Biology L
What is labile ?
The term has loosely been used to describe either a relatively unstable and transient chemical species or a relatively STABLE but reactive species.
What is lability ?
Instability; refers to a state that is easily altered or modified. A phenotype’s capacity to respond differentially to varying environmental conditions. Also called phenotypic plasticity.
What is laccase ?
A copper-containing ENZYME, 1,4-benzenediol oxidase, found in higher plants and microorganisms. Laccases are MULTICOPPER OXIDASES of wide specificity that carry out one-electron oxidation of phenolic and related compounds and reduce O2 to water. The enzymes are polymeric and generally contain one each of TYPE 1, TYPE 2, TYPE 3 COPPER centers per SUBUNIT, where the type 2 and type 3 are close together, forming a trinuclear copper CLUSTER.
What is lactate ?
Alternate name for lactic acid, a chemical created from sugars when broken down for energy in the absence of oxygen.
What is lacteal ?
Numerous small lymphatic vessels in the interior of each intestinal villus, small fingerlike projections of the mucosal layer of the small intestine, that picks up chyme, a thick semifluid mass of partially digested food, and passes it through the lymph system via the thoracic duct to the blood system; aids in the absorption of fats.
What is lagging strand ?
In DNA synthesis, polymerization occurs both in and away from the nearest replication fork. One of two newly created DNA strands is the lagging strand. Found at the replication fork on linear chromosomes, it is synthesized in the direction away from the replication fork. It is the synthesis of a new strand of replication DNA by the creation of short segments of various lengths that are later joined together covalently by the enzyme DNA ligase.
It is made in discontinuous lengths, called Ozark fragments, in the 5’ to 3’ growing-tip (number of atoms in the sugar residues) direction during DNA polymerization, and these are joined covalently at a later time. Since it is not synthesized continuously, it is called discontinuous replication.
The difference between the lagging and leading strands is due to the orientation of the parent template strands. The leading-strand template is facing a 5’ to 3’ direction, but the lagging strand itself is oriented in the 3’ to 5’ direction, so the DNA polymerase responsible
for adding nucleotides has to move backwards away from the replication fork; synthesis is therefore not continuous, but in repeated steps.
There is a gap between the final lagging strand segment and the end of the chromosome. As a result, the 5’ end of the lagging strand will lose some nucleotide every time a cell replicates its DNA.
What is Lamarckism ?
The idea, promoted by Jean Baptiste de Lamarck, that acquired traits can be passed from parent to offspring, i.e., that characteristics or traits acquired during a single lifetime can be transmitted directly to offspring.
What is land bridges ?
Pieces of land once connecting the continents that have since sunk into the sea as part of a general cooling and contraction of the Earth. Believed to have served as migratory passages for animals, plants, and humans.
What is Landsteiner, Karl ?
Landsteiner, Karl (1868–1943) was Austrian Biochemist Karl Landsteiner was born in Vienna on June 14, 1868, to Leopold Landsteiner, a journalist and newspaper publisher, and Fanny Hess. Landsteiner studied medicine at the University of Vienna, graduating in 1891.
From 1898 until 1908 he held the post of assistant in the university department of pathological anatomy in Vienna. In 1908 he received the appointment as prosector in the Wilhelminaspital in Vienna, and in 1911 he became professor of pathological anatomy at the University of Vienna.
Landsteiner, with a number of collaborators, published many papers on his findings in anatomy and immunology, such as the immunology of syphilis and the Wassermann reaction, and he discovered the immunological factors, which he named haptens. He also laid the foundations of the cause and immunology of poliomyelitis.
His 1901 discovery of the major blood groups and his development of the ABO system of blood typing and 1909 classification of the blood of human beings into the now well-known A, B, AB, and O groups, as well as the M and N groups, made blood transfusion a routine medical practice. For this work, he received the Nobel Prize for physiology or medicine in 1930. In 1936 he wrote The Specificity of Serological Reactions, a classic text that helped to establish the science of immunochemistry. In 1940 he discovered the Rh factor, the protein on the surface of red blood cells that determines if the blood type is positive (Rh-positive) or negative (Rh-negative). If the mother has a negative Rh factor (Rh-negative) and the father and fetus are Rh-positive, the mother can become Rh-sensitized and produce antibodies to combat fetal blood cells that cross the placenta into her bloodstream. These antibodies can destroy the fetus’s Rh-positive blood cells, putting it at serious risk of anemia.
In 1939 he became emeritus professor at the Rockefeller Institute. On June 24, 1943, he had a heart attack in his laboratory and died two days later.
What is larva ?
The solitary live, but sexually immature, form of a variety of animal life cycles, e.g., butterflies, flies, wasps, that may, after reaching adulthood, be completely different in morphology, habitat requirements, and food needs. Some larvae have other names, like maggots for flies, grub for beetle larvae, tadpoles for frogs, etc. Insect larvae may molt, i.e., shed layers of skin, several times during their development.
What is lateral line system ?
