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DNA Structure FAQ

written by: •edited by: Paul Arnold•updated: 3/20/2009

If you don't know an exon from an intron, or your nucleotide from your nucleoside, then let Bright Hub Genetics unravel the mysteries of the double helix for you with our DNA Structure FAQ.

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    DNA is packed with millions of chemical bases, squeezed and packaged into a double helix structure inside the chromosomes of our cells. The molecule also comes with a full kit of scientific jargon to explain it, which can seem impenetrable to the lay person. Here we unpick some of the common terms that scientists use when referring to the DNA structure.

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    What is an Exon?

    An exon is a coding section of DNA. It is transcribed and translated to form part of a protein. Each exon codes for a specific part of the newly constructed protein. It was the molecular biologist Walter Gilbert who came up with the term in his article 'Why Genes in Pieces' for the Nature journal in 1978.

    "The notion of the cistron...must be replaced by that of a transcription unit containing regions which will be lost from the mature messenger...which I suggest we call introns (for intragenic regions) - alternating with regions which will be expressed - exons."

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    What is an Intron?

    An intron is a non-coding sequence of DNA. Once they have been removed from precursor mRNA, the remaining sequence containing exons, is ready to be translated into a protein.

    Non-coding regions of DNA were once commonly known as junk DNA, but that view is now changing.

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    How is DNA Packed Into a Nucleus?

    It is an incredibly complex procedure that involves DNA attaching to proteins called histones. Together they wind round to form a nucleosome core which condenses the molecule. Interactions between the exposed tails of the histones causes the DNA to further condense to form a fibre structure, which then forms loops. But even then that's not small enough, and so they are folded into complex structures known as coils. A more detailed explanation of the process is described here.

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    What is a Nucleotide?

    A nucleotide is that part of the DNA structure that consists of a nitrogenous base (i.e. adenine, guanine, cytosine, thyamine), a five-carbon sugar, and three phosphate groups. Nucleotides are the basic structural units of DNA and RNA, the nucleic acids. They are also involved in the body's metabolism and are sources of energy.

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    What is a Nucleoside?

    A nucleoside is part of the DNA structure that consists of a nitrogenous base bound to a ribose or deoxyribose sugar.

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    So Just Who did Discover DNA Anyway?

    A Swiss physician by the name of Frederick Miescher discovered DNA in 1869 as he was studying bandages soaked in pus. Whilst isolating leukocytes from the bodily fluid he managed to extract a high phosphorous-containing substance he called 'nuclein.' It originated inside the nucleus and he did not know that it was the hereditary material. It was Crick and Watson who elucidated the DNA structure in their seminal 1953 paper.






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