Endosymbiosis

When life arose on Earth about 4 billion years ago, the first types of cells to evolve were prokaryotic cells. For approximately 2 billion years, prokaryotic-type cells were the only form of life on Earth. The oldest known sedimentary rocks found in Greenland are about 3.8 billion years old. The oldest known fossils are prokaryotic cells, 3.5 billion years in age, found in Western Australia and South Africa. The nature of these fossils, and the chemical composition of the rocks in which they are found, indicates that these first cells made use of simple chemical reactions to produce energy for their metabolism and growth. Eukaryotic cells evolved into being between 1.5 and 2 billion years ago. Eukaryotic cells appear to have arisen from prokaryotic cells, specifically out of the archaea. Indeed, there are many similarities in molecular biology of contemporary archaea and eukaryotes. However, the origin of the eukaryotic organelles, specifically chloroplasts and mitochondria, is explained by evolutionary associations between primitive nucleated cells and certain respiratory and photosynthetic bacteria, which led to the development of these organelles and the associated explosion of eukaryotic diversity. Today Prokaryotes

Cytoplasm of eukaryotic cell is partitioned by organelle membranes. Organelles together form the endomembrane system.

According to Margulis, the pre-eukaryotic cell engulfed an aerobic bacterium, but rather than digest and kill the bacterium, a symbiotic relationship was born. This relationship, the aerobic bacterium provided energy through ATP and the eukaryotic cell provided an environment to live while protecting the new symbiont from harm in environmental factors such as oxygen. Because almost all living eukaryotes have a mitochondria, it is safe to assume that this event happened before plants and animals split in the evolutionary lineage.After this first evolutionary leap came a

Endosymbiosis is the theory that eukaryotic cells were formed when a prokaryotic cell ingested some aerobic bacteria. The first step of the evolution of a eukaryotic cell is the infolding of the cellular membrane. This process takes place when the plasma membrane folds inwards and develops an envelope around a smaller prokaryotic cell. Once the smaller cell is engulfed, it becomes dependent upon its host cell. It relies on the host cell for organic molecules and inorganic compounds. However, the host cell also benefits because it has an increased output of ATP for cellular activities and becomes more productive. This ATP comes from the mitochondrion (the aerobe) that is engulfed.

Mitochondria are small organelles found in eukaryotic cells which respire aerobically. They are responsible for generating energy from food to ‘power the cell’. They contain their own DNA, reproducing by dividing in 2. As they closely resemble bacteria, it gave the idea that they were derived from bacteria (which were engulfed by ancestors of the eukaryotes we know today). This idea has since been confirmed from further investigations, and it is now widely accepted. (Alberts et al., 2010a)

7. The theory of endosymbiosis says that mitochondria and plastids used to be small prokaryotes living within larger cells. The prokaryotic ancestors of mitochondria and plastids were bacteria engulfed by a larger cell. Because they both benefited from this situation, the bacteria living inside the cell was passed down from generation to generation. The evidence is that mitochondria reproduce and move independently within the cell.

The cells of a eukaryote are different from any other cells because they do not have cell walls, and have organelles. An example of an organelle is the nucleus. Mitochondria are the energy providers for cells. A symbiotic relationship is when to organisms benefit from living together. When one organism lives inside the other, it is known as endosymbiosis. Chloroplasts trap sunlight and make photosynthesis possible. Once two organisms live together for a while, they loose their ability to live

Prokaryotes are ubiquitous, successfully adapting to diverse environments as well as developing symbiotic relationships with host organisms (Lengeler, Drews, & Schlegel, 1999). Prokaryotes may have both autotrophic and heterotrophic characteristics. A cyanobacteria is photosynthetic, commonly called blue-green algae, and may produce toxins (Crayton, 1993). Bacteria are most commonly associated in the general

Chloroplasts are important photosynthetic organelles that present in plant cells. It is believed that chloroplasts evolve from an endosymbiotic event; engulfment of a photosynthetic cyanobacterium by a large heterotrophic host cell (1, 2). During this process proteins in the cyanobacterium has been transferred to the nucleus and also the proteins that are essential for organelle biogenesis has been transferred to the cyanobacterium making it dependent on the host. Although chloroplast proteins have estimated to consist of 3500-4000 different types of polypeptides, the protein coding capacity in chloroplast genes is approximately 200 polypeptides (3, 4). This data further suggest that most of the proteins found in chloroplast are encode by nuclear genome and transport to the chloroplast. At least, a few proteins are use secretory pathway in which first targeted to the endoplasmic reticulum and then transfer to the chloroplast through vesicles (5-7).

