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DNA Facts, National DNA Day 2010, 2011 and Onward

© Donald Reinhardt,2010

The Double Helix of Deoxyribonucleic Acid, Molecule of Chromosomes, Facts to Know and Remember

© Donald Reinhardt,2010
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DNA Double Helix, Nitrogen Base Pairs, National DNA Day
DNA is celebrated as National DNA Day in April once a year, every year. DNA is known as the double helix. The double helix of DNA was announced to the world in 1953 by Watson, Crick, Wilkins and Franklin. DNA contains all the information that makes a species — a bacterium, an insect, a mouse, an elephant, a whale, or a person. DNA is the information storehouse, the data information center or library of codes, that is found in every cell. DNA molecules are double chains (helices) that encode the plans for what a cell is to do, and when it should be done. From a single fertilized egg, to the whole finished organism — the plans are all there in DNA. This is a summary of very important facts about DNA to remember, not only for National DNA Day for 2010 alone, but for 2011, 2012 and beyond — DNA facts to remember for one's whole life to be sure.

DNA, an Acid Macromolecule and the Stained Microscopic Threads of Life or Chromosomes

Miescher a German discovered (1869) nuclein (nucleic acid) in stained white blood cells (leukocytes) in pus from wounds. The nucleus contained chromosomes (chromo = colored; somes = bodies).

Sutton, in 1902 showed that chromosomes physically move and separate, and that the chromosomes' segregations in insects such as grasshoppers support Mendel's segration of traits (now called genes).

The name deoxyribonucleic acid (DNA) means that ribose is missing one oxygen atom (deoxyribose), there are nitrogen bases, and that the overall character of the macromolecule is acid (due to the phosphates).
 
Five Primary Basic, Essential Facts to Know about DNA and the Double Helix

Publication of DNA's structure in 1953 revealed basic facts about DNA's structure and ended a scientific race among several laboratories, including that of Linus Pauling, a Nobel Prize recipent in Chemistry for his studies on The Nature of the Chemical Bond.  Pauling, who was also the discoverer of the alpha-helix of proteins and polypeptides, had proposed a DNA molecule with three helices and phosphates facing toward the inside of the molecule -- this earlier published hypothesis by Pauling was proven incorrect. 

Across the Atlantic in England, James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin were collaborating to determine the structure of DNA. These scientists combined excellent X-ray diffraction photos and modeling experiments to discover and reveal these basic facts of DNA structure:

1. deoxyribose sugars (ribose lacking one oxygen molecule) covalently linked to phosphates form the outer backbone of the DNA molecule. A sugar-phosphate chain is located on each side, and they are linked by nitrogen bases and H-bonds to each other. The overall shape of the DNA molecule is likened to a twisted ladder. 

2. a DNA molecule is a double helix — each sugar phosphate turns and spirals aroud the other sugar phosphate. 

3. there are 4 nitrogen bases in the DNA molecule. 

4. nitrogen bases face each other in pairs, and the nitrogen bases are linked by hydrogen bonds.

5. adenine pairs with thymine, and guanine pairs with cytosine — these are the hydrogen-bonded pairings. 

The DNA model of Watson, Crick, and  Wilkins was built on Chargaff's rules for base pairings of A:T (purine base:pyrimidine base) and G:C (purine base:pyrimidine base), in ratios that are always 1:1, and are shown clearly by the DNA model.

These investigators published a series of papers in 1953 that explained their data and the DNA molecule:

  • A Structure for Deoxyribose Nucleic Acid ; Nature 171, 737-738 (1953).
  • Genetical Implications of the Structure of Deoxyribose Nucelic Acid; Nature 171, 964-967 (1953).
5 Facts of DNA Replication, Templates, DNA Polymerase, Nucleotides, Essential to Double Helix Duplication

To summarize the previous 5 facts, DNA molecules, are double-helices (sing. helix), and all DNA molecules contain specific nucleotides (deoxyriboses + phosphates + nitrogen bases) appropriately paired and arrayed linearly. 

DNA is the major instuctional and informational molecule of cells from prokayotes to eukaryotes. Since Watson and Crick's publications in 1953, DNA science has advanced dramatically, and DNA replication or duplication is an important part of that understanding.

1. Prokaryote (bacterial) cells have DNA that is a double-helix, and this DNA is arranged as a circular (ringed) DNA structures. In contrast to prokaryotes, eukaryote cells have double helices arranged as linear chromosomes

2. Both prokaryotes and eukaryotes use semi-conservative replication of DNA. Each half begins to separate as the hydrogen-bonds are broken. Each DNA sugar phosphate strand remains fully intact as each unwinds and separates from the matching strand. 