A sensory system composed of a longitudinal row of porelike openings that open into tubes in skin on the sides of fish and larval amphibians that is used to detect water and electrical disturbance in their surroundings. The ampullary organs, or ampullae of Lorenzina in fish, detect weak electrical currents generated by other animals, while the neuromasts—a small group of pairs of oppositely oriented hair sensory cells embedded in a gel-filled cupula on either side of the skin surface or in pit organs—detect the direction of water movement. The lateral canal is the portion of the system located on the head, beginning at the junction with the supra and infraorbital canals behind the mid-eye, and extending back to the rear of the head connecting to the lateral line.
What is lateral meristem ?
An embryonic tissue, the meristem, on the portion of a plant that gives rise to secondary growth such as the cambium, vascular cambium, and cork cambium. Runs most of the length of stems and roots. Also called the cambium.
What is Laurasia ?
Laurasia was the northern supercontinent formed after PANGAEA broke up during the JURASSIC PERIOD some 180 million years ago and formed the present continents of North America, Europe, and Asia as well as the land masses of Greenland and Iceland.
What is lava ?
Igneous rock, magma that exits volcanoes and vents and reaches the exterior or surface of the land or seabed.
Who was Laveran, Charles-Louis-Alphonse ?
Laveran, Charles-Louis-Alphonse (1845–1922) French Physician, Protozoologist Charles-Louis-Alphonse Laveran was born in Paris on June 18, 1845, in the house at 19 rue de l’Est, to Dr. Louis Théodore Laveran, an army doctor and professor at the École de Valde-Grâce, and Guénard de la Tour, the daughter and granddaughter of high-ranking army commanders.
After completing his education in Paris at the Collège Saint Baube and later at the Lycée Louisle-Grand, he applied to the Public Health School at Strasbourg in 1863 and attended the school for four years. In 1866 he was appointed a resident medical student in the Strasbourg civil hospitals, and the following year he submitted a thesis on the regeneration of nerves. In 1874 he was appointed to the chair of military diseases and epidemics at the École de Valde-Grâce, previously occupied by his father, and in 1878, when his period of office had ended, he moved to Bône in Algeria until 1883. It was during this period that he carried out his chief researches on the human malarial parasites, first at Bône and later at Constantine.
In 1880 Laveran examined blood samples from malarial patients and discovered amoebalike organisms growing within red blood cells, and he noticed that they divided, formed spores, and invaded unaffected blood cells. He also noted that the spores were released in each affected red cell at the same time and corresponded with a fresh attack of fever in the patient. His researches confirmed that the blood parasites that he had described were in fact the cause of malaria, but his first publications on the malaria parasites were received with skepticism until scientists around the world published confirmative research results. In 1889 the Academy of Sciences awarded him the Bréant Prize for his discovery.
In 1896 he entered the Pasteur Institute as chief of the Honorary Service, and from 1897 until 1907 he carried out many original research projects on endoglobular haematozoa and on sporozoa and trypanosomes. In 1907 he was awarded the Nobel Prize for his work on protozoa in causing diseases. In 1908 he founded the Société de Pathologie Exotique, over which he presided for 12 years.
He was the first to express the view that the malarial parasite must be a parasite of Culicidae, and after this view had been proved by the research of Ronald Ross, he played a large part in the enquiry on the relationships between Anopheles and malaria in the campaign undertaken against endemic disease in swamps, notably in Corsica and Algeria.
From 1900 on, he studied the trypanosomes and published, either independently or in collaboration with others, a large number of papers on these blood parasites. His research concentrated on the trypanosomes of the rat; the trypanosomes that cause nagana and surra; the trypanosome of horses in Gambia; a trypanosome of cattle in the Transvaal; the trypanosomiases of the Upper Niger; the trypanosomes of birds, chelonians, batrachians, and fishes; and finally the trypanosome that causes the endemic disease of equatorial Africa known as sleeping sickness. For 27 years he worked on pathogenic protozoa and the field he opened up by his discovery of the malarial parasites. He died on May 18, 1922.
What is law of equal segregation ?
Gregor Mendel’s first law, which says that two copies of a gene separate during meiosis and end up in different gametes (sperm and ova) and are passed on to offspring.
What is law of independent assortment ?
Gregor Mendel’s second law, which says that after gametes form, the separation of alleles for one gene is independent of the separation of alleles for other genes; genes located on nonhomologous chromosomes are independent from one another. This is not true for genes that are linked, where genes are located close to one another on the same chromosome.
What is lead discovery ?
The process of identifying active new chemical entities that, by subsequent modification, can be transformed into a clinically useful DRUG.
What is lead generation ?
The term applied to strategies developed to identify compounds that possess a desired but nonoptimized biological activity.
What is leading strand ?
One of two new DNA strands that is being replicated continuously, unlike the lagging strand. The strand is made in the 5’ to 3’ direction, placing an –OH group at the 3’ end for continuous polymerization (adding nucleotides) at the 3’ growing tip by DNA polymerase that moves forward when the template strands unwind at the replication fork. It is the DNA polymerase that plays the pivotal role in the process of life, since it is responsible for duplicating the genetic information.