The Endosymbiotic theory is an assumption based on experience and/or limited information about the evolution of the cell. Bacteria are one of the oldest single cellular organisms. They began to make their own food using photosynthesis which then produced enough oxygen to reshape Earth 's atmosphere. This change brought upon diverse bacterial life which include clear evidence that chloroplasts and mitochondria were, at one point, crude bacterial cells. Over the years, chloroplasts and mitochondria became dependent on a host cell. After millions of years of evolution, chloroplasts and mitochondria cannot survive outside of the cell. This is the Endosymbiotic theory. Although this is labeled a theory, there is striking evidence that shows similarities in both bacteria, and mitochondria and chloroplasts. They all have their own DNA (separate from the nucleus), and they both use this DNA to produce proteins and enzymes for their functions.

Passing the cell membrane we find that, eukaryotes have a complex cytoskeleton. Their cytoskeleton consists of a complex network of elements called microtubules and actin filaments. The cytoskeleton not only anchors the cell, but it also aids in movement. Another aid of movement is cilia. Cilia are shorter than flagella and are more numerous. This movement of the cell helps to propel substances across the surface. This movement mechanism is only found in eukaryotes. Prokaryotes do not have cilia, they only have flagella. Flagella also vary from prokaryotes to eukaryotes. Prokaryotes have flagella that are made from flagellin, whereas eukaryotes have flagella that are made from microtubules. They are similar in structure, but differ in the proteins that are used to make them. Moving inside the cell we find ribosomes which both prokaryotes and eukaryotes have. They are similar in function, synthesis organelle and ribosomal RNA sequencing, but not in density. Prokaryotes have a 70S ribosome and eukaryotes have a 80s ribosome. Speaking of proteins, eukaryotes have histones. Histones are proteins that help organize the DNA and order it into

As we all know there are many theories for the evolution of eukaryotic from prokaryotic, but how the prokaryotics came in existence or the beginning of the evolutionary process from one single cell to a complex structure, no one knows for sure, there are only theories for now. Both evolutionists and creationists use evidence to support their theories, but it is difficult to come up with proofs. No one was present as observer when life began, or when the life transformed from single cell prokaryotics to multi cellular eukaryotics neither model of origins can be reproduced in laboratory experiments.

The term ‘eukaryote’ encompasses most of the visible species on the planet. A eukaryotic cell is one who's genetic material and organelles are bound by membranes, as opposed to a prokaryote who’s nucleoid and organelles are not membrane bound and sit within the cell membrane in the protoplasm - this grouping is considered the most fundamental classifications of organisms.

Before eukaryotic cells contained organelles and worked symbiotically as one, life consisted of free-living bacteria. Organelles, such as chloroplasts and mitochondria, that are currently found in eukaryotic cells are theorized to have been separate bacteria before the evolutionary success of the eukaryotic cell. Such idea is proven through the endosymbiotic theory. This concept provides an evolutionary origin for the mitochondrion and chloroplast seen in organisms of today. This theory is held together by DNA evidence found within the organelles themselves. The mitochondrion alone contain its own genome enclosed in the form of circular DNA, as well as their own ribosomes and transfer RNA. Similarly, the chloroplasts have their own genome. When compared to their bacterial ancestors, these DNA sequences resemble that of the respective organelles. The DNA sequences of these genes provide clear evidence to the evolutionary success of the eukaryotic cell.

Eukaryotes come in two grades of organization: single-celled (protists) and multicellular (plants, animals, and fungi). The world today is full of complex multicellular plants and animals: how, why, and when did they evolve from protists?