Biotechnology

part per million of initial sample (e.g., a 100-
base-pair target DNA sequence within the
genome of one of the higher organisms, which
can contain up to 500 million base pairs). The
procedure alleviates the necessity of in vivo
replication of a target DNA sequence, or of
replication of one-of-a-kind tiny DNA sam-
ples (e.g., from a crime scene). See also
IN VITRO
,
IN VIVO
,
POLYMERASE CHAIN REACTION
(
PCR
),
AMPLICON
,
NESTED PCR
,
DEOXYRIBONUCLEIC
ACID
  (
DNA
),
BASE PAIR
  (
bp
),
GENOME
,
SEQUENCE
(
OF A DNA MOLECULE
),
TAQ
,
DNA POLYMERASE
,
PRIMER
 (
DNA
).
Polymorphism (chemical) The property of a
chemical substance crystallizing (or simply
existing) in two or more forms having dif-
ferent structures. For example, diamond and
graphite are two different structures (mani-
festations) of the element carbon. Deoxy-
ribonucleic acid (DNA) is a polymorphic
compound because the polymer can take on
different forms. See also 
A
-
DNA
,
B
-
DNA
,
Z-DNA
,
DEOXYRIBONUCLEIC ACID
  (
DNA
),
DNA
PROFILING
,
POLYMORPHISM
 (
GENETIC
).
Polymorphism (genetic) A name applied to a
condition in which a species of plant or ani-
mal is represented by several distinct, non-
integrating forms or types unrelated to age
or sex. The differences are often in colora-
tion, though any characteristic of the organ-
ism may be involved (e.g., nuclei shape for
polymorphonuclear leukocytes). See also
POLYMORPHONUCLEAR LEUKOCYTES
  (
PMN
),
POLYMORPHONUCLEAR GRANULOCYTES
,
SINGLE
-
NUCLEOTIDE POLYMORPHISMS
  (
SNP
s
),
POLYMOR-
PHISM
 (
CHEMICAL
).
Polymorphonuclear Granulocytes N e u t r o -
phils, eosinophils, and basophils are collec-
tively known as polymorphonuclear
granulocytes. This is due to the fact that
collectively their nuclei are segmented into
lobes and they have granule-like inclusions
within their cytoplasm. See also 
GRANULO-
CYTES
,
BASOPHILS
,
EOSINOPHILS
,
NEUTROPHILS
,
CYTOPLASM
.
Polymorphonuclear Leukocytes (PMN)
Formerly named microphages, they are
phagocytic (i.e., foreign particle-ingesting)
white blood cells that have a lobed nucleus.
For example, during an attack of the com-
mon cold (when virus first invades mucous
membranes of the human nose), the body
responds by making Interleukin-8 (IL-8); a
glycoprotein that attracts large quantities of
polymorphonuclear leukocytes to the
mucous membranes of the nose (to try to
combat the infection). Another example is
when polymorphonuclear leukocytes (PMN)
migrate into a female pig’s uterus within
6 hours after semen is introduced via breed-
ing. PMN remove excess sperm and bacteria,
resulting in a “friendly” environment for
embryos to develop in the uterus. See also
CELLULAR IMMUNE RESPONSE
,
LEUKOCYTES
,
© 2002 by CRC Press LLC

P
POLYMORPHISM
  (
GENETIC
),
VIRUS
,
BACTERIA
,
GLYCOPROTEIN
,
INTERLEUKIN-
8
  (
IL-
8
),
CELL
,
NUCLEUS
,
PLASMA MEMBRANE
.
Polypeptide (protein) A molecular chain of
amino acids linked by peptide bonds. Syn-
onymous with protein. Via the synthesis (of
this “chain”) performed by ribosomes, each
polypeptide (protein) in nature is the ulti-
mate expression product of a gene. All of the
amino acids commonly found in proteins
have an asymmetric carbon atom, except the
amino acid glycine. Thus, the polypeptide is
potentially chiral in nature. See also 
PROTEIN
,
AMINO ACID
,
GENE
,
PEPTIDE
,
STEREOISOMERS
,
CHIRAL COMPOUND
,
EXPRESS
,
RIBOSOMES
,
POLYRIBOSOME
  (
POLYSOME
),
MESSENGER RNA
(
m
RNA
).
