|
Phospholipid Membrane
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 cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus, and 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 pumps. Biological bilayers are usually composed of amphiphilic phospholipids that hav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lipid Bilayer Section
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins Vitamin A, A, Vitamin D, D, Vitamin E, E and Vitamin K, K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing energy, lipid signaling, signaling, and acting as structural components of cell membranes. Lipids have applications in the Cosmetic industry, cosmetic and Food industry, food industries, and in nanotechnology. Lipids are broadly defined as Hydrophobe, hydrophobic or Amphiphile, amphiphilic small molecules; the amphiphilic nature of some lipids allows them to form structures such as vesicle (biology), 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": :wikt:ketoacyl, ketoacyl and isoprene groups. Using this approach, lipids may be divided into eight catego ... [...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] |
Egg (biology)
An egg is an organic vessel grown by an animal to carry a possibly fertilization, fertilized egg cell (a zygote) and to egg incubation, incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the animal hatches. Most arthropods, vertebrates (excluding live-bearing mammals), and Mollusca, mollusks lay eggs, although some, such as scorpions, do not. Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective eggshell, shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering. The largest recorded egg is from a whale shark and was in size. Whale shark eggs typically hatch within the m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fertilization
Fertilisation or fertilization (see American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or offspring. While processes such as insemination or pollination, which happen before the fusion of gametes, are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms, the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation. History In antiquity, Aristotle conceived the formation of new individuals through fusion of male and female fluids, with form and function emerging gradually, in a mode c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acrosome Reaction
For fertilization to happen between a sperm and egg cell, a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. While the fusion of the sperm cell with the egg cell's plasma membrane is relatively straightforward, penetrating the egg's protective layers, such as the zona pellucida, presents a significant challenge. Therefore, sperm cells go through a process known as the acrosome reaction, which is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The acrosome is a membrane-bound organelle of Golgi apparatus origin, commonly located at the tip of the head of the mature spermatozoon, which contains a variety of enzymes and antigens required for fertilization. It was once called "apical body" because of its location, or "perforatorium" on the assumption that it might assist the spermatozoon boring into the egg. As the sperm approaches the zona pellucida of the egg, which is necessary for initiating t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annular Lipid Shell
Annular lipids (also called shell lipids or boundary lipids) are a set of lipids or lipidic molecules which preferentially bind or stick to the surface of membrane proteins in biological cells. They constitute a layer, or an annulus/ shell, of lipids which are partially immobilized due to the existence of lipid-protein interactions. Polar headgroups of these lipids bind to the hydrophilic part of the membrane protein(s) at the inner and outer surfaces of lipid bilayer membrane. The hydrophobic surface of the membrane proteins is bound to the apposed lipid fatty acid chains of the membrane bilayer. For integral membrane proteins spanning the thickness of the membrane bilayer, these annular/shell lipids may act like a lubricating layer on the proteins' surfaces, thereby facilitating almost free rotation and lateral diffusion of membrane proteins within the 2-dimensional expanse of the biological membrane(s). Outside the layer of shell/annular lipids, lipids are not tied down to protei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Integral Membrane Protein
An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All transmembrane proteins can be classified as IMPs, but not all IMPs are transmembrane proteins. IMPs comprise a significant fraction of the proteins encoded in an organism's genome. Proteins that cross the membrane are surrounded by annular lipids, which are defined as lipids that are in direct contact with a membrane protein. Such proteins can only be separated from the membranes by using detergents, nonpolar solvents, or sometimes denaturing agents. Proteins that adhere only temporarily to cellular membranes are known as peripheral membrane proteins. These proteins can either associate with integral membrane proteins, or independently insert in the lipid bilayer in several ways. Structure Three-dimensional structures of ~160 different integral membrane proteins have been determined at atomic resolution by X-ray crystallography or nucle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cholesterol
Cholesterol is the principal sterol of all higher animals, distributed in body Tissue (biology), tissues, especially the brain and spinal cord, and in Animal fat, animal fats and oils. Cholesterol is biosynthesis, biosynthesized by all animal Cell (biology)#Eukaryotic cells, cells and is an essential structural and cholesterol signaling, signaling component of animal cell membranes. In vertebrates, hepatocyte, hepatic cells typically produce the greatest amounts. In the brain, astrocytes produce cholesterol and transport it to neurons. It is absent among prokaryotes (bacteria and archaea), although there are some exceptions, such as ''Mycoplasma'', which require cholesterol for growth. Cholesterol also serves as a Precursor (chemistry), precursor for the biosynthesis of steroid hormones, bile acid and vitamin D. Elevated levels of cholesterol in the blood, especially when bound to low-density lipoprotein (LDL, often referred to as "bad cholesterol"), may increase the risk of ... [...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] |
Fluids
In physics, a fluid is a liquid, gas, or other material that may continuously move and deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear force applied to them. Although the term ''fluid'' generally includes both the liquid and gas phases, its definition varies among branches of science. Definitions of ''solid'' vary as well, and depending on field, some substances can have both fluid and solid properties. Non-Newtonian fluids like Silly Putty appear to behave similar to a solid when a sudden force is applied. Substances with a very high viscosity such as pitch appear to behave like a solid (see pitch drop experiment) as well. In particle physics, the concept is extended to include fluidic matters other than liquids or gases. A fluid in medicine or biology refers to any liquid constituent of the body (body fluid), whereas "liquid" is not used in this sens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Transition
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic State of matter, states of matter: solid, liquid, and gas, and in rare cases, plasma (physics), plasma. A phase of a thermodynamic system and the states of matter have uniform physical property, physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point. Types of phase transition States of matter Phase transitions commonly refer to when a substance tran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase (matter)
In the physical sciences, a phase is a region of material that is chemically uniform, physically distinct, and (often) mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air is a third phase over the ice and water. The glass of the jar is a different material, in its own separate phase. (See .) More precisely, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetization and chemical composition. The term ''phase'' is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter (as where oil and water separate into distinct phases, both in the liquid state). Types of phases Distinct phases may be described as different states of matter such as gas, liquid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
