Carboxypeptidases

27 Mar

Carboxypeptidases
Canis familiaris the dog, the first animal domesti- cated by man and his companion for at least 15,000 years. The dog is a close relative of the gray wolf, Canis lupus. They both have a chromosome number of 39, and species hybrids are fertile. At least 400 different genetic diseases have been identified in dogs, and most of these are homologous to the hu- man conditions (Duchenne and Becker types of muscular dystrophy, Niemann-Pick disease, von Willebrand disease, hemophilia A and B, and testic- ular feminization are examples). The dog genome contains 2.4 Gbp of DNA.

See Appendix A, Mam- malia, Eutheria, Carnivora; Appendix E; dog breeds, wolf. canonical sequence an archetypical sequence (also known as a consensus sequence) to which all variants are compared. A sequence that describes the nucleotides most often present in a DNA seg- ment of interest. For example, in the Pribnow box and the Hogness box, the canonical sequences are TATAAT and TATAAAA, respectively.

The 14 nu- cleotide consensus sequence CCGTNTGYAARTGT has 11 nucleotides that are constant throughout the populations sampled. However, at position 5 any nucleotide (N) can be present, at the position 8 ei- ther pyrimidine (Y) can occur, and at position 11 either purine (R) can occur. See promoter. cap See methylated cap. CAP catabolite activator protein (q.v.). capacitation a process of physiological alterations whereby a sperm becomes capable of penetrating an egg as a consequence of exposure to one or more factors normally present in the female reproduc- tive tract.

It is theorized that a substance coating the sperm head must be removed by these female fac- tors before the sperm can become fully functional for fertilization. capon a castrated domestic fowl. capped 5′ ends the 5′ ends of eukaryotic mRNAs containing methylated caps (q.v.). capping 1. addition of a cap (q.v.) to mRNA mol- ecules. 2. redistribution of cell surface structures to one region of the cell, usually mediated by cross- linkage of antigen-antibody complexes.

Capsicum a genus that includes red peppers and pimentos, C. annum, and green pepper, C. frutes- cens. capsid the protein coat of a virus particle. capsomere one of the subunits from which a virus shell is constructed. Capsomeres may contain several different polypeptide chains. The virus shell is formed by assembling capsomeres about the nucleic acid core in a precise geometrical pattern. See icosa- hedron, Q beta (Qβ) phage, tobacco mosaic virus. Carassius auratus the aquarium goldfish.

A mem- ber of the carp family first described in China 2,300 years ago and bred for ornament since that time. See Appendix A, Chordata, Osteichthyes, Neopterygii, Cypriniformes. carbohydrate a compound, having the general for- mula CxH2xOx. Common examples of carbohydrates are glucose, cellulose, glycogen, and starches (q.v.). carbon the third most abundant of the biologically important elements.

Atomic number 6; atomic weight 12.01115; valence 4; most abundant isotope 12C; radioisotope 14C (q.v.). 3′ carbon atom end nucleic acids are convention- ally written with the 3′ carbon of the pentose to the right. Transcription or translation from a nucleic acid proceeds from 5′ to 3′ carbon. 5′ carbon atom end nucleic acids are convention- ally written with the end of the pentose containing the 5′ carbon to the left. See deoxyribonucleic acid. carbon dioxide sensitivity See sigma virus. Carboniferous the Paleozoic period that gener- ated the great coal deposits.

At this time the land was covered by extensive forests. Seed-bearing ferns and conifers appeared for the first time. Amphibians diversified, and the winged insects and reptiles arose. Cartilagenous fishes were the dominant marine ver- tebrates. In North America, where the stratigraphic record allows Carboniferous strata to be conve- niently subdivided into upper and lower segments, the Carboniferous is replaced by the Pennsylvanian and Mississippian periods. See geologic time divi- sions. carbonyl group a doubly bonded carbon-oxygen group (C=O).

