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Unicellular Organism
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but some are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early organisms emerging 3.5–3.8 billion years ago. Although some prokaryotes live in colonies, they are not specialised cells with differing functions. These organisms live together, and each cell must carry out all life processes to survive. In contrast, even the simplest multicellular organisms have cells that depend on each other to survive. Most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reprodu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ventricaria Ventricosa
''Valonia'' (C. Agardh, 1823) is a genus of green algae in the Valoniaceae family. The genus ''Ventricaria'' is now regarded as a synonym of ''Valonia''. Taxonomy and nomenclature The genus ''Valonia'' belongs to the order Cladophorales and family Valoniaceae. It comprises several taxonomically acceptable species based from available data and literatures. Below is a list of common species of ''Valonia'' found throughout the tropics: *''Valonia fastigiata'' Harvey ex J. Agardh 1823 *''Valonia ventricosa'' J.Agardh 1887 *''Valonia utricularis'' (Roth) Agardh 1823 *''Valonia aegagropila'' C. Agardh 1823 *''Valonia macrophysa'' Kützing 1843 *''Valonia ovalis'' C.Agardh 1822 *''Valonia chlorocladus'' Hauck 1886 *''Valonia cespitula'' Zanardini ex Kützing *''Valonia pachynema'' (G. Martens) Børgesen *''Valonia barbadensis'' W.R.Taylor, 1969 *''Valonia nutrix'' (Kraft & A.J.K.Millar) Kraft, 2007 *''Valonia oblongata'' J.Agardh, 1887 *''Valonia trabeculata'' Egerod, 1952 Genera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multinucleate
Multinucleate cells (also known as multinucleated cells or polynuclear cells) are eukaryotic cells that have more than one nucleus, i.e., multiple nuclei share one common cytoplasm. Mitosis in multinucleate cells can occur either in a coordinated, synchronous manner where all nuclei divide simultaneously or asynchronously where individual nuclei divide independently in time and space. Certain organisms may have a multinuclear stage of their life cycle. For example, slime molds have a vegetative, multinucleate life stage called a plasmodium. Multinucleate cells, depending on the mechanism by which they are formed, can be divided into "syncytia" (formed by cell fusion) or " coenocytes" (formed by nuclear division not being followed by cytokinesis). Some bacteria, such as '' Mycoplasma pneumoniae'', a pathogen of the respiratory tract, may display multinuclear filaments as a result of a delay between genome replication and cellular division. Terminology Some biologists use ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lipid Bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes form a continuous barrier around all cell (biology), cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear envelope, nuclear membrane surrounding the cell nucleus, and biological membrane, membranes of the membrane-bound organelles in the cell. The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed and prevents them from diffusing into areas where they should not be. Lipid bilayers are ideally suited to this role, even though they are only a few nanometers in width, because they are impermeable to most water-soluble (hydrophilic) molecules. Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations and pH by transporting ions across their membranes using proteins called Ion transporter, ion pumps. Biological bilaye ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vesicle (biology And Chemistry)
In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion ( exocytosis), uptake (endocytosis), and the transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes (not to be confused with lysosomes). If there is only one phospholipid bilayer, the vesicles are called ''unilamellar liposomes''; otherwise they are called ''multilamellar liposomes''. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle. Vesicles perform a variety of functions. Because it is separated from the cytosol, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Micelle
A micelle () or micella () ( or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated colloidal system). A typical micelle in water forms an aggregate, with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle centre. This phase is caused by the packing behavior of single-tail lipids in a bilayer. The difficulty in filling the volume of the interior of a bilayer, while accommodating the area per head group forced on the molecule by the hydration of the lipid head group, leads to the formation of the micelle. This type of micelle is known as a normal-phase micelle (or oil-in-water micelle). Inverse micelles have the head groups at the centre with the tails extending out (or water-in-oil micelle). Micelles are approximately spherical in shape. Other shapes, such ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lipid
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. Lipids have applications in the cosmetic and food industries, and in nanotechnology. Lipids are broadly defined as hydrophobic or amphiphilic small molecules; the amphiphilic nature of some lipids allows them to form structures such as vesicles, multilamellar/ unilamellar liposomes, or membranes in an aqueous environment. Biological lipids originate entirely or in part from two distinct types of biochemical subunits or "building-blocks": ketoacyl and isoprene groups. Using this approach, lipids may be divided into eight categories: fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides (derived from condensatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amphiphile
