Why Are Polyglutamines Toxic

Several hypotheses have been offered to explain the toxic nature of polyg-lutamine repeats, though none has yet been conclusively proven, and may yet be wrong in either details or central concept. The Nobel Prize recipient Max Perutz suggested that the expanded polyglutamine repeats promote the formation of protein aggregates. These aggregates often contain ubiquitin, a marker for protein degradation. Expanded polyglutamine proteins may adopt energetically stable structures that resist...

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Chakrabarty, Ananda, 1 61, 4 129 Chaotropic salts, 3 221 Chaperones, molecular (chaper-onins), 1 116-119 discovery of, 1 116 energy requirements, 1 116-117, 1 117 3 203, 4 168 Hsp70 and Hsp60 systems, 1 116, 1 117, 1 118 and human disease, 1 118 Charcot-Marie-Tooth disease, 4 4 Chargaff, Erwin, 1 250-251, 4 172 Chargafps ratios, 1 250-251, 4 172 Charge density, defined, 2 46 Chase, Alfred, 1 204 Chase, Martha, 3 104, 3 105, 4 120 Cheapdate mutant fruit flies, 1 5-6 Cheetahs, population...

Selection of Gene Targeted Cells

Homologous recombination is a very rare event, and scientists using it to modify or knock out mouse genes must identify the cells in which it has occurred. In addition to injecting the gene they are trying to incorporate, scientists also inject selectable genes whose products permit cells to live or cause them to die in the presence of a particular drug. The two most common selectable genes used in gene targeting are the neomycin resistance (neor) gene, which allows cells to survive in the...

Noncoding Triplet Repeat Disorders

The noncoding triplet repeat diseases typically have large and variable repeat expansions that result in multiple tissue dysfunction or degeneration. The triplet repeat sequences vary in this subclass (CGG, GCC, GAA, CTG, and CAG). It is clear that the particular triplet sequence and its location with respect to a gene are important defining factors in dictating the unique mechanism of pathogenesis for each disease. The pathogenic mechanism also varies from disease to disease depending on the...

Gene Therapy

Understanding the genes responsible for SCID has also led to an increased understanding of the genes involved in the overall development of the immune system. It has also helped to unravel the complicated signaling pathways between the cells of the immune system that control and define the immune response itself. There has also been another major benefit. The study of SCID has, in the past, aided in developing an effective program for bone marrow transplantation. Interleukin binds to its...

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Retina light-sensitive layer at the rear of the eye retroviruses RNA-containing viruses whose genomes are copied into DNA by the enzyme reverse transcriptase reverse transcriptase enzyme that copies RNA into DNA ribonuclease enzyme that cuts RNA ribosome protein-RNA complex at which protein synthesis occurs ribozyme RNA-based catalyst RNA ribonucleic acid RNA polymerase enzyme complex that creates RNA from DNA template RNA triplets sets of three nucleotides sarcoma a type of malignant...

The Genetic Architecture of Quantitative Traits

An important goal of genetic studies is to characterize the genetic architecture of quantitative traits. Genetic architecture can been defined in one of four ways. First, it refers to the number of QTLs that influence a quantitative trait. Second, it can mean the number of alleles that each QTL has. Third, it reflects the frequencies of the alleles in the population. And fourth, it refers to the influence of each QTL and its alleles on the quantitative trait. Imagine, for instance, a...

Donor Insemination and Egg Donation

Donor insemination is used when sperm are incapable of fertilizing the egg. Usually this occurs if the male produces very little or no sperm. Sometimes, donor sperm is used when the male partner is the carrier of a genetic disorder that could be transmitted to the baby. Sperm donors should be between ages eighteen and fifty-five, and all should be screened for genetic disorders, such as cystic fibrosis, and for various types of chromosomal abnormalities and infectious disease, including...

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Within seventy-two hours, the zygote develops into the morula, the solid mass of blastomeres formed by the cleavage of the fertilized ovum (egg). After about three to five days in culture, the zygote has become a hollow ball of cells called the blastocyst. During normal embryogenesis, it is the blastocyst that is implanted in the endometrial lining of the uterus. While the embryos are in culture, problems in their development may become apparent. After embryos with...

Applications

Recombinant DNA technology has been used for many purposes. The Human Genome Project has relied on recombinant DNA technology to generate libraries of genomic DNA molecules. Proteins for the treatment or diagnosis of disease have been produced using recombinant DNA techniques. In recent years, a number of crops have been modified using these methods as well. As of 2001, over eighty products that are currently used for treatment of disease or for vaccination had been produced using recombinant...

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Gametes reproductive cells, such as sperm or percent normal T-lymphocytes. Learning from these gene therapy experiences, French researchers modified the procedure. In 2000 they reported successful gene therapy for two infants with SCID-X1. The patients had left the hospital and its protective isolation after a three-month stay. Ten months after gene therapy, they remained healthy, with normal levels of B- and T-lymphocytes and natural killer cells. Thus SCID continues to define the current...

Types and Severity of Immunodeficiency Diseases

Disease severity can range from mild to fatal, depending upon what part of the immune system is affected. Immunodeficiency can originate in normal individuals as a consequence of chemotherapy, viral infections (such as AIDS, which is caused by the HIV virus), or as the result of other processes that prevent immune system function. When immunodeficiency occurs in this manner, it is called acquired. In contrast, immunodeficiency can also be inherited as a genetic mutation that prevents the normal...

