Encyclopedia of Biology

pores. Nuclear pores are found where the inner and
outer membranes are joined. The space is filled with
filamentous material. The pores are involved in regulat-
ing the transport of materials between the nucleus and
the cytoplasm.

nuclearity The number of CENTRAL ATOMs joined in
a single COORDINATIONentity by BRIDGING LIGANDs or
metal-metal bonds is indicated by dinuclear, trinuclear,
tetranuclear, polynuclear, etc.

nuclear magnetic resonance (NMR) spectroscopy
NMR spectroscopy makes it possible to discriminate
nuclei, typically protons, in different chemical environ-
ments. The electron distribution gives rise to a chemical
shift of the resonance frequency. The chemical shift, δ,

of anucleus is expressed in parts per million (ppm) by

its frequency, νn, relative to a standard, νref, and

defined as δ= 10^6 (νn–νref)/νo, where νois the operat-

ing frequency of the spectrometer. It is an indication of

the chemical state of the group containing the nucleus.

More information is derived from the SPIN–SPIN COU-

PLINGs between nuclei, which give rise to multiple pat-

terns. Greater detail can be derived from two- or

three-dimensional techniques. These use pulses of radi-

ation at different nuclear frequencies, after which the

response of the spin system is recorded as a free-induc-

tion decay (FID). Multidimensional techniques, such as

COSY and NOESY, make it possible to deduce the

structure of a relatively complex molecule such as a

small protein (molecular weight up to 25,000). In pro-

teins containing paramagnetic centers, nuclear HYPER-

FINEinteractions can give rise to relatively large shifts

of resonant frequencies, known as contact and pseudo-

248 nuclearity

“normal” tumor

RT/PCR

label with

fluorescent

dyes

combine equal

amounts

hybridize probe

to microarray scan

Prepare cDNA probe Prepare microarray

The nucleic acid probe provides a new way of studying how large numbers of genes interact with each other and how a cell’s regulatory
networks control vast batteries of genes simultaneously. The method uses a robot to precisely apply tiny droplets containing functional
DNA to glass slides. Researchers then attach flourescent labels to DNA from the cell they are studying. The labeled probes are allowed
to bind to complementary DNA strands on the slides. The slides are put into a scanning microscope that can measure the brightness of
each fluorescent dot. The brightness reveals how much of a specific DNA fragment is present, an indicator of how active it is.(Courtesy
of Darryl Leja, NHGRI, National Institutes of Health)