Although there is no-one yet who really understands all the intricate ways this important molecule works in our bodies, scientists are learning more and more every day as a result of their research.
This article includes some scientific nomenclature... … but I hope you will continue to read it anyway. You can skip over the things that don't interest you, there will not be an exam at the end!
DNA stands for deoxyribonucleic acid. The name indicates that it is a slightly acidic molecule that was extracted from the nucleus of cells in living organisms, and it is related to another important molecule, ribonucleic acid (RNA)
Inside a cell
Take your imaginary super-magnifying glasses and look inside the a cell and then further, inside the smaller structure called the nucleus. And when you do, you will not see any DNA molecules floating around.
You will see bundles of protective proteins tightly packed around the outside of the DNA to protect it; and these proteins are again wound tightly into what we can see as chromosomes. Except for the eggs (ova) and sperm cells, each human cell has 46 chromosomes arranged in 23 pairs; one of which comes from the mother and the other from the father. (Other species have different numbers of chromosomes). www.geneagenetics.com.au
You are lucky to have these special imaginary glasses, because chromosomes cannot always be seen with a normal microscope in the lab, only at the special time when the cell is dividing and each chromosome is being duplicated so that one half goes into the new cell (called a daughter cell) and one half stays behind in the original cell.
The very long strands of DNA are tightly wound up and hidden right inside these coils upon coils. They are so thin that each 2 metre-long strand is wound up in a structure too small to see with a normal microscope. What you might find in pictures and animations are just artists interpretations, but with information gleaned from scientists' actual results. Some good descriptions and pictures can be found at: publications.nigms.nih.gov , and animations at: www.dnalc.org
Chemical structure – Imagine a spiral
If we could unravel the chromosomes, and tease apart the protective proteins and unwind the DNA and magnify it up a bit more, we would see the iconic 'double helix'. A helix is another name for a spiral; and is manifest many times in nature from the spiral of the snail shell (scientific name for snails is Helix) to the way a vine grows up a tree.
But this one is special, it has two spirals wound around each other. The long backbones are very strong, and the cross-pieces holding the two strands in place are held by weaker bonds. They can easily break and re-form, so that the two strands can unwind when they are needed, inside the cell.
In wonderful collaborations between science and art, there are many places around the world where structures or art works have been modelled on DNA, some of them can be found below. Looking at these pictures may help you imagine what DNA might look like, if your magnifying spectacles were real.
• Article on the double helix in architecture, which includes a description of the car park at the Sydney Opera House: www.pellsconsulting.com.au
• Garvan Institute of Medical Research, Sydney: www.tourgarvan.org
• Chambourd Castle staircase in France: www.castles.org
• Tower in Kings Park, Perth: www.bgpa.wa.gov.au
• Many other sculptures around the world:
Now start your walk
As you walk along the rigid backbone of this long (now unwound) molecule, your feet will feel an alternating pattern of bumpy bits that are called phosphate and a sugar (the name of the sugar is deoxyribose). If you look along to one side as you follow the spiral gently going round and round always in the one direction – depending on whether you are walking 'up' or 'down', it will always be to your left or right - you will see spokes pointing towards the opposite backbone on the other side of the structure. These are the 'bases'.
There are four different ones – for simplicity we call them A, C, T and G. Every time you see an A on your side, it will link up with a T from the other strand on the other side to form a knobbly 'rung' of a ladder. Every time you have a C on your side, it will match with a G from the other side (and the inverse if you have a T or a G on your side). Some different ways artists have imagined this process can be seen at: library.thinkquest.org or
It is these bases that form the code for all the proteins in our body. Specifically, it is the order of three bases in a row (called a 'codon') that form the code for a particular amino acid, and a long string of amino acids make a protein. The DNA in the nucleus is just the beginning of this process; which will be described in more detail in part 2 of this topic.
DNA's function is to make the proteins that make us who we are
When DNA needs to be used by the cell, specialised enzymes (which in themselves are a specialised type of protein) open up the protective layer, and more, different enzymes unwind the DNA helix by breaking the weak bonds between the bases (temporarily), and even more enzymes copy the information onto a molecule called RNA, as described in Part 2 of this topic.
From the small pieces of RNA, a particular protein – determined by the sequence of bases on the DNA – will be made in the main part of the cell, outside the nucleus and transported to wherever it is needed.
Part of the mechanism for making proteins is in a little molecular 'machine' called a ribosome, and the Nobel Prize in Chemistry was awarded to three researchers (from the UK, the USA and Israel) for their work in visualising and elucidating how this little structure works to translate the coded message from DNA into proteins. (www.nobelprize.org)
Wow. It blows my mind.
It is only by many years of patient and intricate experiments that scientists have come this far in our knowledge. Proverbs 19 verse 2 (NIV) advises: "It is not good to have zeal without knowledge, nor to be hasty and miss the way."
Dr Mark Tronson is a Baptist minister (retired) who served as the Australian cricket team chaplain for 17 years (2000 ret) and established Life After Cricket in 2001. He was recognised by the Olympic Ministry Medal in 2009 presented by Carl Lewis Olympian of the Century. He has written 24 books, and enjoys writing. He is married to Delma, with four adult children and grand-children.
Mark Tronson's archive of articles can be viewed at www.pressserviceinternational.org/mark-tronson.html
