BIO152H5 Chapter Notes - Chapter 4: Erwin Chargaff, Phosphodiester Bond, Ribose

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19 Aug 2013
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Chapter 4: nucleotides are monomers that consist of a sugar, a phosphate group, and a nitrogen-containing base. Rna"s secondary structure includes short double helices and structures called hairpins. Simulations of chemical evolution have not yet produced nucleotides. Sugars and purines are easily made, but pyrimidines and ribose are not easily synthesized: ribose problem: ribose would have had to have been dominant on ancient earth for nucleic acids to form. In cells, enzyme-catalyzed polymerization of nucleotides require the addition of two extra phosphate groups. This reflects the sequence in which nucleotides are added to a growing molecule. Is dna a catalytic molecule: dna"s stability makes it a reliable store for genetic information it is less reactive than rna but more resistant to chemical degradation. Stable molecules such as dna make poor catalysts: because dna does not appear to be able to catalyze any chemical reaction, biologists think that the first life-form was made of rna, not dna.

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