What is lead optimization ?
The synthetic modification of a biologically active compound to fulfill all stereoelectronic, physicochemical, pharmacokinetic, and toxicologic requirements for clinical usefulness.
What is leaf primordia ?
Young leaves at the tip of a shoot formed by the shoot apical meristem.
What is leaf veins ?
A netlike network called reticulate venation in vascular tissue in dicots. The veins are in parallel venation to each other in monocots.
What is learned behavior ?
Behavior that is not fixed but acquired by trial and error or by observing others
What is leghemoglobin ?
A monomeric HEMOGLOBIN synthesized in the root nodules of leguminous plants that are host to nitrogen-fixing bacteria. Has a high affinity for dioxygen and serves as an oxygen supply for the bacteria.
What is legume ?
A pod-bearing plant that is a member of the Leguminosae (Fabaceae) or pea or bean family. These plants form symbiotic relationships with certain nitrogen-fixing bacteria (rizobia) in their root nodules to acquire nitrogen for growth. Examples include beans, peas, lentils, alfalfa, clover, and wildflowers like wild blue lupine (Lupinus perennis).
What is lek ?
A place where males display in groups and females choose for the purpose of fertilization; a special kind of polygynous mating system.
What is lemur ?
Primates (prosimians) of the superfamily Lemuroidea that live in trees; found only on the island of Madagascar and the adjacent tiny Comoro Islands. Related to monkeys, they have large eyes, foxlike faces, and long furry tails (not prehensile). There are only about 30 to 50 living species, 17 of which are endangered. They are small, ranging from about an ounce up to about the size of a house cat.
What is lenticle ?
A pore where gases are exchanged in the stems of woody plants.
What is Leonardo da Vinci ?
Leonardo da Vinci (1452–1519) was Italian Scientist, Artist Leonardo da Vinci, one of the greatest minds of all time, was born on April 15, 1452, near the town of Anchiano near Vinci. He was an illegitimate child of a notary, Piero da Vinci, and a peasant woman named Caterina. In his teenage years he became an apprentice in one of the best art studios in Italy in 1469, that of Andrea Verrocchio, a leading Renaissance master of that time. During this time da Vinci drew La valle dell’Arno (The Arno Valley) in 1473 and painted an angel in Verrocchio’s Baptism of Christ (1475). In 1478 da Vinci became an independent master. Da Vinci is famous for his works of art such as the Mona Lisa, but he is also as famous for his visionary drawings of instruments and machines of the future. He was an artist, scientist, engineer, and architect. He was also one of the first to take detailed observations and to experiment in a scientific manner.
In his later notebook the Codex Leicester, one finds the largest assemblage of da Vinci’s studies relating to astronomy, meteorology, paleontology, geography, and geology. It reveals that his profound scientific observations far outweigh anyone else of his time and documents his passion for research and invention. His interest in light and shadow led him to notice how the earth, moon, and planets all reflect sunlight, for example.
The central topic of the Codex Leicester is the “Body of the Earth” and in particular its transformations and movement of water. This study includes a discussion on the light of the moon, the color of the atmosphere, canals and flood control, the effect of the moon on the tides, and modern theories of the formation of continents.
He was well acquainted with knowledge about his local rocks and fossils (Cenozoic mollusks) and was uncannily prescient in his interpretation of how fossils were found in mountains, theorizing that they had once been living organisms in seas before mountains were raised. Da Vinci contributed a great deal of knowledge to human anatomy with detailed drawings and notes in his anatomical notebooks after having dissected some 19 human cadavers.
Unfortunately, many of his scientific projects and treatises were never completed, since he recorded his technical notes and sketches in numerous notebooks and used mirror script (his writing had to be read in a mirror to be deciphered). It was centuries before the genius of da Vinci was recognized. He died at the age of 67 on May 2, 1519, at Cloux, near Amboise, France.
What is Lepidoptera ?
The taxonomic order that includes butterflies, skippers, and moths. Butterflies have antennae, compound eyes, six pair of legs, a hard exoskeleton, and a body that is divided into a head, thorax, and abdomen. The butterfly’s outer body is covered by tiny sensory hairs and has wings covered by scales.
What is lesion ?
A visible region, such as a wound or fissure, where there is abnormal tissue change in a body part; a structural change due to wound, injury, or disease.
What is lethal mutation ?
A mutant form of a gene that will result in the inviability (death) of the organism if expressed in its phenotype. A conditional-lethal mutation is lethal under one condition but not under another.
What is leukemia ?
Cancer of the developing blood cells in the bone marrow. The rampant overproduction of white blood cells (leukocytes). A fatal cancer that is diagnosed yearly in 29,000 adults and 2,000 children in the United States. There are several types of leukemia
What is leukocyte (white blood cell) ?
