It seems that biology books refer to DNA as 'a' molecule (implying that it is a single continuous uninterrupted strand) ... but in those same books chromosomes are depicted as separate objects containing DNA. Are these illustrations misleading ? Are chromosomes connected end to end by DNA threads ?

(Regardless of the notion that each cell contains maternal and paternal DNA, if you take only one of the two is it a single piece that coils up at regular intervals to form chromosomes or is multiple disjointed chunks and each chunk is coiled into a chromosome)


marked as duplicate by David, Remi.b, Amory, canadianer, iayork Jan 19 '18 at 20:18

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    $\begingroup$ This is a trivial question the answer to which is in almost any book or article that considers chromosomes. I have voted to close on the basis that it shows insufficient research. $\endgroup$ – David Jan 10 '18 at 23:36

Unbroken strands of DNA are single molecules. So Yes, DNA is a molecule. However, the sequence of nucleotides allow for a near infinite variety. So unlike other molecules, like collagen, or water, they cannot be characterized with a unique descriptive name, other than by their sequence. I think this is the cause for confusion, because in this sense, DNA is a class of molecules, and we don't generally give them names. Each chromosome has two unique DNA molecules in diploid organisms (except in rare cases of highly inbred individuals where the two molecules might be identical). So if you have 23 chromosomes, you have 46 DNA molecules in each cell nucleus.


When a book talks about "the DNA of a cell" it is talking about all the DNA molecules which are contained in the cell.

The DNA in a cell exists as separate objects called chromosomes, each of which is usually described as a single long molecule of DNA. (The long molecule has two strands, and coils up around many copies of special protein molecules.)

The chromosomes of a cell are separate, and do not have DNA running between them.


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