Glossary

α: the Greek letter alpha
β: the Greek letter beta
γ: the Greek letter gamma
λ: the Greek letter lambda
σ: the Greek letter sigma
E. coli: the bacterium Escherichia coli
"-ase": suffix indicating an enzyme
acidic: having the properties of an acid; the opposite of basic
acrosomal cap: tip of sperm cell that contains digestive enzymes for penetrating the egg
adenoma: a tumor (cell mass) of gland cells
aerobic: with oxygen, or requiring it
agar: gel derived from algae
agglutinate: clump together
aggregate: stick together
algorithm: procedure or set of steps
allele: a particular form of a gene
allelic variation: presence of different gene forms (alleles) in a population
allergen: substance that triggers an allergic reaction
allolactose: "other lactose"; a modified form of lactose
amino acid: a building block of protein
amino termini: the ends of a protein chain with a free NH₂ group
amniocentesis: removal of fluid from the amniotic sac surrounding a fetus, for diagnosis
amplify: produce many copies of, multiply
anabolic steroids: hormones used to build muscle mass

anaerobic: without oxygen or not requiring oxygen
androgen: testosterone or other masculinizing hormone
anemia: lack of oxygen-carrying capacity in the blood
aneuploidy: abnormal chromosome numbers
angiogenesis: growth of new blood vessels
anion: negatively charged ion
anneal: join together
anode: positive pole
anterior: front
antibody: immune-system protein that binds to foreign molecules
antidiuretic: a substance that prevents water loss
antigen: a foreign substance that provokes an immune response
antigenicity: ability to provoke an immune response
apoptosis: programmed cell death
Archaea: one of three domains of life, a type of cell without a nucleus
archaeans: members of one of three domains of life, have types of cells without a nucleus
aspirated: removed with a needle and syringe
aspiration: inhalation of fluid or solids into the lungs
association analysis: estimation of the relationship between alleles or geno-types and disease
asymptomatic: without symptoms
ATP: adenosine triphosphate, a high-energy compound used to power cell processes
ATPase: an enzyme that breaks down ATP, releasing energy
attenuation: weaken or dilute
atypical: irregular
autoimmune: reaction of the immune system to the body's own tissues
autoimmunity: immune reaction to the body's own tissues
autosomal: describes a chromosome other than the X and Y sex-determining chromosomes
autosome: a chromosome that is not sex-determining (not X or Y)
axon: the long extension of a nerve cell down which information flows
bacteriophage: virus that infects bacteria
basal: lowest level

base pair: two nucleotides (either DNA or RNA) linked by weak bonds
basic: having the properties of a base; opposite of acidic
benign: type of tumor that does not invade surrounding tissue
binding protein: protein that binds to another molecule, usually either DNA or protein
biodiversity: degree of variety of life
bioinformatics: use of information technology to analyze biological data
biolistic: firing a microscopic pellel into a biological sample (from biological/ballistic)
biopolymers: biological molecules formed from similar smaller molecules, such as DNA or protein
biopsy: removal of tissue sample for diagnosis
biotechnology: production of useful products
bipolar disorder: psychiatric disease characterized by alternating mania and depression
blastocyst: early stage of embryonic development
brackish: a mix of salt water and fresh water
breeding analysis: analysis of the offspring ratios in breeding experiments
buffers: substances that counteract rapid or wide pH changes in a solution
Cajal: Ramon y Cajal, Spanish neuroanatomist
carcinogens: substances that cause cancer
carrier: a person with one copy of a gene for a recessive trait, who therefore does not express the trait
catalyst: substance that speeds a reaction without being consumed (e.g., enzyme)
catalytic: describes a substance that speeds a reaction without being consumed
catalyze: aid in the reaction of
cathode: negative pole
cDNA: complementary DNA
cell cycle: sequence of growth, replication and division that produces new cells
centenarian: person who lives to age 100
centromere: the region of the chromosome linking chromatids
cerebrovascular: related to the blood vessels in the brain
cerebrovascular disease: stroke, aneurysm, or other circulatory disorder affecting the brain

