what type of bacteria is believed to have evolved into chloroplasts
THE ORIGIN OF MITOCHONDRIA AND CHLOROPLASTS
Eukaryotes possess complex intracellular organelles, such equally mitochondria and chloroplasts (such equally the spiral chloroplast in the alga Spirogyra). How did these structures evolve?
Endosymbiosis refers to a condition in which one cell lives inside another prison cell for the benefit of both. Is this possible? Yep. At that place are hundreds of known examples of endosymbionts such every bit bacteria living inside of protists, algae living inside corals, worms, clams, fifty-fifty mollusks called nautiloids. For case, in that location are a large number of species in the protozoan family Trypanosomatidae, many of which cause human diseases such as Chaga's disease and African sleeping sickness. Some members of the family unit possess endosymbionts (such every bit Blastocrithidia cullicis, Crithidia deanei, C. desouzai, C. oncopelti , and Heretomonas roitmani ; de Souza, 1999). Non only are endosymbionts known in mod organisms (including modern termites), they have been identified in fossils equally well. Spirochete and protest symbionts of a fossil termite were identified in Miocene amber (Wier, 2002).
Bacterial symbionts in the amoeba Pelomyxa palustris are kept in vacuoles. This species is considered to exist ane of the most primitive eukaryotes and it lives in very depression-oxygen environments. The eukaryotes Plasmodium falciparum and Toxoplasma gondii retain a vestigial plasmid, the apicoplast which is probably derived from a photosynthetic algae which has lost its photosynthetic pathways. The parasitic plant Epifagus virginiana possesses vestigial plasmids (
The parasitic trypanosomes seem to be algae which have lost their chloroplasts, given nuclear genes which appear to have originated from an endosymbiont. Oomycetes appear to be algae which have lost their plastids (Martin, 2003). Entamoeba possesses a vestige of a mitochondria which no longer functions in ATP production (but which may perform other mitochondrial tasks such as reactions involving iron and sulfur) (Martin, 2003).
It is common that genes which were originally present in the endosymbiont eventually are transferred to the host nucleus. Modern chloroplasts encode between 60 and 200 proteins. Most of the ancestral genes seem to have been translocated to the nucleus. Nearly 18% of the nuclear genes of the plant Arabidopsis, seem to have originated from the cyanobacterial endosymbiont (Martin, 2002) and a re-create of the mitochondrial genome (99% identical) has been copied to chromosome 2 (Martin, 2003). The genome of the plastids of dinoflagellates has been greatly reduced, consisting of single-gene minicircles which encode near 15 proteins. Most of the genes for the photosystems take been translocated to the nucleus (Hackett, 2004 ).
Not merely are at that place a number of endosymbionts evolved recently which nonetheless retain most of their ancestral nature, there is also evidence of more aboriginal endosymbiotic events, including the origin of mitochondria and chloroplasts. Mitochondria and chloroplasts are eukaryotic organelles which accept a number of features which suggest they are derived from eubacterial ancestors. They are like in size to leaner and they possess their ain chromosomes which are circular, similar those of bacteria. (As a event, it is wrong to say that human cells have 46 chromosomes: the mitochondrial chromosome composes a 47thursday and it may exist present in many copies in whatever given cell.) Mitochondria and chloroplasts are also like to bacteria in their ribosomes, cytochrome c, genetic lawmaking, translation initiation (utilise the tRNA.fMet), translation initiation factors; and internal structure. Both mitochondria and chloroplasts reproduce by fission as do bacteria and cannot be synthesized past the genes in the nucleus. If they are removed from a jail cell, the prison cell cannot replace them (Gray, 1992).
Both mitochondria and chloroplasts are sensitive to antibiotics which affect bacteria such as streptomycin, spectinomycin, neomycin, and chloramphenicol while they are unaffected by agents such as cyclohexamide that affect the cytoplasm. Many of these antibiotics human activity on bacterial ribosomes. However, eukaryotic mitochondria possess their ain genes which contribute to ribosomes. In that location are two rRNAs encoded past the mitochondrial genome: MTRNR1 (nucleotides 648-1601) and MTRNR2 (nucleotides 1671-32229). Not merely are high doses of certain antibiotics potentially dangerous to all humans (because they inhibit mitochondria in addition to inhibiting bacteria) some people possess variations in these mitochondrial rRNA genes which make their mitochondria more "bacteria-like" and thus tin cause serious reactions if they take an antibiotic. Mutations in mitochondrial genes can cause a number of inherited genetic disorders in humans. For instance, mutations in the mitochondrial MTRNR1 factor tin cause deafness (OMIM).
