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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 .

Phospholipids

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 the reason of swelling due to fracture
Ejaz Reply
how do animals reproduce
Kelvin Reply
be specific because there are so many types of animals and how they reproduce are different
Sheillah
yeah
Chinwendu
what happens when you sneeze
Asuquo Reply
The sneeze center sends out a signal to tightly close your throat, eyes and mouth. Your chest muscles contract and compress your lungs while your throat muscles relax. All of that means air, saliva and mucus is forced out of your nose and mouth. AAAAAHHHH-CHOOOO.
Hassan
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Ayouba
hy
Ejaz
hii
Ishitha
hello
mahesha
Hello
Madu
Am fine
Abavon
how far
Abavon
hello
Sheillah
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Sheillah
with what
Sheillah
I have a question plzz
Sheillah
Outline the process of cell in the body interms of it's function.
Aliruku Reply
what communication method used mainly by plants
Jerda Reply
what is biology
james Reply
Biology is the study of life
Omoloju
define nerve impulse
Karlin Reply
A nerve impulse is the way nerve cells (neurons) communicate with one another. Nerve impulsesare mostly electrical signals along the dendrites to produce a nerve impulse or action potential. The action potential is the result of ions moving in and out of the cell.
Sam
What is the Molecular Biology?
Service Reply
The branch of biology that deals with the structure and function of the macromolecules (e.g. proteins and nucleic acids) essential to life.
Sam
what is botany
Sillah
Description Description Botany, also called plant science, plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field.
Sam
what is the difference between mitosis and meiosis?
Fatima Reply
what is an element
Saidu Reply
Element is any one of the simplest chemical substances that cannot be decomposed in a chemical reaction.
Lucky
an element is a substance that cannot be broken down into any other substance
Akosua
explain why only one sperm fertilisers the ovum
Frazzy Reply
its because other sperms are destroyed on the way
Nasib
A test tube is full of a colourless gas that puts a lighted wooden splint.what gas is this?
Jerda
what is cell
Dau Reply
Cell is the smallest unit of life
Yodit
cell refers of the basic, structural and function unit of an organism
jacob
smallest functional unit of an organism
Nasib
explain for me for ecological factors affecting each of aquatic and terrestrial habitats
Ikeh Reply
Temperature, high humidity
Afriyie
50%
Yodit
temperature,light intensity,Co2
Nasib
what's meosis
Umoke Reply
meiosis this is the type of cell division which reduces the number of chromosomes in order to form a gamete
Caren
meiosis refers to the form of cell division in which a cell divides into four daughter nuclei each containing the same number of chromosomes as the parent cell
Bigenis
yes
Marah
cell division where one cell sprits into 4 daughter cells each having half number of chromosomes as parent cell
Nasib
The end of the linear chromosomes are maintained by
birabwa Reply
Gene
Afriyie
Telomerase
birabwa

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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