The secondary structure of a poly- peptide chain involves hydrogen bonds between the carbonyl group of one residue (amino acid) and the imino (NH) group of the fourth residue down the chain. See alpha helix. carboxyl group a chemical group (COOH) that is acidic because it can become negatively charged (−C−O−) if a proton dissociates from its hydroxyl O group. carboxyl terminal C-terminus (q.v.). carboxypeptidases two pancreatic enzymes (A and B) that hydrolyze protein chains beginning at

Carboxysomes

the carboxyl terminal end of the chain and liberating amino acids one at a time. These enzymes are useful for amino acid sequence studies. carboxysomes See cyanobacteria. carcinogen a physical or chemical agent that in- duces cancer. A carginogen is usually mutagenic, and it either damages nucleic acids directly or indirectly, or it causes a genetic imbalance by inducing a chro- mosomal aberration (q.v.).

See alkylating agent, anti- oncogenes, Boveri theory of cancer causation, ionizing radiation, oncogene, oncogenic virus, proto-onco- gene, ultraviolet radiation. carcinoma a cancer of epithelial tissues (e.g., skin cancer); adenocarcinoma is a cancer of gland epi- thelia. carcinostasis inhibition of cancerous growth. carnivore a meat-eating animal. Also applied to a few insectivorous plants. In classification, a member of the mammalian order Carnivora which contains cats, mongooses, dogs, bears, raccoons, pandas, ot- ters, etc. carotenoids lipid-soluble pigments ranging in color from yellow to red.

The carotenes whose struc- tures appear in the illustration are plant carotenoids. Beta carotene can be enzymatically hydrolyzed into two molecules of vitamin A (q.v.) and is therefore an important provitamin. See anthocyanins. carpel the meristematic whorl of cells that pro- duces the female reproductive organs in angio- sperms. At maturity the carpel refers to the part of the flower that encloses the ovules and extends up- ward to form the pistil. 

carrier 1. an individual heterozygous for a single recessive gene. 2. a stable isotope of an element mixed with a radioisotope of that element to give a total quantity sufficient to allow chemical opera- tions. 3. an immunogenic molecule (e.g., a foreign protein) to which a hapten (q.v.) is coupled, thus rendering the hapten capable of inducing an im- mune response. carrier-free radioisotope a radioisotope essen- tially undiluted with a stable contaminating isotope. carrying capacity the size or density of a popula- tion that can be supported in stable equilibrium with the other biota of a community; symbolized K.

cartilage a skeletal connective tissue formed by groups of cells that secrete into the intercellular space a ground substance containing a protein, colla- gen (q.v.), and a polysaccharide, chondroitin sulfuric acid. cartilage-hair hypoplasia (CHH) a disease inher- ited as an autosomal recessive. Homozygous chil- dren have short limbs because of arrested cartilage growth, and their hair is sparse and light colored. The disease is the first one shown to be caused by mutations in an untranslated gene. The gene, RMRP (q.v.), transcribes an RNA that is used directly as a subunit of a mitochondrial enzyme.

CHH was first observed among the Amish (q.v.), where its fre- quency is about 1.5 per 1,000 live births. See Appen- dix C, 2001, Ridanpaa et al. Carya a genus that includes C. ovata, the shagbark hickory, and C. pecan, the pecan. caryonide a lineage of paramecia that derive their macronuclei from a single macronuclear primor- dium. Such paramecia are generally immediate de- scendants of the exconjugants. caryopsis a dry indehiscent multiple-seeded fruit derived from a compound ovary. The corn ear is an example. caspases a specific group of proteases that func- tion during apoptosis (q.v.).

Caspase is an abbrevia- tion for cysteine-dependent, aspartate-specific prote- ase. Such proteins are initially secreted as inactive precursors. Upon receiving a chemical signal, such procaspases break down into subunits, which are then reassembled into heterotetrameric caspases. There are two classes of caspases. The first, called upstream initiators, serve to transduce signals from the cell surface. These initiators then interact with caspases of the second class, the downstream effect- ors which begin to destoy key cellular substrates.

The death process enters its final phase when cas- pases activate the breakdown of DNA. See cellular signal transduction, separase, tumor necrosis factor. cassette mutagenesis a technique that involves removing from a gene a stretch of DNA flanked on either end by a restriction site (q.v.) and then insert- ing in its place a new DNA segment.

