Protein Synthesis in the Cellular Factory

Protein Synthesis in the Cellular Factory


If you could step inside one of your cells, you’d see something that looks a lot like
a factory building thousands of different molecular machines. It would have tiny assembly
lines starting in the cell’s nucleus and stretching out to structures called ribosomes. These assembly lines start with DNA and build
RNAs and Proteins—-in a very real sense, you. DNA has all the blueprints for everything
the cell will ever need to build. RNAs are assorted molecular machines that
do all kinds of work in the cell. They carry components from place to place, ratchet up
the speed of operations, switch other machines on and off, and relay coded instructions from
the nucleus out to the factory floor. The other product, proteins, are strong molecular
machines that do things like hold the cell together and send signals to other cells. There are two parts to each assembly line:
the first builds RNAs, and the second builds proteins. The process that builds RNAs is called transcription.
It happens in the cell’s central office: the nucleus, where DNA blueprints are stored.
Let’s say that a cell needs to make a transfer RNA, or tRNA, a triangle shaped RNA, which
transports a building material called an amino acid. It starts at a tiny, specific region of DNA
with the code that makes the tRNA we need. This region is called a gene. A protein machine inside the nucleus pries
apart the weak bonds that hold the two strands of DNA together. RNA building blocks swarm
in and form a conga line complementary to the DNA. This RNA strand now needs to fold up. In the
world of tiny cellular machines, shape determines function. RNA’s four bases bond to each other
and give the tRNA its 3D shape. And voila! Our transfer RNA is ready for action. It floats
out of the nucleus and picks up an amino acid. We’ll come back to our tRNA in just a moment. Now let’s look at the second half of the factory’s
assembly line—-making proteins from RNA—-a process called translation. Remember the scrape? This cell needs to make
Thrombin, a protein machine which helps blood clot and make a scab. Thrombin is just one
of the tens of thousands of proteins your cells can make. Before translation begins,
the cell transcribes a special type of RNA called mRNA, or messenger RNA. This mRNA carries
the code for Thrombin out of the nucleus and onto the cellular factory floor. Our mRNA drifts until it runs into a ribosome,
a protein-making machine. The ribosome clamps down around the mRNA.
tRNAs, just like the one we made earlier, drift in. The messenger RNA carries a coded
message, which the tRNAs translate into amino acids—-the language of proteins. This process,
translation, proceeds down the mRNA, creating a chain of bonded amino acids. Just as with
RNA, molecular shape determines molecular function, so these amino acids fold up into
the protein’s 3 dimensional form. Finally, the ribosome comes to a bit of code
that says “ok, we’re done here” and releases its completed protein into the cell. So there you have it. DNA encodes genes to
make RNA machines, and the ribosome translates special mRNA, which in turn makes protein
machines. Unlike most factories, your cell uses just two processes to make tens of thousands
of different molecular machines. It’s like one factory that can build toasters, phones,
cars, and even repair itself.

20 Replies to “Protein Synthesis in the Cellular Factory”

  1. Poor kid, no thromboplastin? No plastids? Who allowed a hemophiliac on a skateboard anyway? Little Skeffington Flerptwoodle bled to death today, through his kneecap, due to a lack of video length. Had he gotten more screen time he might have had a chance to form a scab, but sadly….. no.

  2. This is one the best, most comprehensive, lucid and easy to understand presentations on specialized cell processes. 

  3. “Scientific/learning” videos like this aimed towards adolescents or meant to be understandable for lay people are usually too watered down to teach anything at all. But this is impeccable! From the animation style to use of actual surface structure models for the proteins to even the sound design. I’ll be passing this along to anyone I can!

  4. Man this is very cool! Thank you PBS for creating such a wonderful video. I would also like to thank my Teacher for recomending I watch this truly amazing video. My perceptive of life has changed now. Thank you so much.

    Greetings from Period 3 Bio!

  5. Wow the video is really good, but the entire time I was just thinking of how clean the animations were. Wow! I appreciate "realistic animations" but I think I have even more appreciation for clean and smooth animations like this one where so much is going on!

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