Science Glossary (G-M)

Gastrointestinal refers to the stomach and intestines.
GDP mannose mannosyl hydrolase
GDP mannose mannosyl hydrolase is the protein responsible for the incorporation of carbohydrates into bacterial cell walls. Understanding its structure and function will help control entero-pathogenic bacteria which cause food poisoning.
Gene expression
Gene expression refers to the transcription and translation of a specific part of the DNA code with the ultimate outcome being protein synthesis.
Gene transcription
Gene transcription is the process of constructing a messenger RNA molecule using a DNA molecule as a template, with resulting transfer of genetic information to the messenger RNA.
Genomic means relating to the genome, the genetic material of an organism.
Geophysics is the study of Earth physics including the fields of meteorology, hydrology, oceanography, seismology, volcanology, magnetism, radioactivity and geodesy.
A glovebox is a device used to isolate an area for work with potentially hazardous substances or materials that need to be free from direct contact with the outside environment for any reason. Most gloveboxes used during flight are small, tightly enclosed boxes with a glass panel for viewing and special airtight gloves that a person on the outside can use to manipulate objects inside.
Glucose 6-phosphate dehydrogenase
Glucose-6-phosphate dehydrogenase is an enzyme which participates in the formation of glucose from carbon dioxide as part of the process of photosynthesis.
Glyceraldehyde-3-phosphate dehydrogenase
Glyceraldehyde phosphate dehydrogenase
Glyceraldehyde phosphate dehydrogenase is an enzyme found in cells that participates in the glucose metabolism by removing a hydrogen atom from glyceraldehyde phosphate, a glucose metabolite, and adding a phosphate group to form 1,3 bisphosphoglycerate.
Glycine is an amino acid constituent of proteins in the human body.
Glycolysis rate
Glycosaminoglycan (GAG)
Glycosaminoglycan (GAG) is the polysaccharide unit that makes up proteoglycans, a molecule made of saccharides and proteins. GAGs are extracellular matrix molecules that help give tissues like cartilage their rigid structure.
Granulocyte-colony stimulating factor
Granulocyte-colony stimulating factor is an immunoprotein produced by leukocytes during inflammation which functions to increase the proliferation of granulocytes in the bone marrow.
A gyroscope is a rotating wheel, mounted in a ring or rings, for illustrating the dynamics of rotating bodies, the composition of rotations, etc. It can also be a form of the above apparatus, mounted so delicately as to render visible the rotation of the earth, through the tendency of the rotating wheel to preserve a constant plane of rotation, independently of the earth's motion.

Haptoglobin is a protein present in blood serum that combines with hemoglobin to form a complex that is rapidly removed from the circulation by the liver.
Hematocrit is the percentage of the volume of a blood sample occupied by cells, as determined by a centrifuge or device which separates the cells and other particulate elements of the blood from the plasma. The remaining fraction of the blood sample is called plasmocrit (blood plasma volume).
Hemodynamic means of or relating to the physical dynamics of blood circulation.
Hemoglobin is an iron-containing respiratory pigment contained within red blood cells; it gives the cells their red color. Hemoglobin, which has the unique property of combining reversibly with oxygen, picks up oxygen in the lungs and transports it to the rest of the body.
Hepatic means relating to the liver.
Herpesvirus is one of a group of DNA containing viruses causing latent infections in man and animals.
Hexokinase (HK)
Hexokinase (HK) is an enzyme present in muscle and other tissues. It catalyzes the phosphorylation (adding a phosphor group) of glucose and other hexoses to form a hexose 6-phosphate.
Histochemical refers to the study of intracellular distribution of chemicals, reaction sites, and enzymes.
Histone octamer
Histones are the proteins associated with nucleic acids in the nuclei of plant and animal tissues. An octamer is an aggregate of eight particles attached together.
HIV capsid protein
HIV Capsid Protein is a protein that makes up the outer shell, surrounding the genetic material, of the AIDS virus. This protein is a target for drugs that can fight the AIDS virus.
Homeostasis is the physiological process by which the internal systems of the body (e.g. blood pressure, body temperature, acid-base balance) are maintained at equilibrium despite variations in the external conditions.
A hormone is a substance produced in one part of the body; it passes into the bloodstream and is carried to other distant organs or tissues where it acts to modify their structure or function.
Humoral means circulating in the bloodstream.
Hydroxyproline is a compound similar in structure to the amino acids and is found only in collagen.
Hypertension is abnormally high arterial blood pressure.
Hyperventilation, or overventilation, is described by abnormally fast or deep respiration in which excessive quantities of air are taken in, causing buzzing in the ears, tingling in the extremities and sometimes fainting.
A hypothesis is an assumption not proved by experiment or observation that is made for the sake of testing its soundness.
Hysteresis is any situation in which the value of one variable depends upon whether the other has been increasing or decreasing.

