MUTAAION

Five years of heavy meticulous biology courses, and it all boils down to one single idea:

DNA -> RNA -> Protein

This is known as the central dogma of Biology.

Really, that’s all there is to it. Every single life-form on Earth follows this universal norm (except for retroviruses- these are the viruses that have an RNA rather than a DNA genome and so they go the other way around, hence the “retro” prefix. That group includes the notorious HIV).

Retroviruses aside, all organisms are made up of the same genetic material. So an ant, a clam, an elephant, a bacterium, and us humans, are all made up of the same molecules. What molecules are we talking about? You guessed it, DNA.

DNA stands for deoxyribonucleic acid. Thanks to Watson & Crick in the early ‘50s, we now know that DNA is a double helix that has sugar (deoxyribose) phosphates in the backbone and nitrogenous bases in the middle, connected by hydrogen bonds.The sugar, phosphate, and nitrogenous base moieties are collectively known as a nucleotide.

There are 4 different nucleotides: Adenine (A), Guanine (G), Thymine (T), and Cytosine (C).

The whole of life is based on these 4 “letters”

So if  all organisms carry the same genetic material, how come we’re all different? The difference lies not in the molecule itself, but rather in the order of these molecules, in their sequence.

Alright, so we have a differential DNA sequence, what does this mean? Let’s take a look at the second component of our central dogma, RNA.

RNA stands for Ribonucleic acid (notice the “deoxy” prefix is missing. This is because DNA and RNA differ by one oxygen molecule in the sugar moiety, it is missing in DNA).

In a process termed transcription DNA is transcribed into RNA, particularly messenger RNA or mRNA. As its name indicates, it carries a message. This message will subsequently be translated into proteins in a process known as translation.

There is a specific genetic code that translation follows: The nucleotides are read in groups of 3’s known as codons. A codon will be translated into an amino acid (building blocks of proteins), and hence a whole sequence will eventually give a protein (the final component of the central dogma).

The following table shows the different codons and their corresponding amino acid.


Notice the redundancy in the code: multiple codons can give the same amino acid (this is logical because we have 64 possible codon combinations and only 20 amino acids). Keep this idea in mind, I shall return to it later.

So to sum up: A sequence of DNA will be transcribed into an mRNA which in turn will generate a sequence of amino acids through translation. A few modifications later, a fully-functional protein is produced.

Voila! The crash course on basic genetics is over. Now the fun part (I have an unconventional definition of fun):

Mutations.

We are all familiar with the fact that our cells divide. And for the genetic material to be passed on equally to the daughter cells, it has to be duplicated before it is divided. This duplication process is known as DNA replication.

The enzyme responsible for this process is prone to error and, consequently, a replicated sequence can lack a 100% identity to the original.

Let’s take an example.

In this case, we have a substitution of the A nucleotide by the T nucleotide. This changes the GAG codon to a GTG codon.  This substitution eventually generated another amino acid,Valine instead of Glutamic acid.

The gene in question is the Hemoglobin gene. The hemoglobin protein is found in your red blood cells where it takes on the chore of carrying oxygen from your lungs to the rest of your body. The substituted amino acid has different physio-chemical properties than the original one and subsequently leads to deformed red blood cells. (The picture below depicts the regular red blood cells which are round biconcave disks next to the malformed sickle cells)

 

But mutations do not always end up with deleterious effects. Which reminds me, sickle cell disease actually has an advantage when found in a heterozygous state- that is when only one allele is mutated rather than both. The advantage is a higher resistance to Malaria. How? The agent of Malaria is an intracellular parasite called Plasmodium falciparum. The target cells of this parasite are usually red blood cells. Once inside, the parasite feeds on hemoglobin. The mutated hemoglobin in sickle cell disease is more difficult to digest. (Think of this: What if sickle cell was brought about as a defense to Malaria, and it just so happened to have a different side-effect when found in a homozygous state?)

Pardon the digression, back to our topic.

