아이지 [868099] · MS 2019

2019-02-12 16:44:46
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DNA is the genetic material in all modern cells. Cells pass copies of their DNA to descendant cells, which use instructions encoded in DNA to build proteins. Some of these proteins aid synthesis of new DNA, which is passed along to descendant cells, and so on. Protein synthesis

depends on DNA, which is built by proteins. How did this cycle begin?


In the 1960s, Francis Crick and Leslie Orgel addressed this dilemma by proposing the RNA world hypothesis: Early on, RNA served a dual role, functioning both as a genome and as a catalyst. Evidence that RNA can both store genetic information and function like an enzyme in protein synthesis supports

this hypothesis. RNAs that function as enzymes (called ribozymes) are common

in living cells. For example, some ribozymes cut noncoding bits (introns) out of newly formed RNAs, and the rRNA in ribosomes speeds formation of peptide bonds during protein synthesis 


If the earliest self-replicating genetic systems were RNA-based, then why do all organisms now have a genome of DNA? 

The structure of DNA may hold the answer.

Compared to a double-stranded DNA molecule, a single-stranded RNA breaks more easily and is more prone to replication errors. Thus, a switch from RNA to DNA would have made larger, more stable genomes possible







It was not only the Roman Church that had discovered the power of art to impress and overwhelm. The kings and princes of seventeenth-century Europe were equally anxious to display their might and thus to increase their hold on the minds of the people. They, too, wanted to appear as beings of a different kind, lifted by divine right above the common run of men. This applies particularly to the most powerful ruler of the latter part of the seventeenth century, Louis XIV of France, in whose political programme the display and splendour of royalty was deliberately used. It is surely no accident that Louis XIV invited Bernini to Paris to help with the designing of his palace. This grandiose project never materialized, but another of Louis XIV's palaces became the very symbol of his immense power. This was the palace of Versailles, which was built round about 1660-80. Versailles is so huge that no photograph can give an adequate idea of its appearance. There are no fewer than one hundred and twenty-three windows looking towards the park in each storey. The park itself, with its avenues of clipped trees, its urns and statuary, and its terraces and lakes, extends over miles of countryside.







Until a few years ago, the most extensive attempt to

communicate with chimpanzees went something like this: A newborn chimp was taken into a household with a newborn baby, and both would be raised together-twin cribs, twin bassinets, twin high chairs, twin potties, twin diaper pails, twin babypowder cans.


At the end of three years, the young chimp had, of course, far outstripped the young human in manual dexterity, running, leaping, climbing and other motor skills. But while the child was happily babbling away the chimp could say only, and with enormous difficulty, "Mama," "Papa," and "cup." From this it was widely concluded that in language, reasoning and other higher mental functions, chimpanzees were only minimally competent: “Beasts abstract not."







Alcohol dehydrogenases (ADH) are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to NADH. In humans and many other animals, they serve to break down alcohols that otherwise are toxic, and they also participate in generation of useful aldehyde, ketone, or alcohol groups during biosynthesis of various metabolites. In yeast, plants, and many bacteria, some alcohol dehydrogenases catalyze the opposite reaction as part of fermentation to ensure a constant supply of NAD+.


The first-ever isolated alcohol dehydrogenase (ADH) was purified in 1937 from Saccharomyces cerevisiae (brewer's yeast). Many aspects of the catalytic mechanism for the horse liver ADH enzyme were investigated by Hugo Theorell and coworkers. ADH was also one of the first oligomeric enzymes that had its amino acid sequence and three-dimensional structure determined

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