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15 Cards in this Set

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cells it has three main areas:
The cell membrane, the cytoplasm, and the nucleus.
The cell membrane
is the thin nearly invisible structure that surrounds the cytoplasm 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.

It also connects the the endoplasmic reticulum, and the nuclear membrane
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 (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 in water (this is why gasoline and water do not mix). At the other end of the phospholipid is a phosphate group and several double bonded 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.
Floating around in the cell membrane are different kinds of proteins. These are generally globular 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 proteins that regulate transport and diffusion

Marker proteins that identify the cell to other cells

And receptor proteins that allow the cell to recieve instructions
Steriods are sometimes a component of cell membranes in the form of cholesterol. When it is present it reduces the fluidity of the membrane. Not all membranes contain cholesterol.
cell membrane function
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
cell membrane and regulation of transport
Transport Proteins come in two forms:
Carrier proteins are peripharal proteins which do not extend all the way through the membrane. They move specific molecules through the membrane one at a time.
carrier proteins
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.
channel proteins
In some cases the channnel 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 also use the process of diffusion. In this case a molecule that is moving naturally into the cell through diffusion is used to drag another molecule into the cell. In this example glucose hitches a ride with sodium.
proteins using atp
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) an example of this is the sodium/potassium pump. Here the energy of a phosphate (shown in red) is used to exchange sodium atoms for potassium atoms.
marker proteins
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. They play an important role in organ transplants. If the marker proteins on a transplanted organ are differnt from those of the original organ the body will reject it as a foreign invader.
receptor protein
These proteins are used in intercellular communication. In this animation you can see the a hormone binding to the receptor. This causes the receptor protein release a signal to perform some action.
The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins this process is known as endocytosis. In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this animation an ameba engulfs a food particle.
The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane.