The membrane's main job is to protect the cell from its surroundings.
It separates the cell's interior from the
outside environment and helps it keep its shape.
The membrane is selectively permeable,
which means it allows certain
organic molecules to pass into and out of the interior.
The cell membrane is mainly composed of lipids and proteins.
Its framework consists of a double layer of phospholipids.
Lipids make up fifty percent of most membranes although,
depending on the location, they may make up to eighty percent.
The remainder is made from proteins.
Lipids make the membrane flexible and the proteins help
transfer molecules across the membrane.
There are two major types of proteins:
tightly coiled, rod-shaped fibrous proteins,
which help give the cell support and shape, and
the more compact, globular shaped integral proteins and
peripheral proteins.
These help cells communicate and transport molecules.
Examples include glycoprotein,
pore protein, and channel protein.
Because the cell membrane is mostly lipid, it only
allows lipid soluble substances like
oxygen, carbon dioxide, and steroids to pass through.
Water soluble substances such as glucose, amino acids, ions, and
water need the help of the various
proteins in order to move across the membrane.
Two layers of phospholipid molecules self-assemble,
so that their water-soluble or hydrophilic heads form the
surface and interior of the membrane, and
the water-insoluble or hydrophobic tails face each other.
The fibrous proteins may span the entire membrane and serve as
receptors for the cell.
They communicate with the external environment using hormones and neurotransmitters.
One type of globular protein forms pores to allow
lipid insoluble water molecules to pass through.
Other integral proteins service channels
and selectively support ions including
nutrients such as sugars or amino acids
Channel proteins are usually quite specific,
so each one specializes in transporting
a single substance or group of similar chemical substances.
Globular proteins are peripheral meaning they're associated
with the surface of the cell.
These include enzymes or glycoproteins.
These proteins have carbohydrate
associations that identify the cell.
Cholesterol molecules are embedded in
animal cell membranes but not in plant cell membranes.
They're found dispersed through the cell membrane and help
strengthen the membrane wall.
In addition, they along with phospholipids help make
the membrane impermeable to water-soluble substances.
Cell membranes are integral to cell health.
With their combination of lipids, proteins, and
cholesterol, they are able to complete a
complex variety of tasks essential to life.
Cell membranes keep the outside out and the inside in.
You've completed: Construction of the Cell Membrane.
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