Polyphenols Phytochemicals (e.g., naturally
found in coffee, certain types of grapes, cer-
tain red wines, green tea, cocoa, etc.) that
act as antioxidants when consumed by
humans. For example, polyphenols are nat-
urally produced within the beans of the
cocoa (cacao) tree (Theobroma cacao), and
thus are present in chocolate made from
those beans. Polyphenols naturally produced
in apples have been shown to inhibit certain
bacteria in the human mouth from producing
the particular glucans that lead to a buildup
of plaque on teeth; prevention of such plaque
build-up may help prevent cavities from
forming in teeth. See also 
PHYTOCHEMICALS
,
FLAVONOIDS
,
ATHEROSCLEROSIS
,
ANTIOXIDANTS
,
OXIDATIVE STRESS
,
PHENOLIC HORMONES
,
NUTRACEUTICALS
,
BACTERIA
,
GLUCANS
.
Polyribosome (polysome) A complex of a
messenger RNA (mRNA) molecule on
which ribosomes (ribosomal RNA; rRNA)
are anchored. A number of ribosomes bound
to only a single mRNA molecule. One
mRNA molecule hence functions as a tem-
plate for a number of polypeptide chains at
one time. See also 
RIBOSOMES
,
r
RNA
 (
ribosomal
RNA
),
MESSENGER RNA
 (
m
RNA
).
Polysaccharides Linear and/or branched
(structure) macromolecules (large mole-
cules) composed of many monosaccharide
units (monomers such as glucose) linked by
glycosidic bonds. See also 
GLYCOSIDE
,
MONOSACCHARIDES
,
AMYLOSE
,
AMYLOPECTIN
.
Polysome See
POLYRIBOSOME
.
Polyunsaturated Fatty Acids (PUFA)
Unsaturated fatty acids, possessing more
than one molecular double bond in their
molecular “backbone” (i.e., they contain at
least two less than the maximum possible
number of hydrogen atoms). Enzymes (e.g.,
∆ 12 desaturase) present in some oilseed
plants (soybean, canola, corn/maize, etc.)
convert some monounsaturated fatty acids
(e.g., oleic acid) to some polyunsaturated
fatty acids (e.g., linoleic acid), within their
developing seeds. For example, soybean oil
contains (historical average) 60% polyunsat-
urated fatty acids. Extensive research shows
that polyunsaturated fatty acids (PUFA)
impart a variety of health benefits to humans
that consume them. In general, those health
benefits include anti-inflammatory, anti-
hypertensive (i.e., prevention of high blood
pressure), reduction in cancer risk, reduction
in the blood cholesterol levels, reduction in
the risk of coronary heart disease (CHD),
plus aiding in the development of retina and
brain tissues.
For example, the n-3 (“omega-3”) PUFAs
possess antithrombotic effects and also
reduce blood concentrations of triglycerides.
High dietary levels (in human diet) of the
n-6 (“omega-6”) PUFAs have been related
to a decreased risk of coronary heart disease
(CHD). Research indicates that some of the
beneficial effects of PUFAs occur via PUFA
interactions with several types of nuclear
receptors (present in cells of some human
tissues), which results in (PUFA) modula-
tion of certain gene(s) expression in those
cells. See also 
UNSATURATED FATTY ACID
,
ESSENTIAL FATTY ACIDS
,
THROMBOSIS
,
TRIGLYC-
ERIDES
,
CORONARY HEART DISEASE
 (
CHD
),
CAN-
CER
,
N-
3
FATTY ACIDS
,
SOYBEAN OIL
,
N-
6
FATTY
ACIDS
,
ENZYME
,
DOCOSAHEXANOIC ACID
  (
DHA
),
HIGHLY UNSATURATED FATTY ACIDS
  (
HUFA
),
EICOSAPENTANOIC ACID
  (
EPA
),
CONJUGATED
LINOLEIC ACID
  (
CLA
),
CELL
,
GENE
,
RECEPTORS
,
NUCLEAR RECEPTORS
,
DEOXYRIBONUCLEIC ACID
(
DNA
),
EXPRESS
,
GENE EXPRESSION
,
TRANSCRIP-
TION
,
TRANSCRIPTION FACTORS
,
SOYBEAN PLANT
,
OLEIC ACID
,
LINOLEIC ACID
,
LINOLENIC ACID
.
Porcine Somatotropin (PST) A   h o r m o n e ,
produced in the pituitary gland of pigs, that
increases a swine’s muscle tissue production
© 2002 by CRC Press LLC

P
efficiency. Injecting this hormone causes a
faster growing, leaner pig.
