I am making a DNA model for my class, and I looked up some examples and they all have different sequences of bases. If I choose an arbitrary sequence like:




Is there any reason it would not exist in nature?

  • $\begingroup$ What do you mean by left and right? Or the order of bonds changing? Have you consulted a basic book of biochemistry or molecular biology or looked at the DNA entry for Wikipedia. I have voted close this question as unclear. You need to put more effort into understanding DNA before making models. $\endgroup$
    – David
    Sep 10, 2016 at 21:48
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    $\begingroup$ How do you know I've put no effort into understanding DNA? I've researched this question for a clear answer but have found nothing, which is why I asked here. Stop acting as if an unclear question is an "inconvenience" to the forum as two others kindly answered it. You can't just close a question because it is unclear - a simple edit will fix it. P.S: I don't own a biochemistry or molecular biology book. $\endgroup$
    – MH0517
    Sep 10, 2016 at 22:53
  • $\begingroup$ This is not a forum, but a question and answer site that has certain rules about questions to maintain its usefulness and standards. You can read them here: biology.stackexchange.com/help/how-to-ask. Questions should demonstrate effort — yours does not. The fact that you do not own a biochemistry book is no justification and suggests you are in the wrong place — there are many online resources on DNA. One of the use of the comment facility is to ask for clarification and improvements in the question. This I did and you have not responded. $\endgroup$
    – David
    Sep 11, 2016 at 8:09
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    $\begingroup$ There is no reason. Look up PDB search for your sequence and its likely its already been identified somewhere. What cant be done yet is, take and arbitrary sequence, and say with any certainty what its is for.. that we cant do. Best is comparison against what is already known from any homology $\endgroup$
    – SciEnt
    Sep 11, 2016 at 19:50
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    $\begingroup$ The proposed sequences are so short, it's almost certain they exist in nature. $\endgroup$
    – Armatus
    Sep 18, 2016 at 23:29

4 Answers 4


DNA has a polarity that is based on the numbering of the carbon atoms in the deoxyribose molecules in the sugar phosphate backbones of the two complementary strands.

So, for example, the 3'-OH of one base's sugar is attached, via a phosphate, to the 5'-OH of the sugar on the adjacent base in the strand.

Therefore, we say, that one end of a single-stranded piece of DNA has a 5'-end, and at the other end a 3'-end.

Go no further until you understand this concept and can draw a picture of this.

In Watson and Crick's model for double-stranded DNA the two complementary strands are anti-parallel. In other words, if you imagine the double helix like a ladder, then one of the legs of the ladder is oriented in the 5' --> 3' direction, while the other, complementary strand is oriented in the 3' --> 5' direction.

When we describe a DNA sequence, by convention we read the sequence strands in the 5'--> 3' direction.

So now you should be able to state your query more succinctly.


You must first understand a few things:

  1. What are proteins made of
  2. What is DNA made of
  3. What is the relationship between DNA and proteins

From DNA to proteins

DNA is transcribed into RNA which is then translated into protein. The protein, then has some effect (e.g. could be an enzymatic effect) such as affecting the level of sugar in the cell, digesting some lipids or affecting the expression of other genes.

More information on Khan Academy > Central Dogma

What is DNA made of?

DNA (or at least the genetic code) is made 4 different molecules which are called nucleotides. We abbreviate their names by the letters A,T,C and G.

What are proteins made of?

Proteins are made of amino-acids. There are ~20 different amino acids.

Genetic code

For the interest of your question it is now essential to understand how does the succession of nucleotides A,T,C,G in the DNA is reflected in the protein. This is called the genetic code.

We call a series of three nucleotides, a codon. AAT is a codon for example. Each codon (except special codons) correspond to a specific amino acid. This correspondance is called the genetic code. Here is the universal genetic code (where the T has been replaced by U because RNA contains U instead of T)

enter image description here

Consider for example the codon UAU and AUU (where only the order changes) The first one codes for the amino acid Tyr while the other codes for Ile. So yes, the order matters.

Information theory

Globally speaking, for any information the order of a sequence is of fundamental importance! More information on Khan Academy > Information Theory.

  • $\begingroup$ So, because the order of the bonds differs every time, I could theoretically make a DNA model like this, and it would be correct? AT CG AT CG AT CG AT CG AT CG $\endgroup$
    – MH0517
    Sep 10, 2016 at 21:14
  • $\begingroup$ Please delete the reference to the central dogma. You do not need to give a name to the principal you state and it is not Crick's Central Dogma, which is basically that the information in DNA can go to protein but not in the other direction. I document this in detail in answer to biology.stackexchange.com/questions/49201/… $\endgroup$
    – David
    Sep 10, 2016 at 21:43
  • $\begingroup$ @David I agree it is not worth using this term after all. I was tempted to use it as a consequence of the link to a Khan Academy video that is called central dogma. Is it better now? $\endgroup$
    – Remi.b
    Sep 10, 2016 at 23:31
  • $\begingroup$ You're still using the term "Centra Dogma"... $\endgroup$
    – MattDMo
    Sep 11, 2016 at 16:28
  • $\begingroup$ @Deadfult what does that sequence actually mean? Is it 5'-ATCGATCGATCGATCGATCG-3'? That's fine, as long as you include the antiparallel 5'-CGATCGATCGATCGATCGAT-3' as the paired strand. $\endgroup$
    – MattDMo
    Sep 11, 2016 at 16:32

Base-sequence on a strand will NOT matter until you are telling about a specific gene or motif.

However, when you make 2 strands, you have to STRICTLY maintain the BASE-PAIR RULE.

p.s. Be sure the 2 strands will never touch each other; they'll maintain a same parallel-distance throughout their lengths; and both helix will have the same-direction of coiling (right-handed screw type, for Watson-Crick model and B-DNA).


Yes they do matter. Imagine reading just one side of the DNA strand. This is how the code is actually read, so the order would change that side's reading.


is different than


Notice the different last base making the message different. This can affect transcoding to proteins.

Just like the change of one letter can change the meaning of the english word "petty" to be "patty". The same is true for any encoded message.

  • $\begingroup$ Alright, so let's say I made my model like this then: AT CG AT CG AT CG AT CG AT CG Theoretically, this would be correct right? $\endgroup$
    – MH0517
    Sep 10, 2016 at 19:22
  • $\begingroup$ Correct for what? I have no idea what you are asking $\endgroup$ Mar 4, 2017 at 22:46

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