the answers

What is a characteristic of hypervariable regions (HVR1 and HVR2) in mitochondrial DNA?

<p>They accumulate mutations at a higher rate</p> Signup and view all the answers

How does the mutation accumulation rate in mtDNA compare to that in nuclear DNA?

<p>mtDNA accumulates mutations at a faster rate than nuclear DNA.</p> Signup and view all the answers

Which of the following best describes the significance of 'Mitochondrial Eve' in human ancestry?

<p>She represents the last common matrilineal ancestor of all living humans.</p> Signup and view all the answers

What is the significance of the D loop in mtDNA?

<p>It contains the majority of mutations in mtDNA.</p> Signup and view all the answers

What evidence challenges the conclusion of Cann et al. regarding mtDNA mutation rates?

<p>The mutation rate is not stable over time.</p> Signup and view all the answers

What is indicated by the concept of high copy number per cell in mtDNA?

<p>There are multiple copies of mtDNA that can carry mutations.</p> Signup and view all the answers

Which characteristic distinguishes mtDNA from nuclear DNA?

<p>mtDNA is inherited in a strictly maternal manner.</p> Signup and view all the answers

What is the primary reason for the lower penetrance of LHON in female mutation carriers?

<p>Influence of nuclear genes regulating mitochondrial expression</p> Signup and view all the answers

What is the relationship between the m.A1555G mutation and aminoglycoside antibiotics?

<p>Carriers can suffer hearing loss without exposure to these antibiotics.</p> Signup and view all the answers

What does the male predominance in LHON mutation carriers suggest?

<p>An X-linked susceptibility gene might influence expression.</p> Signup and view all the answers

What critical aspect was confirmed by the Human Fertilisation and Embryology Authority regarding mitochondrial replacement therapy?

<p>Fewer than five children were born using MRT as of April 2023.</p> Signup and view all the answers

Which gene was first identified as a mutation linked to non-syndromic hearing loss?

<p>m.A1555G in the 12S ribosomal RNA gene</p> Signup and view all the answers

What is the significance of Mitochondrial Eve in the context of human genetics?

<p>She represents the most recent common matrilineal ancestor of all modern humans.</p> Signup and view all the answers

What can be inferred about the applicability of population genomics?

<p>It has real-world implications beyond academic understanding.</p> Signup and view all the answers

What does tissue heteroplasmy imply in the context of LHON?

<p>The degree of mutant mtDNA variation in specific tissues</p> Signup and view all the answers

What is the primary inheritance pattern of mitochondrial DNA?

<p>Matrilineal inheritance</p> Signup and view all the answers

Which components are included in the total mtDNA?

<p>13 mRNA, 2 rRNA, and 22 tRNA</p> Signup and view all the answers

What is a key characteristic of homoplasmic mtDNA?

<p>All copies are identical</p> Signup and view all the answers

What is the approximate number of genes encoded by mitochondrial DNA?

<p>37 genes</p> Signup and view all the answers

How does mitochondrial DNA differ from nuclear DNA?

<p>mtDNA is circular and inherited maternally</p> Signup and view all the answers

What prevents the passing on of paternal mitochondrial DNA?

<p>Mitochondria are destroyed in the sperm</p> Signup and view all the answers

What is the prevalence rate of Leber Hereditary Optic Neuropathy (LHON)?

<p>1:50,000</p> Signup and view all the answers

Which mitochondrial mutation accounts for the majority of clinical cases of LHON?

<p>m.G11778A</p> Signup and view all the answers

Which strand of mitochondrial DNA encodes more genes?

<p>Heavy strand</p> Signup and view all the answers

What is a characteristic symptom of Leber Hereditary Optic Neuropathy?

<p>Bilateral blindness</p> Signup and view all the answers

Which type of mutations are most commonly observed in mtDNA?

<p>Heteroplasmic mutations</p> Signup and view all the answers

Which haplogroup is most associated with an increased risk for vision loss in LHON?

<p>J</p> Signup and view all the answers

What type of diseases are associated with mitochondrial DNA?

<p>Mitochondrial diseases</p> Signup and view all the answers

At what age do symptoms of Leber Hereditary Optic Neuropathy typically begin?

<p>From 18 to 35 years</p> Signup and view all the answers

Which of the following haplogroups is found in the European population?

<p>Haplogroup J</p> Signup and view all the answers

How many substitution mutations account for approximately 90% of clinical cases of LHON?

<p>Three</p> Signup and view all the answers

What percentage of female LHON mutation carriers are typically symptomatic?

<p>10%</p> Signup and view all the answers

Which gene mutation is associated with non-syndromic hearing loss?

<p>m.A1555G</p> Signup and view all the answers

What effect does the m.A1555G mutation have in relation to aminoglycoside antibiotics?

