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Lately, we have been talking about DNA, and how AWESOME DNA is. But what we have not talked
about is how DNA actually codes for your traits. Say, for example, we’re talking about your
eye color. Yes, the DNA codes for the genetic information that codes for the color of your
eyes. How exactly does that work? Well, keep in mind that your eyes are the color that
they are based on a pigment that is inside the eyes. In order to have that pigment, your
DNA must code for proteins that help make that pigment, which gives them their color.
So today what we’re going to talk about is how your DNA leads to a protein. This is
actually called protein synthesis. Just like it sounds -whenever you say synthesis - that
means to “make something.” Protein synthesis means to make protein. Whenever we’re talking
about protein synthesis, we also need to realize this is happening in all of your cells. All
of your cells contain your DNA. While not all of the DNA is turned on at any given time
(it’s based on what kind of cell we’re talking about), that DNA is present in the
nucleus of all of your cells. What we have to consider is, "How are we going to get the
genetic information that's in the DNA (which is inside the nucleus) out of the nucleus
so that the cell can start producing the proteins that it needs to make based on the genetic
instructions?" Well in order to answer that question, we need to go into the process of
protein synthesis. In protein synthesis, there are two major steps. One is transcription
and the other is translation. There are actually a lot of “trans” words that we’ll get
into in biology, but just stay with me here. Transcription has a C in it, and translation
has an L in it. I remember that C comes before L in the alphabet, which helps me remember
that transcription comes first. That’s always kind of helped me. Now, transcription is when we’re
going to transcribe the DNA into a message. If you think about that, think where DNA is.
The DNA is always in the nucleus, so we’re starting transcription in the nucleus. The
DNA is going to have matching RNA bases matched up to it with the help of enzymes to make
mRNA. In transcription, we make mRNA. We made a message out of RNA. At the end of transcription,
we have made an mRNA molecule. Remember that’s messenger RNA. One great thing about being
an mRNA? You can get out of the nucleus. The mRNA goes out of the nucleus where it’s
going to attach to a ribosome. Remember, ribosomes make protein. Also remember that the r for
ribosomal RNA is what makes up a ribosome. The messenger RNA is going to go to a ribosome,
which is made out of rRNA, and use the message to build our protein. This step is going to
be called translation because we’re translating our message into protein. We are also outside
of the nucleus, we are in a ribosome so that is our location is now. You know, you can
find a lot of great clips and animations on translation that are just fantastic. What
I like to think of you’ve got this mRNA and it’s in a ribosome and then you have
these tRNAs coming in. tRNA, remember that stands for transfer RNA, they have an amino
acid on them. An amino acid is the monomer for a protein; it is a building block for
protein. If you get a bunch of amino acids together, you build this big ole protein.
All of these tRNAs are looking for the matching bases on the mRNA. When they find the matching base
pairs on the mRNA, they carry and drop off their amino acids that it goes to. So eventually
what ends up happening is you get this big chain of amino acids that have to match up
with the coding on the mRNA. The different amino acids are held together by a peptide
bond, which is basically a protein bond. You end up with a really long protein made of
all these amino acids, which now can be used for all kinds of different body processes
and that could be something, for example, if we’re going to make eye pigment. One
important thing to mention is that when the tRNA is bringing in the amino acids, it reads
the letters on the mRNA in threes. This means that every time you have three bases, that
is how it reads it. So it doesn’t read one letter at a time, it reads it in triplets.
That’s called a codon. A codon is three bases. So, for example, if you had an
mRNA strand, you wouldn’t just read: A, then U, then G, then some other letter. It
would read AUG together in a triplet, a codon. Because it reads in threes, when we get into
mutations we’ll talk about how if you end up taking out one letter it could be very
bad. If you read in threes and you take out one letter, it will mess up your reading frame
for the rest of that strand. When we get into mutations, we’ll really get into that. One
thing I really like to encourage with topics like this in biology, it’s really great
to have some kind of activity so that you can really walk through it. It’s really
hard to visualize this protein synthesis, but if you can do an activity where you’re
actually involved in it, it can help make a lot more sense, I promise. So if you do
a search for “PBS DNA Workshop,” you will pull this great resource. The PBS
DNA Workshop not only has a little workshop of DNA replication, but it also has a great
protein synthesis activity where it will actually let you do the protein synthesis – both
the transcription and translation. It’s highly recommended. Anyway, that’s it for
the Amoeba Sisters, and we remind you to stay curious.
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