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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 reproduction
smart Reply
it is d act of bringing young ones to life
Oyebanji
to ensure survival of a species🚴‍♀️
Michelle
what is a genotype
Collins
what is hazardous
smart
a cell is the smallest unit of a living thing. so we all have cell
smart
It is the formation of a zygote resulting from the fusion of the sperm cell with the ovum.Thus,this results in the production of new species which are genetically dissimilar from their parent cells.
Pallavi
what is size of cell
Mohd Reply
what is size of Hart
Mohd
nanometers=um sign thingie
Michelle
microns=nanometers
Michelle
monomers and polymers of nucleic acids?
Jyrl Reply
dna and rna involvement
Michelle
give me the elements of the soil
Iguma Reply
Air, water, organic matter, inorganic matter
Tshwano
soil water humus air
Veronicah
yap
Beloved
silica, iron
Patience
potassium, sulfur, calcium, carbon
Michelle
what is cell
iyaji Reply
A cell is a smallest fundamental unit of a living organisms.
Kem
the basic structural and functional unit of life
Patience
what is size of cell
Mohd
all things are made up of.....all things cannot exist without pre-exisiting cells...check out the 16th ce tury to learn more about microscope use and cells. i will give a hint: Mr. L.
Michelle
we are all made of cells
Michelle
Nutrition - sensitive intervention
Therowda Reply
what does the sori In fern mean
arhin Reply
biology is the study .exactly what is life?
Jerry
i'm sorry , the study of life
Jerry
how can U identify a person through his blood
Frankyx Reply
through genetic fingerprinting where specific DNA sequences in a person genome can be identified.
Pallavi
by help of genetics and DNA test
Meerbadini
can it also be detected using an RNA test
Frankyx
environmental biology
Ojesola Reply
what is phytoplankton
Ojesola
What is anabolism
Treasure Reply
the break down of substance
Aunty
how many teeth has an adult person
TSEGAY Reply
36
Treasure
32
Favour
32
Kamaluddeen
32 teeth
Meerbadini
32
OLAMIDE
32 (or 36 including the wisdom teeth)
Hailey
32
Sani
26?🤓
Michelle
what is homoestastis
Ayo Reply
hypothalamus negative feedback vs. postive feedback systems.
Michelle
it is the maintenance of a steady internal environment.it is controlled largely by the brain especially the hypothalamus.
Oyebanji
What is a cell
Eric Reply
A cell is the building block of all organisms
Millicent
yes it is , it also helps in functions .
Joezman
cell is structural & functional unit of oraganisms
Meerbadini
it is a building blocks of a living organism
Joezman
it is the basic unit of life in living organisms
Nabwonso
it is the basic unite of life in living organisms
Nabwonso
it is the fundamental unit of life
Adewoye
it is the structural and functional unit of life
Ojesola
Why cells are classify as living and non living things
Millicent Reply
due to such as virus which acts as a living cell inside the cell of an organisms and out side of cell in form of crystals
Meerbadini
because there are living cells which performs complex processes such as reproduction and metabolism then there are dead cells like the top most part of the epidermis or the bark
irish
because there are living cells which performs complex function such as reproduction and metabolism
David
cause otherwise you could call fire alive
Marissa
what's nomenclature
Joseph Reply
assigning scientific name to organism
Azmat
yes, the genius name, and the species name
Justice
it is a scientific naming of organism
Meerbadini

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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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