Cell membrane how does it look like

The cell membrane, also called the plasma membrane, is found in all cells and separates the interior of the cell from the outside environment. The cell membrane consists of a lipid bilayer that is semipermeable. The cell membrane regulates the transport of materials entering and exiting the cell. The plasma membrane, or the cell membrane, provides protection for a cell.

Glycerol is a three-carbon molecule that functions as the backbone of these membrane lipids. Within an individual glycerophospholipid, fatty acids are attached to the first and second carbons, and the phosphate group is attached to the third carbon of the glycerol backbone. Variable head groups are attached to the phosphate. Space-filling models of these molecules reveal their cylindrical shape, a geometry that allows glycerophospholipids to align side-by-side to form broad sheets Figure 1.

Figure 1: The lipid bilayer and the structure and composition of a glycerophospholipid molecule A The plasma membrane of a cell is a bilayer of glycerophospholipid molecules. B A single glycerophospholipid molecule is composed of two major regions: a hydrophilic head green and hydrophobic tails purple. C The subregions of a glycerophospholipid molecule; phosphatidylcholine is shown as an example. The hydrophilic head is composed of a choline structure blue and a phosphate orange. This head is connected to a glycerol green with two hydrophobic tails purple called fatty acids.

D This view shows the specific atoms within the various subregions of the phosphatidylcholine molecule. Note that a double bond between two of the carbon atoms in one of the hydrocarbon fatty acid tails causes a slight kink on this molecule, so it appears bent. When carbon atoms are attached to neighboring carbons by single bonds, they are also bound to two hydrogen molecules each. The two carbons bound to one another by a double-bond in this schematic are bound to only one hydrogen molecule each as a result.

A top row of 15 phospholipids is arranged opposite a bottom row of 15 phospholipids, so that the hydrophobic tails of the top row meet the hydrophobic tails of the bottom row in the middle of the bilayer with the hydrophobic heads on the top and bottom surfaces.

In panel B, a single phospholipid is magnified to show its basic structure. A ball-and-stick diagram in panel C shows the molecular structure of the lipid phosphatidylcholine. Colored highlighting is used to distinguish each of the four structural subregions.

The phospholipid head is shown with the choline region highlighted in blue at the top, and the phosphate group is highlighted in orange below it. The glycerol region that links the phosphate to the two lipid tails is shown in green, and each of the two lipid tails is shown in purple. In panel D, the chemical symbol for each atom that makes up the phosphatidylcholine molecule has been juxtaposed over the molecular ball-and-stick model shown in panel C. The choline group blue is comprised of a nitrogen molecule attached by single bonds to three methyl groups CH3 and one methylene group CH2.

A second methylene group is attached by a single bond to the first methylene group, and to an oxygen molecule that is part of the phosphate group. The phosphate group is comprised of a phosphate molecule attached by single bonds to four oxygen molecules in total. One of these oxygen molecules is attached by a single bond to a terminal methylene group of a glycerol molecule.

The glycerol molecule is a 3-carbon molecule. The central carbon is attached to a hydrogen molecule by a single bond, and the two terminal carbon molecules are both attached to two hydrogen molecules.

One fatty acid tail is attached to the glycerol's terminal carbon that is not attached to the phosphate head, and a second fatty acid tail is attached to the glycerol's central carbon. Each fatty acid is comprised of a terminal carboxyl group COO- that is attached to a long carbon chain. The carbon of each carboxyl group forms a double bond with one oxygen molecule and a single bond with the other oxygen molecule, which is connected by a single bond to the carbon of the glycerol backbone, and a single bond with a carbon from the backbone of the long carbon chain.

In phosphatidylcholine, each fatty acid tail contains 18 carbons, including the carbon of the carboxyl group. The carbons that make up the first tail are attached to each other by single bonds. In the fatty acid chain bound to the glycerol's central carbon, the 9 th carbon in the chain is bound to the 10 th carbon in the chain by a double bond, causing a kink. There are also proteins attached to the inner and outer surfaces of the membrane.

Scientists use the fluid mosaic model to describe the organization of phospholipids and proteins. The model shows you that phospholipid molecules are shaped with a head and a tail region. The head section of the molecule likes water hydrophilic while the tail does not hydrophobic.

Because the tails want to avoid water, they tend to stick to each other and let the heads face the watery aqueous areas inside and outside of the cell. The two surfaces of molecules create the lipid bilayer. Ingrained in the Membrane What about the membrane proteins? Scientists have shown that many proteins float in the lipid bilayer. Some are permanently attached while others are only attached temporarily. A person infected with HIV will quickly develop different populations, or variants, of the virus that differences in these recognition sites distinguish.

In the case of HIV, the problem is compounded because the virus specifically infects and destroys cells involved in the immune response, further incapacitating the host. The modern understanding of the plasma membrane is referred to as the fluid mosaic model.

The plasma membrane is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the outward-facing surface of the membrane.

These form complexes that function to identify the cell to other cells. The fluid nature of the membrane owes itself to the configuration of the fatty acid tails, the presence of cholesterol embedded in the membrane in animal cells , and the mosaic nature of the proteins and protein-carbohydrate complexes, which are not firmly fixed in place.

Plasma membranes enclose the borders of cells, but rather than being a static bag, they are dynamic and constantly in flux. Improve this page Learn More. Skip to main content. Module 5: Cell Membranes.