charge density: ratio of net charge on the protein to its molecular mass
chemotaxis: movement of a cell stimulated by a chemical attractant or repellent
chemotherapeutic: use of chemicals to kill cancer cells
chloroplast: the photosynthetic organelle of plants and algae
chondrocyte: a cell that forms cartilage
chromatid: a replicated chromosome before separation from its copy
chromatin: complex of DNA, histones, and other proteins, making up chromosomes
ciliated protozoa: single-celled organism possessing cilia, short hair-like extensions of the cell membrane
circadian: relating to day or day length
cleavage: hydrolysis
cleave: split
clinical trials: tests performed on human subjects
codon: a sequence of three mRNA nucleotides coding for one amino acid
Cold War: prolonged U.S.-Soviet rivalry following World War II
colectomy: colon removal
colon crypts: part of the large intestine
complementary: matching opposite, like hand and glove
conformation: three-dimensional shape
congenital: from birth
conjugation: a type of DNA exchange between bacteria
cryo-electron microscope: electron microscope that integrates multiple images to form a three-dimensional model of the sample
cryopreservation: use of very cold temperatures to preserve a sample
cultivars: plant varieties resulting from selective breeding
cytochemist: chemist specializing in cellular chemistry
cytochemistry: cellular chemistry
cytogenetics: study of chromosome structure and behavior
cytologist: a scientist who studies cells
cytokine: immune system signaling molecule
cytokinesis: division of the cell's cytoplasm
cytology: the study of cells
cytoplasm: the material in a cell, excluding the nucleus

cytosol: fluid portion of a cell, not including the organelles
de novo: entirely new
deleterious: harmful
dementia: neurological illness characterized by impaired thought or awareness
demography: aspects of population structure, including size, age distribution, growth, and other factors
denature: destroy the structure of
deoxynucleotide: building block of DNA
dimerize: linkage of two subunits
dimorphism: two forms
diploid: possessing pairs of chromosomes, one member of each pair derived from each parent
disaccharide: two sugar molecules linked together
dizygotic: fraternal or nonidentical
DNA: deoxyribonucleic acid
domains: regions
dominant: controlling the phenotype when one allele is present
dopamine: brain signaling chemical
dosage compensation: equalizing of expression level of X-chromosome genes between males and females, by silencing one X chromosome in females or amplifying expression in males
ecosystem: an ecological community and its environment
ectopic expression: expression of a gene in the wrong cells or tissues
electrical gradient: chemiosmotic gradient
electrophoresis: technique for separation of molecules based on size and charge
eluting: exiting
embryogenesis: development of the embryo from a fertilized egg
endangered: in danger of extinction throughout all or a significant portion of a species' range
endogenous: derived from inside the organism
endometriosis: disorder of the endometrium, the lining of the uterus
endometrium: uterine lining
endonuclease: enzyme that cuts DNA or RNA within the chain
endoplasmic reticulum: network of membranes within the cell

endoscope: tool used to see within the body
endoscopic: describes procedure wherein a tool is used to see within the body
endosymbiosis: symbiosis in which one partner lives within the other
enzyme: a protein that controls a reaction in a cell
epidemiologic: the spread of diseases in a population
epidemiologists: people who study the incidence and spread of diseases in a population
epidemiology: study of incidence and spread of diseases in a population
epididymis: tube above the testes for storage and maturation of sperm
epigenetic: not involving DNA sequence change
epistasis: suppression of a characteristic of one gene by the action of another gene
epithelial cells: one of four tissue types found in the body, characterized by thin sheets and usually serving a protective or secretory function
Escherichia coli: common bacterium of the human gut, used in research as a model organism
estrogen: female horomone
et al.: "and others"
ethicists: a person who writes and speaks about ethical issues
etiology: causation of disease, or the study of causation
eubacteria: one of three domains of life, comprising most groups previously classified as bacteria
eugenics: movement to "improve" the gene pool by selective breeding
eukaryote: organism with cells possessing a nucleus
eukaryotic: describing an organism that has cells containing nuclei
ex vivo: outside a living organism
excise: remove; cut out
excision: removal
exogenous: from outside
exon: coding region of genes
exonuclease: enzyme that cuts DNA or RNA at the end of a strand
expression analysis: whole-cell analysis of gene expression (use of a gene to create its RNA or protein product)
fallopian tubes: tubes through which eggs pass to the uterus
fermentation: biochemical process of sugar breakdown without oxygen

