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Central dogma - revisited

New discoveries have expanded on or even contradicted the original Central dogma of molecular biology as proposed by Watson and Crick. These discoveries include multiple alternate pathways of the molecules as well as different types of RNA that you'll need to know. By Tracy Kovach. Created by Tracy Kim Kovach.

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  • leaf green style avatar for user Miguel Barca
    At , I'm a little confused with the concept of epigenetics .. How do the epigenetics mechanisms actually work? The DNA sequence is modified (without changing the underline DNA sequence) by dna methylation and histone modifications. When does that occur? On the replication process? And what is the trigger for those mecanisms? I had a biology class at my college on this matter, and I was told that our behavior, how we live and even our vices can trigger those changes - from smoking, drinking, hunger to stress, depression etc - and have repercussions on the descendants, but I didn't understood very well to how.. Anyone care to elaborate?
    (33 votes)
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    • leaf green style avatar for user Cassie
      We just talked about this in my biology class, so I am by no means an expert, but the general idea is this:

      DNA has "CG" islands, which are cytosines next to guanines in the DNA sequence. Some of those cytosine base pairs are methylated, meaning they have a (-CH3) group attached to them. Since DNA is double stranded, if there is CG next to each other on one strand, there will be CG on the complementary strand, and both of those cytosines are methylated in order to preserve the methylation sequence during replication. When DNA replicates, it keeps one of its parent strands, and an enzyme called DNA methyltransferase is responsible for transferring a methyl group to the daughter strand's cytosine where the parent strand has a cytosine.

      Anyway, these (-CH3) groups prevent the DNA in that area from being transcripted by physically blocking protein binding in that area. Certain environmental factors can cause changes in the methylation pattern and cause some genes to be expressed or repressed. The example given in my class was an experiment with BPA and the Agouti gene. They found that intake of BPA during pregnancy can cause demethylation of the Agouti gene in the offspring, thus causing the gene to be expressed. This particular gene is associated with predisposition to obesity, so by giving the mothers BPA, they altered the phenotype of the offspring without actually altering the DNA sequence.

      I hope that helps!
      (93 votes)
  • leafers seed style avatar for user meganreimer40
    Why are Rosalind Franklin's contributions so overlooked?
    (16 votes)
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    • leaf green style avatar for user Daniel
      Watson, Crick, and Franklin were working on the same problem but using different approaches, and not necessarily with the same goal in mind. Watson and Crick were at the University of Cambridge, while Franklin was at King's College in London.

      Basically, the scientists at King's College had to put together presentations about their research to give to a review committee. One member of the review committee, Max Perutz, happened to be Crick's adviser. Perutz gave Watson and Crick copies of Franklin's research, which proved key to the discovery of the structure of DNA.

      It was all pretty underhanded, and Perutz later issued an apology. Watson and Crick received the Nobel prize for their discovery in 1962. I don't know whether Franklin would have been included in that award, because she died in 1958--and Nobel prizes are not awarded posthumously.
      (39 votes)
  • leaf yellow style avatar for user Tricia Malcolm
    At :58, why doesn't Rosalind Franklin get more credit for her contributions? If the information she discovered was so critical for Watson and Crick.
    (5 votes)
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    • piceratops ultimate style avatar for user Erin Becker
      1) She was a women.
      2) When Watson and Crick were awarded the Nobel prize for their discovery of the structure of DNA, Franklin had already died (of cancer). The Nobel prize is not awarded posthumously , and so Franklin's contributions went unrecognized at the official level.
      (22 votes)
  • leaf green style avatar for user adarshjvq
    How many types of RNA are there?
    (4 votes)
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  • leafers seed style avatar for user meganreimer40
    What is DNA methylation?
    (5 votes)
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  • blobby green style avatar for user poojavasanthi
    How is double-stranded DNA produced from the single-stranded RNA genome of a retrovirus? Is a complementary RNA strand produced, after which DNA strands are synthesized complementary to both the RNA strands?
    (3 votes)
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    • aqualine ultimate style avatar for user Alessandro.M.Rosa
      If we use HIV as an example, the viron comes prepackaged with the viral RNA genome and the Reverse Transcriptase (RT) enzyme premade. The viron fuses to the plasma membrane of the cell and delivers its payload into the cytosol of the cell. Once inside the cytosol, RT synthesizes the complementary DNA copy of the RNA template. RT also has RNAse activity and degrades the RNA template and catalyzes the polymerization of the second strand of DNA. The resulting double stranded DNA is termed a Provirus. The provirus migrates to the nucleus where a viral integrase enzyme, also prepackaged in the viron inserts the provirus into the host cell's DNA. From that point, the host cell begins to produce mRNA transcripts that begin the process of viral protein synthesis and viral replication.
      (10 votes)
  • duskpin sapling style avatar for user Asad
    Yep... SARS... that is the most famous coronavirus... this video hasn't aged well
    (7 votes)
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  • orange juice squid orange style avatar for user Abraham George
    Why is it called the Central Dogma of Biology? What does Dogma mean?
    (4 votes)
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  • leaf green style avatar for user seixastrevor
    What differs between a RNA virus and a retrovirus? Retroviruses exist primarily as RNA (like RNA virus). Is there only difference really one incorporates itself into the genome of the other organisms and the other one doesn't. In RNA viruses your final product in a protein and your final product in a retrovirus is incorporation into the DNA (which will than encode a protein...which makes it more confusing.
    (4 votes)
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    • piceratops ultimate style avatar for user spencersck
      Hey! So from my research I've found that retroviruses are a type of RNA Virus which has DNA as a genomic intermediate. So not all RNA Viruses are retroviruses, but all retroviruses are RNA Viruses. Other types of RNA viruses just don't have to have a DNA intermediate. Hope that helps!
      (6 votes)
  • leafers tree style avatar for user Bahaar Chawla
    This video is meant to discuss ways in which the central dogma is violated. Wouldn't alternative splicing also count as violating the traditional "1 gene-1 protein"?
    (3 votes)
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    • piceratops ultimate style avatar for user spencersck
      Hey Bahaar, you're right! The 1 gene 1 protein element of the central dogma has since been found to have its exceptions. Since alternative splicing can yield various proteins from the same initial RNA transcript, the 1 gene 1 protein clause does not hold. Hope that helps!
      (3 votes)