Porphyrins Complex nitrogenous compounds
containing four substituted pyrroles
covalently joined into a ring structure. When
complexed with a central metal atom it is
called a metalloporphyrin.
Position Effect A change in the expression of
a gene brought about by its translocation to
a new site in the genome. For example, a
previously active gene may become inactive
if placed on a new site in the genome. See
also
GENOME
,
TRANSLATION
,
GENETIC MAP
,
MAP
DISTANCE
,
PROMOTER
.
Positional Cloning A technique used by
researchers to zero in on the gene (s) respon-
sible for a given trait or disease. A genetic
map of the organism’s genome is used to
make an educated guess as to the precise
location of the gene of interest (e.g., near
marker “x” or “y”, etc.). Then those guessed
genes are cloned, inserted into living organ-
isms or cells, and tested to see if the guessed
gene causes expression of the protein of
interest (e.g., a protein that causes the dis-
ease that the researcher is attempting to
cure). See also 
CLONE
  (
A MOLECULE
),
GENE
,
GENE AMPLIFICATION
,
GENE DELIVERY
,
DNA
PROBE
,
GENE MACHINE
,
GENETIC ENGINEERING
,
GENETIC MAP
,
GENETIC MARKER
,
GENOME
,
MAP
DISTANCE
,
FUNCTIONAL GENOMICS
,
POSITION
EFFECT
,
EXPRESS
.
Positive and Negative Selection (PNS) A sep-
aration technique; a technique to speed up
the task of selecting, from thousands of lab-
oratory specimens, the few cells with pre-
cisely the desired genetic changes induced
(via genetic engineering). The thousands of
genetically altered cells are brought about
(produced) by genetic engineering experi-
ments. Many genetic alterations are accom-
plished by injecting or flooding (specimen)
cells with fragments of new genetic material
(genes). A few cells are produced that have
precisely the desired genetic changes among
a large number of cells that do not have the
desired changes. Sort of like a “needle in a
haystack.” By analogy, the few cells possess-
ing the desired trait represent the needles
while the multitude of cells not possessing
the trait represent the hay.
In order to isolate the few desired cells,
the needles must be separated from the hay.
PNS gets rid of the nondesired cells and
leaves only the cells possessing the desired
genetic change. This is accomplished in the
following way. The pieces of newly injected
genetic material are composed not only of
the desired sequence of DNA, but also
another piece of DNA (known as a marker)
which renders only those cells possessing
the desired (genetic) change resistant to cer-
tain antibiotic drugs (such as neomycin) and
certain antiviral drugs (e.g., Ganciclovir™).
When all of the engineered cells are exposed
to the drug (which normally kills all of the
cells) only those cells possessing the desired
genetic change (and the concomitant piece
of DNA providing drug resistance) survive
and hence are “selected.” The other cells not
having the drug resistance are selected
against, and die. See also 
GENETIC ENGINEER-
ING
,
GENE
,
MARKER
 (
GENETIC MARKER
),
Q
-
BETA
REPLICASE TECHNIQUE
,
POLYMERASE CHAIN
REACTION
 (
PCR
)
TECHNIQUE
.
Positive Supercoiling O c c u r s   i n   d o u b l e -
stranded cyclic DNA molecules having no
breaks at all in either strand. If the double
helix (of DNA) is wound further in the same
direction as the winding of the two strands
of the double helix molecule, then the circu-
lar duplex itself takes on superhelical turns.
By analogy, supercoiling or superhelicity
may be described as follows. A piece of rope
composed of two or three smaller strands of
rope 197 Positive Supercoiling are wound
around each other to yield the finished rope.
This is equivalent to the normal double-
stranded DNA. If the ends of the rope are
then joined or tied together and the resultant
circle of rope is again wound in the same
direction as the winding that produced the
rope in the first place, supercoils will be
formed and the rope will become a much
thicker (supercoiled), but shorter, piece of
rope. See also 
DOUBLE HELIX
.
Post-Transcriptional Processing (Modifica-
tion) of RNAs The enzyme-catalyzed pro-
cessing or structural modifications that RNAs
such as mRNAs, rRNAs, and tRNAs must
undergo before they are functionally finished
products. For example, in eucaryotes a block
© 2002 by CRC Press LLC

P
of poly A containing at least 200 AMP res-
idues is enzymatically attached to the 3
′ end
of mRNA in the nucleus of the cell. The
mRNAs with the “tail” are then transferred
to the cytoplasm and the tail enzymatically
removed to form the functional mRNAs. It
is believed that the poly A tail aids in the
transfer of the complex and/or targets the
complex to the cytoplasm. See also 
POST
-
TRANSLATIONAL MODIFICATION OF PROTEIN
m
RNA
,
r
RNA
,
t
RNA
.