3. Each opened DNA strand serves as a template for new nucleotides (deoxyriboses + phosphates + nitrogen bases), which are placed and linked together to form an opposite new DNA chain. 

4. Both strands of DNA are synthesized simultaneously, but in opposite directions in what is called a 5' to 3' direction.
The enzyme DNA polymerase is needed to accomplish this synthesis, and energized nucleotides of ATP, TTP, GTP and CTP are  used to accomplish this task. 

5. The newly-synthesized DNA is half an old strand, and half a new strand — semi-conservative replication is scientifically-proven to occur in bacteria, plants and animals and is the universal mechanism of DNA replication.

5 More DNA Facts, Different Gene DNA Codes Exist for Different Proteins, and the Types and Roles of RNA

DNA is far more interesting and complex than many of the earlier scientists ever thought. New revelations revealed the following important 5 points of DNA coding and protein synthesis.

1. DNA is used to make RNA of 3 types: a. ribosomal RNA (r-RNA),  B. transfer RNA (t-RNA), C. messenger-RNA (m-RNA).

2. Ribosomes are composed of protein + ribosomal RNA. Ribosomes are the sites where protein synthesis occurs.

3. m-RNA contains the coding needed to make a polypetide or protein. Depending on the size of the polypeptide, 3 bases are needed to specify any 1 amino acid. If a protein is 100 amino acids in length, then 300 bases are needed to specify or code for the amino acids of that protein.

4. t-RNA (also known as soluble RNA) carries the amino acids to the messenger-RNA which sticks to the r-RNA. The m-RNA is read progressively by RNA polymerase.  

5. If the 4 bases that are used to make a DNA molecule are combined and arranged in sequences of 3, it is possible to have 64 different combinations or codes. With about 20 known amino acids needed to form a protein, then it is possible to code for all of the common and known amino acids, with some repeats or redundacy in the codes. The DNA code has information for a start code point (typically, methionine) and stop signals (usually 3 different stop signals are possible). This mecahnsim of starts and stops for polypeptide synthesis and coding resembles a capital letter used to start a sentence, and period to end a sentence.

5 Concluding Facts about DNA Coding, Regulation and Mutation to Consider for National DNA Day

The genes of DNA, whether the 1000 in E.coli, or the 25,000 to 30,000 in humans, do not all work at the same time. Here are 5 concluding facts about DNA.

1. Genes are controllable by means of certain regulatory proteins.
2. Some regulatory proteins are repressor proteins -- these proteins inactivate a gene site (portion of DNA) by binding with that site and prohibiting RNA polymerase from transcribing m-RNA.
3. Inducer proteins are also known. These proteins typically remove inhibitory proteins from gene sites, and the inducer proteins, therby, enable RNA polymerase to make mRNA from that gene site.
4. Mutations of the DNA can occur. These mutations may have no effect on m-RNA of the gene, slightly alter the product of the mRNA, or significantly alter the mRNA and the ultimate proteins of the gene.
5. Mutations of base pairs can significantly affect all aspects of a cell's life, and even an organism's life. A protein may be made that is slightly different by a single amino acid, and this will have lonlasting, important effects, as in sickle-cell anemia. Even cancers have been traced to some point or base pair mutaions. These mutations often alter regulatory proteins in such a way that the cancer shows uncontrolled cell multiplication and growth, and ultimately causes death of the organism. This will be discussed soon in another section.

 In conclusion, DNA facts stand out on any day of the year, National DNA Day included. These amazing DNA molecules have revealed to scientists much about life and its regulation and control. Much remains to be discovered and done, and that is why National DNA will be celebrated April 2010, 2011, 2012 and beyond, as far as they eye can see and the mind can explore.

A series of 20 DNA review questions and 20 DNA answers is available for all those who wish to check what they have learned and know about DNA.

Sources

Alters, S and B. Alters. 2006, Biology. John Wiley & Sons Inc., Hoboken, N.J. 755 pp

Lodish, H. et al. 2000. Molecular Cell Biology. Fourth Ed., W. H. Freeman and Co., New York, N.Y.

All the Written Material within Site is Copyrighted 2010 and Owned by Dr. Donald Reinhardt, and this original material is protected legally by this copyright notice and by theDigital Millennium Act. None of this original material may be copied or reproduced without the expressed written consent of the author. 

Donald Reinhardt is a Consultant in Medical and Industrial Microbiology and a Freelance Science writer. He is available for specific assignments for those who are interested – by contacting sciencesuperschool@gmail.com. Other questions related to this teaching site should be directed to sciencesuperschool@gmail.com.