Plasmids are small pieces of Dna which exist exterior major chromosomes. Although virtually all plasmids are known from leaner, some are known to exist in eukaryotic mitochondria. A number of linear mitochondrial plasmids are known in fungi and higher plants, some of which require the presence of two plasmids in order to replicate (Chan, 1991; Greyness, 1992).
Are mitochondria as old as eukaryotes? In comparisons of rRNA molecules, the three groups of eukaryotes which seem to branch off the main ancestral lineage offset (microsporidia, metamonada including the diplomonads, and parabasala including the trchomonads) lack mitochondria (Germot, 1997; Gray, 1992). Although it was originally idea that these primitive eukaryotes were descended from ancestors which diverged after the evolution of the eukaryotic nucleus and earlier the evolution of the mitochondria, that now no longer seems to be the instance. Microsporidia have a ribosome whose size is similar to that of prokaryotes given that they, lonely of the eukaryotes, lack a v.viii S subunit. The large subunit rRNA in microsporidia and prokaryotes is homologous to the 5.8S subunit at its v'terminate (Vossbrink, 1986; Greyness, 1992). Sequence comparisons of a number of molecules (such equally HSP70) suggest that microsporidian nuclei possess genes which seem to have been derived from bequeathed mitochodria which were later lost (Germot, 1997).
These most archaic eukaryotes retain hints that their ancestors possessed mitochondria, including organelles called hydrogenosomes. Hydrogenosomes are intracellular organelles found in a number of eukaryotes that lack mitochondria (such every bit trichomonads) and similar organelles have been observed in some fungi and ciliates. These organelles ferment pyruvate, producing carbon dioxide and molecular hydrogen and generating ATP through substrate level phosphorylation. Although they are coated past a double membrane and employ succinyl CoA synthtase for ATP production like mitochondria, they lack cristae, cytochromes, FoF1 ATPase, or a pyruvate dehydrognease complex. The ferredoxin oxodireductase of hydrogenosomes is homologous to the pyruvate dehydrogenase of mitochondria. Although they lack their own chromosomes, the nuclear genes coding their proteins are similar to mitochondrial genes. It appears that hydrogenosomes and mitochondria take their origin in the same endosymbiontic organelle and that trichomonads diverged from other eukaryotic lineages earlier this endosymbiont had given rise to mitochondria (Bui, 1996; Andersson, 1999).
As a effect, there do not announced to be any modernistic eukaryotic cells whose lineage diverged from others prior to endosymbiotic outcome which resulted in mitochondria. It is possible that these ancient lineages simply have non survived (or take non been discovered) or it is possible that the origin of mitochondria coincided with the origin of the nucleus, and thus, the eukaryotic cell.
MITOCHONDRIA
It is often observed that cells which alive inside other cells take reduced numbers of genes. Fifty-fifty bacterium Rickettsia prowazekii , which is an intracellular parasite which has a reduced genome with merely 834 genes. The genome size of mitochondria varies from 60 to 200 genes in different organisms (
Mitochondrial genomes are typically smaller than 200 kilobase pairs (kbp) in size but they vary from 13.8 kbp in the nematode C. elegans to 2400 kbp in muskmelon Cucumis melo. These mitochondrial genomes consistently encode proteins required for respiration (although at that place are a few variations, such every bit the absenteeism of NADH dehydrogenase in some fugal mitochondria). The mitochondrial genes of plants and some protists typically possess genes for translational proteins and RNAs which are absent (or near absent-minded) in the genomes of fungal and creature mitochondria. Mitochondrial genomes in animals typically have the same gene order (which is invariant in mammals), lack introns (although some have been institute in cnidarians), and possess few non-coding nucleotides (with the least number of noncoding nucleotides being virtually 100 in some ocean urchins) (Gray, 1992). In dissimilarity, establish mitochondria have very depression gene density; less than 10% is coding as opposed to the more than xc% coding in animals (Greyness, 1992). The mitochondrial genes of Reclinomonas
The reduced diversity of tRNA types has resulted from a pressure in mitochondria to reduce the sizes of their genomes. Although many mitochondrial codons depart from the "universal" genetic code, these codon reassignments are specific to unlike lineages. In insects, mammals, and amphibians, the reassignment of AUA to encode methionine has increased the percentage of methionine in mitochondrial proteins. In near eukaryotic mitochondria studied (with the exception of higher plants), UGA has been reassigned to lawmaking for tryptophan, the most highly conserved amino acrid in mitochondrial proteins, and presumably 1 with considerable functional importance (Andersson, 1991).
The outer membrane of the chloroplasts and mitochondria are probably derived from the host cell that engulfed them (
Some have suggested that the ancestors of mitochondria which were engulfed by proto-eukaryotes had not yet evolved the ability to apply oxygen. It has been proposed that mitochondria evolved from an α bacterium which produced hydrogen and carbon dioxide every bit wastes. The first eukaryotes would take lived in anaerobic environments until the endosymbionts adjusted to oxygen (Lopez-Garcia, 1999).
Organelles have kept the major bacterial proteins which performed electron send, but additional subunits accept been added (
Mitochondria apply genes which seem to accept originated from a bacteriophage rather than the ancestral bacterium (Shutt, 2006). Genetic analysis suggests that some of the proteins nowadays in mitochondria may accept originated from viruses which infected the ancestral α proteobacteria (Filee, 2005).
CHLOROPLASTS
Shortly after the evolution of eukaryotes, two lineages evolved. The lineage which evolved into animals, fungi, and choanoflagelleates evolved apartment mitochondrial cristae, positioned the ancestral cilium in the posterior, adult chitin and lanosterol. The lineage which led to plants and most protists began with tubular mitochondrial cristae, an anterior cilium, and developed cellulose and cycloartenol (Cavalier-Smith, 2003). In the 2d group, additional endosymbiotic events occurred which resulted in plastids such every bit chloroplasts.
Eubacterial endosymbionts provided the basis for eukaryote photosynthesis and no archaea perform this type of photosynthesis. Bacteriochlorophyll chiliad from heliobacteria and cyanobacteria (such equally the cyanobacteria in the above photo) is very similar to chlorophyll a from chloroplasts. Gloeobacter violaceus may be the most primitive cyanobacteria given its lack of thylakoids and the presence of its electron transport system on its cell membrane (
While near plastid genomes range in size from 120 to 160 kbp, those in green algae range from 89 kbp to more 400 kbp. The smallest genomes (well-nigh seventy kbp) are known from nonphotosynthetic algae and plants. These plastid genomes back up the thought of a eubacterial endosymbiont since not but homologous genes but also similar gene orders are shared between plastid and eubacterial chromosomes (such equally a cluster of 10 ribosomal poly peptide genes in the same lodge in both plastids and E. coli.) These plastid genes can be organized into operons and controlled by promoters very like to those found in eubacteria. Plastids are similar to eubacteria in their ribosomal subunits, ribosomal proteins, translation initiation, and antibiotic sensitivity. Sequence comparisons of plastid rRNA genes and those of the iii divisions of life identify the plastid genes as being eubacterial and, more specifically, cyanobacterial. (Grey, 1992). Gene comparisons support that there was one single endosymbiotic origin of plastids (Morden, 1992).
One of the membrane proteins of chloroplasts, coded by the gene Toc75, had no known homologs until a like membrane protein was discovered in cyanobacteria (the factor was named SynToc75). In chloroplasts, the protein helps to import other proteins from the cytoplasm to the chloroplast. In cyanobacteria, the poly peptide clearly performs an essential part, since nix mutants do non survive; perhaps it transports a virulence factor from within the jail cell. SynToc75 was shown to be related to proteins institute in all groups of Gram-negative leaner where well-nigh function every bit prokaryotic secretion channels for virulence factors, such every bit hemolysins and adhesins (Reumann, 1999).
The several kinds of plastids in eukaryotes seem to accept arisen from divide endosymbiotic events, given the varying pigments and membrane compositions of the plastids in plants and algae. Some plastids are surrounded by additional membranes which may have originated from the phagosome of their original host. (Gray, 1992). In plants, the plastid replication utilizes proteins homologous to those leaner use in sectionalisation. The tubulin-like protein FtsZ is a bacterial division protein which is likewise required in establish and algae organelles.
