Origins of eukaryotic cells
Chromosomes, each consisting of a linear DNA molecule coiled around basic alkaline proteins called histones. This is a group of reduced diversity.
The cytoplasmic genomes of organelles are at the crossroads of various selective forces, some of which favour their regression such as the need for co-expression of certain genesothers favour the persistence of certain genes in the organelle genome.
Explaining this apparent leap in complexity at the origin of eukaryotes is one of the principal challenges of evolutionary biology.
A theory on the origins of eukaryotic cells mitochondria and chloroplasts worksheet answers
They have chloroplasts called cyanelles that are blue-green in colour, due to the presence of phycocyanins and allophycocyanins in phycobilisomes. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Cryptophytes occur in many environments, particularly aquatic ones oceanic environments, fresh waters, wetland pore waters. Eukaryotic DNA is divided into several linear bundles called chromosomes , which are separated by a microtubular spindle during nuclear division. This question can be addressed in very different ways, depending on whether one considers palaeontological evidence, energy aspects, the origin of the characteristics of the eukaryotic cell or the relationships of the different prokaryotic and eukaryotic lines with respect to each other . This is the case for chloroplasts in terrestrial plants, but also for red and green algae that are close to them [11 ,12]. This conclusion is supported by reconstructions from comparative genomics of the ancestral composition of the key functional systems of the LECA, such as the nuclear pore [ 28 , 69 ], the spliceosome [ 29 ], the RNA interference machinery [ 70 ], the proteasome and the ubiquitin signaling system [ 71 ], and the endomembrane apparatus [ 10 ]. Therefore, although these organelles are highly integrated into the eukaryotic cell, they still reproduce as if they are independent organisms within the cell. The integration of the bacteria will follow and this transition is accompanied on one hand by gene transfer between the two organisms c and on the other hand by the establishment of the nucleus e-h. Fungi and many protists have some substantial differences, however.
But it really isn't very good evidence - it is questionable on two counts. Dring suggested that the eukaryotic cell's nucleus came from the ability of Gram-positive bacteria to form endospores. Endosymbioses found new evolutionary lines.
At the same time, they have acquired the ability to carry out photosynthesis, which is the origin of chloroplast, thus giving them an autotrophic metabolism.
The process of secondary endosymbiosis is not unique to chlorarachniophytes. Given that the current estimate for the gene complement of LECA must be conservative, the genome of LECA is likely to have been as complex as those of typical extant free-living unicellular eukaryotes [ 68 ].
Mitosis: A process of nuclear division in which replicated chromosomes are divided and separated using elements of the cytoskeleton.
Such events may explain the major evolutionary leaps whose evolution seems to be punctuated, which have given rise to the great lines of life and shaped current biological diversity. Similarly, they have the same protein synthesis machinery free 70S ribosomesA huge complex composed of RNAs and ribosomal proteins that allows the translation of mRNAs into proteins.
based on 28 review