A type of blood cell that contains a nucleus but has no pigment. White blood cells (WBC) are found in the blood and are involved in defending the body against infective organisms and foreign substances. They are produced in the bone marrow along with other types of blood cells. There are five types of white blood cell within two main groups, and each has its own characteristics. The polymorphonuclear or granulocyte group comprises the neutrophils, eosinophils, and basophils. The mononuclear group comprises the monocytes and lymphocytes.
White blood cells are the main attackers of foreign substances as part of the immune system.
Neutrophils move out of the blood vessels into the infected tissue and engulf the foreign substances (phagocytosis). Eosinophils migrate to body tissues and release toxic substances to kill foreign substances. Basophils, also called granular leukocytes, digest foreign objects from granules containing toxic chemicals. Monocytes, which contain chemicals and enzymes, ingest dead cells through phagocytosis and develop into macrophages (large white blood cells) as they migrate into various tissues. Lymphocytes, which inhabit the blood, produce antibodies and cells that go after for eign substances. Lymphocytes subtypes are B cells, T cells, NK cells, and null cells.
What is Lewis acid ?
A molecular entity that is an electronpair acceptor and therefore is able to react with a LEWIS BASE to form a LEWIS ADDUCT by sharing the electron pair furnished by the Lewis base.
What is Lewis adduct ?
The adduct formed between a LEWIS ACID and a LEWIS BASE. An adduct is formed by the union of two molecules held together by a coordinate covalent bond.
What is Lewis base ?
A molecular entity able to provide a pair of electrons and thus capable of COORDINATION to a LEWIS ACID, thereby producing a LEWIS ADDUCT.
What is lice ?
Small (1 /6 in. long) wingless insects (Arthropoda: Insecta) that have three pairs of legs, and a body composed of a head, thorax, and abdomen. They have flattened, elongate bodies and somewhat oval heads and a three-stage life cycle (egg, nymph, and adult). The nymphs molt three times before reaching maturity. There are two suborders of lice, Mallophagorida (chewing lice, broad heads with biting mouthparts) and Anoplurorida (sucking lice, narrow heads with sucking mouthparts), and they are found worldwide.
Human lice come in three forms: head lice (Pediculus humanus capitis), body lice (Pediculus humanus humanus), and pubic lice (Pediculus pubis). They feed exclusively on humans, and their survival depends on temperature and humidity conditions associated with human bodies. They desiccate rapidly if they are away from humans for more than 24–36 hours.
What is lichen ?
Lichens are two organisms in one: Having no roots, stems, or leaves, they actually are symbiotic associations of a fungus and a photosynthesizing partner that results in a stable thallus of specific structure. The fungus is almost always an ascomycete, very rarely a basidiomycete (about 20 basidiolichens are known). Lichens are classified as fungi, and their scientific names formally refer to the fungal partner (mycobiont). The photosynthesizing partner (photobiont) can be a green alga, such as Trebouxia or Trentepohlia, or a cyanobacterium (“blue-green alga”), such as Nostoc or Scytonema. The symbiotic unit has a definite, reproducible form that is different from the nonlichenized fungus or alga. A few lichens have two photobionts, and the fungus looks different where each occurs within the thallus; i.e., it may be flat where the green alga grows but have dark bumps where the cyanobacterium occurs, as in Peltigera leucophlebia. The lichen symbiosis thus involves closely merged members from usually two but sometimes three biotic kingdoms.
Worldwide in distribution, lichens can be found on bare soil or sand, grow over mosses and low plants, or become attached to rocks, trees, or almost any other substrate. They are good measures of air quality, since they have great sensitivity to sulfur dioxide (SO2), an indicator of local pollution and acid rain. In addition, their tolerance and accumulation of metals, including heavy metals and radioactive isotopes, are useful indicators of industrial pollution.
Lichens can be classified into several types based on appearance and structure: Fruticose (shrublike) lichens, such as British soldiers (Cladonia cristatella) and common reindeer lichens (Cladina rangiferina), include species that look like tiny trees or columns but also include old man’s beard (genus Usnea), which can dangle from tree branches. Foliose lichens, such as the puffed shield lichen (Hypogymnia physodes) are flat and leaflike. Crustose species, such as the map lichen (Rhizocarpon geographicum), form a “crust” on rocks, wood, or soils, and are very abundant. Squamulose lichens, somewhat similar to crusts, are composed of tiny overlapping or shingle-like flakes; examples are the primary (basal) thalli of Cladonia, and the oyster lichen (Hypocenomyce scalaris), which grows on acidic wood. Umbilicate lichens have leaflike thalli that attach to rocks at a central point; smooth rock tripe (Umbilicaria mammulata) is an example. Jelly lichens, such as the blue jellyskin (Leptogium cyanescens), have a flabby thallus and a cyanobacterial photobiont, and usually occur in damp habitats.
Many lichens have a layered internal morphology, with the bulk of the thallus formed of fungal filaments and the photobiont often restricted to a distinct layer. Fungal hyphae are densely arranged in the upper cortex to exclude other organisms and regulate light intensity to the green algal cells. These are often located just below the cortex. Underlying the algae is the medulla, another layer of much less compact fungal filaments.Some lichens are held on their substrate by medullary fungal hyphae, but many foliose lichens have a lower cortex and special structures called rhizines to hold them in place on tree bark or rock.
