Cell Features
Located in the lipid bilayer of the cell membrane are various proteins.
The middle part of a membrane protein is mostly nonpolar;
it is attracted to the interior of the lipid bilayer but is repelled by
the water on either side of the lipid bilayer. In contrast, the inner
and outer parts of the protein are mostly polar and are therefore
attracted to water. This dual attraction to water holds the protein
in the lipid bilayer. However, the motion and fluidity of phospho-lipids
enable the cell-membrane proteins to move around within
the lipid bilayer.
There are different types of proteins in the cell membrane.
Each type plays a vital role in the life of a cell. Marker proteins,
which are attached to a carbohydrate on the cell's surface, help
other cells recognize their cell typeliver cell or heart cell,
for example. Receptor proteins recognize and bind to specific
substances, such as signal molecules, outside the cell. Various
enzymes in the cell membrane are involved in important biochem-ical
reactions in the cell. Transport proteins aid the movement of
substances into and out of the cell.
Type of protein. Function
6/7. Marker- help other cells recognize their cell type
8/9. Receptor- recognize and bind to specific substances outside the cell.
10/11. Transport- aid the movement of substances into and out of the cell.
In the space provided, write the letter of the term or phrase that best answers
the question.
__D_12. What is the function of enzymes found in the cell membrane?
a. to move substances out of the cell
b. to bind to specific substances
c. to help cells recognize their cell type
d. to assist biochemical reactions in the cell
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