<p>Causes hypersensitivity</p> Signup and view all the answers

What legal milestone related to mitochondrial replacement therapy (MRT) occurred in the UK?

<p>Legalized in 2015</p> Signup and view all the answers

Which of the following factors may influence variable phenotypic expression of LHON?

<p>Degree of mutant mtDNA</p> Signup and view all the answers

What does mitochondrial DNA connect all humans back to?

<p>Mitochondrial Eve</p> Signup and view all the answers

What is the significant increase in vision loss risk associated with the high-risk allele at Xp21?

<p>35-fold increase</p> Signup and view all the answers

Which part of mitochondrial DNA is mostly affected by mutations?

<p>D loop</p> Signup and view all the answers

What is the significance of 'Mitochondrial Eve' in human ancestry?

<p>It represents the most recent common ancestor of all living humans.</p> Signup and view all the answers

During which process is the mitochondrial genetic bottleneck observed?

<p>Oogenesis</p> Signup and view all the answers

What is the estimated mutation rate of mtDNA compared to nuclear DNA?

<p>Higher than nuclear DNA</p> Signup and view all the answers

Which conclusion was drawn by Cann et al. about mtDNA mutations?

<p>Mutations can arise in less than 1000 years.</p> Signup and view all the answers

What distinguishes non-African mtDNA populations from African populations?

<p>Multiple mtDNA lineages</p> Signup and view all the answers

What factor contributes to the high mutation rate in mtDNA?

<p>High copy number per cell</p> Signup and view all the answers

What does the concept of 'Mitochondrial Eve' represent?

<p>The most recent common matrilineal ancestor of all living humans</p> Signup and view all the answers

How many primary haplogroups are represented in mitochondrial DNA?

<p>38</p> Signup and view all the answers

What do HVR1 and HVR2 refer to in mitochondrial DNA?

<p>Hypervariable regions that accumulate mutations</p> Signup and view all the answers

What does the term 'Evolutionary Bottleneck' imply in relation to human population history?

<p>A drastic reduction in genetic diversity due to environmental events</p> Signup and view all the answers

What role does matrilineal descent play in mitochondrial DNA inheritance?

<p>It allows for the passage of mtDNA only through maternal lines</p> Signup and view all the answers

What specifically allows haplogroups to be defined within mtDNA?

<p>Characteristic mtDNA mutations</p> Signup and view all the answers

Study Notes

Mitochondrial DNA Structure and Function

  • Mitochondrial DNA (mtDNA) lacks introns and resides outside the nucleus, similar to prokaryotic DNA organization.
  • mtDNA encodes proteins crucial for the electron transport chain.
  • The heavy chain of mtDNA is guanine-rich, acts as the origin of replication, and its replication/transcription occurs clockwise.
  • Conversely, the light chain, rich in cytosine, replicates counter-clockwise.
  • Mitochondrial DNA polymerase is encoded by the nuclear gene POLG.
  • Replication begins with mtDNA replicating until there are enough copies for two cells; then, binary fission occurs.
  • Mitochondria are found in the sperm midpiece.
  • Fertilization involves fusion of the sperm head with the egg, releasing nuclear content; this prevents paternal mtDNA transmission.

Mitochondrial DNA Inheritance

  • Homoplasmy: All mtDNA copies identical, resulting in identical transmission to offspring.
  • Heteroplasmy: Mutations present in only some mtDNA copies; all children of affected females will inherit some fraction of mutated mtDNA.
  • The proportion of mutant mtDNA in offspring varies due to the mitochondrial genetic bottleneck during egg formation (oogenesis).

Mitochondrial DNA vs. Nuclear DNA

  • Nuclear DNA undergoes homologous recombination during meiosis leading to genetic variation in offspring.
  • mtDNA lacks recombination and therefore is often inherited in a uniform, unchanging way, unlike nuclear DNA.

mtDNA and Population Studies

  • mtDNA is useful for tracing maternal lineages due to its maternal inheritance pattern.
  • The lack of recombination provides consistent patterns for population analysis.
  • High copy number per cell makes mtDNA easier to isolate.
  • A relatively rapid mutation rate provides more data for analysis.

mtDNA Mutations and Evolution

  • MtDNA mutations often occur in non-coding regions (D-loop).
  • "Mitochondrial Eve" represents the most recent common ancestor of all mtDNA in living humans.
  • Evolutionary bottlenecks, such as historical events that caused significant human population decrease, could result in the loss of specific mtDNA lineages.

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Description

Explore the fascinating structure and function of mitochondrial DNA (mtDNA). Learn about its unique characteristics, replication mechanisms, and inheritance patterns, including concepts like homoplasmy and heteroplasmy. This quiz will deepen your understanding of this essential component of cellular function.

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