April 25, DNA Day


‘We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.).

This structure has novel features which are of considerable biological interest.”…

John Watson and Francis Crick in Molecular Structure of Nucleic Acids. A structure for deoxyribose nucleic acid.

Nature No. 4356, April 25, 1953


DNA Day also marks the completion of the Human Genome Project, the 13-year international effort that identified the order, or sequence, of more than 3 billion bases in human DNA. The Human Genome Project was finished in 2003, 50 years after Watson and Crick described DNA as a double helix. (Source: National  Library of Medicine)




I would like to invite you to see two presentations courtesy of the National Genome Research Institute, that, at different levels, present different aspects of Genetics research (the pictures are from the U.S. Department of Energy Genome Program’s Genome Management Information System -GMIS):

1.- How Proteins Are Made



2.- Single Nucleotide Polimorphism:

Making SNPs Make Sense


Additional interesting presentations can be found at:

Online Education Kit: Understanding the Human Genome Project



                                                                                       HAPPY DNA DAY!!!


Classification of Carbohydrates


As you know, carbohydrates or glucids are polyhydroxylated aldehydes or ketones, their derivatives and polymers. Glucose is a typical example of carbohydrates.

Observe that glucose has an aldehyde group (drawed in red) and five hydroxyl groups.

Most of carbohydrates are present with a cyclic structure in nature, as a consequence of internal linkages between the carbonyl carbon (of the aldehyde or ketone group) with one of the hydroxyl groups in the same molecule. This graphic represents glucose in a cyclic form:

Considering the polymerization degree (PD) of carbohydrates, they can be classified in Monosaccharides, Oligosaccharides and Polysaccharides.


Monosaccharides are formed by a single molecule. It means that when hydrolyzed they can not release simpler molecules. Examples of this group of carbohydrates are glucose, ribose and fructose, among others.

Monosaccharides can be subclassified according to different criteria, for example:

According to the main (carbonyl) function:

If the carbonyl group belongs to an aldehyde function, the monosaccharide is classified as an aldose. Glucose is a typical aldose. If the main function is a ketone, then the monosaccharide is classified as a ketose. 

Fructose (see structure below) is a ketose, since it is a polyhydroxylated ketone.

According to the number of carbons:

Monosaccharides can be classified in trioses, tetroses, pentoses, hexoses, heptoses and octoses, according to the number of carbons in the molecule.

According to the steric series:

According to the type of esteroisomers, monosaccharides can be classified as L or D (most of the carbohydrates in the animal kingdom belongs to D series)


According to the kind or anomer:

According to the position of the anomeric hydroxyl, monosaccharides can be classified as Alpha or Beta.



Usually, these criteria are combined for describing a monosaccharide, e.g. a compound can be described as a Beta-D-aldohexose.



 They are formed by 2-9 monomers linked through glycosidic linkages; in other words, when hydrolyzed these compounds release 2 to 9 monosaccharides (some texts say up to 20; in fact, oligosaccharides release “a few” monosaccharides).

According to the number of monosaccharides in the oligosaccharide, oligosaccharides can be dissacharides, trisaccharides, tetrasaccharides, etc. Disaccharides, formed by just 2 monosaccharides, are the most important subgroup of oligosaccharides. Disaccharides that appear in nature are lactose, or milk sugar (formed by galactose and glucose), and sucrose or table sugar (formed by fructose and glucose). Other important disaccharides are produced as result of starch digestion: maltose and isomaltose. These disaccharides are ,both of them, formed by two molecules of glucose, but linked in different ways. Cellobiose is a third dissacharide formed also by two molecules of glucose, but linked in such a way that animals can not break, unless animals have in the digestive system specific microorganisms that hydrolyze these linkages, as herbivors have (Cellobiose is formed as result of the digestion of cellulose).



