Other Typical Characteristics

The clustered genes of the operon typically share a common promoter and a common regulatory region, called an operator. Gene expression requires Figure 2. Regulation of gene expression in the lac operon. RNA polymerase is represented as a five-subunit protein, with two a subunits, one p subunit, one p' subunit and one a subunit. The a subunit binds the promoter and dissociates from the polymerase once elongation of the RNA molecule begins. When lactose is present, some is converted to...

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Muscle biopsy of mitochondrial myopathy patient (modified Gomori trichrome stain) with ragged red fiber showing disorganization and mitochondrial proliferation. Mitochondria stain red. Other muscle fibers also have increased numbers of mitochondria. in coding for electron transport chain subunits is detailed in Figure 1. Human mtDNA contains 16,569 nucleotide bases and encodes thirteen polypeptides of the electron transport chain, twenty-two transfer RNAs (tRNAs) and two ribosomal...

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With the caveat that the intent is not to improve the gene pool, but to prevent suffering. This may mean terminating a pregnancy in which the fetus has a very bleak prognosis, which people opposed to abortion might find unethical. Opponents to this view point out that letting nature take its course can be painful for the fetus and may endanger the life of the woman. The ethics of prenatal diagnosis becomes more complicated when the goal is not to prevent suffering, but to choose a child of a...

The Causes of Nondisjunction and Its Frequency in Humans

Meiosis is a very tightly regulated process, and a whole series of control mechanisms (constituting a number of checkpoints) exist to ensure that everything proceeds in the correct manner. If an error should occur during the process, it is usually corrected. Nondisjunction is the result of a mistake at the level of chromosome segregation, which involves the spindle fibers. In normal meiosis, there is a mechanism that monitors the correct formation of the spindle fibers, the correct attachment...

Endosymbiosis and Genome Reduction

Given the bacterial-like features of mitochondria and chloroplasts (small size, circular genome, and ability to divide on their own), it is believed that each organelle traces its evolutionary history to a free-living bacterial ancestor that was engulfed by a larger cell and then entered into a symbiotic relationship with the host cell. This serial endosymbiotic theory proposes that the evolution of the modern eukaryotic cell was a step-wise association, with the acquisition of the mitochondria...

Schizophrenia and Bipolar Disorder

Schizophrenia is a disorder characterized by psychotic symptoms such as hallucinations, delusions, and disordered thinking, as well as deficits in emotional and social behavior. Numerous family, twin, and adoption studies have provided substantial evidence for genetic factors in the etiology of this dis- etiology causation of disease, or the study of causation order. Nongenetic factors also appear to play an important role. The risk for relatives of an individual with schizophrenia is 6.5...

Tourettes Syndrome

Some psychiatric disorders, like Tourette's syndrome, have significant overlap (co-morbidity) with other psychiatric disorders (OCD and ADHD in the case of Tourette's). This may make the elucidation of genetic causes more difficult. Tourette's syndrome is characterized by multiple motor tics and one or more vocal tics. It has onset before eighteen years and is one and one-half to three times more common in males. Twin, adoption, and segregation analysis studies support a genetic etiology for...

Alterations of Amino Acids

Post-translational control of protein function or structure can be accomplished by chemical alteration of an amino acid side chain or by modification of the ends of the protein backbone. While there are many diverse chemical modifications of amino acids, three common examples are phosphorylation, glycosylation, and ubiquitination. Phosphorylation involves the addition of phosphate to an amino acid side chain, usually to the side chain hydroxyl -OH of serine, threonine, or tyrosine. This...

Viewing Chromosomes

Biologists first tried to visualize the chromosomes in a human cell in the late nineteenth century, with estimates of the total number ranging from 30 to 80. As methods to untangle and stain chromosomes improved, the count narrowed to 46 or 48, and by 1956 was confirmed as 46, or 23 pairs. By 1959, the first chromosomal abnormalities were identified using size and crude staining patterns to distinguish the chromosomes. In the 1970s, vastly cytogeneticists scien- improved staining techniques...

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy DMD is an X-linked recessive disorder with a worldwide occurrence of one in four thousand newborn males, with approximately one-third of the cases arising from new mutations. DMD was named after the French neurologist Duchenne de Boulogne, who described the disorder in 1861. Becker muscular dystrophy BMD , named after Peter Becker, a German geneticist who first described it in the mid-1950s, is a disorder that is very similar to DMD but has a much milder course. In...

Chromosomal Aberrations and Transposons

Structural chromosomal aberrations, the second category of mutations, arise when DNA in chromosomes is broken. The broken ends may remain unrepaired or may be joined with those of another break, to form new combinations of genes, such as translocations. A translocation between chromosomes 8 and 21 in humans causes acute myeloid leukemia by increasing the activity of c-myc, a gene involved in cell replication. Translocations often cause human infertility, because they interfere with the normal...

DNA Methylation and Human Disease

Changes in DNA methylation patterns have been implicated in the development and progression of many types of cancers. Additionally, defects in DNA methylation have been associated with several genetic diseases, including ICF Immunodeficiency, Centromere Instability, and Facial Anomalies , Rett, and Fragile X syndromes, all of which result in variable degrees of mental retardation. This common effect on neurological function may result from the fact that DNA methylation occurs at high levels in...

Differences between Mitosis and Meiosis

Mitosis occurs in all eukaryotic cell tissues and produces genetically identical daughter cells with a complete set of chromosomes. In humans, mitosis produces somatic cells that are diploid, which means they contain two non-identical copies of each of the twenty-three chromosomes. One copy is derived from the person's mother and the other from the person's father. Meiosis, on the other hand, occurs only in testis and ovary tissues, producing sperm and ova eggs . The gametes that are produced...