Comparisons of the genomes of mitochondria and chloroplasts are useful in determing phylogenetic relationships. The chloroplast genome of grasses possess 4 deletions, an inversion, and in insertion in the rpoC2 gene (Clegg, 1994). The lineages of angiosperms which can fix nitrogen are non immediately related in that there are many not-nitrogen fixing plants which are more than closely related to various members. All the same, these nitrogen-fixing groups (and their non-nitrogen fixing relatives) exercise form a clade based on chloroplast factor sequences suggesting that some preadaptations to nitrogen fixation evolved in the early members of this clade and various descendant lineages were able to take advantage of this mechanism to develop the power to ready nitrogen (Soltis, 1995).
The charge per unit of modify in chloroplast DNA changes between loci and between groups of found lineages (Gaut, 1993). Liverworts lack iii mitochondrial introns which are present in all other groups of land plants (including mosses and hornworts), suggesting that liverworts are the earliest land plants and that all other groups share a common ancestry after diverging from the liverwort lineage (Qiu, `1998). In plants, evolution in nuclear genes tends to occur faster than for chloroplast genes whose development is faster than constitute mitochondrial genes (Laroche, 1997). Trypanosomes are considered to be one of the earliest branches of the mitochondria-containing eukaryotes and their mitochondrial sequences back up this position (Gray, 1992). Kinetoplastid protozoa have the most divergent mitochondrial DNA including a chromosome composed of minicricles and a maxicircle (de la Cruz, 1984)
ADDITIONAL ENDOSYBIOTIC EVENTS
Secondary plastids are known in iii of the six major groups of eukaryotes: Rhizaria, Excavata and Chromalveolata. The groups Rhizaria and Excavata captured green algae which immune chlorarachniophytes and euglenids to perform photosynthesis, different other members of these groups. In the group Chromalveolata, a red alga was the source of the secondary plastid. These secondary endosymbioses involve a eukaryote inside a second eukaryote (Lane, 2008).
The remnants of the bequeathed nuclei are nevertheless present every bit nucleomorphs in the eukaryotic endosymbiots of the Cryptophyte and chlorarachniophyte plastids, originally derived from cerise and green algae. The malaria parasite Plasmodium falciparum also retains remnants of a plastid which may be derived from either green or red algae (Teich, 2007).
CENTRIOLES
Other organelles such as peroxisomes, glyoxysomes (plants), glycosomes (trypanosomes), and flagella have been considered for endosymbiotic origin but this has proved more difficult to test (Grayness, 1992). The phylum Archaeprotista includes some 28 families, all of which lack mitochondria and exist in anoxic environments. Most possess a karymastigont organization of organelles in which the flagellum (or related structures) are connected to the nucleus. It may be that the karymastigont is a remnant of the apparatus which start accommodated the structures of the two ancestral cells in the resulting chimeras. Microtubule-organizing centers and other structures may be remnants of the karymastigont (Margulis, 2000).
Some accept suggested that cilia and flagella were originally derived from spirochete leaner which colonized the surface of bequeathed eukaryotes. There have been some reports of Dna associated with basal bodies (at the base of flagella) which might support this. There was a report that greenish alga Chlamydomonas possesses a grouping of linked genes on a 6-9 megabase Deoxyribonucleic acid molecule associated with their basal bodies. Other studies suggested the same for several other protists. This chromosome was reported in the anterior terminate of the elongated nucleus and might contact the basal bodies directly. (Hall, 1995; Hall 1989). Other reports ended that the basal bodies of Chlamydomonas reinhardtii do not contain immunologically detectable Dna (Johnson, 1990; (Johnson, 1991).
In most cells, the centrioles (which are similar to basal bodies) are derived from existing centrioles which replicate. Such a process is reminiscent of the duplication of other endosymbiotic organelles and may support a symbiotic origin for centrioles and basal bodies. In that location are exceptions to this, however. Although most centriolar production occurs through replication of existing centrioles, there are examples of the synthesis of basal bodies de novo, as in meiosis in the fern Marsilea and the protist Naegleria . Mouse embryos lack centrioles until the blastocyst stage, apparently indicating that the nucleus is capable of synthesizing them. (Johnson, 1991; (Hall, 1995)
The unicellular green alga Ostreococcus tauri possesses the smallest eukaryotic genome and its lineage is thought to have diverged very early on in the history of photosynthetic eukaryotes. The genome is 12.56-Mb in size and has a loftier gene density (Derelle, 2006).
Source: http://bio.sunyorange.edu/updated2/GENETICS/10%20mitochondria.htm
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