Mitochondria and Chloroplasts PDF

Mitochondria and chloroplasts Mitochondria and chloroplasts possess their own genomes Eukaryotic cells may have many copies of organelle genomes Inheritance of organellar genomes can be uniparental (from just one parent) or biparental In humans, mitochondrial genomes are passed from mother to offsp...

Mitochondria and chloroplasts Mitochondria and chloroplasts possess their own genomes Eukaryotic cells may have many copies of organelle genomes Inheritance of organellar genomes can be uniparental (from just one parent) or biparental In humans, mitochondrial genomes are passed from mother to offspring, which can be used to trace relationships Toshoji et al. 2012 Copyright 2023, Morton SUNY Brockport  Monday Tuesday Wednesday Thursday Friday Week of Dec 2 Lecture Lecture Lecture (10:10-11) (10:10-11) (10:10-11) Office hour Office hour Office hours (11-12) Lab (104) (11-12) (11-1pm) (12:30-3:15) Lab (104) (1:25-4:10) Monday Tuesday Wednesday Thursday Friday Week of Dec 9 FINAL!!!!! REVIEW 8am-10am (12:30-2pm) Edwards 100 REVIEW Lennon 206 (2pm-3:30) Lennon 206 Mitochondria and chloroplasts Objectives Be able to explain properties of organellar genomes Be able to analyze mitochondrial inheritance relationships in pedigrees Be able to explain the endosymbiosis theory Toshoji et al. 2012 Copyright 2023, Morton SUNY Brockport  True or false: all of the DNA in eukaryotic cells is in the nucleus True False Copyright 2023, Morton SUNY Brockport Eukaryotic cells have many different kinds of organelles Eukaryotic cell Some organelles: Nucleus Endoplasmic reticulum Golgi apparatus Mitochondria Lysosomes https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/12-ultrastructure-of- cells/eukaryotic-cells.html Copyright 2023, Morton SUNY Brockport Mitochondria Mitochondria are the “powerhouse” of the cell. They produce ATP for the cell through cellular respiration. This involves oxidative phosphorylation (electron transport ultimately leads to the phosphorylation of ADP into ATP) Cells with high metabolic demands tend to have more mitochondria Mitochondria have their own DNA! What other organelle in eukaryotes has its own DNA? https://en.wikipedia.org/wiki/Mitochondrial_DNA Copyright 2023, Morton SUNY Brockport Chloroplasts also have their own genome Chloroplasts are organelles found in plants and photosynthetic algae Chloroplasts contain chlorophyll and are the site of photosynthesis (conversion of light energy into chemical energy) Chloroplasts have their own DNA! https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/cell-compartmentalization-and-its-origins/a/chloroplasts-and-mitochondria Copyright 2023, Morton SUNY Brockport Mitochondrial DNA (mtDNA) In humans, the mitochondrial DNA (mtDNA) is circular and 16,569bp Contains 37 genes 2 rRNA genes 22 tRNA genes 13 protein genes All of the proteins encoded by mtDNA are subunits of enzyme complexes used in oxidative phosphorylation Mitochondria need way more than just 13 proteins to function! Mitochondria contain 1,000-1,500 distinct proteins The vast majority of these proteins are encoded by genes in the nucleus Like nuclear DNA, mtDNA can have polymorphisms and mutations. These mutations can sometimes cause disease. Also, between species, the sizes, numbers, and identities of genes in mitochondria can differ Copyright 2023, Morton SUNY Brockport Mitochondria DNA (mtDNA) is present in multiple copies Mitochondrial Nuclear DNA Individual eukaryotic cells may contain multiple organelles (more than just one mitochondrion in a typical eukaryotic cell! Can vary from one to thousands) nucleus Each mitochondrion may contain multiple copies of its chromosome Mitochondria can do DNA replication, transcription and translation in their matrix Mitochondrial DNA https://www.istockphoto.com/illustrations/mitochondrion Copyright 2023, Morton SUNY Brockport Is all the mtDNA in a cell identical? Maybe or maybe not! A cell or organism in which all A cell or organism in which not all copies of an organelle gene copies of an organelle gene are the are the same is said to exhibit same is said to exhibit homoplasmy heteroplasmy nucleus nucleus Copyright 2023, Morton SUNY Brockport  How are organelle genomes replicated when a cell divides? Replication of the organelle genomes is not tightly coupled to the cell cycle When the cell divides in mitosis, the organelles in the cytoplasm are randomly distributed to the daughter cells Random segregation of organelles during replication is called replicative segregation A homoplasmic cell will give A heteroplasmic cell might give daughters homoplasmic daughters that are homoplasmic or heteroplasmic Copyright 2023, Morton SUNY Brockport Homoplasmic Heteroplasmic How are organelle genomes replicated when a cell divides? If mutations arise in the organellar genome, a particular daughter cell may or may not inherit it. The proportion of organelles (and cells) with the mutation can affect if there is a phenotype Replicative segregation can lead to genetically mosaic organisms with some mutant cells and some wild-type cells Copyright 2023, Morton SUNY Brockport  In humans, where do a zygote’s organelles come from? Zygote = the diploid cell that results from fertilization (fusion of a male gamete and female gamete) A. The female gamete (the egg) B. The male gamete (the sperm) C. Equally from the male and female gametes D. Neither parent. Zygotes make all of their organelles anew from their nuclear DNA Copyright 2023, Morton SUNY Brockport Organellar inheritance Organellar inheritance refers to transmission of genes on mitochondrial and chloroplast chromosomes, as opposed to nuclear chromosomes Uniparental inheritance (from one parent only) ex. Mitochondria in humans are from the mother. In most plants, chloroplasts and mitochondria come from female parent (some exceptions ex. cucumbers get their mitochondria from their male parent) Uniparental from the mother is also called ‘maternal inheritance’ Biparental inheritance (from both parents) ex. Mitochondria from both mating types in yeast Some members of geranium family https://en.wikipedia.org/wiki/Cucumber Park et al. 2021 https://en.wikipedia.org/wiki/Pelargonium_zonale Copyright 2023, Morton SUNY Brockport Mitochondrial inheritance in mammals Some consequences of maternal inheritance of the mitochondrial genome: 1. Predictions of mitochondrial mutation inheritance can be made based on mother’s genotype 2. Maternal lineage of organisms can be examined 3. Trees constructed from mtDNA will show the maternal history of a species 4. Human genetic diseases caused by mitochondrial mutations are maternally inherited Copyright 2023, Morton SUNY Brockport Mitochondrial inheritance in a pedigree What inheritance for a mtDNA-based disease might look like In reality: the inheritance is usually not so clean-looking. Heteroplasmy (mix of WT and mutant mitochondria) might lead to different expressivity/incomplete penetrance “Non-Mendelian” Copyright 2023, Morton SUNY Brockport Mitochondrial inheritance in mammals There are over 150 mtDNA mutations associated with disorders The phenotypes of such diseases are often highly pleiotropic, because of the dependence of cells on mitochondrial function in oxidative phosphorylation Copyright 2023, Morton SUNY Brockport Example mitochondrial disease with incomplete penetrance In mitochondrial disorders such as the optic neuopathy shown in this pedigree, while all affected children have an affected mother, not all of the children of affected mothers are affected (incomplete penetrance) There are three possible reasons for incomplete penetrance of the disorder 1) the effects of heteroplasmy 2) the influence of nuclear genes 3) the effect of environmental factors Copyright 2023, Morton SUNY Brockport Heteroplasmy and inheritance of disease In human pedigrees, heteroplasmic mothers may produce heteroplasmic, homoplasmic mutant, or homoplasmic wild-type offspring. It depends on how the mitochondria ended up distributed in her oocytes Germ cell When the new heteroplasmic zygote divides and develops into a person, different cells and different tissues may wind up with different ratios of wild-type and mutant mitochondria Copyright 2023, Morton SUNY Brockport Differences between tissues can also affect disease Heteroplasmic individuals undergo replicative segregation in somatic cells, which may mean that different cells and different tissues may end up with different ratios of wild-type-to-mutant mitochondria Disease symptoms will develop only if the tissues that are vulnerable to the disorder contain a high proportion of mutant mitochondria Copyright 2023, Morton SUNY Brockport Discovery of organellar inheritance Carl Correns – German botanist. One of the three botanists who re- discovered Mendel’s work! Studied Mirabilis jalapa (“Four o’clock flower” or “Marvel- of-Peru”) The white leaves were due to a chloroplast defect! Erwin Baur was doing similar work on geraniums https://en.wikipedia.org/wiki/Mirabilis_jalapa https://en.wikipedia.org/wiki/Carl_Correns Copyright 2023, Morton SUNY Brockport Discovery of organellar inheritance In 1957, Japanese biochemist Yasutane Chiba isolated DNA from chloroplasts, leading to the proposed idea that chloroplasts and mitochondria had their own genomes. https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/cell-compartmentalization-and-its-origins/a/chloroplasts-and-mitochondria Copyright 2023, Morton SUNY Brockport Discovery of organellar inheritance Heteroplasmy can explain some types of plant variegation Toshoji et al. 2012 Copyright 2023, Morton SUNY Brockport Mother-child identity of mitochondrial DNA Even though inherited mtDNA mutations may or may not show phenotypic penetrance, all of the mtDNA in a person came from their mother Mothers and their children share identical mitochondrial DNA Mitochondrial DNA can be used to find matches between mothers and offspring, or grandmothers and grandchildren Copyright 2023, Morton SUNY Brockport Grandmothers of Plaza de Mayo In 1976-83 an Argentinian dictatorship kidnapped political opponents and their families from their homes https://en.wikipedia.org/wiki/Grandmothers_of_the_Plaza_de_Mayo – Parents were often killed and their children adopted by soldiers or In 1984, Mary-Claire King members of the reigning political worked with this group, class assessing mtDNA. mtDNA – As many as 500 babies were would have been passed abducted with their mothers from grandmother to daughter to