This cassette can contain base substitutions or deletions at specific sites, and the phenotypic effects that result give in- sight into relative importance of specific subseg- ments of the region to the functioning of the gene or its product. cassettes loci containing functionally related nu- cleotide sequences that lie in tandem and can be substituted for one another. The mating-type rever- sals observed in yeast result from removing one cas- sette and replacing it by another containing a differ- ent nucleotide sequence. Mating-type loci in yeast contain homeoboxes (q.v.).

caste a class of structurally and functionally spe- cialized individuals within a colony of social insects. cat any of a number of domesticated breeds of the species Felis catus. Popular breeds include SHORT- HAIRED BREEDS: Domestic Shorthair, Siamese, Bur- mese, Abyssinian, Russian Blue, Havana Brown, Manx, and Rex; LONG-HAIRED BREEDS: Persian, An- gora, and Himalayan.

catabolism metabolic breakdown of complex mol- ecules to simpler products, often requiring catabolic enzymes and accompanied by the release of energy. catabolite a compound generated by the break- down of food molecules. catabolite activating protein (CAP) a constitu- tively produced, dimeric, positive regulator protein in bacteria that, when bound to a promoter region and cAMP, facilitates transcription by RNA poly- merase of certain catabolite-sensitive adjacent genes in inducible and glucose-sensitive operons (such as the lac operon of E. coli).

Also known as cyclic AMP receptor protein (CRP) or catabolite gene activator (CGA) protein. catabolite repression the reduction or cessation of synthesis of enzymes involved in catabolism of sugars such as lactose, arabinose, etc., when bacteria are grown in the presence of glucose. The enzyme adenyl cyclase is inhibited by glucose from convert- ing ATP to cyclic adenosine monophosphate (cAMP); cAMP must complex with catabolite activator pro- tein (CAP) in order for RNA polymerase to bind to promoters of genes responsible for enzymes capable of catabolizing sugars other than glucose. Therefore, in the presence of glucose, less CAP protein is avail- able to facilitate the transcription of mRNAs for these enzymes.

catalase an enzyme that catalyzes the reaction of H2O2 → H2O + 1⁄2O2. Catalase is especially abun- dant in the liver, where it is contained in peroxi- somes (q.v.). See acatalasemia, antioxidant enzymes, superoxide dismutase. catalyst a substance that increases the rate of a chemical reaction without being consumed. En- zymes are biological catalysts. catarrhine referring to primates of the infraorder Catarrhini that includes the Old World (African and Asian) monkeys, great apes, and humans. These pri- mates are characterized by nostrils that are close-set and directed forward or downward, and they do not have prehensile tails.

Compare with platyrrhine. See Cercopithecus ethiops, Hylobates, Macacca mulatta, Pan. catastrophism a geological theory proposing that the earth has been shaped by violent events of great magnitude (e.g., worldwide floods, collisions with asteroids, etc.); the opposite of uniformitarianism (q.v.). cat cry syndrome a syndrome of multiple congeni- tal malformations in humans with a deficiency in the short arm of chromosome 5. Infants with this condi- tion produce a peculiar cry that sounds like a cat mewing. Also known as the cri du chat syndrome.

category a rank in a taxonomic hierarchy to which one or more taxa may be assigned: e.g., phylum, class, order, family, genus, species. catenane a structure made up of two or more in- terlocking rings. catenate to convert two or more rings into a sys- tem of interlocking rings. catenins a family of intracellular proteins that are a component of the junctional complexes which me- diate adhesion between cells and signal contact inhi- bition (q.v.).

In humans, alpha and beta catenins are encoded by genes at 5q31 and 3p22, respectively. The sequences of the two genes show no similarity. The alpha and beta proteins form 1:1 heterodimers, and they attach the inward-reaching carboxyl ends of molecules of cadherins (q.v.) to actin (q.v.) fila- ments within the cell.

