Central Dogma - Video Tutorials & Practice Problems
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Central Dogma of Molecular Biology
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In this video we're going to do a quick refresher on the central dogma of molecular biology. And so recall from your previous biology courses that the central dogma of molecular biology casually refers to both the processes of transcription and translation. Now recall from your previous biology courses that the process of transcription is a process that will build an RNA molecule by using a DNA molecule as the coding template and recall that the process of translation is the process that builds a protein molecule by using the encoded messages of RNA. Now as we move forward in separate videos, we will briefly refresh your memory on the process of transcription as well as the process of translation. Now what you may not have known about the central dogma of molecular biology is that it only casually refers to both the processes of transcription and translation. But it directly refers to the unidirectional flow or in other words, the one directional flow of biochemical information from DNA to protein. And so in other words, what we're saying is that it is possible for DNA to be replicated. It's also possible for RNA to be reverse transcribed back into DNA. But once the transfer of nucleic acid information goes to protein, this is an irreversible process or a one directional or unidirectional process. And so if we take a look at our image down below we can better visualize this. And so notice on the left hand side over here we're showing you a DNA molecule and so we know that DNA, can be replicated and so this circular arrow going from DNA back to DNA is just representing the process of DNA replication. Now in addition to the DNA being replicated, we know that the DNA can be used as a coding template to build a molecule RNA. And so this arrow that goes, forwards here from DNA to RNA, is the process of transcription. Also, this RNA could be used as a template to build a corresponding DNA molecule and so that would be the reverse arrow going backwards from RNA to DNA. And so, this reverse arrow is going to be reverse transcription because it's the opposite of transcription. And then of course, we know that the RNA molecule can encode a message for building a protein and this is the process of translation. And so once again, the central dogma of molecular biology only casually refers to transcription and translation. However, directly refers to this unidirectional flow of information here, this one directional flow of information. So notice we only have one arrow going from left to right from RNA to protein. And so once the information in nucleic acids has been transferred to a protein, this is an irreversible process and the protein is not going to be used as a template for building a corresponding RNA, that does not happen. And so this unidirectional flow of information is what the central dogma of molecular biology directly refers to and this applies to all living organisms. And so this here concludes our brief refresher on the central dogma of molecular biology and as we move forward, once again, we'll get to talk, a little bit more about transcription and translation to refresh your memories from your biology courses. And so I'll see you all in that video.
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Transcription
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So later in our course, we're gonna talk a lot of details about transcription. But in this video, we're just gonna do a quick review. So recall that transcription uses an enzyme known as RNA polymerase. And in our previous videos, we talked about how words that end in A s e tend to be enzymes. And RNA polymerase is an enzyme, and it's an enzyme that polymerizes or builds RNA. So the function of this enzyme can kind of be read backwards, an enzyme that builds RNA. And so RNA polymerase can build many types of RNA, including messenger RNA or mRNA. And the RNA molecules that are built by RNA polymerase are built in a specific direction. And that direction is from the 5 prime to the 3 prime end of the molecule. And it does that by aligning free RNA nucleotides to a DNA template, as we already know. And so, RNA molecules, recall, have the same exact sequence as the DNA coding strand, with the exception that all of the thymines in the DNA are replaced with uracils in the RNA. And so let's take a look at our example below. And quick secret, this diagram here is not nearly as complicated as it looks. And so we've got a DNA molecule that stretches across the diagram, and the DNA molecule has 2 strands. It's got a dark colored purple strand and a light colored purple strand, and these strands go in opposite directions. They are anti parallel. And in the back, notice that we have this big pink thing that's kind of hard to miss. So has the ability to unwind the DNA, and we can see that here. When it unwinds the DNA, it separates the DNA coding strand from the DNA template strand. And the DNA template strand, which is down below here, is literally used as a template to build the RNA. And so free RNA nucleotides are aligned to the template and added to the 3 prime end of the mRNA molecule. And so the RNA is always gonna grow from the the DNA is being rewound back into its original state. And so over here on the far right, notice that this is a representation of the DNA molecule and the RNA molecule on the left. And so the dark colored purple strand goes from 5 prime to 3 prime, from left to right, and so this is a representation of that strand. The, light colored strand goes from 5 prime to 3 prime from right to left, and so that's represented here. And the RNA molecule goes from 5 prime to 3 prime from left to right. And so we're given the DNA sequence of the coding strand, and we have 2 questions. What's the sequence of the template strand and what is the sequence of the RNA strand? And so recall our base pairing rules. A's always pair with t's, and g's always pair with c's. And so, when we apply that here, here, g's pair with c's, a's pair with t's, and c's pair with g's again. And so, this is the sequence of our template strand. Now, what's the sequence of our RNA strand? Is it going to be the same as the coding strand or the same as the template strand? And recall, we've already said that the RNA molecule has the same sequence as the coding strand, with the exception that thymines are replaced with uracils. And so that means that our RNA strand down here is gonna have the same sequence as our coding strand. So we're gonna have g g a, except we're gonna replace thiamines with uracils, and c. And so transcription is a fundamental process that occurs in every single organism, so it's good to touch up on the basics. And in our next video, we're gonna do a recap on translation. So I'll see you guys in that video.