grandchild, In 1977, women whose children or and the grandmothers grandchildren had disappeared could prove their formed a human rights organization to biological relatedness find them (Abuelas de Plaza de Mayo) Over 130 illegally adopted children have been identified Copyright 2023, Morton SUNY Brockport  I. 1 2 3 4 II. 1 2 3 4 5 ? III. 1 You would like to use mitochondrial DNA to try to determine if III-1 is a member of the family shown in this pedigree. II-2 and II-3 are dead as indicated with a slash and you are unable to collect mitochondrial DNA from them. If III-1 is a member of this family his mitochondrial DNA should match: A) I-1 and II-1 only B) I-1, I-2 and II-1 only C) I-1, I-3, II-1, and II-4 only D) I-3 and II-4 only E) I-3, II-4, and II-5 only Maitreya Dunham, UW Copyright 2023, Morton SUNY Brockport Mitochondrial DNA and populations Mitochondrial DNA sequences are used as a tool for deciphering genealogical history Mitochondria are strictly maternally inherited in mammals, with no recombination of alleles Once a mitochondrial mutation becomes homoplasmic in the germ cells of a female, the mutation is transmitted to all of her offspring; maternal lineages can be traced back in time and can allow identification of a common ancestor Copyright 2023, Morton SUNY Brockport MtDNA can be used to trace a common human ancestor Analysis of genetic variation in the mitochondrial genome can trace human ancestry All of us received our mtDNA from our biological mothers, who received theirs from their biological mothers… Following back the matrilineal lineage (line of descent through females) will eventually point to a matrilineal Most Recent Common Ancestor https://en.wikipedia.org/wiki/Mitochondrial_Eve Copyright 2023, Morton SUNY Brockport MtDNA can be used to trace a common human ancestor Analyses like this indicate that mtDNA of all humans living today is descended from a woman living in East Africa between 120,000 and 200,000 years ago This individual is sometimes referred to as “mitochondrial Eve” That does NOT mean she was the only woman around at the time! Other women were definitely around who could have contributed to the population today – all of them just had their genetic contribution pass through sons at some point in some generation Copyright 2023, Morton SUNY Brockport  Evolutionary tree (from mtDNA sequencing) indicates an African origin of all humans -Earliest branches are exclusively African -Support an African origin of modern humans about 150,000 - 200,000 years ago -The greatest genetic diversity is present in Africa non-African mitochondrial Eve -Non-African populations African have a subset of the genetic diversity of African populations -Fossil record also supports African origin Leo Pallanck, UW Copyright 2023, Morton SUNY Brockport Mitochondrial haplogroups, their migration patterns, and their dates of origin Stewart and Chinnery 2015 Copyright 2023, Morton SUNY Brockport Why do mitochondria and chloroplasts have their own DNA? Mitochondria and chloroplasts have a lot in common with bacteria: The double-membrane system in chloroplasts and mitochondria is similar to a membrane system found in bacteria Mitochondria and chloroplasts are about the same size as bacteria Circular genome Lack histones The transcriptional and translational machinery used in mitochondria and chloroplasts closely resembles that of bacteria The protein-coding sequences of organellar genes are more like those of bacteria than like either nuclear genes of eukaryotes or the sequences of archaea Copyright 2023, Morton SUNY Brockport The endosymbiosis theory Anaerobic cell Endosymbiosis is a Aerobic cell interdependent, mutually beneficial relationship between organisms (where one organism lives inside the other) It is hypothesized that mitochondria and chloroplasts are the descendents of formerly free- living bacteria that were engulfed by ancient eukaryotic cells and then became endosymbionts https://learn.genetics.utah.edu/content/cells/organelles/ Copyright 2023, Morton SUNY Brockport Evolution of mitochondria Evidence indicates that mitochondria are monophyletic, all descended from a single ancestor Combined with evidence of similarity between mitochondria and bacteria, this suggests a single endosymbiotic event gave rise to mitochondria 1.5-2 billion years ago The closest living relatives of mitochondria are free-living α-proteobacteria Over time, genetic material was passed from the organelle to the nucleus Copyright 2023, Morton SUNY Brockport Evolution of chloroplasts Chloroplasts are also monophyletic, descended from a single endosymbiotic event at least 1.2 billion years ago The closest relatives of chloroplasts are free-living cyanobacteria Existing cyanobacteria have much larger genomes than chloroplasts, thus large-scale gene loss took place during the evolution of chloroplasts Cyanobacteria photo – Robert Calentine https://microbewiki.kenyon.edu/index.php/Cyanobacteria_and_Cyanotoxins Copyright 2023, Morton SUNY Brockport Reminders about this week No problem set this week (study for your final!) No reflection this week (study for your final!) Come to office hours and the review sessions for anything that is unclear! Copyright 2023, Morton SUNY Brockport