Some lichens are held on their substrate by medullary fungal hyphae, but many foliose lichens have a lower cortex and special structures called rhizines to hold them in place on tree bark or rock.
There are only about 100 algal partners, but there are as many fungal partners as there are lichen species, which number about 14,000. The fungus receives sugars and other nutrients from the photobiont and provides a stable and secure structure in which it lives, provides water, and shields the photobiont from the sun’s desiccating rays. Lichens reproduce vegetatively in three basic ways: fragmentation of the thallus, and by two kinds of tiny vegetative propagules that contain both partners—soredia, the more common, and isidia, which are slightly larger and heavier. Isidia and soredia are dispersed by wind, water, and animal agents. Lichens are slow growers and are particularly good pioneer species in disturbed habitats.
Lichens have been used as food, especially by caribou in winter; as medicine and dyes; as dwarf “trees” in model railroad setups and architectural plans; and in holiday wreaths and arrangements. And many harsh landscapes are much enriched by their subtle beauty.
What is life table ?
A tabular and numerical representation of mortality of births for each age group and includes various groups of information such as probabilities of death, survival, and life expectancies.
What is ligament ?
One component of the musculoskeletal system that also consists of tendons, bones, and muscles. Ligaments are collagen-rich connective structures, a band of fibrous tissue that attaches and binds bone to bone and to cartilage and that supports organs in place.
What is ligand ?
A molecule, ion, hormone, or compound that binds to a specific receptor site that binds to another molecule.
The atoms or groups of atoms bound to the CENTRAL ATOM. The root of the word is sometimes converted into the verb to ligate, meaning to coordinate as a ligand, and the derived participles ligating and ligated. This use should not be confused with its use to describe the action of LIGASEs (a class of ENZYMEs).
The names for anionic ligands, whether inorganic or organic, end in -o. In general, if the anion name ends in -ide, or -ate, the final -e is replaced by -o, giving -ido, and -ato, respectively. Neutral and cationic ligand names are used without modification. Ligands bonded by a single carbon atom to metals are regarded as radical substituents, their names being derived from the parent hydrocarbon, from which one hydrogen atom has been removed. In general, the final letter -e of the name is replaced by -yl.
In biochemistry the term ligand has been used more widely: if it is possible or convenient to regard part of a polyatomic molecular entity as central, then the atoms or groups or molecules bound to that part may be called ligands.
What is ligand field ?
Ligand field theory is a modified CRYSTAL FIELD theory that assigns certain parameters as variables rather than taking them as equal to the values found for free ions, thereby taking into account the potential covalent character of the metal-LIGAND bond.
What is ligand gated ion channel receptor ?
Ion channels are specialized pores in the cell membrane that help control and transfer electrical impulses (action potentials) in the cell. They regulate the flow of sodium, potassium, and calcium ions into and out of the cell. The ligand gated ion channel receptor is a signal receptor protein in a cell membrane that can act as a channel for the passage of a specific ion across the membrane. When activated by a signal molecule, it allows or blocks the passage of the ion. This results in a change in ion concentration that often affects cell functioning.
What is ligase ?
An ENZYME of EC class 6, also known as a synthetase, that catalyzes the formation of a bond between two SUBSTRATE molecules coupled with the HYDROLYSIS of a diphosphate bond of a NUCLEOSIDE triphosphate or similar cosubstrate.
What is light microscope ?
A common laboratory instrument that uses optics to bend visible light to magnify images of specimens placed on an attached platform, or other viewing area.
What is light reactions ?
A major component of photosynthesis in which a group of chemical reactions occur in the thylakoid membranes of chloroplasts that harvest energy from the sun to produce energy-packed chemical bonds of ATP and NADPH and that give off oxygen as a by-product.
What is lignin ?
A complex amorphous polymer in the secondary cell wall (middle lamella) of dead woody plant cells that cements or naturally binds cell walls to help make them rigid. Highly resistant to decomposition by chemical or enzymatic action, it is the major source material for coal. It also acts as support for cellulose fibers. Cells that contain lignin are fibers, sclerids, vessels, and tracheids.
What is limbic system ?
The limbic system underlies the corpus callosum, an area that provides communication and links to the two cerebral hemispheres, and is a collective term referring to several brain parts, an interconnected neural network or collection of bodies including the hippocampus, cingulate cortex, and the amygdala. The limbic structures are important in the regulation of visceral motor activity and emotional expression. The amygdala deals with emotion, while the cingulate cortex plays a role in emotional behavior, and the hippocampus deals with spatial and memory functions.
What is linkage ?
Refers to the tendency for two genes that reside next to each other on a chromosome to remain together, “linked,” during reproduction. The closer they are to each other, the lower the chance of separation during DNA replication, and therefore the greater the chance that they will be inherited with each other. Linked genes are an exception of Mendel’s laws of inheritance, specifically the law of independent assortment, which states that pairs of genes segregate independently of each other when germ cells are formed.
