Pyrimidine base pairing, purine

A transition is a point mutation that replaces a purine-pyrimidine base pair with a different purine-pyrimidine base pair. For example, an A-T base pair becomes a G-C base pair. 

Attention has been drawn to the fact that the size and shape of the purine-pyrimidine base pair in this case is rather similar to the size and shape of the benzo[a]pyrene nucleus, which is a powerful carcinogen ( ,). That carcinogen is known to bind covalently to the N2 position of guanine (15). In the present lattice the planar purine-pyrimidine base pair rests in a position close to the guanine N2. Thus, this mode of interaction may also be a model for the interaction of planar carcinogen molecules with mA. 

Fig. 1. Elements of DNA. stricture (a) a deoxypolynucleotide chain, which reads d(ACTG) from 3 — 5 or d(GTCA) from 3 — 5 and (b) and (c) the Watson-Crick purine-pyrimidine base pairs, A-T and G-C. respectively, where—s represents aliachinenl lo the deoxyribose...

The above-mentioned purine-pyrimidine base-pairing scheme consists, as it is well known, of hydrogen bonding between specific, complementary base pairs, namely, adenine-thymine [or uracil in ribonucleic acid (RNA)] and guanine-cytosine (Fig. 1) (shorthand notations A-T or A-U and G-C). The specificity of the bonding concerns both this exclusiveness and the steric arrangement which is... 

TRANSITION MUTATION A base-pair substitution mutation in which the purine pyrimidine base-pair orientation is preserved, as in adenine thymine -+ guanine cytosine. 

Fig. 2.7. Hydrogen-bond n-cooperativity in purine-pyrimidine base pairing...

Frey MN, Koetzle TF, Lehmann MS, Hamilton WC (1973) Predsion neutron diffraction structure determination of protein and nucleic acid components. XII. A study of hydrogen bonding in the purine-pyrimidine base pair 9-methyladenine and 1-methylthymine. J Chem Phys 59 915-924... 

R203 S. H. Chou, NMR Studies of DNA Structures Containing Sheared Purine-Purine and Purine-Pyrimidine Base Pairs , p. 303... 

The diameter of the double helix is 2.0 nm. This is dictated by the dimensions of the purine-pyrimidine base pairs. The helix completes one turn every ten base pairs. One complete turn is 3.4 nm. Thus each base pair advances the helix by 0.34 nm. 

Transition Mutation - A mutation that changes a purine-pyrimidine base pair to a different purine-pyrimidine base pair. An example is a transition from G-C to A-T. 

The two chains are held together by purine-pyrimidine base pairs connected by hydrogen bonds. Adenine is always paired with thymine, and guanine is always paired with cytosine. 

Since G-quartet (or G-tetrad) consists of four guanine bases, its square is at least twice as large as the square of usual DNA purine-pyrimidine base pair. So a specific quadmplex binder should contain a large aromatic/heteroaromatic core, larger... 

Piezoelectridty of DMA was reported by Duchesne [30. It is known that the molecular conformadan of sodium salt of deoxyribotmclic add (DNA) is double-hdix with a regular stacking of purine-pyrimidine base pairs above 75% relative humidity, but it becomes diaordcred state below 55% relative humidity (31). 

Figure 3. Purine-pyrimidine base-pairing structures as found in DNA (Watson-Crick configurations).

---