DNA, chromosomes, and genes; how are they linked?


03 May 2015

    Through talking to people for a long time now, I have figured that there is a misunderstanding or I may say a lack of understanding of how many people associate DNA with chromosomes, and genes. This is one of those cases that you ‘kinda know but not really’…

    When we talk about DNA or Deoxyribonucleic Acid, we mean the main building blocks of the ‘genetic material’ inside our cells. These are long strands of units called ‘nucleotides’ which are lined up in a way to shape up a helical ladder. The rungs of the ladder are formed by special chemical bonds between the nucleotides that are sitting across from each other. The ladder side rails are composed of sugar and phosphate molecules (yes there is sugar and phosphor in your DNA!)
    Believe it or not, it is known that there is about 2 METERS (~6.6 feet) of DNA in each cell of your body!!

    So, if there is such a long strand of DNA is every cell, how does it fit in there? (Note that the typical animal cell diameter is something between 10 and 100 micrometers!). The answer lies within a condensed packaging system, probably one of the most efficient known packaging systems in nature!), called a chromosome.

    I’m sure most of you have seen a picture of a chromosome and may know that there are 46 chromosomes (23 pairs!) in each cell of our body (exception: egg and sperm have 23 chromosomes each). It is known that the 2-meter-long DNA in each cell is packaged into these 46 chromosomes!! For super-efficient packaging, DNA is wrapped around protein structures in multiple magnitudes (imagine the shape of a knitting yarn) and forms the tightly packaged chromosomes. Normally, for DNA ‘to be read’, the tight packaging would loosen up and make the DNA available to enzymes…

    Photo credit: www.nature.com (http://www.nature.com/nrendo/journal/v7/n4/images/nrendo.2010.215-f2.jpg)

    Photo credit: www.nature.com (http://www.nature.com/nrendo/journal/v7/n4/images/nrendo.2010.215-f2.jpg)


    Finally, what are genes and what is their relationship with DNA and chromosomes? Well, the DNA strands packaged as chromosomes are divided into ‘segments’ called genes. Genes contain recipes to make proteins inside the cells. Not all regions of DNA inside the cell are part of genes. The term ‘junk DNA’ refers to the regions of DNA that are not genes. However, scientists are further expanding their knowledge of these regions every day and are surprised to learn that many of these regions are not actually junk and may have vital roles inside the cells of an organism!

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