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L-glucose: the enantiomorph (mirror image) of
D-glucose Unlike the ubiquitous D-glucose, L-glucose is rarely if ever
found in Nature.
L-glutamate: the anion of dissociated L-glutamic acid The sodium
salt has long been used in China as a food additive and is marketed in
more recent times under the name "Accent" in the US.
L-glutamic acid: HOOCCH2CH2CH(NH2)COOH,
one of the common
α-amino acids found in most protein hydrolysates.
lac-operon: a segment of the ring-like DNA of E. coli, which
contains the base sequence coded for the synthesis of three proteins:
β-galactosidase coded by the Z-gene,
β-galactoside permease coded by the Y-gene and
β-galactoside acetylase coded by the AC gene.
lactose: milk sugar Upon hydrolysis each mole of lactose yields
one mole of D-galactose and one mole D-glucose.
lactose permease: See
β-galactoside permease.
Langmuir adsorption isotherm: an equation describing the
"hyperbolic" (See "hyperbolic" curve.) relationship between the
concentration of free solute and that of its adsorbed form on localized
sites, introduced in 1918 by Irving Langmuir (1881-1957) (For an
illustrative example, see second term on the right-hand side of Equation
A 10 in Appendix 1.)
Laplacian physics: French astronomer and mathematician, Marquis
Pierre Simon de Laplace (1749-1827) was the last of the leading 18th
century European mathematicians. His two great works one on the theory
of probability and the other on celestial mechanics together showed how
the study of astronomy and the development of mathematics were closely
interwoven. Laplacian physics is just an expression for mathematically
oriented physics.
latent heat of vaporization, heat of vaporization: the difference
in the heat content or enthalpy of one mole of a substance in liquid and
vapor forms at the same temperature and pressure.
Law of conservation of energy: Although energy may be converted
from one form to another, it cannot be created or destroyed. This law
was first introduced by H. von Helmholtz in 1847 when he was a military
surgeon barely 26 years old. But Annalen, the major journal for physics,
rejected his manuscript entitled "Über
die Erihaltung der Kraft" ("On the Conservation of Energy"). However, he
received warm praises from the military boss, who mistook his "Kraft" for
military power.
Law of macroscopic neutrality: This law states that for any
subject of macroscopic dimensions, the total number of positive charges
it carries must be at all time essentially equal to the total number of
negative charges it carries. A departure from this neutrality
corresponding to a quantity of charged particles or ions far too small
to be detected chemically would create an electrostatic potential far
above what is compatible with known facts. The following example,
modified after one given by E.A.Guggenheim,97 pp 330-331
shows why. Consider a spherical living cell 0.1 micron (10-4
cm or 10-6 m) in radius. Let us imagine that, against the Law
of Macroscopic Neutrality, we removed a (minute) quantity of К+
equal to 10-18 mole from the cell. This removal leaves the
cell with an excess of negative charges of 10-18 faradays or
0.965 × 105 ×
10-18 = 9.65 × 10-14
coulombs. Now, the electric potential
ψ of a charged sphere of radius r in an aqueous medium is
determined by
ψ = Q/εr,
where Q is the electric charge and
ε, the permittivity of the aqueous medium (equal to 78.5
× 1.11 × 10-10
coul./volt m =8.72 × 10-9
coul./volt m. at 25° C). Substituting the values, we have
ψ = (9.65 × 10-14)/(8.72
× 10-9 ×
105) = 11 volt. This is far above the electrical potential
difference observed across normal living cells, which are in the range
of 0.1 volt and lower. Assuming that this spherical cell contains the
usual 100 mmoles/kg. of K+, the normal K+ content
of the spherical cell is then (4/3)πr3
× 10-4 = 4.19 ×
(10-4)3 × 10-4
= 4.19 × 10-16 mole. The
hypothetical quantity of K+ removed (10-18 mole)
is thus only 10-18/(4.19 ×10-16)
= 2.39 × 10-3 or 0.239% of the
total cell K+. Nonetheless, removal of even this small a
quantity of free cation by itself (unaccompanied by an equivalent amount
of free anion or in exchange of an equivalent amount of free cation) is
not permitted.
Law of parsimony: See Occam's razor.
Law of partition. Law of distribution: See Berthelot-Nemst
distribution law.
Leucocyte, leukocyte: See white blood cell.
LFCH: See Ling's fixed charge hypothesis.