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Translation
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5m
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So you guys already know that translation is completed by ribosomes. But recall that there are also specialized RNA molecules called transfer RNAs or t RNAs that are also involved. And you've learned that ribosomes create proteins by reading the mRNA strand in 3 nucleotide chunks called codons. And these codons are interpreted with a genetic code. And down below, we have a genetic code shown by this table. A genetic code. And down below we have a genetic code shown by this table. And recall that tRNA's pair with amino acids. Acids. And each of the tRNA's contains a anticodon, contains an anticodon that is complementary to the codons of the mRNA. And so down in our example below, we're gonna use the genetic code to fill in the blanks throughout our diagram. And so notice in the back, we have this big teal structure that we know as the ribosome and ribosomes have a large and a small ribosomal subunit. If this were a eukaryotic ribosome, it would be an 80 s ribosome with a 60 s large subunit and a 40 s small subunit. But if this were a prokaryotic ribosome, it would be a 70 s ribosome with a 50 s large subunit and a 30 s small subunit. Large subunit and a 30 s small subunit. So in addition to the ribosome, we also have an mRNA molecule in the purple. And the mRNA molecule has a 5 prime and a 3 prime end and it also has a sequence. And the first three letters of this sequence correspond to our codon, codon, our first codon, which is AUG. And up above, we have our tRNA molecule, and we also have 2 more tRNA molecules shown in these positions. And notice that the tRNA molecules are associated and pair with amino acids that are shown up above. And in addition to pairing with amino acids, t RNAs also have an anticodon, which are shown at the bottom of these t RNAs. And the anticodons, recall, pair and, are complementary to the codons of the mRNA. And so recall that the genetic code here uses the codons of the mRNA, not the anticodons of the tRNAs. And so recall that the genetic code, the first letter of the codon limits you to a specific row. The second letter of the codon limits you to a specific column. And the 3rd letter of the codon limits you to a specific position within the block. And so our first codon is AUG. So A limits us to this row, U limits us to this column and to this block, and G limits us to this exact position within the block, which corresponds to a methionine amino acid. And we can see that that's true, that here we have a methionine amino acid, and that corresponds to an AUG codon. And so notice that our ribosome is moving in this direction. So it's moving from the 5 prime to the 3 prime end of the mRNA. And so it's moving in this direction and then here comes our tRNA that's making its way into this position. And notice that our next codon on the mRNA is UGG. And so for the anticodon, U's recall, are pretty much t's, so they pair with a's. So we can put an a here for the anticodon. G's again pair with c's. So our anticodon is gonna be a c c. Now, again, when we use the genetic code, be sure that you're using the codons of the mRNA, not the anticodons of the tRNA. So we're gonna use UGG, not ACC. Now, when we use UUG, I'm sorry, UGG, we get UGG and that's a tryptophan, and we can see that that is true, that here we have a tryptophan, and the tryptophan corresponds with a UGG codon. So now the ribosome, is going to link the methionine and tryptophan amino acids to start creating a protein. And now, it can the ribosome keeps moving, so now these t RNAs start to shift into the empty slots and eventually, they'll shift out of the ribosome completely. So now here comes our next tRNA making its way to the ribosome. And notice that our next codon is U U C, U U C. And so again, U's are pretty much t's and they pair with a's. So here we have a a g, because these are the codons. And so now, this is gonna make its way in here. And again, recall that the genetic code uses the codons of the mRNA, not the anticodons of the tRNA. So we're gonna use UUC, and notice that UUC gets us phenylalanine. So up here, we can put PHE for phenylalanine. And then again, this will also be connected to the chain of amino acids that continues to grow as t RNAs continue to feed in. And so, again, what'll happen is this n over here will end up being the n terminal end of the protein, whereas the last, amino acid that comes in will end up being the c terminal end of the protein. And recall that translation is a process that all living organisms do and the genetic code is pretty much universal and applies to all living organisms with some minor exceptions here and there. Now, in our next video, we're gonna directly compare transcription and translation. So I'll see you guys in that video.
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Transcription vs. Translation
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In this video, we're going to quickly compare transcription and translation. Transcription is in the left column in light blue whereas translation is in the right column in light pink. So for the product formed, we know that transcription builds RNA molecules, whereas translation builds proteins. Now, for the macromolecule change, we know that transcription uses DNA nucleic acids to build RNA nucleic acids, but we're still under the nucleic acid macromolecule category, and And so for that reason, we'll go ahead and put no here. Now for translation on the other hand, we're going from RNA nucleic acids to amino acids and proteins. So there's definitely a change in the macro molecule category. Now, for the major enzyme or structure, we know that transcription uses RNA polymerase or an enzyme that polymerizes or builds RNA. Now, for translation on the other hand, we know that we use ribosomes. Now, for the location of transcription, it's going to occur wherever the DNA is because the DNA acts as a template to build the RNA. And in eukaryotic cells, this is going to be the nucleus. Now for translation, it occurs in the cytoplasm of the cell. Now for the direction prime end prime end. However, in translation, the protein that's being built is being built from the end to the c terminal end of the protein. And so this concludes our comparison of transcription and translation, and I'll see you guys in the practice videos.
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Problem
Problem
What is the central dogma of molecular biology directly referring to?
A
Unidirectional Translation
B
Multidirectional Translation
C
Unidirectional Transcription
D
Multidirectional Transcription & Translation
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Problem
Problem
Consider a DNA template strand of the following sequence: 5'-A C T G C C A G G A A T-3'.
A) What is the sequence of the corresponding DNA coding strand? Include directionality.
DNA Template Strand: 5'-A C T G C C A G G A A T-3'.
DNA Coding Strand:
B) What is the sequence of the corresponding mRNA strand? Include directionality.
mRNA Strand:
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Problem
Problem
Consider a DNA coding strand with the following sequence: 3'-C T T C A T A G C T C G-5'.
Use the genetic code to determine the corresponding amino acid sequence of the translated protein.