A Cell Thing
Section: Cell Features
Read the passage below. Then answer the questions that follow.
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.
SKILL: RECOGNIZING CAUSE AND EFFECT
Read each question, and write your answer in the space provided.
1. The first paragraph describes a cause-and-effect relationship between the
structure of a membrane protein and the lipid bilayer. The cause in this
relationship is the nonpolar middle part of a membrane protein. What is
the effect? It is repelled by the water on either side of the lipid bilayer.
2. Another cause-and-effect relationship detailed in the first paragraph explains
that the inner and outer parts of a membrane protein are attracted to water.
What is the cause? The...
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