Post-Translational Modification of Protein
Enzymatic processing of a polypeptide chain
after its translation from its mRNA, i.e.,
addition of carbohydrate moieties to the pro-
tein or the removal of a portion of the
polypeptide chain in order to produce a func-
tional protein in the correct environment.
See also 
POLYPEPTIDE
 (
PROTEIN
),
MOIETY
,
MES-
SENGER RNA
 (
m
RNA
),
ENZYME
,
RIBOSOMES
,
CAR-
BOHYDRATES
,
GLYCOPROTEIN
.
Potato Late Blight A fungal disease of the
potato plant (Solanum tuberosum) caused by
the fungus Phytophthora infestans. During
the 1840s, this plant disease struck the potato
crops of Ireland and Europe, leading to the
starvation of more than one million people
(principally in Ireland, because that nation
was very dependent on potatoes for food).
See also 
FUNGUS
.
PPA See
PLANT PROTECTION ACT
.
PPFM See
P I N K
P I G M E N T E D
F A C U L T A T I V E
METHYLOTROPH
.
PPO Acronym for Protoporphyrinogen Oxi-
dase. See also 
ACURON
™
GENE
.
PR Proteins See
PATHOGENESIS RELATED PROTEINS
.
Prebiotics Chemical compounds or microor-
ganisms (e.g., yeasts) — administered alone
or in combination (e.g., in the feed rations
of animals) — that (generally) act to stimu-
late growth of beneficial types of bacteria
within the digestive system of animals (e.g.,
livestock). Those compounds can include
some organic acids (propionic acid, malic
acid, etc.). For example, adding certain
strains of yeast (culture) and malate (malic
acid) to cattle feed rations has been shown
to stimulate Selenomonas ruminantium bacte-
ria (growth) in the rumen (i.e., the “first stom-
ach” in cattle). Selenomonas ruminantium
tend to constitute 22–51% of the total bacteria
in a typical rumen, and are important for
optimal digestion (e.g., of the grass eaten by
that animal).
Inulin, and several fructose oligosaccha-
rides, etc. act as prebiotics in the human diges-
tive system (e.g., by stimulating growth of
Bifidus species of bacteria in the digestive sys-
tem). For animal feed rations, in addition to
fructose oligosaccharides, transgalacto-oli-
gosaccharides may be added, to also act as
prebiotics. See also 
PROBIOTICS
,
YEAST
,
BAC-
TERIA
,
BIFIDUS
,
INULIN
,
FRUCTOSE OLIGOSACCHA-
RIDES
,
TRANSGALACTO
-
OLIGOSCCHARIDES
,
STRAIN
.
Pribnow Box T h e   c o n s e n s u s   s e q u e n c e
T-A-T-A-A-T-G centered about 10 base
pairs before the starting point of bacterial
genes. It is a part of the promoter and is
especially important in binding RNA poly-
merase. See also 
RNA POLYMERASE
,
TATA
HOMOLOGY
,
HOMEOBOX
,
PROMOTER
,
BASE PAIR
(
bp
).
Primary Structure Refers to the sequence of
amino acids in a protein “molecular” chain,
or to the linear sequence of nucleotides in a
polynucleotide (RNA or DNA) molecular
chain. See also 
POLYPEPTIDE
 (
PROTEIN
),
AMINO
ACID
,
PROTEIN
,
STRUCTURAL GENE
,
STRUCTURAL
GENOMICS
,
NUCLEOTIDE
,
PROTEOMICS
,
DEOXY-
RIBONUCLEIC ACID
  (
DNA
),
RIBONUCLEIC ACID
(
RNA
).
Primer (DNA) A short sequence deoxyribo-
nucleic acid (DNA) that is paired with one
strand of the template DNA, in the Poly-
merase Chain Reaction (PCR) technique. In
PCR testing (e.g., a paternity test), the
primer is selected to be complementary to
the analytically relevant sequence of DNA.
