Bacteria Bacteria ( Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology. Etymology Origin and early evolution Morphology Many bacterial species exist simply as single cells, others associate in characteristic patterns: Neisseria form diploids (pairs), Streptococcus form chains, and Staphylococcus group together in "bunch of grapes" clusters. Even more complex morphological changes are sometimes possible. Cellular structure Structure and contents of a typical gram-positive bacterial cell (seen by the fact that only one cell membrane is present). Intracellular structures The bacterial cell is surrounded by a cell membrane (also known as a lipid, cytoplasmic or plasma membrane). Many important biochemical reactions, such as energy generation, use concentration gradients across membranes. Extracellular structures Endospores Growth and reproduction
Cell nucleus HeLa cells stained for the cell nucleus DNA with the BlueHoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed. Because the nuclear membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions. History Between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. Structures Nuclear envelope and pores Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins. Nuclear lamina
Chromista Groups Chromista has been defined in different ways at different times. The name Chromista was first introduced by Cavalier-Smith in 1981; the earlier names Chromophyta, Chromobiota and Chromobionta correspond to roughly the same group. It has been described as consisting of three different groups: In 2010, Thomas Cavalier-Smith indicated his desire to move Alveolata, Rhizaria and Heliozoa into Chromista. Some examples of classification of the Chromista and related groups are shown below. Chromophycées (Chadefaud, 1950) The Chromophycées (Chadefaud, 1950), renamed Chromophycota (Chadefaud, 1960), included the current Ochrophyta (autotrophic Stramenopiles), Haptophyta (included in Chrysophyceae until Christensen, 1962), Cryptophyta, Dinophyta, Euglenophyceae and Choanoflagellida (included in Chrysophyceae until Hibberd, 1975). Chromophyta (Christensen 1962, 1989) Chromophyta (Bourrelly, 1968) Chromista (Cavalier-Smith, 1981) See also Cabozoa
Prokaryote Cell structure of a bacterium , one of the two domains of prokaryotic life. The division to prokaryotes and eukaryotes reflects two distinct levels of cellular organization rather than biological classification of species. Prokaryotes include two major classification domains: the bacteria and the archaea . [ edit ] Relationship to eukaryotes The division to prokaryotes and eukaryotes is usually considered the most important distinction among organisms. The genome in a prokaryote is held within a DNA / protein complex in the cytosol called the nucleoid , which lacks a nuclear envelope . [ 5 ] The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. Prokaryotes lack distinct mitochondria and chloroplasts . [ edit ] Sociality While prokaryotes are still commonly imagined to be strictly unicellular, most are capable of forming stable aggregate communities.
Eukaryote Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell (haploid cells). These act as sex cells (gametes – each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes) resulting from genetic recombination during meiosis. Cell features Eukaryotic cells are typically much larger than those of prokaryotes. Internal membrane Detail of the endomembrane system and its components A 3D rendering of an animal cell cut in half. The nucleus is surrounded by a double membrane (commonly referred to as a nuclear membrane or nuclear envelope), with pores that allow material to move in and out. Vesicles may be specialized for various purposes.
Six kingdoms Biofilm IUPAC definition Aggregate of microorganisms in which cells that are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS) adhere to each other and/or to a surface. Note 1: A biofilm is a fixed system that can be adapted internally to environmental conditions by its inhabitants. Note 2: The self-produced matrix of extracellular polymeric substance, which is also referred to as slime, is a polymeric conglomeration generally composed of extracellularbiopolymers in various structural forms. Microbes form a biofilm in response to many factors, which may include cellular recognition of specific or non-specific attachment sites on a surface, nutritional cues, or in some cases, by exposure of planktonic cells to sub-inhibitory concentrations of antibiotics. When a cell switches to the biofilm mode of growth, it undergoes a phenotypic shift in behavior in which large suites of genes are differentially regulated. Formation Development
Mitochondrion Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy History The first observations of intracellular structures that probably represent mitochondria were published in the 1840s. Richard Altmann, in 1894, established them as cell organelles and called them "bioblasts". The term "mitochondria" itself was coined by Carl Benda in 1898. Leonor Michaelis discovered that Janus green can be used as a supravital stain for mitochondria in 1900. In 1939, experiments using minced muscle cells demonstrated that one oxygen atom can form two adenosine triphosphate molecules, and, in 1941, the concept of phosphate bonds being a form of energy in cellular metabolism was developed by Fritz Albert Lipmann. The first high-resolution micrographs appeared in 1952, replacing the Janus Green stains as the preferred way of visualising the mitochondria. In 1967, it was discovered that mitochondria contained ribosomes. Structure
Archezoa Archaezoa is composed of two kingdoms of protists, Kingdom Diplomadida and Kingdom Parabasala. These 2 kingdoms are grouped together because they lack mitochondria. The Archaezoa hypothesis suggests that these two kingdoms originally had mitochondria, but lost them before mitochondria became symbionts of protists. De la diversité au sein des bactéries La diversité est une des clés de de la résistance bactérienne aux antibiotiques. Une étude de l’université de Washington précise un mécanisme dans les cellules bactériennes qui est une clé de cette diversité. Un nouveau mode de diversification Lorsqu’elle se divise, une bactérie peut donner naissance à deux cellules qui possèdent le même génome mais pour lesquelles le partage des organites cellulaires n'a pas été équitable. Ainsi une bactérie qui possède un flagelle va donner naissance à une cellule munie de cette structure et à une autre qui en est dénuée mais qui pourra en fabriquer un grâce à sa machinerie génétique. C'est un autre moyen pour les cellules de se diversifier. C-di-GMP. Un mécanisme impliqué dans les infections nosocomiales Des tests ont prouvé que chez le bacille pyocyanique (bactérie fortement pathogène et difficile à traiter), les cellules ayant des niveaux élevés de c-di-GMP ont tendance à rester immobiles et à adhérer aux surfaces pour former des colonies.
Evolution of cells The first cells The origin of cells was the most important step in the evolution of life on Earth. The birth of the cell marked the passage from pre-biotic chemistry to partitioned units resembling modern cells. If life is viewed from the point of view of replicator molecules, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. Partitioning may have begun from cell-like spheroids formed by proteinoids, which are observed by heating amino acids with phosphoric acid as a catalyst. Another possibility is that the shores of the ancient coastal waters may have served as a mammoth laboratory, aiding in the countless experiments necessary to bring about the first cell. Phospholipids are composed of a hydrophilic head on one end, and a hydrophobic tail on the other.  The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. Genetic code and the RNA world Quotes