Remember the redundancy of the genetic code I mentioned earlier? Consider this: what if a mutation occurred in such a way as to generate a different codon, but one that codes for the same amino acid? Well in  that case, we have no problem, and what would’ve taken place is termed a silent mutation.

Another case would be having a mutation in a non-coding part of the DNA. Only 3% of our (humans) DNA is coding (i.e gives a protein), the rest is known as junk DNA.

This sounds like a total waste of space and energy. Why house 97% of useless DNA, better yet, why go through the trouble of replicating it at every cell division? You have to keep in mind that all cellular processes demand energy and resources. A dead-end process that aimlessly uses up these resources would surely be eliminated by evolution.

How is it then, that junk DNA was preserved?

Well, this brings us to the reason why I chose to write this article. When people hear the word “mutation”, they automatically assume it is a bad thing. It needs to be clarified that mutation is not an aberration, otherwise it would’ve been immediately (in evolutionary time) gotten rid of. Mutation is a necessity for the the perpetuity of life. It is the motor that drives the whole of evolution, by constantly supplying natural selection with a myriad of different “options” that would be then cherry-picked in accordance with the pressure in question.

We seem to have reached an obstacle. How do we allow mutation to take place while simultaneously avoiding any deleterious effects?

It seems evolution has devised an ingenious scheme yet again. Junk DNA.

With no selection pressure against it, the accumulation of mutations is unleashed, paving the way for the possible emergence of a new gene that might be favored by natural selection.

 

Newly-acquired genes can easily be observed in experiments performed on bacteria. This is because they have a very small generation time (optimal conditions can give you a new generation every 20 minutes) and because selective pressures can be easily applied.

First idea that should come to mind? Anti-biotics. Try growing a bacterial cell culture on a petri dish that has a certain anti-biotic embedded in it. Most colonies will probably die out. Eventually though, one colony will develop a resistance to that anti-biotic and spread like wildfire. The advantageous trait will be passed on from generation to generation until your whole petri dish is swarming with resistant bacteria.

This is why you shouldn’t pop anti-biotics like M&Ms. It’ll be like the experiment we talked about, except, you are the petri dish.

 

Well, to wrap this up, I hope you can now see mutation in a new light and you can better comprehend how evolution takes place.

For my next article.. no, I’ll leave you in suspense.

Stay tuned.

 

 

 

 

 

 

 

 

 

 

 

 




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Comments

comments

10 Comments

  1. Sami Ab.

    Quite interesting.

    “A dead-end process that aimlessly uses up these resources would surely be eliminated by evolution.”

    Can you elaborate more, on how would anything be eliminated by evolution? and what decides whether a certain molecule is to be preserved (like DNA) or eliminated ?

  2. Think of it this way: Organism A uses its energy efficiently. Organism B wastes some of its energy by spending it on some useless feature. Now consider the presence of a certain stressful condition, example: paucity of food, lack of water, disease, being chased by a predator etc.. Such conditions usually demand more energy. Who do you think would be a better candidate when it comes to surviving these conditions?

    It’s just like the tail being eliminated in apes. It’s there, it’s of no use (because apes colonized the ground rather than tree canopies), then why bother keeping it and wasting energy on it (by constantly supplying it with oxygen, nutrients, heat, etc..) ?

    Keep in mind, that when talking about evolution eliminating a certain feature, it is only doing so by eliminating the organism that is carrying that feature, rather than the feature itself.
    So you will probably find the feature somewhere else in the animal (or another) kingdom, provided it conferred some kind of advantage to is survival. In this case, the tail is still found in monkeys.

    The only thing that decides which feature should and shouldn’t be preserved, is whether the organism carrying this feature lives long enough to pass it on. (Yes, long enough, not just long. Expect an article about this)

  3. CedarBlood

    “provided it conferred some kind of advantage to is survival. In this case, the tail is still found in monkeys.”
    I beg to differ.from the top of my head i can think of Ostriches that still have small wings that are useless.
    hello Karen…
    umm… just out of interest did you spell mutation “MUTAAION” on purpose or was it a typo…
    Excellent article by the way
    :)Cheers!

