Cell Membrane Fluidity | Role of cholesterol
Articles Blog

Cell Membrane Fluidity | Role of cholesterol

Cholesterol is Abundant in Cell Membranes Cholesterol is found in every cell of your
body. It is especially abundant in the membranes of these cells, where it helps maintain the
integrity of these membranes, and plays a role in facilitating cell signaling– meaning
the ability of your cells to communicate with each other so you function as a human, rather
than a pile of cells. Molecule for molecule, cholesterol can make
up nearly half of the cell membrane.1 Since it is smaller and weighs less than other molecules
in the cell membrane, it makes up a lesser proportion of the cell membrane’s mass, usually
roughly 20 percent.2 Cholesterol is also present in membranes of
organelles inside the cells, although it usually makes up a smaller proportion of the membrane.
For example, the mitochondrion, the so-called “power-house” of the cell, contains only three
percent cholesterol by mass, and the endoplasmic reticulum, which is involved in making and
modifying proteins, is six percent cholesterol by mass. 3 Cholesterol Maintains the Integrity of the
Cell Membrane Surrounding each of our cells is a membrane
called the plasma membrane. The plasma membrane is a continuous double-layer of phospholipids,
interweaved with cholesterol and proteins. Phospholipids are composed of two fatty acids
attached to a phosphate compound as a head. The phosphate head is water-soluble, also
called “hydrophilic” (water-loving), and the fatty-acids are water-insoluble, or “hydrophobic”
(water-fearing). Since outside the cell is a water-containing, or aqueous, environment,
and inside the cell is also aqueous, the phosphate heads of the phospholipids face both the cell’s
inside and the environment outside the cell, while the fatty acids face the inside of the
membrane. The membrane is fluid, and the molecules are
always moving. It has about the same consistency as olive oil. Cholesterol is an amphipathic molecule, meaning,
like phospholipids, it contains a hydrophilic and a hydrophobic portion. Cholesterol’s hydroxyl
(OH) group aligns with the phosphate heads of the phospholipids. The remaining portion
of it tucks into the fatty acid portion of the membrane. Because of the way cholesterol is shaped,
part of the steroid ring (the four hydrocarbon rings in between the hydroxyl group and the
hydrocarbon “tail”) is closely attracted to part of the fatty acid chain on the nearest
phospholipid. This helps slightly immobilize the outer surface of the membrane and make
it less soluble to very small water-soluble molecules that could otherwise pass through
more easily.4 Without cholesterol, cell membranes would
be too fluid, not firm enough, and too permeable to some molecules. In other words, it keeps
the membrane from turning to mush. Cholesterol Helps Maintain the Fluidity of
Cell Membranes While cholesterol adds firmness and integrity
to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain
its fluidity. At the high concentrations it is found in
our cell’s plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate
the phospholipids so that the fatty acid chains can’t come together and cyrstallize.5 Therefore, cholesterol helps prevent extremes–
whether too fluid, or too firm– in the consistency of the cell membrane. Cholesterol Helps Secure Important Proteins
in the Membrane The plasma membrane contains many proteins
that perform important functions like channeling or pumping substances into and out of the
cell, attaching to other cells, forming borders to keep other proteins in one specific part
of the cell, communicating with nearby cells, or responding to endocrine hormones from far-away
cells. Because certain proteins’ size or shape requires
a thicker phospholipid bed to sit in, and because certain proteins need to stick together
to function properly, the fluidity of the cell membrane, where the molecules are constantly
moving randomly, could pose a problem. Fortunately, the plasma
membrane contains many lipid rafts where proteins
are secured. A lipid raft contains high concentrations of cholesterol and sphingolipids– a type
of phospholipid– containing longer and more saturated fatty acid tails. Because the fatty acids are longer and more
saturated (straighter), they aggregate more, which cholesterol also helps. That part of
the membrane is also thicker, making it ideal for accommodating certain proteins.6 Since the fatty acids in lipid rafts are longer,
the phospholipids also move in sync with the phospholipids on the other side of the membrane. In the rest of the membrane, the phospholipids
on one side of the
membrane move independently of those on the other.7 By stabilizing certain proteins together in
lipid rafts, cholesterol is important to helping these proteins maintain their function. This could range from forming blood clots
or thinning blood, to allowing sugar into your
cells, to burning fat, to regulating calcium in your blood, and literally includes, in
some way, most of the functions in your body, although which proteins exist in lipid rafts
and which do not is still being researched. It
is the proteins, after all, by which cells
communicate with
one another. If cells didn’t communicate with one another, you and I would be a large pile of unrelated cells rather than the individuals that we are.

100 thoughts on “Cell Membrane Fluidity | Role of cholesterol

  1. excellent explanation, one question though: since arctix foxes are mammals, the temperature of inside of their bodies is always the same, and it doesn't vary that much from the temperature of the inside of the body of e.g. desert fox, so how come their cell membranes get colder and need to produce more cholersterol?

  2. watching your vedios before my profffesor cover it in class, so I can understand what he is talking bout in depth . thank you so much

  3. you are the best person who explains every concept in detail with proper logic and explanation.
    people ask me how do i score such good marks in biochemistry well they wouldn't believe me when i say i learned all the concepts online via your channel
    thank you soo much
    hope your channel keeps on growing

  4. U r the best professor ..sir only bcz of u my biology is easy to learn .. I learn more from u as compare to my class.. thank u soo much sir

  5. Passion and true efforts never fails us.. & You are an example for it.. your videos reflect your passion towards science.. thanks for sharing knowledge..

    Please Sir I have presentation in this research paper can you give some tips how can I prepare presentation and please
    explain this paper for me.([email protected]) my email ID.

  7. Amazing explanation. I had confusion regarding role of cholesterol in membrane fluidity. But thank u shomu sir … ur wonderful lecture helps me a lot to understand this topic..
    Carry on… from me…Superlike

  8. Hello Sir …
    I am Prem and I am big fan of you..
    I am from U.P East (Jhansi) and I preparing CSIR NET LIFE SCIENCE.
    I have watched lots of video lectures from your channel. Those are very helpful for exam ,So please sir keep updating new lectures…
    I want to attend the classroom batch but it is my bad luck that I don't attend class room batch bcz of distance.
    I want to get hard study material from your coaching and your helpful suggestions also…
    Thank you sir..😘

  9. Thank u sir

    How crystaline str of hydrophobic tails r useful in case of animal found in hot climate??

    Yupp it restrict the fuidity,mobility

    Bt it usefull??

    Please explain

  10. Please sir tell me the difference between the sturture of the cholesterol in both the region at cold temp nd hot temp which help in the manage the fluidity

Leave a Reply

Your email address will not be published. Required fields are marked *

Back To Top