fibroblast: undifferentiated cell normally giving rise to connective tissue cells
fluorophore: fluorescent molecule
forensic: related to legal proceedings
founder: population
fractionated: purified by separation based on chemical or physical properties
fraternal twins: dizygotic twins who share 50 percent of their genetic material
frontal lobe: one part of the forward section of the brain, responsible for planning, abstraction, and aspects of personality
gamete: reproductive cell, such as sperm or egg
gastrulation: embryonic stage at which primitive gut is formed
gel electrophoresis: technique for separation of molecules based on size and charge
gene expression: use of a gene to create the corresponding protein
genetic code: the relationship between RNA nucleotide triplets and the amino acids they cause to be added to a growing protein chain
genetic drift: evolutionary mechanism, involving random change in gene frequencies
genetic predisposition: increased risk of developing diseases
genome: the total genetic material in a cell or organism
genomics: the study of gene sequences
genotype: set of genes present
geothermal: related to heat sources within Earth
germ cell: cell creating eggs or sperm
germ-line: cells giving rise to eggs or sperm
gigabase: one billion bases (of DNA)
glucose: sugar
glycolipid: molecule composed of sugar and fatty acid
glycolysis: the breakdown of the six-carbon carbohydrates glucose and fructose
glycoprotein: protein to which sugars are attached
Golgi network: system in the cell for modifying, sorting, and delivering proteins
gonads: testes or ovaries
gradient: a difference in concentration between two regions
Gram negative bacteria: bacteria that do not take up Gram stain, due to membrane structure

Gram positive: able to take up Gram stain, used to classify bacteria
gynecomastia: excessive breast development in males
haploid: possessing only one copy of each chromosome
haplotype: set of alleles or markers on a short chromosome segment
hematopoiesis: formation of the blood
hematopoietic: blood-forming
heme: iron-containing nitrogenous compound found in hemoglobin
hemolysis: breakdown of the blood cells
hemolytic anemia: blood disorder characterized by destruction of red blood cells
hemophiliacs: a person with hemophilia, a disorder of blood clotting
herbivore: plant eater
heritability: proportion of variability due to genes; ability to be inherited
heritability estimates: how much of what is observed is due to genetic factors
heritable: genetic
heterochromatin: condensed portion of chromosomes
heterozygote: an individual whose genetic information contains two different forms (alleles) of a particular gene
heterozygous: characterized by possession of two different forms (alleles) of a particular gene
high-throughput: rapid, with the capacity to analyze many samples in a short time
histological: related to tissues
histology: study of tissues
histone: protein around which DNA winds in the chromosome
homeostasis: maintenance of steady state within a living organism
homologous: carrying similar genes
homologues: chromosomes with corresponding genes that pair and exchange segments in meiosis
homozygote: an individual whose genetic information contains two identical copies of a particular gene
homozygous: containing two identical copies of a particular gene
hormones: molecules released by one cell to influence another
hybrid: combination of two different types
hybridization (molecular): base-pairing among DNAs or RNAs of different origins

hybridize: to combine two different species
hydrogen bond: weak bond between the H of one molecule or group and a nitrogen or oxygen of another
hydrolysis: splitting with water
hydrophilic: "water-loving"
hydrophobic: "water hating," such as oils
hydrophobic interaction: attraction between portions of a molecule (especially a protein) based on mutual repulsion of water
hydroxyl group: chemical group consisting of-OH
hyperplastic cell: cell that is growing at an increased rate compared to normal cells, but is not yet cancerous
hypogonadism: underdeveloped testes or ovaries
hypothalamus: brain region that coordinates hormone and nervous systems
hypothesis: testable statement
identical twins: monozygotic twins who share 100 percent of their genetic material
immunogenicity: likelihood of triggering an immune system defense
immunosuppression: suppression of immune system function
immunosuppressive: describes an agent able to suppress immune system function
in vitro: "in glass"; in lab apparatus, rather than within a living organism
in vivo: "in life"; in a living organism, rather than in a laboratory apparatus
incubating: heating to optimal temperature for growth
informed consent: knowledge of risks involved
insecticide: substance that kills insects
interphase: the time period between cell divisions
intra-strand: within a strand
intravenous: into a vein
intron: untranslated portion of a gene that interrupts coding regions
karyotype: the set of chromosomes in a cell, or a standard picture of the chromosomes
kilobases: units of measure of the length of a nucleicacid chain; one kilo-base is equal to 1,000 base pairs
kilodalton: a unit of molecular weight, equal to the weight of 1000 hydrogen atoms
kinase: an enzyme that adds a phosphate group to another molecule, usually a protein