What is linkage map ?
A map that shows the relative positions of genetic loci on a chromosome, determined by how often the loci are inherited together. Linked genes are usually inherited together and are located close to each other on the chromosome. The distance is measured in centimorgans (cM). Genes that are located on different chromosomes follow Mendel’s principle of independent assortment, while genes that are on the same chromosome do not sort independently. The closer the two genes are to each other on a chromosome, the greater the chance that they will remain together during meiosis instead of crossing over. Researchers can construct a genetic map showing the relative positions of the genes on the chromosomes by comparing appearance of a trait to appearance of marker phenotypes. The distance between closely spaced genes can be expressed in “map units” reflecting relative frequency of recombination.
What is linked genes ?
Genes that are located close to each other on the same chromosome and do not show independent assortment. This results in parental allele combinations occurring greater than recombinant arrangements. A set of closely linked genes that are inherited together are called a haplotype. Some diseases are a result of abnormalities in certain gene combinations. X-linked diseases such as hemophilia, color blindness, and some muscular dystrophies are caused by genes located on the X chromosome. Sex-linked diseases are caused by a mutant gene on part of the X chromosome and affects men, since they do not have a Y chromosome of the XY pair that has a compensating normal gene.
What is lipid ?
A large group of hydrophobic (water insoluble) molecules that are the building blocks of cell membranes and liposomes (lipid vesicles) and contain fatty acids; the principal components of fats, oils, waxes, triglycerides, and cholesterol. They are insoluble in water but soluble in solvents such as alcohol and ether. The phospholipid bilayer of the plasma membrane is a double layer of phospholipid molecules arranged so that the hydrophobic “tails” lie between the hydrophilic “heads.” Also known as fat, they easily store in the body and are an important source of fuel for the body.
Who was Lipmann, Fritz Albert ?
Lipmann, Fritz Albert (1899–1986) was German Biochemist Fritz Albert Lipmann was born on June 12, 1899, in Koenigsberg, Germany, to Leopold Lipmann and his wife Gertrud Lachmanski.
Between 1917 and 1922 he was educated at the Universities of Koenigsberg, Berlin, and Munich, where he studied medicine and received an M.D. degree in 1924 at Berlin. In 1926 he was an assistant in Otto MEYERHOF’s laboratory at the Kaiser Wilhelm Institute, Berlin, and received a Ph.D. in 1927. He then went with Meyerhof to Heidelberg to conduct research on the biochemical reactions occurring in muscle.
In 1930 Lipmann went back to the Kaiser Wilhelm Institute in Berlin and then to a new institute in Copenhagen in 1932. Between 1931 and 1932 he served as a Rockefeller fellow at the Rockefeller Institute in New York and identified serine phosphate as the constituent of phosphoproteins that contains the phosphate.
He went to Copenhagen in 1932 as a research associate in the Biological Institute of the Carlsberg Foundation. In 1939 he came to America and became research associate in the department of biochemistry at Cornell Medical School, New York, and in 1941 joined the research staff of the Massachusetts General Hospital in Boston, first as a research associate in the department of surgery, then heading his own group in the Biochemical Research Laboratory of the hospital. In 1944 he became an American citizen. In 1949 he became professor of biological chemistry at Harvard Medical School, Boston. In 1957 he was appointed a member and professor of the Rockefeller Institute, New York.
In 1947 he isolated and named coenzyme A (or CoA). He later determined the molecular structure (1953) of this factor that is now known to be bound to acetic acid as the end product of sugar and fat breakdown in the absence of oxygen. It is one of the most important substances involved in cellular metabolism, since it helps in converting amino acids, steroids, fatty acids, and hemoglobins into energy. For his discovery of this coenzyme he was awarded the 1953 Nobel Prize in physiology or medicine. He died on July 24, 1986, in Poughkeepsie, New York.
What is lipophilicity ?
Represents the AFFINITY of a molecule or a moiety (portion of a molecular structure) for a lipophilic (fat soluble) environment. It is commonly measured by its distribution behavior in a biphasic system, either liquid-liquid (e.g., partition coefficient in octan-1-ol/water) or solid-liquid (retention on reversedphase high-performance liquid chromatography (RPHPLC) or thin-layer chromatography (TLC) system). See also HYDROPHOBICITY.
What is lipoprotein ?
Since lipids are hydrophobic (water insoluble), certain lipids like cholesterol and triglycerides are coated or bonded with a protein so they can be carried in the blood. Since it is not possible to determine the exact lipoprotein content in blood due to the variety of lipoproteins, the medical profession talks about low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs) that transport fats and cholesterol through the blood.
What is lipoxygenase ?
A nonheme iron ENZYME that catalyzes the INSERTION of O2 into polyunsaturated fatty acids to form hydroperoxy derivatives.
What is lithosphere ?
The solid inorganic uppermost portion or mantle of the Earth that includes the surface land and that of the ocean basin and is about 60 miles thick.
