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DNA and Amino Acids
I think that all of you know that I went to the University of Texas and got me a degree in Biological science and in the process took Zoology 320 which was titled "Human Genetics and Cytology" and was supposed to teach me all about what goes on chemically in a human cell. I suppose that Zoology 320 did teach me that or at least gave it a good old try but you must remember that I took the course in 1947 and I am here to tell you that things have changed since 1947. Actually the same things are going on in a human cell in 2008 as went on in the cell in 1947 but what we know about what was going on in the cell is entirely different from what we thought was going on in the cell in 1947. For one thing the substance that we call DNA had not really been discovered in 1947–it was 1953 before James Watson and Francis Crick solved the molecular structure of DNA and changed just about everything that we thought about the cells in the human body–and in every plant. Only today did I learn a little about what Watson and Crick started in 1953. Let me tell you about it.
We use the symbol "DNA" in order not to have to repeat the true chemical name of the thing we are talking about which is "deoxyribonucleic acid". DNA is easier. There are just four components that make up DNA. These four components are Adenine, Cytosine, Guanine and Thymine and scientists refer to these as "nucleotide bases". We will just call them "bases" for short and designate them by the first letter of their chemical name as A, C, G, T,. Now remember that these things are not alive. They are just chemicals. Unusual chemicals to be sure but still just chemicals like water or battery acid or baking soda.
These chemicals or bases appear joined together like a long string of pearls and wrapped in pairs that twist around each other in every cell of the body. If we look at one of these strands in the chromosome of a cell we can see what the order of the "pearls" of bases is and might describe a short strand as ATTCAG while the next strand we look at and identify the pearls is TAAGTC. In fact it was the same Watson and Crick who discovered that if one of the strand of a pair is ATTCAG then the other strand mated with it HAS to be TAAGTC or the pair will fall apart. An A mates only with a T and a G only with a C otherwise the two strands fall apart.
Now if we have all these lovely chemicals in every cell of our bodies and if they are regimented so to combine in spiral pairs what good do they do us. What is their function? Well DNA is sort of like a retired business man of 80–it don't DO nothin'–but it does tell other things what to do.
Who does it tell? Why the amino acids of course. Now if you can spare one ( I pulled mine off my chest) pull out a hair and look at it in a good light. You will see a little translucent bulb down at the bottom of the hair. There are roughly one million cells in that little hair follicle. The function of those one million cells is to make hair. Hair is mostly keratin, a complex protein made by combining certain amino acids. Now human cells are very single minded. If this is a hair follicle cell it is only interested in making hair–it has nothing to do with making bone, or blood, or spit–it just wants to make hair.
So in some way we (we being me) don't yet understand, the amino acids in the hair follicle cell shut down all of the DNA except that portion which has the recipe for making keratin out of amino acids–the secret being which amino acids and how much of each in each hair which is "written" on the DNA and that portion of the DNA remains functional as long as it is in the hair follicle. In all of this remember that there are just four "bases". All of the instructions to the amino acids are made up of the order in which the hair determining DNA informs the amino acids by the order of the bases like ATGACCTCCTTC might indicate red hair and result in more of one amino acid than another hair follicle DNA on a different persons. Actually Watson and Crick have found that the cell reads the recipe in groups of three like ATG-ACC-TCC-TTC.. Think of the two words "derail" and "redial"—same letters but entirely different meaning. The secret is in the order in which the four bases appear on any given "string of genetic pearls". There are 29 different amino acids in every human cell. The genetic code ATG calls up the amino acid methionine, ACC is threonine, TCC is serine, TTC is phenylalanine. And this same code works in every cell of every animal or plant in the world–it is a universal code.
I am absolutely amazed and aghast at the complexity and yet simplicity of all of this. Since about 1940 I have accepted that genes determine what we are. Those pearls on the strands of DNA are genes and the sequence of the bases on the DNA strands determines our makeup–and I had to be 80 years old to understand how they did it. Incidentally I think that Crick and Watson are pretty smart fellers.
Most of what is above I learned today reading "The Seven Daughters Of Eve" by Bryan Sykes. Good book!
Just thought it might be interesting to you.
dad, granpa, ami
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