Cell membranes are way more complicated than you think - Nazzy Pakpour
-
0:07 - 0:11Cell membranes are structures
of contradictions. -
0:11 - 0:17These oily films are hundreds of times
thinner than a strand of spider silk, -
0:17 - 0:21yet strong enough to protect
the delicate contents of life: -
0:21 - 0:25the cell's watery cytoplasm,
genetic material, organelles, -
0:25 - 0:28and all the molecules it needs to survive.
-
0:28 - 0:35How does the membrane work,
and where does that strength come from? -
0:35 - 0:37First of all, it's tempting to think of a
cell membrane -
0:37 - 0:40like the tight skin of a balloon,
-
0:40 - 0:43but it's actually something
much more complex. -
0:43 - 0:46In reality, it's constantly in flux,
-
0:46 - 0:49shifting components back and forth
to help the cell take in food, -
0:49 - 0:51remove waste,
-
0:51 - 0:54let specific molecules in and out,
-
0:54 - 0:56communicate with other cells,
-
0:56 - 0:58gather information about the environment,
-
0:58 - 1:01and repair itself.
-
1:01 - 1:05The cell membrane gets this resilience,
flexibility, and functionality -
1:05 - 1:08by combining a variety
of floating components -
1:08 - 1:13in what biologists call a fluid mosaic.
-
1:13 - 1:15The primary component of the fluid mosaic
-
1:15 - 1:19is a simple molecule
called a phospholipid. -
1:19 - 1:23A phospholipid has a polar,
electrically-charged head, -
1:23 - 1:24which attracts water,
-
1:24 - 1:28and a non-polar tail, which repels it.
-
1:28 - 1:31They pair up tail-to-tail
in a two layer sheet -
1:31 - 1:38just five to ten nanometers thick
that extends all around the cell. -
1:38 - 1:40The heads point in towards the cytoplasm
-
1:40 - 1:43and out towards the watery fluid
external to the cell -
1:43 - 1:47with the lipid tails
sandwiched in between. -
1:47 - 1:52This bilayer, which at body temperature
has the consistency of vegetable oil, -
1:52 - 1:55is studded with other types of molecules,
-
1:55 - 1:56including proteins,
-
1:56 - 1:57carbohydrates,
-
1:57 - 2:00and cholesterol.
-
2:00 - 2:04Cholesterol keeps the membrane
at the right fluidity. -
2:04 - 2:08It also helps regulate communication
between cells. -
2:08 - 2:10Sometimes, cells talk to each other
-
2:10 - 2:13by releasing and capturing
chemicals and proteins. -
2:13 - 2:15The release of proteins is easy,
-
2:15 - 2:19but the capture of them
is more complicated. -
2:19 - 2:23That happens through a process called
endocytosis -
2:23 - 2:26in which sections of the membrane
engulf substances -
2:26 - 2:30and transport them into the cell
as vesicles. -
2:30 - 2:32Once the contents have been released,
-
2:32 - 2:37the vesicles are recycled and returned
to the cell membrane. -
2:37 - 2:42The most complex components
of the fluid mosaic are proteins. -
2:42 - 2:44One of their key jobs is to make sure
-
2:44 - 2:48that the right molecules
get in and out of the cell. -
2:48 - 2:50Non-polar molecules, like oxygen,
-
2:50 - 2:52carbon dioxide,
-
2:52 - 2:53and certain vitamins
-
2:53 - 2:57can cross the phospholipid
bilayer easily. -
2:57 - 3:02But polar and charged molecules can't
make it through the fatty inner layer. -
3:02 - 3:07Transmembrane proteins stretch
across the bilayer to create channels -
3:07 - 3:12that allow specific molecules through,
like sodium and potassium ions. -
3:12 - 3:15Peripheral proteins floating
in the inner face of the bilayer -
3:15 - 3:20help anchor the membrane to the cell's
interior scaffolding. -
3:20 - 3:25Other proteins in cell membranes
can help fuse two different bilayers. -
3:25 - 3:29That can work to our benefit,
like when a sperm fertilizes an egg, -
3:29 - 3:34but also harm us,
as it does when a virus enters a cell. -
3:34 - 3:37And some proteins move within
the fluid mosaic, -
3:37 - 3:42coming together to form complexes
that carry out specific jobs. -
3:42 - 3:46For instance, one complex might
activate cells in our immune system, -
3:46 - 3:50then move apart when the job is done.
-
3:50 - 3:53Cell membranes are also the site
of an ongoing war -
3:53 - 3:57between us and all the things
that want to infect us. -
3:57 - 4:01In fact, some of the most toxic
substances we know of -
4:01 - 4:06are membrane-breaching proteins
made by infectious bacteria. -
4:06 - 4:10These pore-forming toxins poke
giant holes in our cell membranes, -
4:10 - 4:14causing a cell's contents to leak out.
-
4:14 - 4:17Scientists are working on developing
ways to defend against them, -
4:17 - 4:20like using a nano-sponge
that saves our cells -
4:20 - 4:24by soaking up
the membrane-damaging toxins. -
4:24 - 4:29The fluid mosaic is what makes
all the functions of life possible. -
4:29 - 4:32Without a cell membrane,
there could be no cells, -
4:32 - 4:35and without cells,
there would be no bacteria, -
4:35 - 4:36no parasites,
-
4:36 - 4:37no fungi,
-
4:37 - 4:39no animals,
-
4:39 - 4:41and no us.
- Title:
- Cell membranes are way more complicated than you think - Nazzy Pakpour
- Description:
-
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View full lesson: https://ed.ted.com/lessons/cell-membranes-are-way-more-complicated-than-you-think-nazzy-pakpour
Cell membranes are structures of contradictions. These oily films are hundreds of times thinner than a strand of spider silk, yet strong enough to protect the delicate contents of life: the cell’s watery cytoplasm, genetic material, organelles, and all the molecules it needs to survive. How does the membrane work, and where does that strength come from? Nazzy Pakpour investigates.
Lesson by Nazzy Pakpour, animation by Zedem Media.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:21
Jessica Ruby edited English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour | ||
Sara Malaguti commented on English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour | ||
Ciro Gomez commented on English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour | ||
Jessica Ruby approved English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour | ||
Jessica Ruby accepted English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour | ||
Jessica Ruby edited English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour | ||
Jennifer Cody edited English subtitles for Cell membranes are way more complicated than you think - Nazzy Pakpour |
Ciro Gomez
4:05. It's not "These poor-forming toxins" but "These pore-forming toxins"
Sara Malaguti
Thank you Ciro. Anyway, my translation is referred to the expression "pore -forming toxins". I have been looking to this expression on some quoted scientific websites (Researchgate, Nature and NCBI) to make sure about the meaning and its translation in Italian. So I'm pretty sure of my translation, which is "tossine perforanti". Bye!