Chemistry Reference
In-Depth Information
(a)
(b)
(c)
(d)
FIGURE 1.6
Selective binding sites in transport proteins for Na
þ
,K
þ
,Ca
2
þ
, and Cl
. (a) Two Na
þ
binding sites in the LeuT Na
þ
-dependent
pump. (b) Four K
þ
binding sites in the KcsA K
þ
channel. (c) Two Ca
2
þ
binding sites in the Ca
2
þ
ATPase pump. (d) Two central Cl
binding
sites in a mutant ClC Cl
/H
þ
exchanger.
(From
Gouax and MacKinnon, 2005
.
)
Chernobyl, and continues to represent an environmental hazard. Cs is also used in atomic clocks, accurate to one
second every few hundred thousand years.
The alkaline earths, beryllium, magnesium, calcium, strontium, barium, and radium, together constitute Group 2
of the periodic table. They are usually found in relatively un-reactive forms, bound to oxygen: the free metals still
have a tendency to lose their outer electrons, but less easily than the Group 1 elements, and are a little less reactive.
Be is extremely toxic in man, causing inflammation of the lungs and lung cancer. On account of its lightness, it
is used in aircraft manufacture, and its silicate forms the beautiful green gemstones, emerald and aquamarine. Mg
is essential, as is Ca. The role of Mg is intimately intertwined with phosphate, involved in many phosphoryl
transfer reactions, as Mg-ATP in muscle contraction, in the stabilisation of nucleic acid structures, as well as in the
catalytic activity of ribozymes (catalytic RNA molecules). It is also found as the metal centre in the light-
absorbing pigments, chlorophylls, in photosynthetic organisms. Ca, a crucial second messenger signalling key
changes in cellular metabolism, is also important in muscle activation, in the activation of many proteases, both
intra- and extracellular, and as a major component of a range of bio-minerals, including bone (Chapter 19). Sr, Ba,
and Ra have no biological importance. Sr gives the dramatic crimson colour to fireworks, and is used as an additive
in the glass of TV sets and monitors. However, its radioisotope Sr
90
can get absorbed into the bone in place of Ca.
The insoluble sulfate of Ba is used for 'bariummeals' in order to take X-ray pictures of the digestion of food by the
stomach. Traces of Ra (and polonium) were isolated from pitchblende uranium ore by Pierre and Marie Curie in
1898 (one ton of pitchblende typically yields about one seventh of a gram of radium). Marie Curie received the
Nobel Prize for chemistry on December 10, 1911, 'for services to the advancement of chemistry by the discovery
of the elements radium and polonium'. She was the first woman to win the Nobel Prize, and the first person ever to