Li+: lithium ion, carrying a single positive electric
charge.
libration: revolving around a primary object ligand: a group, ion
or molecule coordinated to a central atom in a complex Example, oxygen
in hemoglobin.
light microscopy: the use of, or investigations with microscopes
magnifying and making visible small objects illuminated with ordinary
light.
linear conformation: straight-line or fully-extended conformation
usually referring to macromolecules like proteins, which may assume more
than one conformation.
linear correlation coefficient: Usually represented by the
letter, r, a linear correlation coefficient is a number varying from 0
to 1.0, which measures the closeness of the linear relationship between
two variable Y and X. r2, called coefficient of
determination, is a rough estimate of the proportion of the
variation of Y that can be attributed to its linear regression on X.
linear regression analysis: a functional relationship between two
variables often empirically determined is called regression When that
relationship can be represented by a straight line, that regression is
called linear. The statistical examination for a possible linear
regression between two variables is called linear regression analysis.
linear model: a theoretical model (in the AI Hypothesis) of a
singly charged oxygen atom of a fixed oxyacid anion interacting with a
monovalent cation in which the free cation, the fixed oxyacid anion as
well as a varying number of water molecules are arranged in a linear
array.
linear polymer: a nonbranching long molecule built from many
similar smaller units (called monomers) joined end-to-end.
linear protein: a protein existing in the fully-extended
conformation.
Ling's fixed charge hypothesis, LFCH: a quantitative
(statistical) theory of selective accumulation of K+ over Na+
in living cells and models, based on the theory of enhanced counterion
association with a fixed ion carrying an opposite electric charge and
preferential (one-on-one) selective adsorption due to stronger
electrostatic interaction with the smaller hydrated К+ over
the larger hydrated Na+ and associated concepts.
Ling's theory of enhancement of association through site fixation:
See theory of enhancement of association through site fixation.
Ling-Walton centrifugation method: See centrifugation method.
living state: according to the AI Hypothesis, the high (negative)
energy, low entropy state assumed by protoplasm and cells of all plants,
animals and microbes between their birth and death
localized adsorption: a concept first introduced in 1916-1918 by
Irving Langmuir, in which adsorption takes place at specific localized
sites on solid surfaces.
lock and key analogy: first introduced by Emil Fischer to
illustrate his concept that a substrate binds onto a site on an enzyme
because the substrate fits the steric and geometric characteristics This
concept was later extended to include drug action where drugs are like
keys that fit onto stereospecific receptor site.
lone pair electrons: Each atom contains a nucleus carrying a
certain number of positively charged protons and a matching number of
negatively-charged electrons orbiting around the nucleus in groups of
increasing number—except the outermost shell which cannot exceed eight.
This is the well-known octet rule. When the outermost shell has 8
electrons, the maximum stability is reached as in the case of the noble
gas, neon, for atoms of the first row of the periodic table, and argon
for the second row. Thus of the eight electrons of the oxygen atom in H20,
two single covalent bonds each with two electrons are formed, leaving
four of the valence electrons unshared. Quantum mechanical treatment of
valence shows that to form a covalent or electron pair bond, a stable
orbital for each atom and two electrons with opposing spins are
required. The most stable electronic structure of an atom is reached
when all its stable orbitals are used either in electron pair bond
formation or in occupancy by an unshared pair of electrons with opposing
spins. In a water molecule, the two unshared pairs of electrons with
opposing spins are examples of lone pair electrons.
long-range attributes: inherent characteristics that can be
perceived from a distance away.
lymphocyte: a colorless weakly-motile cells produced in the lymph
tissues and making up about 20-30% of the leukocytes of human blood.
lysine: a basic
α-amino acid found in most protein hydrolysates When present in a
protein as a lysine residue, it endows the protein with a fixed cationic
ε-amino group.
lysine residue: Like almost all other
α-amino acids, lysine possesses an
α-amino group and an
α-carboxyl group each attached to the first carbon or
α-carbon atom. When lysine is incorporated into a polypeptide or
protein, its
α-amino group reacts with the
α-carboxyl group of the immediately neighboring amino acid on one
side to form a peptide bond (after losing a molecule of water) while its
α-carboxyl group also forms a peptide bond (after losing a water
molecule) with
α-amino group of its neighboring amino acid residue on the other
side. The reminder of the lysine residue forms the lysine residue's side
chain. The lysine side chain carries a positively charged
ε-amino group which is one of the important fixed cations of all
proteins.
lysis: a process of disintegrating or dissolution (as of red
blood cells).
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