It is the growing end of the DNA chain and
it simply provides a free 3
′-OH end at which
the enzyme DNA polymerase adds on deox-
yribonucleotide units (monomers). Which
deoxyribonucleotide is added is dictated by
base pairing to the template DNA chain.
Without a DNA primer sequence a new DNA
chain cannot form, since DNA polymerase
is not able to initiate DNA chains. See also
DEOXYRIBONUCLEIC ACID
  (
DNA
),
SEQUENCE
  (
OF
A DNA MOLECULE
),
TEMPLATE
,
COMPLEMENTARY
(
MOLECULAR GENETICS
),
DOUBLE HELIX
,
POLY-
MERASE
,
POLYMERASE CHAIN REACTION
  (
PCR
),
© 2002 by CRC Press LLC

P
POLYMERASE CHAIN REACTION
 (
PCR
)
TECHNIQUE
,
NESTED PCR
.
Prion Proteinaceous structures (molecules)
found in the plasma membrane (surface) of
cells, in the brains of all vertebrate animals.
In 1982, Dr. Stanley Prusiner discovered that
misshapen (mutated) versions can cause the
neurodegenerative disease Bovine Spongi-
form Encephalopathy (BSE) in cattle, and
the neurodegenerative diseases Creutzfeld-
Jakob Disease (CJD), kuru, Gerstmann-
Straussler-Scheinker Syndrome, and Fatal
Familial Insomnia (FFI) in humans.
Dr. Prusiner named these molecules prions
for “proteinaceous infected particle,”
because, unlike infectious pathogenic bacte-
ria or viruses, prions do not contain DNA.
The dye named Congo Red, and IDX (a
derivative of the chemotherapeutic doxoru-
bicin) have shown some ability to slow
prion-caused neurodegeneration. See also
PROTEIN
,
CELL
,
PLASMA MEMBRANE
,
MUTANT
,
BACTERIA
,
DEOXYRIBONUCLEIC ACID
  (
DNA
),
PROTEIN STRUCTURE
,
BSE
,
PROTO
-
ONCOGENES
,
STRESS PROTEINS
,
MONOCLONAL ANTIBODIES
.
Proanthocyanidins The chemical compo-
nents within North American cranberries
(Vaccinium macrocarpon) and blueberries
(genus Vaccinium) that impart health bene-
fits to humans who consume those cranber-
ries/blueberries. For example, when humans
consume cranberries, these chemical com-
pounds prevent Escherichia coli bacteria
from adhering to the cells lining the human
urinary tract (thereby helping to prevent
some urinary tract infections). See also
ANTHOCYANIDINS
,
PHYTOCHEMICALS
,
NUTRACEU-
TICALS
,
CELL
,
ESCHERICHIA COLIFORM
 (
E
.
COLI
).
Probe A relatively small molecule that can be
used to sense the presence and condition of
a specific protein, DNA fragment, RNA
fragment, or nucleic acid by a unique inter-
action with that macromolecule. See also
DNA PROBE
,
HYBRIDIZATION
 (
MOLECULAR GENET-
ICS
),
BACTERIAL ARTIFICIAL CHROMOSOMES
(
BAC
),
YEAST ARTIFICIAL CHROMOSOMES
  (
YAC
),
HUMAN ARTIFICIAL CHROMOSOMES
  (
HAC
),
MARKER ASSISTED SELECTION
,
SOUTHERN BLOT
ANALYSIS
,
FLUORESCENCE IN SITU HYBRIDIZATION
(
FISH
).
Probiotics Compounds that (generally) act to
stimulate growth of beneficial types of bac-
teria within the digestive system of animals
(e.g., livestock). For example, organic acids
(propionic acid, acetic acid, lactic acid, citric
acid, etc.) act to inhibit the growth/multipli-
cation of pathogens (disease-causing micro-
organisms) in the digestive system of
monogastric (i.e., single-stomach) animals
such as poultry and swine. Those acids are
able to pass through the outer cell membrane
(plasma membrane) of pathogenic bacteria
and fungi. Once inside those pathogens’
cells, the acids dissociate, and acidify the
cells’ interior (which disrupts the cells’ pro-
tein synthesis, growth, and replication of the
pathogen). See also 
PREBIOTICS
,
BIFIDUS
,
CIT-
RIC ACID
,
FRUCTOSE OLIGOSACCHARIDES
,
PATHO-
GEN
,
MICROORGANISM
,
BACTERIA
,
FUNGUS
,
CELL
,
ACID
,
PLASMA MEMBRANE
.