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Chromatogram produced by an Applied Biosystems automated DNA sequencer. DNA sequence is read by a computer based on the fluorescent dye color associated with each band (represented as a peak) on the gel. taining all the components described above, but with no radioisotopes. In the A reaction, the primer carries a dye at one end that fluoresces green when struck with a laser. In the C reaction, the primer carries a dye that fluoresces blue. The G reaction's primer has a yellow dye on...

The Genetic Basis of Transplant Rejection

Research that began in the 1940s gave geneticists the first hints that a portion of the mammalian genome contained a cassette of genes that governed the acceptance or rejection of transplanted tissues. This grouping of genes was labeled the major histocompatibility complex (MHC). Subsequently, it has been found that the MHC also contains genes that are genome the total genetic material in a cell or organism Five knockout piglets, considered to be the first of their kind, were raised with the...

Types of Transplants

There are four basic types of transplants, which reflect the genetic relationship of the recipient to the donor. The autograft is the transfer of tissue from one location of an individual's body to another location that is in need of healthy tissue in other words, the recipient is also the donor. Common examples of autografts are skin transplants in burn patients and bypass surgery in patients suffering from coronary heart disease. The syngraft is a transplantation procedure carried out between...

The Mechanisms of Transplant Rejection

The immune system's attack on foreign tissue is mediated by lymphocytes, phagocytic cells, and various other white blood cells. Various subgroups of lymphocytes have different responsibilities. Once stimulated, the B-lymphocytes (derived from bone marrow) will develop into a cell that produces antibodies (soluble proteins that specifically seek out invaders). Antibodies may cause hemorrhaging by attaching to the lining of blood vessels in the transplant and then activating a naturally occurring...

In vitro Fertilization

When performed by an experienced practitioner and in an experienced clinic, IVF generally results in pregnancy rates of about 28 percent after one attempt and 51 percent after three. One study has reported the pregnancy rate after six attempts as being 56 percent. Another has reported it as being 66 percent. Generally, one attempt at IVF is made per menstrual cycle. The IVF process begins when couples are first screened. Clinicians first must rule out infertility in the male partner. If the...

Mechanisms of Functional Tumor Suppressor Loss

There are three main ways in which a cell can lose the functionality of its tumor suppressor genes. Chromosomal aberrations, such as balanced reciprocal translocations, can occur. In such translocations, two unlike chromosomes switch segments. The most common such aberration is the chromosome 11 and 22 t(11 22) (q23 q11) translocation. It occurs in 10 to 15 of every 10,000 newborns and is the most common cause of childhood leukemia. The chromosome 9 and 22 t(9 22)(q34 q11) translocation gives...

Viral Cancers

Infection with certain viruses can also result in cell transformation, stable genetic changes in the cell that result in disregulated cell growth and extended growth potential (immortalization). In animals, such virally induced cellular changes can result in cancer. This correlation was first made by Harry Rubin and Howard Temin in the 1950s, when they observed that Rous sarcoma virus, a retrovirus capable of inducing solid tumors in chickens, could also cause biochemical and structural changes...

Twin Studies to Investigate the Cause of Parkinsons Disease

An example of the use of investigations in twins to understand more about a disease is provided by recent work in Parkinson's disease. Parkinson's disease (PD) is a progressive neurodegenerative disease causing slowness, tremor, and problems with walking and balance. PD is rare before age fifty but becomes more common thereafter, with increasing age. The cause of PD has long been debated. Both genetic and environmental causes have been suggested, but neither has been definitively shown....

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Rhabdoviruses are helical viruses and include the virus that causes rabies and vesicular stomatitis virus (VSV), a common laboratory virus. The lipid-containing envelope is embedded with glycoprotein (G) spikes. A layer of a matrix protein (M) forms a bridge between G and the nucleocapsid proteins (N). Also included in the virion are several molecules of the RNA-dependent RNA polymerase (Large or L protein) and its cofactor, the phosphoprotein (P). The genes for these proteins are arranged as...

Gamete Intrafallopian Transfer

An alternative to IVF and intrauterine embryo transfer is gamete intrafal-lopian transfer (GIFT), introduced more than twenty years ago. In this procedure, the egg and sperm are collected as they would be for IVF procedures. However, instead of allowing fertilization to take place in a culture dish, the egg and sperm are transferred surgically into the woman's fallopian tube. This allows fertilization to occur in the fallopian tube, just as occurs in a natural pregnancy. The transfer can only...

Twin Studies and Concordance

Insight into such questions can be gleaned by several types of studies that compare twins. Comparison of MZ twins reared apart is one type of study but is hampered by the extreme rarity of such twin pairs. Another type of study, comparing MZ twins to DZ twins, is more commonly done, because there are many hundreds of thousands of such twin pairs worldwide. Data on twins have been collected by numerous research groups who have created large and growing databases (registries) that can be mined...

Retroviruses and Cancer

Retroviruses are among several types of viruses that can induce cancer in the host organism. So-called slowly transforming viruses are exemplified by human T-lymphotropic virus (HTLV), which causes leukemia (a type of blood cancer) in humans. These viruses induce malignancy by a process called insertional mutagenesis. The initial event is thought to be retroviral integration near, and subsequent activation of, a cellular oncogene (c-onc). Examples of c-onc include genes for growth factors,...