Immune system
The immune system provides the body with a defense against infection, afforded by the presence of circulating antibodies and white blood cells. Antibodies are manufactured specifically to deal with the antigens associated with different diseases as they are encountered, while white blood cells attack and destroy foreign particles in the blood and tissues, including antigen-antibody complexes.
An immunoglobulin is one of a class of structurally related proteins consisting of two pairs of polypeptide chains, one pair of light (L) low molecular weight chains and one pair of heavy (H) chains, all four linked together by disulfide bonds. On the basis of the structural and antigenic properties of the H chains, Ig's are classified (in order of relative amounts present in normal human serum) as IgG, IgA, IgM, IgD and IgE. Antibodies are Ig's, and all Ig's probably function as antibodies.
Immunohistochemical is the staining of tissues using monoclonal antibodies.
Infrared is the part of the invisible spectrum that is contiguous to the red end of the visible spectrum.
Insulin is a hormone secreted by the pancreas that promotes glucose utilization, protein synthesis, and the formation and storage of lipids. The chemical structure of insulin is completely known and insulin obtained from various animals is used in the treatment of diabetes.
An interferometer is a device that is used to study a sample of protein solution by passing a laser light through the sample.
Interpersonal means being, relating to, or involving relations between persons.
Intervertebral refers to the flexible plate of fibrocartilage that connects any two adjacent vertebrae in the backbone or spine.
Intracellular fluid
Intracellular fluid is the fluid located within cells.
An invertebrate is any animal that does not have a backbone.
Isokinetic dynamometer
An isokinetic dynamometer is a device that measures the strength of different muscle groups.
Isometric describes the contraction of muscles when the fibers increase in tension, but do not shorten in length. Isometric exercises can be induced in muscles that are used when a limb is made to pull or push against something that does not move.
An isotope is one of two or more atoms of the same chemical element that have the same number of protons in their nucleus but different numbers of neutrons. Most elements in nature consist of a mixture of isotopes. Example: hydrogen is known to have three isotopes - hydrogen (1 proton, no neutrons), deuterium (1 proton, 1 neutron), and tritium (1 proton, 2 neutrons).

Kinematics is the study of motion and the forces required to produce it. This includes the different forces at work during the movement of a single part of the body, and more complex movements such as running and climbing.
Kinetics is the study of acceleration, motion or rate of change.
KiloPascal (kPA) is the metric unit for pressure.

Labeled water (H2 18O)
Labeled water (H2 18O) is a naturally occurring form of water which contains the rare 18O isotope of oxygen (the common isotope of oxygen is 16O).
Lactate Dehydrogenase (LDH)
Lactate dehydrogenase (LDH) describes a group of four enzymes involved in the oxidation of lactate to pyruvate.
Lactulose is a nonabsorbable synthetic sugar which is used as a cathartic (laxative) in chronic constipation or in the treatment of hepatic coma.
A lectin is a plant (usually seed) or animal protein that affects agglutination, precipitation, or other phenomena resembling the action of specific antibody, but that is not an antibody in that it was not evoked by an antigenic stimulus.
Lignin is a substance related to cellulose that provides rigidity and together with cellulose forms the woody cell walls of plants and the cementing material between them.
A lipid is one of a group of naturally occurring compounds, also known as fat, that are soluble in organic solvents such as chloroform or alcohol, but insoluble in water. Lipids are important dietary constituents, not only because of their high energy value, but also because certain vitamins and essential fatty acids are associated with them.
Liquid-liquid diffusion crystallization
Liquid-liquid diffusion crystallization is a technique used for growing protein crystals. It consists of a protein solution and precipitating solution separated by an liquid interface. Diffusion across the interface saturates the protein solution causing the proteins to crystallize.
A load is the overall force to which a structure is subjected in supporting a weight or mass or in resisting externally applied forces.
Lower Body Negative Pressure (LBNP)
To apply Lower Body Negative Pressure (LBNP), the lower body (legs and hips) is placed in a sealed chamber. Suction applied to the chamber causes body fluid to move from the chest and upper body to the lower body. This shift of fluid is very similar to the shift of fluid that occurs when people stand upright.
Lumbar 3
The lumbar 3 is the third vertebrae (counted from the head) of the lumbar spine.
Lumbar spine
The lumbar spine, or lumbar vertebrae, are the five bones of the backbone that are situated between the thoracic vertebrae and the sacrum in the lower part of the back. They are the largest of the unfused vertebrae and have stout processes for attachment of the strong muscles of the lower back.
A lymphocyte is a type of white blood cell present in blood, lymph nodes, spleen, thymus gland, gut wall and bone marrow. Important to the immune system, they produce circulating antibodies and T-lymphocytes, which are primarily responsible for cell-mediated immunity and can differentiate into helper, killer or suppressor cells.
Lysozyme is an enzyme that hydrolyzes the 1,4-beta links between N-acetylmuramic acid and N-acetylglucosamine, and thus destructive to cell walls of certain bacteria. It is present in tears and other body fluids, in egg whites and in some plant tissues.

