Biomedical subjects

G F Joyce

Publications and source records attributed to G F Joyce.

21 records · Page 2Linked to original sources

PubMed1984

Non-enzymatic template-directed synthesis of RNA copolymers.

Cytosine-rich RNA copolymers facilitate the template-directed synthesis of complementary oligomers from mononucleotide 5'-phospho-2-methylimidazolides (Fig. 1). The efficiency of this reaction falls sharply as the ratio of cytosine to non-cytosine in the template is decreased. This is a severe limitation for self-replication because it means that any cytosine-rich polynucleotide that can serve as a good template will produce a cytosine-poor complementary strand that is unable to direct further rounds of synthesis. Studies with low-ratio random copolymer templates have shown that the efficiency can be increased by adjusting initial monomer concentrations and by providing additional activated monomers during later stages of the reaction. The oligomeric reaction products can be studied in detail using high performance liquid chromatography. It is possible to separate oligonucleotides on the basis of chain length and base composition. Thus a wealth of information is available to characterize the distribution of products over the course of the reaction and under a variety of reaction conditions.

Base Sequence↗

PubMed1983

The instability of the autogen.

The autogen theory has sought to provide a mechanism for the rapid origin of a self-replicating chemical system from short, random oligomers. The autogen is considered in terms of hypercycle theory, and its dynamic behavior is subjected to fixed point analysis. It is shown that the components of the autogen are incapable of stable coexistence.

Catalysis↗

PubMedDate not supplied

Chiral selection in poly(C)-directed synthesis of oligo(G).

Theories of the origin of optical asymmetry in living systems place fundamental importance on the amplification of optical asymmetry by an autocatalytic process. The replication of a polynucleotide is one obvious choice for such an autocatalytic growth mechanism. If an optically homogeneous polynucleotide could replicate by directing the polymerization of monomers of the same handedness, while excluding monomers of the opposite handedness, its chiral descendants would come to dominate what was once an achiral environment. Recently, two highly efficient template-directed reaction systems have been developed for the oligomerization of activated guanosine mononucleotides (Fig. 1) on a poly(C) template. The synthesis of L-guanosine 5'-mononucleotide makes it possible to study chiral selection in these systems. We report here that poly(C)-directed oligomerization of activated guanosine mononucleotides proceeds readily if the monomers are of the same optical handedness as the template, and is indeed far less efficient if the monomers are of the opposite handedness. However, in template-directed reactions with a racemic mixture, monomers of the opposite handedness to the template are incorporated as chain terminators at the 2'(3') end of the products. This inhibition raises an important problem for many theories of the origin of life.

Chromatography, High Pressure Liquid↗