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Biological membrane
 
 
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A biological membrane or biomembrane is an enclosing or separating amphipathic layer that acts as a barrier within or around a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
. It is, almost invariably, a lipid bilayer
Lipid bilayer

A lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cell ....
, composed of a double layer of lipid
Lipid

Lipids are broadly defined as any fat-soluble , naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others....
-class molecules, specifically phospholipid
Phospholipid

File:Phospholipid.svgFile:phospholipid_structure.pngFile:Phosphatidyl-Choline.svgPhospholipids are a class of lipids and are a major component of all cell membranes....
s and cholesterol
Cholesterol

Cholesterol is a lipidic, waxy alcohol found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes where it is required to establish proper membrane permeability and membrane fluidity....
, with occasional proteins
Integral membrane protein

An Integral Membrane Protein is a protein molecule that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes Denaturation agents....
 intertwined, some of which function as channels
Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of all living cell s by allowing the flow of ions down their electrochemical gradient....
.

membranes typically define enclosed spaces or compartment
Compartment

In heraldry, a compartment is a design placed under the Shield , usually rocks, a grassy mount, or some sort of other landscape upon which the supporters are depicted as standing....
s in which cells may maintain a chemical
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 or biochemical
Biochemistry

Biochemistry is the study of the chemistry processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
 environment
Environment (biophysical)

The biophysical environment is the symbiosis between the physics environment and the biological life forms within the environment, and include all variables that comprise the Earth's biosphere....
 that differs from the outside.






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A biological membrane or biomembrane is an enclosing or separating amphipathic layer that acts as a barrier within or around a cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
. It is, almost invariably, a lipid bilayer
Lipid bilayer

A lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cell ....
, composed of a double layer of lipid
Lipid

Lipids are broadly defined as any fat-soluble , naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others....
-class molecules, specifically phospholipid
Phospholipid

File:Phospholipid.svgFile:phospholipid_structure.pngFile:Phosphatidyl-Choline.svgPhospholipids are a class of lipids and are a major component of all cell membranes....
s and cholesterol
Cholesterol

Cholesterol is a lipidic, waxy alcohol found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes where it is required to establish proper membrane permeability and membrane fluidity....
, with occasional proteins
Integral membrane protein

An Integral Membrane Protein is a protein molecule that is permanently attached to the biological membrane. Such proteins can be separated from the biological membranes only using detergents, nonpolar solvents, or sometimes Denaturation agents....
 intertwined, some of which function as channels
Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of all living cell s by allowing the flow of ions down their electrochemical gradient....
.

Function

Such membranes typically define enclosed spaces or compartment
Compartment

In heraldry, a compartment is a design placed under the Shield , usually rocks, a grassy mount, or some sort of other landscape upon which the supporters are depicted as standing....
s in which cells may maintain a chemical
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 or biochemical
Biochemistry

Biochemistry is the study of the chemistry processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
 environment
Environment (biophysical)

The biophysical environment is the symbiosis between the physics environment and the biological life forms within the environment, and include all variables that comprise the Earth's biosphere....
 that differs from the outside. For example, the membrane around peroxisome
Peroxisome

Peroxisomes are organelles from the Microbody family and are present in almost any eukaryote cell. They participate in the metabolism of fatty acids and many other metabolites....
s shields the rest of the cell from peroxide
Peroxide

A peroxide is a compound containing an oxygen-oxygen chemical bond. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately....
s, and the plasma membrane separates a cell from its surrounding medium. Most organelle
Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
s are defined by such membranes, and are called membrane-bound organelles.

Probably the most important feature of a biomembrane is that it is a selectively-permeable structure. This means that the size, charge
Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields....
, and other chemical properties of the atoms and molecules attempting to cross it will determine whether they succeed to do so. Selective permeability is essential for effective separation of a cell or organelle from its surroundings. Biological membranes also have certain mechanical or elastic properties
Elasticity of cell membranes

A cell membrane defines a boundary between the living cell and its environment. It consists of lipids, proteins,carbohydrates etc. Lipids and proteins are dominant components of membranes....
.

If a particle is too large or otherwise unable to cross the membrane by itself, but is still needed by a cell, it could either go through one of the protein channels or be taken in by means of endocytosis
Endocytosis

Endocytosis is the process by which cell s absorb material from outside the cell by engulfing it with their cell membrane. It is used by all cells of the body because most substances important to them are large Chemical polarity molecules that cannot pass through the hydrophobic plasma membrane or cell membrane....
.

Types of biological membranes

  • Cell membrane
    Cell membrane

    The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
  • Mucous membrane
    Mucous membrane

    The mucous membranes are linings of mostly germ layer origin, covered in epithelium, which are involved in absorption and secretion. They line various body cavities that are exposed to the external environment and internal organ ....
  • S-layer
    S-layer

    An S-layer is a part of the cell envelope commonly found in bacteria, as well as among archaea. It consists of a monomolecular layer composed of identical proteins or glycoproteins....


See also

  • Membrane lipids
    Membrane lipids

    The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol....
  • Endomembrane system
    Endomembrane system

    The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles....
     that divides the cell into organelles
  • Outer membrane
    Outer membrane

    The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane include a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's peptidoglycan by Braun's lipoprotein....
     or inner membrane
    Inner membrane

    The inner membrane is the biological membrane of an organelle or Gram-negative bacteria that is within an outer membrane.In eukaryotic cells, this inner membrane is present within the nuclear envelope, mitochondria and plastids like the chloroplast....
     of an organelle
  • Biofilm
    Biofilm

    A biofilm is a structured community of microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface....
  • Membrane protein
    Membrane protein

    A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. More than half of all proteins interact with membranes....
  • Osmosis
    Osmosis

    Osmosis is the diffusion of a solvent through a Semipermeable membrane, from a solution of low solute concentration to a solution with high solute concentration , up a solute concentration gradient....


External links

  • on biological membranes