Protein Translation 1

Protein Translation 1

– So let’s say I have a piece of mRNA. And this mRNA was transcribed
or copied from a piece of DNA. And it’s holding information. And let’s say that each
one of these rectangles on our mRNA is one nucleotide. Every group of three nucleotides is going to code for one amino acid. So three nucleotides, or one codon. A codon is simply three nucleotides. Code for one amino acid. And what we want to do is we want to read this piece of mRNA. And put together all the
amino acids that it codes for in the precise order
that they’re coded for to make a polypeptide. So a polypeptide is a chain of
amino acids strung together. And now I want to take this polypeptide and fold it into all sorts of interesting shapes to make a protein. And some proteins actually have more than one polypeptide chain, like the protein hemoglobin for example. So hemoglobin is a protein in our blood that helps us carry oxygen. And it’s made up of
four polypeptide chains that are folded in a very
precise shape or a conformation. So the question is, how
do we get from this piece of mRNA to the polypeptide that we want? In other words, how do we
read this piece of mRNA? And the answer to that question is, through a process known
as protein translation. And protein translation
happens in an organelle in a cell called the ribosome. Which is the picture that
you’re seeing right in middle. And so let’s recap. So protein translation is
a process by which we’re going to take a piece of
mRNA and we’re going to run it through the ribosome. And the ribosome is going to put together the corresponding chain of amino acids known as a polypeptide. And where are these ribosomes found? Ribosomes are found in
the cytoplasm of the cell. And they’re also found
in a different organelle called the endoplasmic reticulum. And there are two types
of endoplasmic reticulum. There’s the smooth endoplasmic reticulum and the rough endoplasmic reticulum. And the ribosomes are found in the rough endoplasmic reticulum. And so by looking at this picture you can see that the ribosome
is made up of two units. A larger one and a smaller one. And here we get into some differences between eukaryotic cells
and prokaryotic cells. So let’s make a quick chart. We have eukaryotic cells
and prokaryotic cells. And in eukaryotic cells,
the larger sub unit is 60 S. It’s kind of way to measure it. And in a minute we’ll get
to what that S stands for. And the smaller unit is 40 S. But if the two units are
together combined they are 80 S. And in prokaryotic cells
the larger unit is 50 S. The smaller unit is 30 S. But if we combine them
together, they are 70 S. And you’re probably thinking
that I’m really bad at math because 60 plus 40 is not
80 and 50 plus 30 is not 70. So to clarify that let’s
talk about what this S is. So the S stands for a unit of
measurement called, Svedberg. And the Svedberg measures the rate of sedimentation of the ribosomes. So let’s explain what that is. So if I were to take a test tube and if I put some ribosomes
into this test tube, some big ones, some little ones, some larger sub units, some smaller ones, some of them are combined
large and small units. And of course the ribosomes are suspended in some sort of liquid. So if I were to take this test tube and spin it down in the centrifuge these ribosomes would all
fall down to the bottom. Settle at the bottom of the
tube at different rates. So the Svedberg measure
is the rate at which the ribosomes will fall to
the bottom of the test tube. And because the Svedberg does
not necessarily measure size the numbers are not additive. They don’t necessarily add up. So the next thing I wanna ask you is, so the ribosome is putting
together it’s polypeptide, he’s stringing together the amino acids, but where are the amino acids coming from? Like, where are they? And the answer to that question is that floating around in the cytoplasm and in the endoplasmic reticulum we have these molecules called tRNA. And they hold onto amino acids and bring the amino acids to the ribosome. So let’s see what a tRNA
molecule looks like. And I’m just gonna get rid of some of this RNA that’s coming out of the ribosome. And here’s our tRNA molecule. And I did not draw this to scale. So a tRNA molecule is really
much smaller than the ribosome. So it has this clover like shape and in real life it’s
actually a 3D structure. So we know it’s made up of RNA. So what does that T stand for? That T stands for the word transfer. So this is transfer RNA
and the reason it’s called transfer RNA is because
it’s job is literally to transfer amino acids to the ribosome. So it’s kind of like a mail man. It holds on to this
package, the amino acid. And it’s job is to bring
the package, or amino acid, to the proper address,
which is the ribosome. Or more specifically, a particular place on the mRNA that’s in the ribosome. But we’re not gonna get into that in such great detail right now. So let’s focus on this tRNA molecule. I want to look at one particular place on the tRNA molecule. This part right over here. And Im just gonna make some room. And I picked that part
because if you can see between the two yellow lines there
are three nucleotides there. And I want to blow up
those three nucleotides. And let’s say that these three
nucleotides are GG and G. And so the codon that’s
complementary to GGG is CCC. And the codon CCC happens to code for the amino acid proline. And so this particular tRNA molecule is going to carry the amino
acid proline right over here. And it happens to be that the bond between the amino acid
and this tRNA molecule is a very high energy bond. It’s relatively unstable
and just keep that in mind because we’ll talk about
that a little bit more later. Let’s do this again so that we get a clear idea of what’s going on. Let’s say that the codon that we’re looking at did not read GGG. Let’s say it read UUU. And again, remember we’re focusing on this bit right over here. And so the codon that’s
complementary to UUU is AAA. And AAA codes for the amino acid lysine. And so this particular tRNA molecule is going to carry the amino
acid lysine right over here. And so the part on the tRNA molecule, the part over here that determines which amino acid the tRNA
molecule is going to hold is called the anticodon. And then it’s complementary codon right over here is just a codon. And just bear in mind that the anticondon and codon are complementary to each other. And try not to get confused. The tRNA molecule is
not going to hold onto the amino acid that’s
coded for by the anticodon. So UUU happens to code for
the amino acid phenylalanine. But this tRNA molecule does
not carry phenylalanine. The tRNA molecule carries the amino acid that’s coded for by the codon that’s complementary to the anticodon. So in our case, the anticodon is UUU. The complementary codon is AAA. AAA codes for lysine. And so this particular tRNA molecule is going to carry the amino acid, lysine.

25 Replies to “Protein Translation 1”

  1. thank u, ur videos r very helpful but please make them short. sometimes the extra info makes ppl impatient

  2. Very helpful video, she expressed concepts clearly and has given me a better understanding. And she has a nice, subtle accent which added to the video.

  3. this woman blabs so much, this video is meant to explain the process of tranlation, and she always goes off topic about the size of things and everything, can you just please explain the process first and then write all the random things you want like size and differences bet euk and prok…

  4. This video is like the one I am getting from my lectures. They normally leave out some fine details to help student spend more time on other references. Overall a nice video, thank you.

  5. I'm trying to understand yet losing brain cells while doing so, on how she got 60 + 40 = 80??? can someone please explain this to me, am I missing something…?

  6. Sometimes it is bad to bring different topics together. I am in the middle of the video and still didn’t begin the translation process

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