knocking out: deleting of a gene or obstructing gene expression
laparoscope: surgical instrument that is inserted through a very small incision, usually guided by some type of imaging technique
latent: present or potential, but not apparent
lesion: damage
ligand: a molecule that binds to a receptor or other molecule
ligase: enzyme that repairs breaks in DNA
ligate: join together
linkage analysis: examination of co-inheritance of disease and DNA markers, used to locate disease genes
lipid: fat or wax-like molecule, insoluble in water
loci/locus: site(s) on a chromosome
longitudinally: lengthwise
lumen: the space within the tubes of the endoplasmic reticulum
lymphocytes: white blood cells
lyse: break apart
lysis: breakage
macromolecular: describes a large molecule, one composed of many similar parts
macromolecule: large molecule such as a protein, a carbohydrate, or a nucleic acid
macrophage: immune system cell that consumes foreign material and cellular debris
malignancy: cancerous tissue
malignant: cancerous; invasive tumor
media: (bacteria) nutrient source
meiosis: cell division that forms eggs or sperm
melanocytes: pigmented cells
meta-analysis: analysis of combined results from multiple clinical trials
metabolism: chemical reactions within a cell
metabolite: molecule involved in a metabolic pathway
metaphase: stage in mitosis at which chromosomes are aligned along the cell equator
metastasis: breaking away of cancerous cells from the initial tumor
metastatic: cancerous cells broken away from the initial tumor
methylate: add a methyl group to

methylated: a methyl group, CH₃, added
methylation: addition of a methyl group, CH₃
microcephaly: reduced head size
microliters: one thousandth of a milliliter
micrometer: 1/1000 meter
microsatellites: small repetitive DNA elements dispersed throughout the genome
microtubule: protein strands within the cell, part of the cytoskeleton
miscegenation: racial mixing
mitochondria: energy-producing cell organelle
mitogen: a substance that stimulates mitosis
mitosis: separation of replicated chromosomes
molecular hybridization: base-pairing among DNAs or RNAs of different origins
molecular systematics: the analysis of DNA and other molecules to determine evolutionary relationships
monoclonal antibodies: immune system proteins derived from a single B cell
monomer: "single part"; monomers are joined to form a polymer
monosomy: gamete that is missing a chromosome
monozygotic: genetically identical
morphologically: related to shape and form
morphology: related to shape and form
mRNA: messenger RNA
mucoid: having the properties of mucous
mucosa: outer covering designed to secrete mucus, often found lining cavities and internal surfaces
mucous membranes: nasal passages, gut lining, and other moist surfaces lining the body
multimer: composed of many similar parts
multinucleate: having many nuclei within a single cell membrane
mutagen: any substance or agent capable of causing a change in the structure of DNA
mutagenesis: creation of mutations
mutation: change in DNA sequence
nanometer: 10^-9(exp) meters; one billionth of a meter

nascent: early-stage
necrosis: cell death from injury or disease
nematode: worm of the Nematoda phylum, many of which are parasitic
neonatal: newborn
neoplasms: new growths
neuroimaging: techniques for making images of the brain
neurological: related to brain function or disease
neuron: nerve cell
neurotransmitter: molecule released by one neuron to stimulate or inhibit a neuron or other cell
non-polar: without charge separation; not soluble in water
normal distribution: distribution of data that graphs as a bell-shaped curve
Northern blot: a technique for separating RNA molecules by electrophoresis and then identifying a target fragment with a DNA probe
Northern blotting: separating RNA molecules by electrophoresis and then identifying a target fragment with a DNA probe
nuclear DNA: DNA contained in the cell nucleus on one of the 46 human chromosomes; distinct from DNA in the mitochondria
nuclear membrane: membrane surrounding the nucleus
nuclease: enzyme that cuts DNA or RNA
nucleic acid: DNA or RNA
nucleoid: region of the bacterial cell in which DNA is located
nucleolus: portion of the nucleus in which ribosomes are made
nucleoplasm: material in the nucleus
nucleoside: building block of DNA or RNA, composed of a base and a sugar
nucleoside triphosphate: building block of DNA or RNA, composed of a base and a sugar linked to three phosphates
nucleosome: chromosome structural unit, consisting of DNA wrapped around histone proteins
nucleotide: a building block of RNA or DNA
ocular: related to the eye
oncogene: gene that causes cancer
oncogenesis: the formation of cancerous tumors
oocyte: egg cell
open reading frame: DNA sequence that can be translated into mRNA; from start sequence to stop sequence

