A report on Cell membrane and Lipid bilayer

Illustration of a Eukaryotic cell membrane
This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine.
Comparison of Eukaryotes vs. Prokaryotes
The three main structures phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer.
Examples of the major membrane phospholipids and glycolipids: phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer).
Schematic cross sectional profile of a typical lipid bilayer. There are three distinct regions: the fully hydrated headgroups, the fully dehydrated alkane core and a short intermediate region with partial hydration. Although the head groups are neutral, they have significant dipole moments that influence the molecular arrangement.
A detailed diagram of the cell membrane
TEM image of a bacterium. The furry appearance on the outside is due to a coat of long-chain sugars attached to the cell membrane. This coating helps trap water to prevent the bacterium from becoming dehydrated.
Illustration depicting cellular diffusion
Diagram showing the effect of unsaturated lipids on a bilayer. The lipids with an unsaturated tail (blue) disrupt the packing of those with only saturated tails (black). The resulting bilayer has more free space and is, as a consequence, more permeable to water and other small molecules.
Diagram of the arrangement of amphipathic lipid molecules to form a lipid bilayer. The yellow polar head groups separate the grey hydrophobic tails from the aqueous cytosolic and extracellular environments.
Illustration of a GPCR signaling protein. In response to a molecule such as a hormone binding to the exterior domain (blue) the GPCR changes shape and catalyzes a chemical reaction on the interior domain (red). The gray feature is the surrounding bilayer.
Alpha intercalated cell
Transmission Electron Microscope (TEM) image of a lipid vesicle. The two dark bands around the edge are the two leaflets of the bilayer. Historically, similar images confirmed that the cell membrane is a bilayer
Diagram of the Cell Membrane's structures.
Human red blood cells viewed through a fluorescence microscope. The cell membrane has been stained with a fluorescent dye. Scale bar is 20μm.
3d-Adapted AFM images showing formation of transmembrane pores (holes) in supported lipid bilayer
Illustration of a typical AFM scan of a supported lipid bilayer. The pits are defects in the bilayer, exposing the smooth surface of the substrate underneath.
Structure of a potassium ion channel. The alpha helices penetrate the bilayer (boundaries indicated by red and blue lines), opening a hole through which potassium ions can flow
Schematic illustration of pinocytosis, a type of endocytosis
Exocytosis of outer membrane vesicles (MV) liberated from inflated periplasmic pockets (p) on surface of human Salmonella 3,10:r:- pathogens docking on plasma membrane of macrophage cells (M) in chicken ileum, for host-pathogen signaling in vivo.
Schematic showing two possible conformations of the lipids at the edge of a pore. In the top image the lipids have not rearranged, so the pore wall is hydrophobic. In the bottom image some of the lipid heads have bent over, so the pore wall is hydrophilic.
Illustration of lipid vesicles fusing showing two possible outcomes: hemifusion and full fusion. In hemifusion, only the outer bilayer leaflets mix. In full fusion both leaflets as well as the internal contents mix.
Schematic illustration of the process of fusion through stalk formation.
Diagram of the action of SNARE proteins docking a vesicle for exocytosis. Complementary versions of the protein on the vesicle and the target membrane bind and wrap around each other, drawing the two bilayers close together in the process.

The cell membrane consists of a lipid bilayer, made up of two layers of phospholipids with cholesterols (a lipid component) interspersed between them, maintaining appropriate membrane fluidity at various temperatures.

- Cell membrane

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.

- Lipid bilayer
Illustration of a Eukaryotic cell membrane

16 related topics with Alpha

Overall
An example of an ATP-dependent flippase in the ABC transporter family, isolated from C. jejuni. The two polypeptide chains in the homodimer structure are shown in red and blue. The extracellular surface is oriented at the top of the image and the ATP-binding domains are located at the bottom, on the cytosolic side.

Flippase

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An example of an ATP-dependent flippase in the ABC transporter family, isolated from C. jejuni. The two polypeptide chains in the homodimer structure are shown in red and blue. The extracellular surface is oriented at the top of the image and the ATP-binding domains are located at the bottom, on the cytosolic side.

Flippases (rarely spelled flipases) are transmembrane lipid transporter proteins located in the membrane which belong to ABC transporter or P4-type ATPase families.

The possibility of active maintenance of an asymmetric distribution of molecules in the phospholipid bilayer was predicted in the early 1970s by Mark Bretscher.

