H

H. pylori A bacteria that has been linked (e.g., cause) to gastric ulcers and other gastric problems in humans. That link was first announced by Barry Marshall in the early

1990s. See also BACTERIA, HELICOBACTER PYLORI. H. virescens See HELIOTHIS VIRESCENS (H. VIRE-

SCENS).

H. zea See HELICOVERPA ZEA (H. ZEA).

HA Abbreviation for the word hemagglutinin.

See also HEMAGGLUTININ.

Habitat The natural environment of an organism within an ecosystem. The place, in an ecosystem, where an organism lives. See

also ECOLOGY.

HAC See HUMAN ARTIFICIAL CHROMOSOMES (HAC).

HACCP See HAZARD ANALYSIS AND CRITICAL

CONTROL POINTS (HACCP).

Hairpin Loop A section of highly curving, single-stranded DNA or RNA formed when a long piece (string) of the DNA or RNA bends back on itself and hydrogen-bonds (is able to base pair) in some regions to form double-stranded regions. The structure can be visualized by taking a human hair, bending it back on itself and holding it in such a way as to half its original length. The section where the two ends of hair lie next to each other represents the section of doublestranded DNA or RNA. At one end the hair will have to make a sharp turn and will form a loop. This loop represents the singlestranded hairpin loop. See also RIBONUCLEIC

ACID (RNA), DEOXYRIBONUCLEIC ACID (DNA).

Halophile Microorganisms that require NaCl (salt) for growth (they are called obligate halophiles). Those that do not require it, but can grow in the presence of high NaCl concentrations, are called facultative halophiles. Natural habitats containing high salt concentrations are, for example, the Great Salt Lake

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in Utah, the Dead Sea in Israel, and the Caspian Sea in Russia. See also HABITAT.

	HAP Gene See LOW-PHYTATE CORN.
	Haploid A cell with one set of chromosomes;
	half as many chromosomes as the normal
	somatic body cells contain. A characteristic
	of sex cells. See also GAMETE.	H
	Haplophase A phase in the life cycle of an
	organism in which it has only one copy of
	each gene. The organism is then said to be
	haploid. Yeast can exist as true haploids.
	Humans are haploid for only a few genes
	and cannot exist as true haploids. See also
	HAPLOID.
	Haplotype A subgroup (e.g., an ethnic minor-
	ity, all members of a genetically related fam-
	ily group, etc.) of organisms (e.g., humans)
	whose phenotype results in their body
	responding in the same way to a physical
	agent (a certain pharmaceutical, a toxin, a
	food, etc.). For example, more than 70% of
	black people in North America are lactose
	intolerant (their bodies cannot metabolize
	the lactose sugar in cow’s milk), but fewer
	than 19% of Caucasian people in North
	America are lactose intolerant. Analogous to
	that, the drugs acetaminophen, aspirin, and
	Valium remain in the bodies of women (who
	constitute a haplotype) longer than in the
	bodies of men. Haplotypes for the β2-adren-
	ergic gene are predictive of asthma patients’
	response to the pharmaceutical albuterol.
	See also PHARMACOGENOMICS, HERITABILITY,
	HEREDITY, TRAIT, GENETICS, PHENOTYPE, TOXIN,
	INSULIN, METABOLISM, SINGLE-NUCLEOTIDE
	POLYMORPHISMS (SNPs).
	Hapten A small foreign molecule that will
	stimulate an immune system response (e.g.,
	antibody production) if the small molecule
	(now called a haptenic determinant) is

© 2002 by CRC Press LLC

attached to a macromolecule (carrier) to make it large enough to be recognized by the immune system. See also EPITOPE, CELLULAR

IMMUNE RESPONSE, HUMORAL IMMUNITY.

Haptoglobin A protein which is a component in human blood; that can occur in one of two different molecular forms (i.e., a “large” version of that molecule or a “small” version of that molecule). The “small” version of haptoglobin is very effective at capturing and removing free radicals (high-energy oxygen atoms which bear an “extra” electron) from the bloodstream before they damage tissues (e.g., in the eye, kidneys, and/or arteries).

HThe “large” version of haptoglobin, which is the only haptoglobin molecule in the bloodstream of one particular haplotype (genetic subgroup) of people, is not effective at capture/removal of those free radicals (e.g., generated at a high rate in people with diabetes disease), so diabetics within that particular haplotype tend to suffer extreme damage to eyes, kidneys, and arteries (sometimes necessitating limb amputation). See

also FREE RADICAL, HAPLOTYPE, INSULIN, OXI-

DATIVE STRESS.

Hardening See COLD HARDENING, HYDROGENA-

TION.

Harpin A protein naturally produced by the Erwinia amylovora bacteria (which usually causes the plant disease known as fire blight in apple trees, pear trees, and some ornamental plants of the rose family). Discovered in 1992 by Zhong-Min Wei and colleagues, harpin causes numerous species of plants to initiate a protective/defensive response (cascade) against bacteria, viruses, fungi, and some insects and nematodes. Harpin also causes plants (i.e., that it is sprayed onto) to increase their photosynthesis and to have increased root growth/proliferation; which can lead to greater crop yields. See also PRO-

TEIN, BACTERIA, PHYTOALEXINS, PATHOGENESIS

RELATED PROTEINS, SIGNALING, SIGNALING MOL-

ECULE, SIGNAL TRANSDUCERS AND ACTIVATORS

OF TRANSCRIPTION (STATs), SALICYLIC ACID (SA),

JASMONIC ACID, SYSTEMIC ACQUIRED RESISTANCE

(SAR), CASCADE, R GENES, NEMATODES.

Harvesting A term used to describe the recovery of microorganisms from a liquid culture (in which they have been grown by man).

This is usually accomplished by means of filtration or centrifugation. See also MICRO-

ORGANISM, CULTURE MEDIUM, ULTRACENTRI-

FUGE, DIALYSIS.

Harvesting Enzymes Enzymes that are used to gently dissociate (break apart) cells in living tissues in order to produce single, separate cells that can then be established and propagated in a cell culture reactor. Harvesting enzymes are also used to dissociate cells that have been grown for some time in a cell culture reactor. See also CELL CULTURE, MAMMA-

LIAN CELL CULTURE, ENZYME, CULTURE MEDIUM.

Hazard Analysis and Critical Control Points (HACCP) A quality control program (for food processing) to systematically prevent hazards (e.g., pathogens) from entering the production process. HACCP was initially developed in the 1950s by the Pillsbury Company to supply food products for astronauts in America’s space program. Under HACCP, food processors/handlers must analyze and identify in advance the points where hazards are most likely to occur, and eliminate them. For example, because melons lie in pathogen-contaminated dirt while growing, a “critical control point” for restaurants serving sliced melon is cleansing of the knife after each melon is cut (to prevent the knife carrying pathogens from one infected melon to other melons). See also PATHOGEN, RAPID

MICROBIAL DETECTION (RMD).

Heat-Shock Proteins See STRESS PROTEINS. Heavy-Chain Variable (VH) Domains T h e

regions (domains) of the antibody (molecule’s) “heavy chain” that vary in their amino acid sequence. The “chains” (of atoms) comprising the antibody (immunoglobulin) molecule consist of a region of variable (V) amino acid sequence and a region in which the amino acid sequence remains constant (C). An antibody molecule possesses two antigen binding sites, and it is the variable domains of the light (VL) and heavy (VH) chains which contribute to this antigen binding ability. See also ANTIBODY,

PROTEIN, IMMUNOGLOBULIN, SEQUENCE (OF A

PROTEIN MOLECULE), ANTIGEN, AMINO ACID,

COMBINING SITE, DOMAIN (OF A PROTEIN), LIGHT-

CHAIN VARIABLE (VL) DOMAINS.

© 2002 by CRC Press LLC

Hedgehog Proteins Signaling molecules (consisting of “signaling protein” with cholesterol molecule attached to it), that direct/control tissue differentiation during mammal embryo development (into various organs, limbs, etc.). The signaling protein (within an embryo cell) cleaves itself into two peptides, one of which then acts as a transferase (i.e., enzyme that catalyzes the addition of a functional group to a given molecule — in this case to the other “hedgehog peptide”). When the cell then secretes the cholesterol/peptide molecule, the cholesterol (functional group) “anchors” it to the cell surface, while the “signaling protein” end of the cholesterol/peptide directs differentiation of nearby cells. See

also PROTEIN, SIGNALING MOLECULES, SIGNALING,

CHOLESTEROL, SIGNAL TRANSDUCTION, PEPTIDE,

CELL, TRANSFERASES, ENZYME, FUNCTIONAL

GROUP, CELL DIFFERENTIATION.

