Two interesting things about DNA

Image of Chromosomes from a human male. Image courtesy of NIH

Image of Chromosomes from a human male. Where do these chromosomes live inside a cell? Image courtesy of NIH

Until my first child was born I had never had a Biology lesson in my life.  At my school Biology was an option and I chose Latin instead, leaving me with a lifelong feeling of inadequacy on topics biological  Timendi causa est nescire. But I have diligently read Scientific American for the last 30 years and tried hard to learn the meanings of the long words. But despite my best efforts I have always been confused about the relationship between DNA and Chromosomes. However a few weeks ago a chance comment on a Science Chat Web Site referred to two important facts that I should have known, but did not:

Fact 1: DNA in human cells is not one molecule, but 23 pairs of quite separate molecules. Whenever I have heard people speak of DNA in cells I had only ever noticed references to a single molecule. So I couldn’t understand how chromosomes – see the picture at the head of the article – were formed. Chromosomes appear to be 46 quite separate objects. Ahhhh. Now I understand. DNA just refers to the double helical structured arrangement of nucleic acids – but there are 46 important strands of DNA within each cell.

Fact 2: The 46 molecules spend most of their time in a ball in the cell nucleus. The 46 strands of DNA don’t exist as chromosomes when the cell is functioning normally. They only separate and form the characteristic chromosome shapes just before the cell divides.

This information is, I think, present in the Wikipedia article on chromosomes, but I find biological descriptions so jargon-laden that I can barely understand them! Anyway – learning these two facts, I felt like I had made progress. Perhaps soon I will be able to figure out how my children got here! Omnia causa fiunt

The relationship between strands of DNA and the structure of chromosomes.

The relationship between strands of DNA and the structure of chromosomes. The figure covers a range of magnification of about a factor 1000. Click to Enlarge (Wikimedia Commons)

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One Response to “Two interesting things about DNA”

  1. Richard Gilham Says:

    Good stuff- it’s also interesting to note that the two halves of the DNA double helix are not held together with ‘proper’ chemical bonds.

    So, how long woukd a DNA molecule be when straighened out? How much would a mole of DNA weigh?

    How many undergrad chemistry tutorials have featured these as ‘fun extension questions’?

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