# Double helix Assembly

A long chain of organic molecule will somehow snap on 3 links forming 4 shorter strings. Then realign themselves together or self-assemble to form a double helix dna strand. Like a twisted ladder with 50 base pair rungs. The Adenine pairs with Thymine while the Cytosine pairs with Guanine. Can you discover the sequence of the resulting dna strand?

Full sequence:

$$\scriptsize\textsf{AC TA CG AT GC GA GA CG TG AG TA GC AC TA CG AT TG AT GC TA CG CT CT GC AC}$$
$$\scriptsize\textsf{TC AT CG CG TC AG TC TG TA GA GT CG CG AC TC TA CA GA CT GA CG TG AT GC TA}$$

Edited solution:

Lets say it has 4 parts with 3 cuts:
$$\scriptsize\color{red}{\textsf{AC TA CG AT GC GA GA CG TG AG TA GC }}|~ \color{orange}{\textsf{AC TA CG AT TG AT GC TA CG CT CT GC AC}}$$
$$\scriptsize\color{orange}{\textsf{TC AT CG }}|~\color{green}{\textsf{CG TC AG TC TG TA GA GT CG }}|~\color{blue}{\textsf{CG AC TC TA CA GA CT GA CG TG AT GC TA}}$$

Reverse the 3rd part and place it alongside the 4th part, like so:
$$\scriptsize\color{darkgreen}{\textsf{GC TG AG AT GT CT GA CT GC }}$$
$$\scriptsize\color{blue}{\textsf{CG AC TC TA CA GA CT GA CG TG AT GC TA}}$$

Now add the 2nd part to the reversed 3rd part, and the 1st part to the 4th:
$$\scriptsize\color{darkgreen}{\textsf{GC TG AG AT GT CT GA CT GC }}\color{orange}{\textsf{AC TA CG AT TG AT GC TA CG CT CT GC AC TC AT CG }}$$
$$\scriptsize\color{blue}{\textsf{CG AC TC TA CA GA CT GA CG TG AT GC TA }}\color{red}{\textsf{AC TA CG AT GC GA GA CG TG AG TA GC }}$$

• The way this answer was originally written made it very difficult to understand what was being done, even though the answer itself was fully correct. I've adjusted it so there's no longer a confusing reference to six parts, and color coded things so it's easier to see how the pieces fit back together. If you feel I've misrepresented the solution, feel free to roll it back.
– Rubio
Aug 26 '19 at 1:34

I think, barring transcription errors, we have the total beginning sequence

ACTA CGAT GCGA GACG TGAG TAGC ACTA GCAT TGAT GCTA CGCT CTGC ACTC ATCG CGTC AGTC TGTA GAGT CGCG ACTC TACA GACT GACG TGAT CGTA

(cut into smaller bits for readability.)

This is 100 total base pairs, so we would like to look for a way to make 3 cuts that results in a 50 bp strand, and it's compliment made up of 3 smaller strands.

We want to make the following cuts

ACTA CGAT GCGA GACG TGAG TAGC || ACTA GCAT TGAT GCTA CGCT CTGC ACTC ATCG CGTC AGTC TGTA GAGT CGCG ACTC TA || CA GACT GACG || TGAT CGTA
giving us the strands
1. ACTA CGAT GCGA GACG TGAG TAGC,
2. ACTA CGAT TGAT GCTA CGCT CTGC ACTC ATCG CGTC AGTC TGTA GAGT CGCG ACTC TA,
3. CA GACT GACG and
4. TGAT CGTA.
If we take strand 2 to be the main backbone, then we can build a complementary sequence by concatenating 4, then 1, and then 3 in reverse order, which gives the double stranded sequence
ACTA GCAT TGAT GCTA CGCT CTGC ACTC ATCG CGTC AGTC TGTA GAGT CG
TGAT CGTA ACTA CGAT GCGA GACG TGAG TAGC GCAG TCAG ACAT CTCA GC