N

NAD(nicotinamide adenine dinu-
cleotide)A coenzyme, derived from
the B vitamin nicotinic acid, that
participates in many biological dehy-
drogenation reactions. NAD is charac-
teristically loosely bound to the
enzymes concerned. It normally car-
ries a positive charge and can accept
one hydrogen atom and two elec-
trons to become the reduced form,
NADH. NADH is generated during the
oxidation of food; it then gives up its
two electrons (and single proton) to
the electron transport chain, thereby
reverting to NAD+and generating
three molecules of ATP per molecule
of NADH.
NADP(nicotinamide adenine dinu-
cleotide phosphate) differs from NAD
only in possessing an additional
phosphate group. It functions in the
same way as NAD although anabolic
reactions (see anabolism) generally
use NADPH (reduced NADP) as a hy-
drogen donor rather than NADH. En-

zymes tend to be speciÜc for either

NAD or NADP as coenzyme.

nano-Symbol n. A preÜx used in

the metric system to denote 10–9. For

example, 10–9second = 1 nanosecond

(ns).

nanotechnologyThe develop-

ment and use of devices that have a

size of only a few nanometres. Re-

search has been carried out into very

small components, which depend on

electronic effects and may involve

movement of a countable number of

electrons in their action. Such de-

vices would act much faster than

larger components. Considerable in-

terest has been shown in the produc-

tion of structures on a molecular

level by suitable sequences of chemi-

cal reactions. It is also possible to ma-

nipulate individual atoms on surfaces

using a variant of the *atomic force

microscope.

nanotubeSee buckminster-

fullerene.

CONH 2

site of reduction to NADH

phosphate group

attached here to

form NADP

NHNHNH 222

NNN

NNN NNN

NNN

+++

OOO NNN

HH

OHOHOH OHOHOH

CHCHCH 222

HHH

OOO

O PPPO–

OOO

OOO CHCHCH 222

H

OOO

H

H

OHOHOH

H

OHOHOH

O PPPO–

NAD