Crystal structure of Potassium channel Kv1.2/2.1 Chimera. Calculated hydrocarbon boundaries of the lipid bilayer are indicated by red and blue lines.

Membrane protein

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Membrane proteins are common proteins that are part of, or interact with, biological membranes.

Membrane proteins are common proteins that are part of, or interact with, biological membranes.

Crystal structure of Potassium channel Kv1.2/2.1 Chimera. Calculated hydrocarbon boundaries of the lipid bilayer are indicated by red and blue lines.
Schematic representation of transmembrane proteins: 1. a single transmembrane α-helix (bitopic membrane protein) 2. a polytopic transmembrane α-helical protein 3. a polytopic transmembrane β-sheet protein The membrane is represented in light-brown.
Schematic representation of the different types of interaction between monotopic membrane proteins and the cell membrane: 1. interaction by an amphipathic α-helix parallel to the membrane plane (in-plane membrane helix) 2. interaction by a hydrophobic loop 3. interaction by a covalently bound membrane lipid (lipidation) 4. electrostatic or ionic interactions with membrane lipids (e.g. through a calcium ion)

Integral membrane proteins are a permanent part of a cell membrane and can either penetrate the membrane (transmembrane) or associate with one or the other side of a membrane (integral monotopic).

Peripheral membrane proteins are temporarily attached either to the lipid bilayer or to integral proteins by a combination of hydrophobic, electrostatic, and other non-covalent interactions.

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Phospholipid scramblase

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Scramblase is a protein responsible for the translocation of phospholipids between the two monolayers of a lipid bilayer of a cell membrane.

Scheme of a liposome formed by phospholipids in an aqueous solution.

Liposome

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Scheme of a liposome formed by phospholipids in an aqueous solution.
Liposomes are composite structures made of phospholipids and may contain small amounts of other molecules. Though liposomes can vary in size from low micrometer range to tens of micrometers, unilamellar liposomes, as pictured here, are typically in the lower size range with various targeting ligands attached to their surface allowing for their surface-attachment and accumulation in pathological areas for treatment of disease.
A micrograph of phosphatidylcholine liposomes, which were stained with fluorochrome acridine orange. Method of fluorescence microscopy (1250-fold magnification).
Various types of phosphatidylcholine liposomes in suspension. Method of phase-contrast microscopy (1000-fold magnification). The following types of liposomes are visible: small monolamellar vesicles, large monolamellar vesicles, multilamellar vesicles, oligolamellar vesicles.
Pictorial representation of targeted theranostics liposomal delivery

A liposome is a spherical vesicle having at least one lipid bilayer.

The resemblance to the plasmalemma was obvious, and the microscope pictures served as the first evidence for the cell membrane being a bilayer lipid structure.

Schematic diagram of an ion channel. 1 - channel domains (typically four per channel), 2 - outer vestibule, 3 - selectivity filter, 4 - diameter of selectivity filter, 5 - phosphorylation site, 6 - cell membrane.

Ion channel

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Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore.

Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore.

Schematic diagram of an ion channel. 1 - channel domains (typically four per channel), 2 - outer vestibule, 3 - selectivity filter, 4 - diameter of selectivity filter, 5 - phosphorylation site, 6 - cell membrane.
Selectivity filter allowing only potassium ions through the potassium channel (PDB: 1K4C).
Birth of an Idea (2007) by Julian Voss-Andreae. The sculpture was commissioned by Roderick MacKinnon based on the molecule's atomic coordinates that were determined by MacKinnon's group in 2001.

Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane, controlling the flow of ions across secretory and epithelial cells, and regulating cell volume.

Such "multi-subunit" assemblies usually involve a circular arrangement of identical or homologous proteins closely packed around a water-filled pore through the plane of the membrane or lipid bilayer.

Diagram of lipid vesicles showing a solution of biomolecules (green dots) trapped in the vesicle interior.

Artificial cell

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Engineered particle that mimics one or many functions of a biological cell.

Engineered particle that mimics one or many functions of a biological cell.

Diagram of lipid vesicles showing a solution of biomolecules (green dots) trapped in the vesicle interior.
Standard artificial cell (top) and drug delivery artificial cell (bottom).
Representative types of artificial cell membranes.
Schematic representation of encapsulated cells within artificial membrane.

Phospholipid membranes are an obvious choice as compartmentalizing boundaries, as they act as selective barriers in all living biological cells.

Although not completely artificial because the cytoplasmic components as well as the membrane from the host cell are kept, the engineered cell is under control of a synthetic genome and is able to replicate.