Video transcript

Hey. So you may have seen another video in which I talk about the central dogma of molecular biology, and this being the work of Francis Crick and James Watson, who delineated the structure of DNA and determined the flow of information to be from DNA to RNA to protein. And while this is the traditionally held view of the flow of information in living organisms, there have also been a lot of new discoveries that extend or even contradict the central dogma. And so I'm going to expand on some of those ideas here. And so this is the central dogma revisited. Before I go on and touch on those new ideas though, I would like to highlight the legacy of another famous scientist whose work was so, so critical to elucidating the double helix structure of DNA. And that was the work of Rosalind Franklin, seen here. And her contributions often go overlooked, of which I am just as guilty. And Franklin's work on the X-ray diffraction images of DNA and her interpretation of that data were key to confirming the helical structure of DNA. And so whenever there's a mention of Watson and Crick, Rosalind Franklin deserves a shout out as well. So now on to the conflicting versions of the central dogma of molecular biology. As I said before, the traditional held view of the central dogma was that the flow of information occurs from DNA to RNA to protein. And DNA goes to DNA via replication, from DNA to RNA via transcription, and from RNA to protein via translation. And basically proteins perform virtually all the tasks within living cells and make up the very structure of those cells. It would be premature though to think that information flows in these pathways only and that proteins are the final expression of the information encoded in our DNA. So now that we have a firm foundation what the central dogma was as it was conceived originally, we can explore some of the newer discoveries that have been made that expand on this concept. And the first idea is that of reverse transcription, in which information flows backward, if you will, from RNA to DNA. And reverse transcriptase is an enzyme that generates complementary DNA or cDNA from an RNA template. And reverse transcriptase is needed for the replication of retroviruses, including HIV, is probably the most well known one. And these retroviruses use the enzyme to reverse transcribe their RNA genomes back into DNA, which is then integrated into the host genome and replicated along with it. So this is the first idea-- it was discovered back in 1970-- that violated the central dogma. It was very unpopular at first, saying that information can actually flow from RNA back to DNA. Now another example of an alternate pathway for information flow is demonstrated by a group of viruses called RNA viruses. Now, these viruses have their genetic material stored as RNA, as opposed to DNA. And they can have their genome directly used by host cell replication machinery as if it were messenger RNA and then translated directly into protein. Or they can have their RNA serve as a template for another RNA strand, that is then used for protein translation. Some well-known examples of RNA viruses are the coronavirus, which was responsible for the SARS epidemic; the influenza virus responsible for the flu, that you have to get a shot for every year, and also paramyxovirus, which is the virus responsible for measles. Now, the next idea that represents a deviation from the central dogma as it was originally conceived is the discovery of what is called noncoding RNA or ncRNA. Noncoding RNA is a functional RNA molecule that skips this last step of being translated into a protein and can directly perform functions within the cell as an RNA molecule. Now, two examples of functional RNA molecules that you might be familiar with are transfer RNAs and also ribosomal RNA, both of which are used for the translation of messenger RNAs into proteins. Now a final consideration that I'll be bringing up that sort of expands on the central dogma is the field of epigenetics, which is the study of heritable changes in gene activity that are not caused by changes in DNA sequence. So unlike in simple genetics where changes in phenotype are based on changes in genotype, epigenetics describes the mechanism where the same DNA sequence can be modified, resulting in a different phenotype without changes to the underlying DNA sequence. Now, some examples of mechanisms that produce such changes are DNA methylation and also histone modification. And this can help explain why you can have the same DNA in each of the cells of your own body, but those cells don't necessarily look or behave the exact same way. For example, the DNA contained in the nucleus of, say, one of your muscle cells is the same DNA that's contained in one of your skin cells, the same DNA in the nucleus of those cells, but these two cells are different because the expression of that DNA is modified by these epigenetic mechanisms. And these epigenetic mechanisms allow the transcription of only certain genes within the genome, depending on the type of cell.