  4. You’re on fire, eh my friend? Don’t get me wrong, I love arguing.

    So for starters, yes, the title was intended to be misspelled. I saw potential with the letters “A” and “T” being adjacent, just like (some) Adenine and Thymine residues in DNA. (Come on, give me some credit, I proof-read my work).

    Now for your comment on ostriches. Yes they still have their wings, but compare those wings to those found on birds that actually do fly, and you will see a significant reduction in size (called rudimentary or vestigial features, just like the coccyx in humans being a vestigial tail). So give it time, evolution is a slow process 🙂

  5. CedarBlood

    Quote: “but compare those wings to those found on birds that actually do fly, and you will see a significant reduction in size”

    Not true. Compared to birds that actually fly, ostriches have a large wingspan; 2 metres in fact.
    If you meant proportionally to their size then yes.

    Keep in mind that just because their wings aren’t used for flight any more, doesn’t mean that they will/must fade away with time.
    There is even a chance that the wings will get bigger, who knows really.
    However, I have made a mistake saying ostrich wings are useless. They are used in mating, insulation, balance to name a few.
    Regardless, vestigial features don’t have to be eliminated, they may even return.
    Cheers

  6. Proportionally, evidently.
    Their wings will not fade away, anatomically speaking, provided they serve a function. But a functional wing will (insofar as flight is concerned).

    “There is a chance that the wings will get bigger, who knows really.” Yes exactly. Why, then, did you protest my previous statement concerning the surprises that evolution has yet to disclose?

  7. CedarBlood

    Hello again!
    hope every thing is well
    “There is no telling whether this version will be modified or not in the future”
    I protested this sentence since the version(a specie) will most defiantly be modified with time. but how? we don’t know
    were as a trait being eliminated or not that’s something else.

    if the sentence was “There is no telling whether this version will be eliminated or not in the future”
    then I would have agreed.
    You have to understand that my point of view is that vestigial features don’t necessarily have to be eliminated.
    cheers

  8. Oh no! No no no. When I say version, I am talking about a specific trait, not about a certain species. Please keep up. The trait is eliminated by eliminating the organism carrying it, not the whole species!

    Correction: Vestigial features don’t necessarily have to be eliminated PROVIDED they have a function, regardless of whether this function has changed or not. (I keep repeating myself please stop making us move in circles. An example would probably help. See? Repetition again!)

  9. CedarBlood

    Quote : “undesirable traits would have been carefully filtered out while good ones were preserved, ultimately giving rise to the final and perfect version”
    I understood version to mean the currant “version” of humans, not a version of a trait.
    If you meant a version of a trait then i agree with
    “There is no telling whether this version will be modified or not in the future”
    However I still disagree with the final and perfect version quote. even for a trait.
    An appendix has almost no function and yet it still is there
    you will then say , ” Ah , but the appendix will disappear in time!”
    I say ! maybe…
    we don’t know
    we can speculate all we want, still it wont make a difference to what will happen.
    we’ve experience the appendix in its form as it is now.
    the appendix, as it is right now,a blind-ended tube that has no apparent function and it change from a blind-ended tube that had a function.
    hence humans could digest the cellulose molecules that are found in plants and now humans can’t.
    the trait is gone , and it wasn’t in error
    it simply wasn’t as much useful any more.
    and as for the final and perfect version
    you said it yourself : “There is no telling whether this version will be modified or not in the future”
    so you can’t say final
    and we dont know what a perfect trait would be, its a standard that on changing and relative.
    hence, saying final and perfect version is misleading, inaccurate and unscientific.
    that was my initial point.
    hope this clears things up.
    cheers

  10. So now you are taking me back to something we discussed months ago. I’m sorry I won’t have this debate again. Just re-read whatever I had to say back then.

    And no, humans never were able to digest cellulose. Not even herbivores digest cellulose. This can only be accomplished with the aid of the symbiotic microflora of the gut.

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