In Xenopus, beta catenins pro- vide the first signal of dorsal ventral polarity in the embryo. cathepsin any of certain proteolytic enzymes thought to reside in lysosomes (q.v.). Such enzymes are abundant, for example, in metamorphosing tad- poles during the resorption of the tail. cathode the negative electrode to which positive ions are attracted. Contrast with anode. cation a positively charged ion so named because it is attracted to the negatively charged cathode. Contrast with anion. Cattanach translocation a translocation in the mouse discovered by B. M. Cattanach.

The aberra- tion involves an X chromosome into which a seg- ment of autosome 7 has been translocated. The insertion carries the wild-type alleles of three auto- somal genes that control the color of the fur. Studies on mice heterozygous for the Cattanach transloca- tion have shown that during X-chromosome inacti- vation in somatic cells, the genes in the inserted au- tosomal segment are turned off sequentially in order of their distances from the X chromosomal element. Thus, the X inactivation spreads into the attached autosomal segment, but does not travel unabated to the end of the segment.

cattle any of a number of domesticated breeds of the species Bos taurus. Popular breeds include BEEF CATTLE: Hereford, Shorthorn, Aberdeen-Angus, and Santa Gertrudis; DAIRY CATTLE: Holstein-Friesian, Jersey, Guernsey, Ayrshire, and Brown Swiss. See ru- minant mammals. caudal (cad) a gene in Drosophila (located at 2-54) which produces a transcript that is localized at the posterior pole of the embryo. The cad gene is essen- tial for the development of the hindgut. It encodes a protein 472 amino acids long that contains a ho- meodomain (q.v.).

This protein (CAD) activates the transcription of various target genes, including fushi tarazu (q.v.). caveolae flask-shaped invaginations 50-100 nm in diameter that are observed in the plasma mem- branes of mammalian cells such as adipocytes, endo- thelial cells, and muscle cells. Caveolae are involved in cholesterol transport and cellular signal transduc- tion (q.v.) through the binding of immune and growth factor receptors.

Endocytosis involving ca- veolae does not feed into the lysosome pathway, and therefore macromolecules that are internalized in caveolar vesicles avoid being degraded. Bacteria that can express FimH (q.v.) use caveolae to invade phagocytes, and since the phagosomes do not fuse with lysosomes, the bacteria remain viable. caveolins principal protein components of caveo- lae (q.v.). Caveolin 3 is a muscle-specific form of ca- veolin encoded by a human gene at 3p25.

Null mu- tations of this gene cause an autosomal dominant form of muscular dystrophy. Cavia porcellus the guinea pig or cavy, a rodent living wild in the Andean region of South America, but domesticated and used as a laboratory animal. Numerous mutants are known, affecting hair color and texture. Immune response genes were discov- ered in this species. See Appendix A, Chordata, Mammalia, Rodentia; Appendix C, 1963, Levine, Ojia, and Benacerraf. C banding a method for producing stained regions around centromeres. See chromosome banding tech- niques. cc cubic centimeter. See milliliter. C13/C12 ratio the ratio between the heavy, stable isotope of carbon and the normal isotope in a sample of interest. Since organisms take up C12 in prefer- ence to C13, the ratio is used to determine whether or not the carbon in the specimen is of biological origin. cccDNA covalently closed, circular DNA. CD4+ cells, CD8+ cells See T lymphocyte.

CD4, CD8 receptors proteins on the surface of T lymphocytes (q.v.) that determine their responses to antigens. Lymphocytes with the CD8 proteins on their surfaces function as killer T lymphocytes (Tk cells). Lymphocytes with the CD4 proteins on their surfaces function as helper T lymphocytes (Th cells). These secrete interleukins (q.v.), which activate Tk cells and B lymphocytes. See immunoglobulin do- main superfamily. CD99 the protein encoded by the human gene MIC2 (q.v.). Cdc 14, cdc genes See cell division cycle genes. cdc kinases cell division cycle kinases. See cyclins. cdks cyclin-dependent kinases. See cyclins. cDNA (copy DNA) single-stranded, complemen- tary DNA produced from an RNA template by the action of RNA-dependent, DNA polymerase (re-

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