opiate: opium, morphine, and related compounds
organelle: membrane-bound cell compartment
organic: composed of carbon, or derived from living organisms; also, a type of agriculture stressing soil fertility and avoidance of synthetic pesticides and fertilizers
osmotic: related to differences in concentrations of dissolved substances across a permeable membrane
ossification: bone formation
osteoarthritis: a degenerative disease causing inflammation of the joints
osteoporosis: thinning of the bone structure
outcrossing: fertilizing between two different plants
oviduct: a tube that carries the eggs
ovulation: release of eggs from the ovaries
ovules: eggs
ovum: egg
oxidation: chemical process involving reaction with oxygen, or loss of electrons
oxidized: reacted with oxygen
pandemic: disease spread throughout an entire population
parasites: organisms that live in, with, or on another organism
pathogen: disease-causing organism
pathogenesis: pathway leading to disease
pathogenic: disease-causing
pathogenicity: ability to cause disease
pathological: altered or changed by disease
pathology: disease process
pathophysiology: disease process
patient advocate: a person who safeguards patient rights or advances patient interests
PCR: polymerase chain reaction, used to amplify DNA
pedigrees: sets of related individuals, or the graphic representation of their relationships
peptide: amino acid chain
peptide bond: bond between two amino acids
percutaneous: through the skin
phagocytic: cell-eating

phenotype: observable characteristics of an organism
phenotypic: related to the observable characteristics of an organism
pheromone: molecule released by one organism to influence another organ-ism's behavior
phosphate group: PO₄ group, whose presence or absence often regulates protein action
phosphodiester bond: the link between two nucleotides in DNA or RNA
phosphorylating: addition of phosphate group (PO₄)
phosphorylation: addition of the phosphate group PO₄^3-
phylogenetic: related to the evolutionary development of a species
phylogeneticists: scientists who study the evolutionary development of a species
phylogeny: the evolutionary development of a species
plasma membrane: outer membrane of the cell
plasmid: a small ring of DNA found in many bacteria
plastid: plant cell organelle, including the chloroplast
pleiotropy: genetic phenomenon in which alteration of one gene leads to many phenotypic effects
point mutation: gain, loss, or change of one to several nucleotides in DNA
polar: partially charged, and usually soluble in water
pollen: male plant sexual organ
polymer: molecule composed of many similar parts
polymerase: enzyme complex that synthesizes DNA or RNA from individual nucleotides
polymerization: linking together of similar parts to form a polymer
polymerize: to link together similar parts to form a polymer
polymers: molecules composed of many similar parts
polymorphic: occurring in several forms
polymorphism: DNA sequence variant
polypeptide: chain of amino acids
polyploidy: presence of multiple copies of the normal chromosome set
population studies: collection and analysis of data from large numbers of people in a population, possibly including related individuals
positional cloning: the use of polymorphic genetic markers ever closer to the unknown gene to track its inheritance in CF families
posterior: rear

prebiotic: before the origin of life
precursor: a substance from which another is made
prevalence: frequency of a disease or condition in a population
primary sequence: the sequence of amino acids in a protein; also called primary structure
primate: the animal order including humans, apes, and monkeys
primer: short nucleotide sequence that helps begin DNA replication
primordial soup: hypothesized prebiotic environment rich in life's building blocks
probe: molecule used to locate another molecule
procarcinogen: substance that can be converted into a carcinogen, or cancer-causing substance
procreation: reproduction
progeny: offspring
prokaryote: a single-celled organism without a nucleus
promoter: DNA sequence to which RNA polymerase binds to begin transcription
promutagen: substance that, when altered, can cause mutations
pronuclei: egg and sperm nuclei before they fuse during fertilization
proprietary: exclusively owned; private
proteomic: derived from the study of the full range of proteins expressed by a living cell
proteomics: the study of the full range of proteins expressed by a living cell
protists: single-celled organisms with cell nuclei
protocol: laboratory procedure
protonated: possessing excess H⁺ ions; acidic
pyrophosphate: free phosphate group in solution
quiescent: non-dividing
radiation: high energy particles or waves capable of damaging DNA, including X rays and gamma rays
recessive: requiring the presence of two alleles to control the phenotype
recombinant DNA: DNA formed by combining segments of DNA, usually from different types of organisms
recombining: exchanging genetic material
replication: duplication of DNA
restriction enzyme: an enzyme that cuts DNA at a particular sequence