Polysaccharides are carbohydrates formed by more than 9 monosaccharides (some texts say more than 10 monosaccharides, other texts say more than 20…in fact, they usually are formed by a lot of monosaccharides!). When the polysaccharides are formed by the same type of monosaccharides, they are called homopolysaccharides.




The molecules that form starch, glycogen and cellulose are formed by hundreds of molecules of just one type of monosaccharides (glucose, in this cases), linked through glycosidic linkages. These polysaccharides are typical examples of homopolysaccharides.

If the polysaccharide is formed by different types of monosaccharides, then it is called a heteropolysaccharide. Hyaluronic acid, formed by thousands of alternant units of glucuronic acid and N-acetylglucosamine, is an example of heteropolysaccharides.

Hyaluronic acid is an important component of the extracellular matrix in the skin and the conective tissue. This compound has received lately a lot of attention from the media as an antiaging agent.

About Dragon Metabolism (again).

Of course, the post “New lights on Dragon Metabolism”, posted on April 1st. was a joke for April Fools day. I invented

the whole Dragogenin issue!

Some clues that could have allowed the readers to detect that it was a joke:       

          The date of the release of the information, April 1st., is repeated three times along the post.


          The News Agency:  It is not Reuters, or UPI, or AP or AFP, but an imaginary AMP (Adenosin MonoPhosphate agency!).


          The place where the information was released: Nogare, an imaginary place, whose name is the name of the famous dragon movies “Eragon” written backwards.


          Komodo University: Of course, an imaginary University.


          The reference to imaginary, mythological creatures as ancient dragons that were living in Europe in the V -VII centuries.


          And of course, the note at the end of the post: “This post was released on April, 1st, 2009 (Happy A.F.)”, meaning Happy  April Fools!


Conclusions: Do not believe everything you read, mainly if it is on April Fools!



New Lights on Dragon Metabolism


AMP. – Nogare, April, 1st:  A scientific team of Komodo University has reported today the discovery of a gen, in the mitochondria of salivary glands of Komodo’s dragon, that apparently was the responsible of the release of thermal energy in ancient dragons.


This gen that is not expressed in nowadays dragons apparently codifies the production of Dragogenin, a multifunctional protein involved in the production of heat.


This protein was produced in the laboratories of Nogare branch of Komodo University, by the insertion of the gen in E. coli. This multifunctional protein is formed by three different subunits: Subunit DgA, which shows what have been called “a pseudo-NADH.H+ dehydrogenase activity”, subunit DgB, with an activity very similar to cytochrome oxidase, and DgC, a transmembrane protein that acts as channel used for the return of protons from the intermembane space to the mitochondrial matrix.


The NADH.H+ dehydrogenase activity of Dragonenin is very peculiar since it uses NADH.H+ as substrate but its mechanism of action is very similar to the mechanism of Complex III: it pumps protons to the intermembrane space and these protons return to the matrix through the “shortcut” channels of the transmembrane proteins (DgC), while the electrons released from the Hydrogens are transferred to the DgB subunit. Since these subunits have a similar activity to cytochrome oxidase, the electrons are eventually transferred to Oxygen.


Because of the high potential difference between the NADH.H+/NAD+ and the O2/O= systems, the reaction catalyzed by the Dragogenin releases a high amount of energy mainly in the form of heat, since the Dg-C shortcut channel acts as uncoupler, avoiding the use of the energy in the synthesis of ATP by Complex V.  It seems that the generated heat was enough to vaporize the saliva in the dragon’s mouth, so, in fact, these ancient dragons could burn someone with their breath, thought the generation of fire looks improbable.


Current Dragons with repressed Dragogenin gen: 



Weedy Sea Dragon

Weedy Sea Dragon

Draco Volans

Draco Volans

Draco Dussumieri

Draco Dussumieri


Representation of a ancient dragon that lived in Europe around V to VII centuries A.D. 

Note: This post was released on April, 1st, 2009 (Happy A.F.) 

Please, check this related post: About Dragon metabolism (again)