Biology Flash Cards

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Biology Definitions

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Lac OperonThe Lactose Operon is a well studied example of Gene Regulation. Some bacteria have three genes (called "lacZ", "lacY", and "lacA") that enable the bacteria to digest lactose. These three genes are disabled when there is no lactose present, and enabled in the presence of lactose. In this way, the cell does not waste energy creating the lactose-digesting proteins unless it needs them. These bacteria also have a regulatory gene called "lacI" that produces a protein that binds to a site near the promoter for lacz, blocking (or regulating) transription of of the 3 lac proteins. In the presence of lactose, the lacI protein binds to lactose, is modified, and is then unable to bind to the lacZ promoter site, allowing the 3 lac genes to be expressed, and allowing the cell to digest lactose. The lacZ, lacY, and lacA genes are together called the "Lac Operon" because they are transcribed together into a single mRNA.Gene Regulation, Operon, LacZ, LacY
Lac PlusA cell is "Lac Plus" if it can utilize Lactose as a Carbon source. A bacterial colony is "Lac Plus" if it can grow if plated on Lactose. If plated on XGAL with rich media, the XGAL will turn blue when it is cleaved.Lac Operon, XGAL
Lac RepressorProtein which regulates the Lac Operon by binding (or not binding) to the promoter site for the Lac Operon, preventing its translation. When Lactose is present in the cell, this protein is modified so that it cannot bind to the Promoter for the Lac Operon. The Lac Repressor is an example of a DNA binding protein.Lac Operon, LacI, LacZ, LacY, LacA
LacAGene in the Lac Operon which encodes Transacetylase.Lac Operon, LacZ, LacY
LacIMonocistronic gene which regulates the polycistronic Lac Operon. The protein from this gene, called the Lac Repressor, binds to the promoter site for the Lac Operon, preventing its translation of LacZ, LacY, and LacA. When Lactose is present in the cell, it binds to this protein and modifies it so that it no longer binds to the promoter site. Lac Operon
Lactose PermeaseA regulated protein, spanning the surface of a bacterial cell that allows Lactose to enter the cell.Lac Operon, LacY, Gene Regulation
LacYGene in Lac Operon which encodes Lactose Permease that allows Lactose to enter the cell.Lac Operon, LacZ, LacZ
LacZGene in the Lac Operon responsible for creating the protein Beta-Galactosidase, a protein that that splits lactose into glucose and galactose.Lac Operon, LacY, LacA
Lagging StrandDNA has two strands joined together with opposite orientations. One is oriented in the 5' to 3' direction (the lagging strand), and one is oriented in the 3' to 5' direction (the leading strand). During DNA Replication, the two strands separate, one contiguous section at a time. The leading strand is oriented 3' to 5' and it creates a contiguous new DNA strand oriented from 5' to 3'. The lagging strand is oriented in the "wrong" direction, 5' to 3'. Because its complementary strand (with a 3' to 5' orientation) cannot add polymers on the 5' end, it repeatedly uses new primers to start new small strands of DNA (Okazaki Fragments) which are joined together with ligase.Leading Strand, Okazki Fragments, Ligase, Primer
Law of Independent AssortmentMendel's second law. States that different traits of an organism are inherited independently. For example, in peas, inheritance of roundness is not in any way correlated with inheritance of greenness (because they are on separate chromosomes). It was later discovered that genes on the same chromosome do have varying degrees of correlation in their inheritance, depending on their distance from each other.Mendelian Genetics, Law of Segregation, Chromosome, Chromosomal Theory of Inheritance
Law of SegregationMendel's first law. States that for a given trait (e.g. roundness, wrinkledness, etc.) each individual has two different "factors" (alleles) that can influence this trait. A child receives a random choice of one of these factors from each of its parents. For example, in peas, if a homozygous round parent is bred with a homozygous wrinkled parent, the child will have an allele for roundness and an allele for wrinkledness on homologous chromosomes in the same gene location.Mendelian Genetics, Law of Independent Assortment, Chromosomal Theory of Inheritance, Allele, Chromosome, Homologous, Homozygous, Gene
LawnWhen a scientist plates out bacteria on a petri dish, the section that contains bacterial cells is called the lawn, and the empty sections (perhaps containing bacterialphage which have killed the cells) are called plaques. Also called a "Bacterial Lawn".Plaque, Bacteria
Leading StrandDNA has two strands joined together with opposite orientations. One is oriented in the 5' to 3' direction (the lagging strand), and one is oriented in the 3' to 5' direction (the leading strand). Starting with a primer, a DNA strand which complements the leading strand is created contiguously with DNA Polymerase. In contrast, the lagging strand requires much more work (Okazaki Fragments, many Primers, and Ligase) to create a complementary strand.DNA, Replication, Ligase, Okazaki Fragment
LibraryUsing DNA Cloning to "purify" (isolate) all the genes in a genome, a scientist can produce many different colonies of bacteria, with each colony containing precisely one specific gene from the original genome of study. The combination of all these colonies is referred to as a "Library", a "Library of Clones", or a "Recombinant Library". Each colony can then be "withdrawn" from the "library" when a scientist wishes to study a particular gene.DNA Cloning, Recombinant DNA
LigandA signal-triggering molecule which binds to a site on a target molecule, changing the function and form of the target and thus enabling a biochemical pathwayCell, Receptor, Binding Site
LigaseThe enzyme which is used to join together Okazaki fragments. When DNA separates its strands during replication, one of the strands, the lagging strand, is oriented the "wrong" way (5' to 3'), and Okazaki fragments are created which are then joined together using ligase. When a scientist engages in DNA Cloning, overhangs created by restriction enzymes will cause DNA molecules to hydrogen bond together. A scientist can then use Ligase to covalently bond each of the strands of DNA, completing the DNA Recombination.Okazki Fragments, DNA, Replication, Ligate
LigateTo join together. When DNA separates its strands during replication, one of the strands, the lagging strand, is oriented the "wrong" way (5' to 3'), and Okazaki fragments are created which must later be ligated together (using ligase)Okazki Fragments, DNA, Replication, Ligase
Light ChainAntibodies (Immunoglobulins) are made up of a heavy chain and a light chain. Note that both the heavy and light chains have a stochastic (random) fusion of V,D, and J Segments.Antibody, V Segment, D Segment, J Segment
Linnaean Classification (Taxonomy)A rank-based system for classifying biological systems, developed by Carolus Linnaeus circa 1735. Originally, he specified three kingdoms (Animale, Vegetabile and Lapideum -> "animal, vegetable, and mineral"), which were subsequently divided into phyla (divisions), classes, orders, families, genera, and species. There have been many revisions of this taxonomy, and there is still some controversy. Current systems have two or three "domains" (Bacteria , Archaea, Eukarya) at the top of the hierarchy, followed by six kingdoms (Animals, Plants, Fungi, Protists, Archaea, Bacteria). Prokaryote, Eukaryote
LupusAn often fatal autoimmune disease in which the immune system recognizes (attacks) many different tissues, because, in its early development, the immune system did not eliminate B Cells which recognize (attack) "Self Proteins".V Segment, J Segment, D Segment, Antibody, Antigen, Hypermutaion, Self Proteins
LysosomesLysosomes are cellular organelles found in animals which digest cellular waste, foreign invaders (viruses and bacteria) and also "food" particles which have been imported into the cell inside vacuoles. The lysosome "digests" these molecules using acidic enzymes. The lysosome maintains an internal pH of 4.5 as required by its digestive enzymes. When the cell imports extra-cellular particles (Endocytosis) via vacuoles, the Lysosomes fuse with vacuoles and "digest" their contents. Most viruses "escape" before the lysosomal fusion step, but some viruses use the lysosome to remove their protein coat ('uncoating"), thus freeing their nucleic acids.Organelle, Virus

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