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Ted ED
Construction of Cell Membrane
00:28 - 03:11
Nazzy Pakpour explains in depth the science behind Cell Membranes, and discusses the function of the cell membrane, how it works, and what it is constructed of.
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Video Transcript
0:25
and all the molecules it needs to survive.
0:28
How does the membrane work, and where does that strength come from?
0:34
First of all, it's tempting to think of a cell membrane
0:37
like the tight skin of a balloon,
0:39
but it's actually something much more complex.
0:43
In reality, it's constantly in flux,
0:45
shifting components back and forth to help the cell take in food,
0:49
remove waste,
0:51
let specific molecules in and out,
0:54
communicate with other cells,
0:55
gather information about the environment,
0:58
and repair itself.
1:00
The cell membrane gets this resilience, flexibility, and functionality
1:04
by combining a variety of floating components
1:08
in what biologists call a fluid mosaic.
1:13
The primary component of the fluid mosaic
1:15
is a simple molecule called a phospholipid.
1:19
A phospholipid has a polar, electrically-charged head,
1:22
which attracts water,
1:24
and a non-polar tail, which repels it.
1:27
They pair up tail-to-tail in a two layer sheet
1:31
just five to ten nanometers thick that extends all around the cell.
1:37
The heads point in towards the cytoplasm
1:39
and out towards the watery fluid external to the cell
1:42
with the lipid tails sandwiched in between.
1:47
This bilayer, which at body temperature has the consistency of vegetable oil,
1:51
is studded with other types of molecules,
1:55
including proteins,
1:56
carbohydrates,
1:57
and cholesterol.
2:00
Cholesterol keeps the membrane at the right fluidity.
2:03
It also helps regulate communication between cells.
2:07
Sometimes, cells talk to each other
2:09
by releasing and capturing chemicals and proteins.
2:13
The release of proteins is easy,
2:15
but the capture of them is more complicated.
2:18
That happens through a process called endocytosis
2:23
in which sections of the membrane engulf substances
2:25
and transport them into the cell as vesicles.
2:30
Once the contents have been released,
2:32
the vesicles are recycled and returned to the cell membrane.
2:36
The most complex components of the fluid mosaic are proteins.
2:42
One of their key jobs is to make sure
2:43
that the right molecules get in and out of the cell.
2:48
Non-polar molecules, like oxygen,
2:50
carbon dioxide,
2:51
and certain vitamins
2:53
can cross the phospholipid bilayer easily.
2:56
But polar and charged molecules can't make it through the fatty inner layer.
3:02
Transmembrane proteins stretch across the bilayer to create channels
3:06
that allow specific molecules through, like sodium and potassium ions.