What is littoral zone ?
The shallow shoreward region of a freshwater body, just beyond the breaker zone, and where light penetrates to the bottom sediments, giving rise to a zone that is colonized by rooted plants called helophytes; a region of a lake or pond where the water is less than 6 meters deep; in oceanography, the line extending from the high water line to about 200 meters; also called the intertidal zone where submersion of tides is a normal event. The near-surface open water surrounded by the littoral zone is the limnetic zone, which gets ample light and is dominated by plankton. The littoral system is divided into a eulittoral (lower, middle, and upper) and a sublittoral (or subtidal, or supratidal) zone, the zone exposed to air only at its upper limit by the lowest spring tides. They are separated at a depth of about 50 meters. The term is also frequently used interchangeably with intertidal zone.
What is liverwort ?
A green photosynthetic bryophyte belonging to the family Hepaticae (division Hepatophyta). A small, simple plant that lives in moist, shady areas with wide, flat leaves that lie close to the ground. Liverworts reproduce with spores and have one of two forms: thalloid liverworts (Marchantiidae) and leafy liverworts (Jungermanniidae). Liverworts have no roots, but have thin (one-cell thick) rootlike structures known as rhizoids that serve for attachment and water absorption. Liverworts comprise two separate generations: the gametophyte generation and the sporophyte generation. There are around 6,000 species of liverworts worldwide, with some 4,000 species belonging to the Jungermanniales.
What is lizards ?
Lizards are vertebrates that belong to the class Reptilia, which contains some 27 families. Lizards and snakes are scaled reptiles. Lizards were first found in the Jurassic period about 213 million years ago. There are about 3,500 species of lizards worldwide living in warm tropics and subtropical climates, as well as in temperate regions, and they can be as large as the 10-foot Kimodo dragon. They have long bodies, typically with four legs and a tail, have movable eyelids, and external ear openings. They can lose a tail and regenerate a new one. Lizards may be the most successful reptiles living today.
What is locus ?
The specific position or location on a chromosome that is occupied by a gene. The plural form is loci.
Who was Loewi, Otto ?
Loewi, Otto (1873–1961) was Austrian Physician, Pharmacologist Otto Loewi was born on June 3, 1873, in Frankfurt-am-Main, Germany, to Jacob Loewi, a merchant, and Anna Willstätter. He attended the humanistic gymnasium (grammar school) locally from 1881 to 1890 and entered the Universities of Munich and Strassburg as a medical student in 1891. In 1896 he received a doctor’s degree at Strassburg University.
After spending a few months working in the biochemical institute of Franz Hofmeister in Strassburg, he became an assistant to Carl von Noorden, clinician at the city hospital in Frankfurt during 1897–98. In 1898 he became an assistant of Professor Hans Horst Meyer, a renowned pharmacologist at the University of Marburg-an-der-Lahn and a professor of pharmacology in Vienna. In 1905 Loewi became associate professor at Meyer’s laboratory, and in 1909 he was appointed to the chair of pharmacology in Graz. In 1940 he moved to the United States and became research professor at the School of Medicine of New York University, New York City, where he remained until his death.
His neurological researches during the period 1921–26 provided the first proof that chemicals were involved in the transmission of impulses from one nerve cell to another and from neuron to the responsive organ. It was for his discovery of the chemical transmission of nerve impulses that he received the Nobel Prize in physiology or medicine in 1936, jointly with Sir Henry DALE. Loewi spent his years investigating the physiology and pharmacology of metabolism, the kidneys, the heart, and the nervous system. He became an American citizen in 1946 and died on December 25, 1961.
What is logistic growth ?
A model developed by Belgian mathematician Pierre Verhulst (1838) that states that the growth rate is dependent on population density and restricted by carrying capacity. Growth is represented by an S-curve, and the growth rate declines as the population increases. The pattern of growth is a slow start, an explosive middle growth period, and then a flattening of the curve as growth slows.
What is long-day plant ?
A plant affected by photoperiodism. A plant that needs more light than dark for flowering. Long-day plants are spinach, lettuce, and wheat. Others such as calceolaria, philodendron, and tuberous begonias need 14 to 18 hours of light for flowering. Longday plants form flowers during day lengths of more than 12 hours and are both indoor and outdoor plant types.
What is longevity ?
The act of living for a long period of time.
What is loop of Henle ?
One of the six structural and functional parts of the kidney’s nephron, along with Bowman’s capsule, glomerulus, proximal convoluted tubule, distal convoluted tubule, and collecting tubule. The long hairpin turn, or loop of Henle, extends through the medulla from the end of the proximal convoluted tubule to the start of the distal convoluted tubule. It has a descending limb called the proxima straight tubule that reabsorbs water, and an ascending limb that reabsorbs NaCl, ending with the distal straight tubule. It is the major site of water and salt reabsorption. Some parts of it are permeable to water and impermeable to materials such as salt or ammonia in the urine, and vice versa. Also called the ansa nephroni.
What is low-spin ?
