Micrograph of rough endoplasmic reticulum network around the nucleus (shown in the lower right-hand area of the picture). Dark small circles in the network are mitochondria.
This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine.
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
The three main structures phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer.
3D rendering of endoplasmic reticulum
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 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.
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.
Electron micrograph showing smooth ER (arrow) in mouse tissue, at 110,510× magnification.
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.
Skeletal muscle fiber, with sarcoplasmic reticulum colored in blue.
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.
Ca2+-antagonized transport into the endoplasmic reticulum (CaATiER) model
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.
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 phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol.

- Endoplasmic reticulum

In contrast, eukaryotes have a range of organelles including the nucleus, mitochondria, lysosomes and endoplasmic reticulum.

- Lipid bilayer
Micrograph of rough endoplasmic reticulum network around the nucleus (shown in the lower right-hand area of the picture). Dark small circles in the network are mitochondria.

8 related topics with Alpha

Overall

Eukaryote

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Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

The endomembrane system and its components
Simplified structure of a mitochondrion
Longitudinal section through the flagellum of Chlamydomonas reinhardtii
Structure of a typical animal cell
Structure of a typical plant cell
Fungal Hyphae cells: 1 – hyphal wall, 2 – septum, 3 – mitochondrion, 4 – vacuole, 5 – ergosterol crystal, 6 – ribosome, 7 – nucleus, 8 – endoplasmic reticulum, 9 – lipid body, 10 – plasma membrane, 11 – spitzenkörper, 12 – Golgi apparatus
This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation.
Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes
One hypothesis of eukaryotic relationships – the Opisthokonta group includes both animals (Metazoa) and fungi, plants (Plantae) are placed in Archaeplastida.
A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups
The three-domains tree and the Eocyte hypothesis
Phylogenetic tree showing a possible relationship between the eukaryotes and other forms of life; eukaryotes are colored red, archaea green and bacteria blue
Eocyte tree.
Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex.

Various tube- and sheet-like extensions of the nuclear membrane form the endoplasmic reticulum, which is involved in protein transport and maturation.

They have two surrounding membranes, each a phospholipid bi-layer; the inner of which is folded into invaginations called cristae where aerobic respiration takes place.

Onion (Allium cepa) root cells in different phases of the cell cycle (drawn by E. B. Wilson, 1900)

Cell (biology)

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Basic structural and functional unit of life forms.

Basic structural and functional unit of life forms.

Onion (Allium cepa) root cells in different phases of the cell cycle (drawn by E. B. Wilson, 1900)
Structure of a typical prokaryotic cell
Structure of a typical animal cell
Structure of a typical plant cell
Detailed diagram of lipid bilayer of cell membrane
A fluorescent image of an endothelial cell. Nuclei are stained blue, mitochondria are stained red, and microfilaments are stained green.
Deoxyribonucleic acid (DNA)
Human cancer cells, specifically HeLa cells, with DNA stained blue. The central and rightmost cell are in interphase, so their DNA is diffuse and the entire nuclei are labelled. The cell on the left is going through mitosis and its chromosomes have condensed.
Diagram of the endomembrane system
Prokaryotes divide by binary fission, while eukaryotes divide by mitosis or meiosis.
An outline of the catabolism of proteins, carbohydrates and fats
An overview of protein synthesis.
Within the nucleus of the cell (light blue), genes (DNA, dark blue) are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA (red) that is then transported out of the nucleus and into the cytoplasm (peach), where it undergoes translation into a protein. mRNA is translated by ribosomes (purple) that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.
Staining of a Caenorhabditis elegans highlights the nuclei of its cells.
Stromatolites are left behind by cyanobacteria, also called blue-green algae. They are the oldest known fossils of life on Earth. This one-billion-year-old fossil is from Glacier National Park in the United States.
Robert Hooke's drawing of cells in cork, 1665

This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids, which are amphiphilic (partly hydrophobic and partly hydrophilic).