In chemistry, an amphiphile (), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'', nonpolar) properties. Such a compound is called amphiphilic or amphipathic. Amphiphilic compounds include surfactants and detergents. The phospholipid amphiphiles are the major structural component of cell membranes. Amphiphiles are the basis for a number of areas of research in chemistry and biochemistry, notably that of lipid polymorphism. Organic compounds containing hydrophilic groups at both ends of the molecule are called bolaamphiphilic. The micelles they form in the aggregate are prolate. Structure The lipophilic group is typically a large hydrocarbon moiety, such as a long chain of the form CH3(CH2)n, with n > 4. The hydrophilic group falls into one of the following categories: # charged groups #* anionic. Examples, with the lipophilic part of the molecule represented by ''R'', are: #** carboxylates: RCO2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ribocells
The first universal common ancestor (FUCA) is thought to be a non-cellular entity that was the earliest organism with a genetic code capable of biological translation of RNA molecules into peptides to produce proteins. Its descendants would include the last universal common ancestor (LUCA) and every modern cell. FUCA would also be the ancestor of ancient sister lineages of LUCA, none of which have modern descendants, but which are thought to have horizontally transferred some of their genes into the genome of early descendants of LUCA. FUCA is thought to have been composed of progenotes, proposed ancient biological systems that would have used RNA for their genome and self-replication. By comparison, LUCA would have had a complex metabolism and a DNA genome with hundreds of genes and gene families. Origins Long before the appearance of compartmentalized biological entities like FUCA, life had already begun to organize itself and emerge in a hypothesized pre-cellular era ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ribozyme
Ribozymes (ribonucleic acid enzymes) are RNA molecules that have the ability to Catalysis, catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demonstrated that RNA can be both genetic material (like DNA) and a biological catalyst (like protein enzymes), and contributed to the RNA world hypothesis, which suggests that RNA may have been important in the evolution of prebiotic self-replicating systems. The most common activities of natural or Directed evolution, ''in vitro'' evolved ribozymes are the cleavage (or Ligation (molecular biology), ligation) of RNA and DNA and peptide bond formation. For example, the smallest ribozyme known (GUGGC-3') can aminoacylate a GCCU-3' sequence in the presence of PheAMP. Within the ribosome, ribozymes function as part of the large subunit ribosomal RNA to link amino acids during Translation (biology), protein synthesis. They also participate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RNA World
The RNA world is a hypothetical stage in the evolutionary history of life on Earth in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage. Alexander Rich first proposed the concept of the RNA world in 1962, and Walter Gilbert coined the term in 1986. Among the characteristics of RNA that suggest its original prominence are that: * Like DNA, RNA can store and replicate genetic information. Although RNA is considerably more fragile than DNA, some ancient RNAs may have evolved the ability to methylate other RNAs to protect them. The concurrent formation of all four RNA building blocks further strengthens the hypothesis. * Enzymes made of RNA ( ribozymes) can catalyze (start or accelerate) chemical reactions that are critical for life, so it is conceivable that in an RNA world, ribozymes might have preceded enzymes made of protein. * Many coenzymes that have ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Origin Of Life
Abiogenesis is the natural process by which life arises from abiotic component, non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to organism, living entities on Earth was not a single event, but a process of increasing complexity involving the formation of a planetary habitability, habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. The transition from non-life to life has never been observed experimentally, but many proposals have been made for different stages of the process. The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. It primarily uses tools from biology and chemistry, with more recent approaches attempting a synthesis of many sciences. Life functions through the specialized ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protocell
A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a rudimentary precursor to cells during the origin of life. A central question in evolution is how simple protocells first arose and how their progeny could diversify, thus enabling the accumulation of novel biological emergences over time (i.e. biological evolution). Although a functional protocell has not yet been achieved in a laboratory setting, the goal to understand the process appears well within reach. A protocell is a pre-cell in abiogenesis, and was a contained system consisting of simple biologically relevant molecules like ribozymes, and encapsulated in a simple membrane structure – isolating the entity from the environment and other individuals – thought to consist of simple fatty acids, mineral structures, or rock-pore structures. Overview Compartmentalization was important in the origin of life. Membranes form enclosed compartments that are sepa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
