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This illustration shows a phospholipid bilayer with proteins and cholesterol embedded in it. Integral membrane proteins span the entire membrane. Protein channels are integral membrane proteins with a central pore through which molecules can pass. Peripheral proteins are associated with the phospholipid head groups on one side of the membrane only. A glycoprotein is shown with the protein portion of the molecule embedded in the membrane and the carbohydrate portion jutting out from the membrane. A glycolipid is also shown with the lipid portion embedded in the membrane and the carbohydrate portion jutting out of the membrane.
The fluid mosaic model of the plasma membrane describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins. Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

The principal components of a plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrates attached to some of the lipids and some of the proteins. A phospholipid is a molecule consisting of glycerol, two fatty acids, and a phosphate-linked head group. Cholesterol, another lipid composed of four fused carbon rings, is found alongside the phospholipids in the core of the membrane. The proportions of proteins, lipids, and carbohydrates in the plasma membrane vary with cell type, but for a typical human cell, protein accounts for about 50 percent of the composition by mass, lipids (of all types) account for about 40 percent of the composition by mass, with the remaining 10 percent of the composition by mass being carbohydrates. However, the concentration of proteins and lipids varies with different cell membranes. For example, myelin, an outgrowth of the membrane of specialized cells that insulates the axons of the peripheral nerves, contains only 18 percent protein and 76 percent lipid. The mitochondrial inner membrane contains 76 percent protein and only 24 percent lipid. The plasma membrane of human red blood cells is 30 percent lipid. Carbohydrates are present only on the exterior surface of the plasma membrane and are attached to proteins, forming glycoproteins , or attached to lipids, forming glycolipids .


The main fabric of the membrane is composed of amphiphilic, phospholipid molecules. The hydrophilic    or “water-loving” areas of these molecules (which look like a collection of balls in an artist’s rendition of the model) ( [link] ) are in contact with the aqueous fluid both inside and outside the cell. Hydrophobic , or water-hating molecules, tend to be non-polar. They interact with other non-polar molecules in chemical reactions, but generally do not interact with polar molecules. When placed in water, hydrophobic molecules tend to form a ball or cluster. The hydrophilic regions of the phospholipids tend to form hydrogen bonds with water and other polar molecules on both the exterior and interior of the cell. Thus, the membrane surfaces that face the interior and exterior of the cell are hydrophilic. In contrast, the interior of the cell membrane is hydrophobic and will not interact with water. Therefore, phospholipids form an excellent two-layer cell membrane that separates fluid within the cell from the fluid outside of the cell.

A phospholipid molecule ( [link] ) consists of a three-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate-containing group attached to the third carbon. This arrangement gives the overall molecule an area described as its head (the phosphate-containing group), which has a polar character or negative charge, and an area called the tail (the fatty acids), which has no charge. The head can form hydrogen bonds, but the tail cannot. A molecule with this arrangement of a positively or negatively charged area and an uncharged, or non-polar, area is referred to as amphiphilic    or “dual-loving.”

Questions & Answers

what is genetic
Nad Reply
what is écosystème
what is écosystème
what is écosystème
what is écosystème
discuss adaptations of flight in birds
Cassim Reply
what is an enzymes
Joseph Reply
mention two types of metabolic
what is a cell?
is the biological catalyst that speed up chemical reaction in the living thing
an enzymes is a biological catalyst that speed up a chemical reaction in living organisms and it is protein in nature
enzymes are protein that act as biological catalysts
what agglutriation
enzymes are biological catalysts that speed up the chemical reactions in a living organism
what is photosynthesis
Conast Reply
photosynthesis is the process by which green plants manufacture their own food from water and carbon dioxide using sunlight as a source of their energy releasing oxygen as a by-product.
what is the function of thé utérus
what are runners
Godfrey Reply
what is an environment
Bwambale Reply
diagrams are not indicated, why?
Simon Reply
diagrams for what?
A vaccination is a treatment which makes the body stronger against an infection. The body fights infections using the immune system, which is made up of millions upon millions of cells including T cells and B cells.
define the term immunity
can simply defined as an exemption from an attack
is the ability of an organism to resist a particular infection or toxin by a specific antibodies or sensitized white blood cells
difference between cell and cell membrane
Sunday Reply
cell is a basic unit of living body however cell membrane is a protective layer of cell.
very good
which topic would you like to discuss today?
what do you understand by the term vaccine?
guy I need the answer of this question what occurs during photosynthesis
REAL Reply
Photosynthesis is the process that plants use to convert light into food. During this process, plants create carbohydrates starting with only carbon dioxide and water. Sunlight provides the energy that makes photosynthesis possible.
@Stanley,that's how I could as well put it
what are different between genotype and phenotype
Martha Reply
what is light microscope and electronic microscope
what occurs during photosynthesis
what are importance of biology
what is the meaning of computer science
genotype is the genetical constitution of the gene
what is ecology
Adeyemo Reply
what is zoology
zoology branch of biology that study animals
a branch of biology which deals with the study of animals
A plant is a living thing that grows in the earth and has a stem, leaves, and roots
Bello Reply
what is a plant
dalitso Reply
A plant is a living thing that grows in the earth and has a stem, leaves, and roots
a plant is an is a living thing that is classified under autothrops because it makes its own food through the process of photosynthesis .
a plant is also known as autotropic category and a plant have root & stem
what is plant
Odion Reply
Plants are autotrophic
Then animal are heterotrophic
what are organisms
Godfred Reply
Living structures
living and non living which charectrised by different properties
organisms living and nonliving components of the environment with distinct xtics

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