Helicobacter pylori Bacteria. See also H. PYLORI. Helicoverpa zea (H. zea) Known as the corn earworm (when it is on corn plants), and known as the tomato fruitworm (when it is on tomato plants), this is one of three insect species that is called “bollworms” (when on cotton plants). H. zea chews on those crop plants, and is one of the insects that can act as a vector (carrier) of Aspergillus flavus fungus. In 1997, scientists at the U.S. Department of Agriculture created/optimized a monoclonal antibody against Helicoverpa zea vitellin, which thus holds potential to be used as a means to control that insect. See also B.t.

KURSTAKI, HELIOTHIS VIRESCENS (H. VIRESCENS),

FUNGUS, PECTINOPHORA GOSSYPIELLA, ASPERGILLUS

FLAVUS, CORN, MONOCLONAL ANTIBODIES (MAb).

Heliothis virescens (H. virescens) Known as the tobacco budworm (when it is on tobacco plants), this is one of three insect species that is called “bollworms” (when they are on cotton plants). As part of Integrated Pest Management (IPM), farmers can utilize the parasitic Euplectrus comstockki wasp to help control the tobacco budworm/cotton bollworm. When that wasp’s venom is injected into Heliothis larva, it stops the larva from molting (and thus maturing). See also B.t.

KURSTAKI, HELICOVERPA ZEA (H. ZEA), PECTINOPHORA GOSSYPIELLA, INTEGRATED PEST MANAGEMENT (IPM).

Helix A spiral, staircase-like structure with a
repeating pattern described by two simulta-
neous operations (rotation and translation).
It is one of the natural conformations exhib-
ited by biological polymers. See also BIOMI-
METIC MATERIALS, ANALOGUE.
Helper T Cells (T4 cells) T cells (lympho-
cytes) which bind B cells (upon recognizing
a foreign epitope on B cell surface). The
binding stimulates B cell proliferation by
secreting B cell growth factor. See also
B CELLS , CYTOKINES, T CELL, T CELL RECEPTORS,
SUPPRESSOR T CELLS.
Hemagglutinin (HA) A special protein that
some viruses utilize to gain entry into the cells	H
they have “targeted.” The HA protein helps
the virus adhere to the cell it targets. Hemag-
glutinin is also utilized to refer to specific plant
cell proteins (lectins) that are naturally pro-
duced by certain plants such as the soybean
plant (Glycine max (L) Merrill). The presence
of those lectin molecules (e.g., on surfaces of
root cells of the soybean plant) help nitrogen-
fixing Rhizobium japonicum bacteria to
adhere to soybean plant roots, where they
begin to “fix nitrogen” (i.e., create natural
nitrate fertilizer, which improves the soil and
helps plants to grow). See also PROTEIN, VIRUS,
CELL, LECTINS, SOYBEAN PLANT, NITROGEN FIXA-
TION, BACTERIA, NITRATES, NODULATION.
Hematologic Growth Factors (HGF) A class
of colony stimulating factors (proteins) that
stimulates bone marrow cells to produce cer-
tain types of red and white blood cells. Some
colony stimulating factors are:
1. Granulocyte-macrophage colony stim-
ulating factor (GM-CSF)
2. Granulocyte-monocyte colony stimu-
lating factor
3. Granulocyte colony stimulating factor
(GM-CSF)
4. Erythropoietin (EPO)
5. Interleukin-3 (IL-3)
6. Macrophage colony stimulating factor
(M-CSF)
Hematopoietic Growth Factors Growth fac-
tors that stimulate the body to produce blood
cells. See also GROWTH FACTOR, INTERLEUKIN- 6
(IL- 6).

© 2002 by CRC Press LLC

HER-2 RECEPTOR.

