Jichu

Nucleotide Biosynthesis Points of Commonality an d Difference   Learning the pathways of nucleotide synthesis can be a daunting task. You have both purines and pyrimidines to deal with. How best to go about learning these steps is the lesson of this tutorial. The first thing to take note of is that both the purines and the pyrimidines have many points in common in their pathways. Knowing what these are allows you to absorb the information from a comparative perspective as opposed to two separate pathways. Having one to match with the other is the key to making points stick. Lets start by looking at the basic ring systems of purine and pyrimidines. The first thing we note is the size.  The pyrimidine ring is smaller and has two fewer nitrogens, and one less carbon. That doesn’t help, except to inform us that a purine ring requires more C and N donors. Next we look at the composition. Lets start with the chemical formulas. Again, we see the major factor is twice the

Biochem. J. (1997) 322, 213±221 (Printed in Great Britain) Biosynthesis of ‘ essential ’ amino acids by scleractinian corals Lisa M. FITZGERALD* and Alina M. SZMANT‹ Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149, U.S.A. DOI:  10.1042/bj3220213 Animals rely on their diet for amino acids that they are incapable either of synthesizing or of synthesizing in sufficient quantities to meet metabolic needs. These are the so-called ` essential amino acids'. This set of amino acids is similar among the vertebrates and many of the invertebrates. Previously, no information was available for amino acid synthesis by the most primitive invertebrates, the Cnidaria. The purpose of this study was to examine amino acid synthesis by representative cnidarians within the Order Scleractinia. Three species of zooxanthellate reef coral, Montastraea faŠeolata, Acropora cerŠicornis and Porites diŠaricata, and two spe