In any COORDINATION entity with a particular dn (1 < n < 9) configuration and a particular geometry, if the n electrons are distributed so that they occupy the lowest possible energy levels, the entity is a low-spin complex. If some of the higher-energy d orbitals are occupied before all the lower-energy ones are completely filled, then the entity is a high-spin complex.
What is luminescent ?
The act of emitting light without causing heat (called cold light). Bioluminescence is the act of producing light by biological organisms, e.g., firefly; luminescent bacteria (Photobacterium phosphoreum); and fox fire in the form of Clitocybeilludens (Omphalotus olerius), Panellus stypticus, and Armillaria mellea. The lanthanides are a special group of elements (elements cerium [Ce, atomic no. 58] through lutetium [Lu, atomic no. 71] within the periodic table that have trivalent cations that emit light. When these elements are absorbed into materials, the materials can become luminescent after being excited by an electrical current (electroluminescence) or by absorbing light (photoluminescence). As the ions relax to their ground state, they release light.
What is lumper ?
A taxonomist who prefers to classify organisms into relatively small groups, emphasizing similarities. Opposite of a splitter.
What is lung ?
The basic respiratory organ of air-breathing vertebrates. The basic function of the respiratory system is for lungs to supply oxygen to tissues and remove excess carbon dioxide from the blood. This is accomplished by inspiration, the movement of air into the lungs, and expiration, movement out of the lungs. Exchange of gases occurs at the internal surface of the lungs by diffusing oxygen from the lungs into the blood, while carbon dioxide (CO2) diffuses from the blood into the lungs. Gas is transported in the blood, and the circulatory system distributes oxygen throughout the body while collecting CO2 for return to the lungs. Ventilation, or airflow to the lungs, and perfusion, blood flow through lung capillaries, are the main factors that determine the overall pulmonary function. The ventilation/ perfusion ratio needs to be fairly constant in all parts of the lung for the most effective transfer of respiratory gases.
Lungs are saclike structures of varying complexity, depending on the organism. They are connected to the outside by a series of tubes and a small opening. In humans, the lungs can be found in the thoracic cavity and consist of the internal airways; the alveoli, tiny, thin-walled, inflatable sacs where oxygen and carbon dioxide are exchanged; the pulmonary circulatory vessels; and elastic connective tissues. The exchange of gases in the lungs takes place by breathing, chest movements that inhale air and exhale or force gases such as carbon dioxide out.
What is lyase ?
An ENZYME of EC class 4 that catalyzes the separation of a bond in a SUBSTRATE molecule.
What is lymph ?
A clear, colorless, watery fluid that contains white blood cells and antibodies. Lymph bathes the tissues, passes through lymph-node filters and returns to the blood stream. The lymphatic system is a system of vessels and lymph nodes that returns fluid and protein to the blood, and it is separate from but parallel to the circulatory system. Lymph flows through lymph nodes and is transformed into lymphocytes, a special kind of white blood cell that helps create the immune system and comprises up to 50 percent of all white blood cells.
What is lymphocyte ?
A white blood cell that identifies foreign objects such as bacteria and viruses in the body and produces antibodies and cells that target them. There are different types of lymphocytes, the most important of which are: B cells that produce specific antibodies to destroy foreign objects; T cells that attack cells that are infected by viruses, cancer cells, and other foreign tissue; NK (natural killer) cells that kill cancer cells and cells infected by viruses through phagocytosis; and null cells, also NK-type cells that attack certain targets. These cells occupy less than 1 percent in circulating blood as they travel from the blood to the lymph and lymph nodes and back into the circulating blood. Other types of lymphocytes include acidophilic or eosinophilic, agranular, nongranular or lymphoid, basophilic, granular, heterophilic, neutrophilic, polymorphonuclear, and activated.
What is lysis ?
Biological term for destruction or killing, as in bacteriolysis or the rupturing of a cell membrane with resulting loss of cytoplasm.
What is lysogenic cycle ?
A stage in viral development when a virus inserts its genome in a host genome and lies dormant until outside factors initiate the new genetic material to be transcribed. It then goes into a lytic cycle, a massive replication of new viruses, and lyses (destroys the cell membrane) the host cell.
What is lysosome ?
A small organelle found in eukaryotic cells that is surrounded by a membrane and contains digestive hydrolytic enzymes and chemicals that are strongly acidic. Lysosomes fuse with the vascular membrane, grab the food, and digest it, breaking it down into usable parts. Lysosomes also work with leukocytes by digesting leukocytes that have engulfed foreign objects or cleaned up damaged cells.
What is lysozyme ?
A basic enzyme or antibacterial product that can be found in tears, saliva, perspiration, the nasal cavity, egg whites, animal fluids, and some plant tissues. It attacks the cells walls of gram-positive bacteria by cleaving the muramic acid [beta(1-4)-N-acetylglucosamine] linkage in the cell walls of this class of bacteria.
What is lytic cycle ?
The viral replication that releases new phages (particles) through the lysis of the host cell.
What is lytic virus ?
A virus that causes lysis of the host cell.
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