Download Cell membrane

Huang Wen Ying
黄文英
Institute of Physiology
Physical education school of JXNU
Email: [email protected]
Chapter 1
 THE
CELL AND TIS
REGULATORY MECHANISMS
Structure and function of the cell



The cell membrane
Its general structure
Its function

The nucleus
Its structure
Its function

The cytoplasm


1.Structure and function of the cell
1.1.Cell membrane

The cell membrane is the thin nearly
invisible structure that surrounds the
cytoplasm（细胞质） of the cell. In this
section we will talk about its structure and
its function. In the image at the left you
can see that it is a continuous membrane
that completely surrounds the cell.
Cell membrane

It also connects the endoplasmic
reticulum
（内质网）, and the nuclear membrane
（核膜）. In the image below we have
colored the membrane to highlight its
composition. The yellow represents the
phospholipids （磷脂）. The purple
represents the membrane proteins 。
Cell membrane

Here we see a cross section of the cell
membrane you should notice two different
structures: The phospholipids are the
round yellow structures with the blue tails,
the proteins are the lumpy（团，块）
structures that are scattered around
amoung the phospholipids
Cell membrane
phospholipid （磷脂）

This is a simple representation of a phospholipid.
the yellow structure represents the hydrophillic
（亲水的） or water loving section of the
phospholipid. The blue tails that come off of the
sphere represent the hydrophobic（疏水的） or
water fearing end of the Phospholipid. Below is
a structural model of a phospholipid that
explains what these terms mean.
phospholipid （磷脂）

The two long chains coming off of the bottom of
this molecule are made up of carbon and
hydrogen. Because both of these elements
share their electrons evenly these chains have
no charge（电荷） (gasoline is also a
hydrocarbon). Molecules with no charge are not
attracted to water; as a result water molecules
tend to push them out of the way as they are
attracted to each other. This causes molecules
with no charge not to dissolve （溶解）in water
(this is why gasoline and water do not mix). At
the other end of the phospholipid is a phosphate
（磷酸盐） group and several double bonded
（键）oxygens. The atoms at this end of the
molecule are not shared equally. This end of the
molecule has a charge and is attracted to water.

If you mix phospholipids （磷脂）in water
they will form these double layered
structures. The hydrophillic （亲水的）
ends will be in contact with water. The
hydrophibic ends will face inwards
touching each other.
phospholipids

Floating around in the cell membrane are
different kinds of proteins. These are
generally globular（球形的） proteins.
They are not held in any fixed pattern but
instead float around in the phospholipid
layer. Generally these proteins structurally
fall into three catagories...
There are carrier（载体） proteins that
regulate transport and diffusion（扩散）
Marker proteins that identify the cell to
other cells
And receptor proteins that allow the cell
to receive instructions

Steriods（类固醇） are sometimes
（往往）a component of cell
membranes in the form of cholesterol
（胆固醇）. When it is present it
reduces the fluidity of the embrane.
Not all membranes contain
cholesterol
Steriods

The cell membrane's function, in general,
revolves around is membrane proteins.
General functions include: Receptor
proteins which allow cells to communicate,
transport proteins regulate what enters or
leaves the cell, and marker proteins which
identify the cell

Transport Proteins come in two forms:
Carrier proteins are peripheral proteins
which do not extend all the way through
the membrane. They move specific
molecules through the membrane one at a
time.

Channel proteins extend through the
bilipid （双脂层）layer. They form a pore
through the membrane that can move
molecules in several ways.

These are carrier proteins. They do not
extend through the membrane. They bond
and drag molecules through the bilipid
layer and release them on the opposite
side.

In some cases the channel proteins simply
act as a passive pore. Molecules will
randomly move through the opening in a
process called diffusion. This requires no
energy, molecules move from an area of
high concentration to an area of low
concentration.

Symports(同向转运） also use the
process of diffusion. In this case a
molecule that is moving naturally into the
cell through diffusion is used to drag （拖）
another molecule into the cell.

Some proteins actively use energy from
the ATPs in the cell to drag molecules
from area of low concentration to areas of
high concentration (working directly
against diffision)

Marker proteins extend across the cell
membrane and serve to identify the cell. The
immune system uses these proteins to tell
friendly cells from foreign invaders. They are as
unique as fingerprints（指纹）. They play an
important role in organ transplants. If the marker
proteins on a transplanted organ are different
from those of the original organ the body will
reject it as a foreign invader.
Marker proteins

These proteins are used in intercellular
communication. In this animation you can
see the a hormone（GLU） binding to the
receptor. This causes the receptor protein
release a signal to perform some action
receptor protein

The cell membrane can also engulf （吞没）
structures that are much too large to fit through
the pores in the membrane proteins this process
is known as endocytosis（内吞入胞）. In this
process the membrane itself wraps around the
particle（颗粒） and pinches（夹） off a vesicle
（泡，囊）inside the cell. In this animation an
ameba engulfs a food particle.
endocytosis

The opposite of endocytosis is exocytosis
（胞吐作用）. Large molecules that are
manufactured（制造） in the cell are
released through the cell membrane.
exocytosis