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PROTEIN SYNTHESIS

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

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