131 research outputs found
Long-Term Memory: Scaling of Information to Brain Size
The material bases of information - paper, computer discs - usually scale
with information quantity. Large quantities of information usually require
large material bases. Conventional wisdom has it that human long-term memory
locates within brain tissue, and so might be expected to scale with brain size
which, in turn, depends on cranial capacity. Large memories, as in savants,
should always require large heads. Small heads should always scale with small
memories. While it was previously concluded that neither of these predictions
was invariably true, the evidence was weak. Brain size also depends on
ventricle size, which can remain large in some survivors of childhood
hydrocephaly, occupying 95% of cranial volume. Yet some of these have normal or
advanced intelligence, indicating little impairment of long-term memory. This
paradox challenges the scaling hypothesis. Perhaps we should be looking further
afield?Comment: 10 pages, 1 figure; submitted to Biological Theory 20th Feb 2013; a
requested revision was submitted 28th July 201
Which way up? Recognition of homologous DNA segments in parallel and antiparallel alignment
Homologous gene shuffling between DNA promotes genetic diversity and is an
important pathway for DNA repair. For this to occur, homologous genes need to
find and recognize each other. However, despite its central role in homologous
recombination, the mechanism of homology recognition is still an unsolved
puzzle. While specific proteins are known to play a role at later stages of
recombination, an initial coarse grained recognition step has been proposed.
This relies on the sequence dependence of the DNA structural parameters, such
as twist and rise, mediated by intermolecular interactions, in particular
electrostatic ones. In this proposed mechanism, sequences having the same base
pair text, or are homologous, have lower interaction energy than those
sequences with uncorrelated base pair texts; the difference termed the
recognition energy. Here, we probe how the recognition energy changes when one
DNA fragment slides past another, and consider, for the first time, homologous
sequences in antiparallel alignment. This dependence on sliding was termed the
recognition well. We find that there is recognition well for anti-parallel,
homologous DNA tracts, but only a very shallow one, so that their interaction
will differ little from the interaction between two nonhomologous tracts. This
fact may be utilized in single molecule experiments specially targeted to test
the theory. As well as this, we test previous theoretical approximations in
calculating the recognition well for parallel molecules against MC simulations,
and consider more rigorously the optimization of the orientations of the
fragments about their long axes. The more rigorous treatment affects the
recognition energy a little, when the molecules are considered rigid. However
when torsional flexibility of the DNA molecules is introduced, we find
excellent agreement between analytical approximation and simulation.Comment: Paper with supplemental material attached. 41 pages in all, 4 figures
in main text, 3 figures in supplmental. To be submitted to Journa
Chirality pairing recognition, a unique reaction forming spiral alkaloids from amino acids stereoselectively in one-pot
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