Video Transcript
Which molecule found within a
phospholipid bilayer of animal cells provides structural support to the
membrane? (A) Cellulose, (B) starch, (C)
myosin, (D) actin, or (E) cholesterol.
The phospholipid bilayer is the
arrangement of molecules that make up the membrane of cells. This question asks us about
structural support in the membrane of animal cells specifically. Let’s consider the options.
Cellulose is a structural molecule,
which makes up the cell wall in plant cells. It is not found in animal cells, so
we can eliminate (A). Starch is a complex carbohydrate
also found in plant cells as a way to store glucose. Starch is also not found in animal
cells, so we can eliminate (B). Myosin is found in muscle cells as
part of the contraction mechanism. But it is not found in the membrane
portion of those cells. So we can eliminate (C). Actin is also primarily found in
muscle cells as part of the contraction mechanism. But it is not found within the
membrane structure. So we can eliminate (D) as
well.
Cholesterol is a lipid molecule
that does occur between the phospholipid molecules of the cell membrane in
animals. It has a hydrophilic head and a
rigid, bulky hydrophobic tail that interacts with the hydrophobic phospholipid tails
in the bilayer. In cold temperatures, the
phospholipids become more closely packed together and can become too tight, rigid,
and prone to break. Cholesterol disrupts this tight
organization with its bulky tail, keeping the phospholipids from packing too closely
together. This increases membrane
fluidity.
In very hot temperatures,
phospholipids begin to separate more from each other. But the cholesterol tail keeps
strong interactions with the phospholipids around it and pulls them together. This prevents the membrane from
becoming too fluid.
We can thus see that cholesterol
does provide structural support to cell membranes where it occurs. Therefore, the correct answer is
(E). Cholesterol is found in the
phospholipid bilayer of animal cell membranes and provides structural support to the
cell membrane.
