Are adenosine and adenine the same?

Nucleobases, nucleosides, nucleotides, DNA, RNA

The five nucleobases

There are a total of five nucleobases, which are divided into pyrimidine and purine bases:

The three pyrimidine bases are: uracil, thymine and cytosine. There is a special feature here in that uracil only occurs in RNA, while thymine occurs instead in DNA.

The two purine bases are: adenine and guanine.

The free bases are in equilibrium with tautomers.

Key substance adenine

Life probably began with that Hydrocyanic acid (Hydrogen cyanide, HCN). This became, among other things, the key substance Adenine built up (see e.g. Lehninger: Biochemie). Adenine has many uses in living nature: as a nucleotide (AMP = adenosine monophosphate) in RNA (ribonucleic acid) and DNA (deoxyribonucleic acid), in the form of ATP (adenosine triphosphate) as the most important energy carrier in the cell, as a component of the hydrogen carrier NAD+/ NADH (nicotinamide adenine dinucleotide) and FAD / FADH2 (Flavin adenine dinucleotide), as a component of coenzyme A, as cyclo-AMP (cAMP).

Nucleosides and nucleotides

If a nucleobase is linked to the sugar ribose (an aldopentose) with elimination of water, one arrives at the relevant one Nucleoside, and further by esterification with phosphoric acid in the 5'-position (that is the hydroxymethyl group of the ribose) to one Nucleotide. The four nucleotides that occur in RNA are abbreviated with the first letter, i.e. A, U, C and G. In DNA, the ribose has been replaced by the deoxy sugar 2'-deoxyribose. The following diagram shows the nucleobase, the nucleoside and the nucleotide (AMP) as well as adenosine 3 ', 5'-monophosphate (Cyclo-AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP) using the example of adenine.

Ribonucleic acid (RNA)

In ribonucleic acid (RNA), nucleotides are linked via phosphoric acid diester groups to form an oligomer or polymer, the 5 'position of one nucleotide being linked to the 3' position of the following nucleotide. Messenger RNA (mRNA) serves as a template for protein synthesis (translation) in the ribosomes. A codon from three nucleobases determines which amino acid is incorporated (genetic code). The amino acids to be incorporated are bound to the transfer RNA (tRNA), which carries a base triplet complementary to the codon (see below) for recognition.

Deoxyribonucleic acid (DNA)

In 1953 J.D. Watson and F.H.C. Crick from the ratio of the base frequencies (A and T on the one hand and C and G on the other hand are almost equally frequent) and from the results of X-ray structure examinations on a Double helix structure of deoxyribonucleic acid (DNA) with two specific base pairs closed. The nucleobases adenine and thymine or cytosine and guanine are held together by two or three hydrogen bonds.

Quantum chemical calculations

The DFT calculations (density functional theory) cited below were carried out with the help of the program deMon2k (RKS / DZVP-GGA) with the help of the program molden (processing of input and output, images).



A-T base pair



C-G base pair

Calculated N ... O or N ... N distances of the hydrogen bonds: approx. 0.29 nm, length of the hydrogen bonds: approx. 0.19 nm.

Energetic consideration

In the following, the "total energies" obtained in the DFT calculations and the energies of the base pairs caused by the hydrogen bonds are listed (gas phase, without zero point vibrational energies, without thermal contributions; 1 au = 1 Hartree = 2625.50 kJ / mol; 1 cal = 4.184 J .)

moleculeEnergy in au (Hartree)deMon2k output filedeMon2k-molden-file
Uracil-414.478951970.out.mol
Thymine-453.758832803.out.mol
Adenine-466.914883018.out.mol
Cytosine-394.599435648.out.mol
Guanine-542.101506220.out.mol
A-T base pair-920.696339985.out.mol
C-G base pair-936.746414989.out.mol

Formation energy of the A-T base pair: ΔE = -0.022624164 au = -59.400 kJ / mol
Formation energy of the C-G base pair: ΔE = -0.045473121 au = -119.390 kJ / mol

DNA models

The DNA models with 15 base pairs shown below were constructed using the spartan5 program.

literature

  • Albert L. Lehninger: "Biochemistry" (Wiley-VCH, Weinheim, 1977)

Author: BKi, © 2015