propene and used to make acrylic
resins.
propenyl group (allyl group) The
organic group H 2 C=CHCH 2 –.
propionaldehyde See propanal.
propylene See propene.
propyl group The organic group
CH 3 CH 2 CH 2 –.
prostaglandin Any of a group of
organic compounds derived from
*essential fatty acids and causing a
range of physiological effects in ani-
mals. Prostaglandins have been de-
tected in most body tissues. They act
at very low concentrations to cause
the contraction of smooth muscle;
natural and synthetic prostaglandins
are used to induce abortion or labour
in humans and domestic animals.
Two prostaglandin derivatives have
antagonistic effects on blood circula-
tion: thromboxane A 2 causes blood
clotting while prostacyclin causes
blood vessels to dilate. InÛammation
in allergic reactions and other dis-
eases is also thought to involve
prostaglandins.
prosthetic group A tightly bound
nonpeptide inorganic or organic
component of a protein. Prosthetic
groups may be lipids, carbohydrates,
metal ions, phosphate groups, etc.
Some *coenzymes are more correctly
regarded as prosthetic groups.
protactinium Symbol Pa. A radio-
active metallic element belonging to
the *actinoids; a.n. 91; r.a.m.
231.036; r.d. 15.37 (calculated); m.p.
< 1600 °C (estimated). The most stable
isotope, protactinium–231, has a
half-life of 3.43 × 104 years; at least
ten other radioisotopes are known.
Protactinium–231 occurs in all ura-
nium ores as it is derived from ura-
nium–235. Protactinium has no
practical applications; it was discov-
ered by Lise Meitner and Otto Hahn
in 1917.
A- Information from the WebElements site
protamine Any of a group of pro-
teins of relatively low molecular
weight found in association with the
chromosomal *DNA of vertebrate
sperm cells. They contain a single
polypeptide chain comprising about
67% arginine. Protamines are thought
to protect and support the chromo-
somes.protease (peptidase; proteinase;
proteolytic enzyme) Any enzyme
that catalyses the hydrolysis of pro-
teins into smaller *peptide fractions
and amino acids, a process known as
proteolysis. Examples are *pepsin
and *trypsin. Several proteases, act-
ing sequentially, are normally re-
quired for the complete digestion of
a protein to its constituent amino
acids.
protecting group A group used to
protect a certain functional group in
a chemical synthesis. For example,
a hydroxyl group (–OH) can be
converted into an acetyl group
(–OOCCH 3 ) to protect it taking part in
a certain step of the synthesis. In this
case, the acetyl is the protecting
group. Later it can easily be changed
back into the original hydroxyl
group.protein Any of a large group of or-
ganic compounds found in all living
organisms. Proteins comprise carbon,
hydrogen, oxygen, and nitrogen and
most also contain sulphur; molecular
weights range from 6000 to several
million. Protein molecules consist of
one or several long chains (*polypep-
tides) of *amino acids linked in a
characteristic sequence. This se-
quence is called the primary structure
of the protein. These polypeptides
may undergo coiling or pleating, the441 protein
p