retina: light-sensitive layer at the rear of the eye
retroviruses: RNA-containing viruses whose genomes are copied into DNA by the enzyme reverse transcriptase
reverse transcriptase: enzyme that copies RNA into DNA
ribonuclease: enzyme that cuts RNA
ribosome: protein-RNA complex at which protein synthesis occurs
ribozyme: RNA-based catalyst
RNA: ribonucleic acid
RNA polymerase: enzyme complex that creates RNA from DNA template
RNA triplets: sets of three nucleotides
salinity: of, or relating to, salt
sarcoma: a type of malignant (cancerous) tumor
scanning electron microscope: microscope that produces images with depth by bouncing electrons off the surface of the sample
sclerae: the "whites" of the eye
scrapie: prion disease of sheep and goats
segregation analysis: statistical test to determine pattern of inheritance for a trait
senescence: a state in a cell in which it will not divide again, even in the presence of growth factors
senile plaques: disease
serum (pl. sera): fluid portion of the blood
sexual orientation: attraction to one sex or the other
somatic: nonreproductive; not an egg or sperm
Southern blot: a technique for separating DNA fragments by electrophoresis and then identifying a target fragment with a DNA probe
Southern blotting: separating DNA fragments by electrophoresis and then identifying a target fragment with a DNA probe
speciation: the creation of new species
spindle: football-shaped structure that separates chromosomes in mitosis
spindle fiber: protein chains that separate chromosomes during mitosis
spliceosome: RNA-protein complex that removes introns from RNA transcripts
spontaneous: non-inherited
sporadic: caused by new mutations
stem cell: cell capable of differentiating into multiple other cell types

stigma: female plant sexual organ
stop codon: RNA triplet that halts protein synthesis
striatum: part of the midbrain
subcutaneous: under the skin
sugar: glucose
supercoiling: coiling of the helix
symbiont: organism that has a close relationship (symbiosis) with another
symbiosis: a close relationship between two species in which at least one benefits
symbiotic: describes a close relationship between two species in which at least one benefits
synthesis: creation
taxon/taxa: level(s) of classification, such as kingdom or phylum
taxonomical: derived from the science that identifies and classifies plants and animals
taxonomist: a scientist who identifies and classifies organisms
telomere: chromosome tip
template: a master copy
tenets: generally accepted beliefs
terabyte: a trillion bytes of data
teratogenic: causing birth defects
teratogens: substances that cause birth defects
thermodynamics: process of energy transfers during reactions, or the study of these processes
threatened: likely to become an endangered species
topological: describes spatial relations, or the study of these relations
topology: spatial relations, or the study of these relations
toxicological: related to poisons and their effects
transcript: RNA copy of a gene
transcription: messenger RNA formation from a DNA sequence
transcription factor: protein that increases the rate of transcription of a gene
transduction: conversion of a signal of one type into another type
transgene: gene introduced into an organism
transgenics: transfer of genes from one organism into another
translation: synthesis of protein using mRNA code

translocation: movement of chromosome segment from one chromosome to another
transposable genetic element: DNA sequence that can be copied and moved in the genome
transposon: genetic element that moves within the genome
trilaminar: three-layer
triploid: possessing three sets of chromosomes
trisomics: mutants with one extra chromosome
trisomy: presence of three, instead of two, copies of a particular chromosome
tumor: mass of undifferentiated cells; may become cancerous
tumor suppressor genes: cell growths
tumors: masses of undifferentiated cells; may become cancerous
vaccine: protective antibodies
vacuole: cell structure used for storage or related functions
van der Waal's forces: weak attraction between two different molecules
vector: carrier
vesicle: membrane-bound sac
virion: virus particle
wet lab: laboratory devoted to experiments using solutions, cell cultures, and other "wet" substances
wild-type: most common form of a trait in a population
Wilm's tumor: a cancerous cell mass of the kidney
X ray crystallography: use of X rays to determine the structure of a molecule
xenobiotic: foreign biological molecule, especially a harmful one
zygote: fertilized egg