Endoplasmic reticulum: The endoplasmic reticulum (ER) is a transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface that secrete proteins into the ER, and the smooth ER, which lacks ribosomes. The smooth ER plays a role in calcium sequestration and release and also helps in synthesis of lipid.

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.

Organelle

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Organelle is a specialized subunit, usually within a cell, that has a specific function.

Organelle is a specialized subunit, usually within a cell, that has a specific function.

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.
Structure of Candidatus Brocadia anammoxidans, showing an anammoxosome and intracytoplasmic membrane

Organelles are either separately enclosed within their own lipid bilayers (also called membrane-bound organelles) or are spatially distinct functional units without a surrounding lipid bilayer (non-membrane bound organelles).

They include structures that make up the endomembrane system (such as the nuclear envelope, endoplasmic reticulum, and Golgi apparatus), and other structures such as mitochondria and plastids.

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

Vesicle (biology and chemistry)

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Scheme of a liposome formed by phospholipids in an aqueous solution.
Sarfus image of lipid vesicles.
Electron micrograph of a cell containing a food vacuole (fv) and transport vacuole (tv) in a malaria parasite.

In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer.

Transport vesicles can move molecules between locations inside the cell, e.g., proteins from the rough endoplasmic reticulum to the Golgi apparatus.

Structures of some common lipids. At the top are cholesterol and oleic acid. The middle structure is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone. At the bottom is the common phospholipid phosphatidylcholine.

Lipid

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Biomolecule that is soluble in nonpolar solvents.

Biomolecule that is soluble in nonpolar solvents.

Structures of some common lipids. At the top are cholesterol and oleic acid. The middle structure is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone. At the bottom is the common phospholipid phosphatidylcholine.
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.
Phosphatidylethanolamine
Sphingomyelin
Chemical structure of cholesterol.
Prenol lipid (2E-geraniol)
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.

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.

Triglyceride synthesis takes place in the endoplasmic reticulum by metabolic pathways in which acyl groups in fatty acyl-CoAs are transferred to the hydroxyl groups of glycerol-3-phosphate and diacylglycerol.

Human cell nucleus

Nuclear envelope

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Human cell nucleus
A volumetric surface render (red) of the nuclear envelope of one HeLa cell. The cell was observed in 300 slices of electron microscopy, the nuclear envelope was automatically segmented and rendered. One vertical and one horizontal slice are added for reference.
Nuclear pores crossing the nuclear envelope
Breakdown and reassembly in mitosis.

The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surrounds the nucleus, which encloses the genetic material.

The outer nuclear membrane is continuous with the endoplasmic reticulum membrane.

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).

Cholesterol

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Any of a class of certain organic molecules called lipids.

Any of a class of certain organic molecules called lipids.

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).
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Lipid logistics: transport of triglycerides and cholesterol in organisms in form of lipoproteins as chylomicrons, VLDL, LDL, IDL, HDL.
Cholesterolemia and mortality for men and women 60 years
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.
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Cholesterol units conversion
Steroidogenesis, using cholesterol as building material
Space-filling model of the Cholesterol molecule
Numbering of the steroid nuclei

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.

Two molecules of farnesyl pyrophosphate then condense to form squalene by the action of squalene synthase in the endoplasmic reticulum.

Phospholipid arrangement in cell membranes.

Phospholipid

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Alcohol residue .

Alcohol residue .

Phospholipid arrangement in cell membranes.
Phosphatidylcholine is the major component of lecithin. It is also a source for choline in the synthesis of acetylcholine in cholinergic neurons.
Phospholipid bilayers are the main structural component of the cell membranes.

They can form lipid bilayers because of their amphiphilic characteristic.

Phospholipid synthesis occurs in the cytosolic side of ER membrane that is studded with proteins that act in synthesis (GPAT and LPAAT acyl transferases, phosphatase and choline phosphotransferase) and allocation (flippase and floppase).