Hematopoietic Stem Cells Certain stem cells present (e.g., in infants’ bodies, and in the umbilical cords of newborn infants), that can be differentiated (via chemical signals in the growing body) to give rise to red blood cells and the infection-fighting cells of the immune system. See also STEM CELLS, MULTI-

POTENT ADULT STEM CELLS, MESODERMAL ADULT

STEM CELLS, CELL, ORGANISM, SIGNALING.

Heme The iron-porphyrin prosthetic group of a class of proteins called “heme proteins.”

See also PROSTHETIC GROUP, CHELATING AGENT,

PROTEIN, TRANSFERRIN.

Hemoglobin An oxygen-transporting respira-

Htory pigment; it is present in humans, animals, and some plants (e.g., land plants that withstand occasional immersion/flooding). In humans, hemoglobin is carried in the red blood cells (erythrocytes), and is responsible for the red color of the blood. It is composed of two pairs of identical polypeptide chains and iron-containing heme groups, comprising the (total) hemoglobin molecule. The molecular structure of hemoglobin was determined by Max Perutz in 1959. A human disease known as sickle-cell anemia is caused by a (genetically induced) small change in the hemoglobin molecule’s structure (in victims

of that disease). See also HEME, POLYPEPTIDE

(PROTEIN), GENETICS, BILIRUBIN, HEREDITY,

ERYTHROCYTES, PROTEIN STRUCTURE.

Hemostasis See FIBRIN.

Heparin A polysaccharide sulfuric acid ester found in the liver, lung, and other tissues that prolongs the clotting time of blood by preventing the formation of fibrin. Used in vas- c u l a r s u rg e r y a n d i n t r e a t m e n t o f postoperative thrombosis and embolism. See

also FIBRIN, THROMBOSIS.

HER-2 Gene Abbreviation for Human Epidermal growth factor Receptor-2 gene, an oncogene that is responsible for approximately 30% of breast cancers (i.e., in those women whose body over-expresses that particular oncogene, and it spreads via metastaticism). In addition to conventional treatments (mastectomy, chemotherapy, etc.), the U.S. Food and Drug Administration (FDA) in 1998 approved use of a humanized monoclonal antibody (trastuzumab) to be utilized

alone, or in combination with, certain chemotherapy agents (e.g., paclitaxel) against such metastatic breast cancers. That monoclonal antibody attaches to the extracellular domain (i.e., portion of the Her-2 receptor sticking out of the surface of breast tissue cells) and downregulates the Her-2 gene, i.e., resulting in fewer Her-2 receptors being produced on the plasma membrane surfaces of that woman’s breast tissue cells. See also GENE, RECEPTORS,

HER-2 RECEPTOR, RAS GENE, EGF RECEPTOR, ONCOGENES, CANCER, EXPRESS, EXPRESSIVITY, MONO-

CLONAL ANTIBODIES (MAb), B R C A G E N E S ,

PACLITAXEL, FOOD AND DRUG ADMINISTRATION

(FDA), PLASMA MEMBRANE.

HER-2 Protein See

HER-2 Receptor An epidermal growth factor receptor (protein molecule embedded in the surface of cells) that is present in abundance attached to the plasma membrane surface of breast tissue cells in humans possessing the HER-2 gene. See also RECEPTORS, EPIDERMAL

GROWTH FACTOR RECEPTOR, PLASMA MEMBRANE,

HER-2 GENE.

Herbicide Resistance See HERBICIDE-TOLERANT

CROP.

Herbicide-Resistant Crop See HERBICIDE-TOL-

ERANT CROP.

Herbicide-Tolerant Crop Crop plants, cultivated by man, that have been altered to be able to survive application(s) of one or more herbicides by the incorporation of certain gene(s), via either genetic engineering, natural mutation, or mutation breeding (i.e., soaking seeds in mutation-causing chemicals, or bombardment of seeds with ionizing radiation, to cause random genetic mutations, followed by selection of the particular mutation in which herbicide-tolerance occurs).

Because it has been utilized for decades, most relevant national laws consider mutation breeding to be one of the so-called “traditional plant breeding” techniques. For example, European laws that require special labeling of food products containing genetically engineered (via rDNA) crops do not require such special labeling for food products that contain crops created via mutation breeding. Several crops (soybean, canola, cotton, etc.) are made tolerant to glyphosateor sulfosate-containing

© 2002 by CRC Press LLC