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Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 17 - Organelle Inheritance and the Evolution of Organelle GenomesProblem 26
Chapter 17, Problem 26

Most large protein complexes in mitochondria and chloroplasts are composed both of proteins encoded in the organelle genome and proteins encoded in the nuclear genome. What complexities does this introduce for gene regulation (i.e., for ensuring that the appropriate relative numbers of the proteins in a complex are produced)?

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1
Understand that the proteins in large complexes of mitochondria and chloroplasts are encoded by two separate genomes: the organelle genome and the nuclear genome. This introduces the challenge of coordinating gene expression between these two genomes.
Recognize that the organelle genome and the nuclear genome are located in different cellular compartments, which means that communication and signaling pathways must exist to synchronize their gene expression.
Consider that the transcription and translation processes for nuclear-encoded proteins occur in the cytoplasm, while organelle-encoded proteins are transcribed and translated within the organelle. This spatial separation requires precise timing and regulation to ensure the correct stoichiometry of proteins in the complex.
Account for the fact that nuclear-encoded proteins often need to be imported into the organelle after synthesis. This involves additional regulatory mechanisms, such as targeting signals on the proteins and transport machinery in the organelle membranes.
Reflect on the role of feedback mechanisms, where the assembly state of the protein complex or the availability of organelle-encoded proteins might influence the expression of nuclear-encoded genes, ensuring balanced production of all components.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Organelle vs. Nuclear Genome

The organelle genome refers to the DNA found within mitochondria and chloroplasts, which encodes a small number of proteins essential for their function. In contrast, the nuclear genome contains the majority of genetic information in eukaryotic cells, including genes for proteins that are imported into these organelles. Understanding the interplay between these two genomes is crucial for grasping how protein complexes are assembled and regulated.
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Gene Regulation

Gene regulation involves the mechanisms that control the expression of genes, ensuring that proteins are produced in the right amounts and at the right times. In the context of mitochondria and chloroplasts, this regulation is complex because it requires coordination between the nuclear and organelle genomes, necessitating communication pathways that can respond to the needs of the organelles based on their functional status.
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Protein Complex Assembly

Protein complex assembly refers to the process by which multiple protein subunits come together to form a functional unit. In mitochondria and chloroplasts, the assembly of these complexes is complicated by the need for proteins encoded by both the organelle and nuclear genomes to be synthesized, imported, and correctly assembled, which requires precise regulation to maintain the appropriate stoichiometry and functionality of the complexes.
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Related Practice
Textbook Question

Wolves and coyotes can interbreed in captivity, and now, because of changes in their habitat distribution, they may have the opportunity to interbreed in the wild. To examine this possibility, mitochondrial DNA from wolf and coyote populations throughout North America—including habitats where the two species both reside—was analyzed, and a phylogenetic tree was constructed from the resulting data. A sequence from a jackal was used as an outgroup, and a sequence from a domestic dog was included, demonstrating wolves as the origin of domestic dogs. What do you conclude about the possibility that interspecific hybridization occurred between wolves and coyotes on the basis of this phylogenetic tree?

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Textbook Question

Considering the phylogenetic assignment of Plasmodium falciparum, the malarial parasite, to the phylum Apicomplexa, what might you speculate as to whether the parasite is susceptible to aminoglycoside antibiotics?

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Textbook Question

Elysia chlorotica is a sea slug that acquires chloroplasts by consuming an algal food source, Vaucheria litorea. The ingested chloroplasts are sequestered in the sea slug's digestive epithelium, where they actively photosynthesize for months after ingestion. In the algae, the algal nuclear genome encodes more than 90% but not all of the proteins required for chloroplast metabolism. Thus it is suspected that the sea slug actively maintains ingested chloroplasts, supplying them with photosynthetic proteins encoded in the sea slug genome. How would you determine whether the sea slug has acquired photosynthetic genes by horizontal gene transfer from its algal food source? Discuss the steps required for heritable endosymbiosis to eventuate, and their plausibility.

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Textbook Question

Mothers will pass on a mitochondrial defect to their offspring. In a type of gene therapy, one approach to circumvent this problem is to have two different maternal contributions, with the nucleus of the female with the defective mitochondria being placed in an enucleated egg derived from a female with normal mitochondria. After fertilization, the resulting offspring would have three parental sources of DNA—with nuclear DNA derived from a mother and a father, and mitochondrial DNA derived from another 'mother.' Recently, children with this genetic makeup have been born, but the elimination of defective mitochondria is not complete, with the amount of defective mitochondria derived from the defective mother ranging from 0 to 9%. Discuss potential complications resulting from such a mixture of genomes.

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