Levels of Organization Image Map
How do the membranes interact with the proteins?

Drs. Danielli and Davson's "sandwich" model of proteins and lipid seemed reasonable at the time and was accepted for several decades. But more research revealed that some portions of proteins were anchored IN the double layer of lipids. 

Membrane proteins are classified into two groups, depending on how they are anchored to the membrane.
  Peripheral Protein Image

Peripheral proteins are anchored on the side of the membrane and do not go completely through the membrane.

Integral Protein Image

Integral proteins pass completely through the membrane, with parts of the protein hanging out of either side of the membrane. 

 

Because integral proteins pass completely through the membrane, they can provide a channel to let substances move into and out of cells (see the channel in the picture to the right.) You might think of this like a miniature sponge. The size and shape of the channels regulate the size of the molecules that can pass through these protein gateways.

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