Macromolecular describes a molecule of colloidal size such as proteins, nucleic acids, and polysaccharides.
Magnesium (Mg)
Magnesium is a silvery metallic element essential to life. It is necessary for the proper functioning of muscle and nervous tissue and is involved in the transmission of nerve impulses.
Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI) is a noninvasive method that utilizes the properties of magnetism to create nondestructive, three-dimensional, internal images of the soft tissues of the body, including the brain, spinal cord and muscle.
Marangoni convection
Marangoni convection is the primary surface tension-driven force in a float zone. Thermal gradients along the free surface of the float zone drive the convection.
Maximal heart rate
Maximal heart rate is two-hundred twenty (220) minus the subject's age in years.
A meristem is a plant tissue usually made up of small cells that are capable of dividing indefinitely and give rise to similar cells or cells that differentiate into definitive tissues and organs (flowers).
The mesencephalon is the part of the brain lying between the forebrain and hindbrain. The trochlear and oculomotor nerves arise in the mesencephalon, and it contains structures important in the visual and auditory pathways, as well as other structures. The embryonic mesencephalon develops into the adult mesencephalon.
Mesophyll is the internal tissue of a plant leaf, excluding the vascular bundles. All mesophyll cells contain chloroplasts, for photosynthesis, which lie close to the edge of the cell to gain maximum light and gas supply. Mesophyll tissue also contains numerous intercellular spaces, which communicate with the atmosphere outside the leaf via stomata.
Messenger Ribonucleic Acid (mRNA)
Messenger Ribonucleic acid (mRNA) is a transcription of a gene that combines with ribosomal RNA (rRNA) and transfer RNA (tRNA) to facilitate protein synthesis.
Metabolic means of or relating to metabolism.
A metabolite is a substance that takes part in the process of metabolism, which involves the breakdown of complex organic constituents of the body with the liberation of energy for use in bodily functioning. The various compounds that take part in or are formed by these reactions are called metabolites.
Methane is an odorless gas produced by the decomposition of organic matter.
Acceleration is measured as the rate of change of velocity with respect to time. Microacceleration is a minute (very small) acceleration force.
A microbe, also called microorganism, is any organism too small to be visible to the naked eye. Bacteria, viruses, protozoans, certain fungi and some algae are microorganisms.
Microbial means of or relating to microorganisms.
Microbiota are microscopic organisms in a specific environment.
Microgravity is a state in which gravity is reduced to almost negligible levels, such as during space flight.
A microorganism, or microbe, is any organism too small to be seen by the naked eye. Bacteria, viruses, protozoa, and some fungi and algae are microorganisms.
Mineralogy is the scientific study of minerals, which are any naturally occurring, homogeneous inorganic substances having a definite chemical composition and characteristic crystalline structure, color and hardness.
Mitigation is the act of making less severe or intense.
Modal means of or relating to, or characteristic of a mode, which is any numerous patterns of wave motions, as of acoustic waves.
A monocyte is the largest form of white blood cell with a kidney-shaped nucleus; its function is the ingestion of foreign particles such as bacteria and tissue debris. Monocytes belong to the group of phagocytes.
Morphology is the science of the structure of animals and plants.
Motility is the power to move spontaneously.
Musculoskeletal refers to the system of muscles and bones in vertebrates.
Myocardial infarction
Myocardial infarction is necrosis, or tissue death, of a portion of cardiac muscle caused by obstruction in a coronary artery; a heart attack.

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