A report on Cholesterol and Lipid bilayer

Substrate presentation; PLD (blue oval) is sequestered into cholesterol-dependent lipid domains (green lipids) by palmitoylation. PLD also binds PIP2(red hexagon) domains (grey shading) located in the disordered region of the cell with phosphatidylcholine (PC). When cholesterol decreases or PIP2 increases in the cell, PLD translocates to PIP2 where it is exposed to and hydrolizes PC to phosphatidic acid (red spherical lipid).

This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine.

The three main structures phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer.

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.

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.

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.

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

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.

Lipid logistics: transport of triglycerides and cholesterol in organisms in form of lipoproteins as chylomicrons, VLDL, LDL, IDL, HDL.

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.

Cholesterolemia and mortality for men and women 60 years

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.

Reference ranges for blood tests, showing usual, as well as optimal, levels of HDL, LDL, and total cholesterol in mass and molar concentrations, is found in orange color at right, that is, among the blood constituents with the highest concentration.

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.

Steroidogenesis, using cholesterol as building material

Space-filling model of the Cholesterol molecule

A particularly important example in animal cells is cholesterol, which helps strengthen the bilayer and decrease its permeability.

- Lipid bilayer

The hydroxyl group of each cholesterol molecule interacts with water molecules surrounding the membrane, as do the polar heads of the membrane phospholipids and sphingolipids, while the bulky steroid and the hydrocarbon chain are embedded in the membrane, alongside the nonpolar fatty-acid chain of the other lipids.

- Cholesterol

5 related topics with Alpha

Cell membrane

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Biological membrane that separates the interior of all cells from the outside environment (the extracellular space) and protects the cell from its environment.

Comparison of Eukaryotes vs. Prokaryotes

Examples of the major membrane phospholipids and glycolipids: phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer).

Illustration depicting cellular diffusion

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.

Diagram of the Cell Membrane's structures.

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.

Lipid

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Biomolecule that is soluble in nonpolar solvents.

I2 - Prostacyclin (an example of a prostaglandin, an eicosanoid fatty acid)

LTB4 (an example of a leukotriene, an eicosanoid fatty acid)

Example of an unsaturated fat triglyceride (C55H98O6). Left part: glycerol; right part, from top to bottom: palmitic acid, oleic acid, alpha-linolenic acid.

Structure of the saccharolipid Kdo2-lipid A. Glucosamine residues in blue, Kdo residues in red, acyl chains in black and phosphate groups in green.

Self-organization of phospholipids: a spherical liposome, a micelle, and a lipid bilayer.

Lipids also encompass molecules such as fatty acids and their derivatives (including tri-, di-, monoglycerides, and phospholipids), as well as other sterol-containing metabolites such as cholesterol.

Glycerophospholipids, usually referred to as phospholipids (though sphingomyelins are also classified as phospholipids), are ubiquitous in nature and are key components of the lipid bilayer of cells, as well as being involved in metabolism and cell signaling.

Endoplasmic reticulum

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The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding.

1 Nucleus
2 Nuclear pore
3 Rough endoplasmic reticulum (RER)
4 Smooth endoplasmic reticulum (SER)
5 Ribosome on the rough ER
6 Proteins that are transported
7 Transport vesicle
8 Golgi apparatus
9 Cis face of the Golgi apparatus
10 Trans face of the Golgi apparatus
11 Cisternae of the Golgi apparatus

A 2-minute animation showing how a protein destined for the secretory pathway is synthesized into the rough endoplasmic reticulum, which appears at the upper right approximately halfway through the animation.

Electron micrograph showing smooth ER (arrow) in mouse tissue, at 110,510× magnification.

Skeletal muscle fiber, with sarcoplasmic reticulum colored in blue.

Ca2+-antagonized transport into the endoplasmic reticulum (CaATiER) model

The two types of ER share many of the same proteins and engage in certain common activities such as the synthesis of certain lipids and cholesterol.

The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol.

Phospholipids, such as this glycerophospholipid, have amphipathic character.

Amphiphile

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Chemical compound possessing both hydrophilic (water-loving, polar) and lipophilic (fat-loving) properties.

Cross-section view of the structures that can be formed by biological amphiphiles in aqueous solutions. Unlike this illustration, micelles are usually formed by non-biological, single-chain, amphiphiles, soaps or detergents, since it is difficult to fit two chains into this shape.

The lipid bilayer, the material that makes up cell membranes.

They arrange themselves into lipid bilayers, by forming a sheet composed of two layers of lipids.

Although phospholipids are the principal constituents of biological membranes, there are other constituents, such as cholesterol and glycolipids, which are also included in these structures and give them different physical and biological properties.

Biosynthesis

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Multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms.

Uridine monophosphate (UMP) biosynthesis

'Thymidylate synthase reaction: dUMP + 5,10-methylenetetrahydrofolate ⇔ dTMP + dihydrofolate

Ctp synthase mechanism: UTP + ATP + glutamine ⇔ CTP + ADP + glutamate

As DNA polymerase moves in a 3' to 5' direction along the template strand, it synthesizes a new strand in the 5' to 3' direction

Glutamine oxoglutarate aminotransferase and glutamine synthetase

The diaminopimelic acid lysine biosynthetic pathway

The tRNA anticodon interacts with the mRNA codon in order to bind an amino acid to growing polypeptide chain.

Familial hypercholesterolemia causes cholesterol deposits

Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides.

3) Simple compounds that join to create a macromolecule. For example, fatty acids join to form phospholipids. In turn, phospholipids and cholesterol interact noncovalently in order to form the lipid bilayer. This reaction may be depicted as follows: