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Glossary back AIDS, acquired immunodeficiency syndrome - An incurable (at the time of this writing) disease that results from infection by the human immunodeficiency (HIV) virus. AIDS symptoms build up as the concentration of HIV viruses in the body increases, usually over a period of years. Eventually, AIDS victims loose their abilities to fight infections. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back ATP (adenosine triphosphate) – A relatively stable, high energy molecule used to fuel chemical reactions within cells. ATP is the ‘universal energy carrier’ molecule in nature, performing energy exchange and energy transport functions in all living things. ATP is an adenine-containing nucleoside triphosphate that releases free energy when one of its phosphate bonds is hydrolyzed – a reaction that yields ADP, Adenosine diphosphate, as a product. The ADP is recycled to ATP through the addition of an activated phosphate group coupled to energy-producing reactions. NH2 N N O– – O P O– O P O– O P O N CH2 N O O O O OH Visualizing Cell Processes OH (rd Edition) © BioMEDIA ASSOCIATES Glossary back bacteriophage - A virus that infects only bacteria. The term is usually shortened to ‘phage’. A TEM of several bacteriophage viruses. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back capsid - The protein shell that encloses the viral genome. These are built from subunits called capsomeres. The capsid conforms to the shape of the virus, and may be helical, polyhedral or more complex in shape. The capsid is also called a ‘protein jacket’. Capsid Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back capsomere - The building block protein molecule found in the capsid covering of a virus. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back CD4 molecule - A molecule present on the surface of helper T-lymphocytes that is normally used for cell-cell interactions. The HIV virus uses this protein as a receptor, thus gaining access to the T-lymphocyte through receptor mediated endocytosis. HIV Virus CD4 molecule Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back DNA polymerase – The enzyme that catalyzes the addition of nucleotide bases to the 3’ end of replicating DNA strands. DNA polymerase follows the replication fork as it opens, promoting the addition of new phospho-diester bonds in the DNA backbone chain (of the leading strand), as the new bases line up. These reactions involve the expenditure of energy. DNA polymerase also acts to check for replication errors, and repairs them as the strands are replicating. DNA polymerase also catalyses the replication of the lagging strand, but in this case, the enzyme functions a short way down the strand from the replication fork, in order to build in the 5’ to 3’ direction. This creates Okazaki fragments along the lagging strand. DNA polymerase Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back DNA virus - A virus with a genome made up of deoxyribonucleic acid, DNA. This genome can be directly inserted into the host-cell genome where it directs the cell to replicate copies of the virus. Viruses with a genome made from RNA are called RNA viruses. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back glycoprotein - A protein with a carbohydrate covalently bonded to it. Most secreted proteins and most proteins on the outer surface of the cell are glycoproteins. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back helper T-lymphocyte - One of the types of blood cells in the human immune system. Tlymphocytes function in cell-mediated immunity. Helper T-cells secrete protein factors called cytokines which help to regulate B cells and T cells in the immune system. Lymphocytes differentiate from stem cells in the bone marrow and mature in the thymus. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back HIV, human immunodeficiency virus - The virus that causes AIDS. HIV is thought to have evolved relatively recently in Africa from a related virus. It’s considered the most deadly virus known. HIV is spread only by direct contact with infected bodily fluids such as blood or semen. HIV particle HIV entering host cell Visualizing Cell Processes New HIV particles escaping (rd Edition) © BioMEDIA ASSOCIATES Glossary back host range - The limited number of different types of host cells that a type of virus can infect or parasitize. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back influenza - The condition caused by the common ‘flu’ virus with symptoms such as fever, aches, stomach upset, and coughing. New genetic strains of influenza regularly arise in human populations, spreading rapidly over large portions of the world. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back lysogenic cycle - A reproductive cycle used in some DNA bacteriophages that reproduces the viral genome without killing the host cell. After infecting a host bacterium, the viral DNA becomes integrated with a host’s DNA. The bacterium continues to divide, producing many new bacteria cells, each with a copy of the viral DNA. Each of these is capable of initiating a second virus reproductive cycle inside its host cell (the lytic cycle) where multiple copies of the entire virus are produced by the host. In the lytic cycle, the host cell breaks apart, releasing the completed viruses into the environment – killing the host cell. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back lysogenic - Certain viruses, in the form of a prophage, can become integrated into a host cell genome. At some point after this, the viral genes can become active causing the host cell to produce copies of the virus that will cause the host cell to break open or lyse. This type of infection is termed lysogenic. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back lytic cycle - A reproductive cycle used in double stranded DNA bacteriophages where multiple copies of the entire virus are produced by the host. In the lytic cycle, the host cell breaks apart, releasing the completed viruses into the environment – killing the host cell. viral entry into cell virus cell DNA coat protein viral genome enters cell DNA transcription replication RNA translation DNA capsid protein assembly coat protein lysing of cell membrane and release of viral replicates The lytic cycle of a virus. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back obligate intracellular parasite - Those parasites that can only reproduce from within the cytoplasm of an infected host cell. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back prophage - The section of viral genome that has been inserted into a host bacterium’s genome. In DNA viruses, this is the same DNA as inserted by the phage, while in RNA viruses, this DNA is first produced by reverse transcription. bacteriophage Injected DNA Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back protein jacket -The capsid, or outer protein coat, of a virus. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back provirus - The section of DNA in a host cell’s genome that arises from DNA injected by a virus into the nucleus of a host. Provirus Host DNA and RNA polymerase Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back retrovirus - An RNA viruses that replicates inside a host by first making a DNA template of itself using the enzyme, reverse transcriptase. From the root, retro , meaning backward. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back reverse transcriptase - The enzyme that promotes the reverse action of transcription, creating a DNA template from a molecule of RNA. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back RNA polymerase - The enzyme that catalyzes the transcription of messenger RNA from a DNA template. RNA polymerase Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back RNA virus - A virus with a genome made up of ribonucleic acid, RNA. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back T-4 virus - A highly-studied bacteriophage that infects the common intestinal bacterium, Escherechia coli . Like the T-2 and T-6 phages (which also infect E. coli ), the T-4 virus has an icosohedral (see diagram below) ‘head’ region enclosing the viral DNA, and a collapsing tail structure with attached fibers that allows the virus to insert its DNA into the host cell. T-4 bacteriophage Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back temperate virus - A virus that is capable of two different reproductive modes within the host cell: the lysogenic mode or cycle, and the lytic mode or cycle. In the lysogenic mode, the virus reproduces without killing the host cell. After infecting a host bacterium, the viral DNA becomes integrated with a host’s DNA. The bacterium continues to divide, producing many new bacteria cells, each with a copy of the viral DNA. Each of these is capable of initiating a different reproductive cycle inside its host cell (the lytic cycle) where multiple copies of the entire virus are produced by the host. In the lytic cycle, the host cell breaks apart, releasing the completed viruses into the environment – killing the host cell. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back transcription - The process whereby the genetic code on DNA molecules is translated into a corresponding code on RNA molecules. The process involves the enzyme, RNA polymerase, which reads the DNA code and matches nucleotides in a growing strand of RNA based on DNA-RNA base pairing rules. For each transcription unit on the DNA, a complementary molecule of mRNA is formed as a result of transcription. During transcription, RNA nucleotides are matched with corresponding DNA nucleotides. Visualizing Cell Processes RNA polymerase opens the two DNA strands and reads the template strand as RNA nucleotides are added. (rd Edition) © BioMEDIA ASSOCIATES Glossary back vaccine - A harmless or relatively harmless variant or derivative of a microscopic pathogen that stimulates the body’s immune system to produce antibodies against the pathogen. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back viral envelope - A membrane that covers the capsid of some viruses. These membranes include membrane created by the host cell along with proteins and glycoproteins programmed by the viral genome. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back virus - An infective, parasitic genome of DNA or RNA covered by a protective protein coat. Viruses are on the boundary between living organisms and simple molecules. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES Glossary back viurlent viruses - Viruses that depend entirely on the lytic mode or cycle of reproduction to propagate. In the lytic cycle, multiple copies of the virus are made by the host cell. The host cell then breaks apart (lyses), releasing the new viruses. Other viruses, called temperate viruses, have a dual mode of reproduction with the possibility of either the lytic cycle, or a lysogenic cycle where the viral genome is reproduced as the host cell divides, potentially through many generations. Visualizing Cell Processes (rd Edition) © BioMEDIA ASSOCIATES