UBIQUITIN-PROTEASOME PATHWAY The cellular life relies on the activity of proteins. In each cell, the abundance and thereby the activity of every protein is tightly controlled. It is the result of a balance between synthesis from the genome and degradation by proteolysis.

• The degradation of proteins by the ubiquitin-proteasome pathway

The ubiquitin-proteasome pathway is the major process responsible for the degradation of proteins in all human cells.

It is a highly specific, temporally controlled and tightly regulated process that plays a major role in nearly every aspect of cellular biochemistry. Protein degradation by the ubiquitin-proteasome pathway has been demonstrated to contribute prominently to the regulation of DNA repair, gene expression, apoptosis, cell cycle and the immune response.

• Ubiquitin and human diseases

Given the high number of cellular pathways that are controlled by proteins degradation, it is not surprising that alterations of the ubiquitin-proteasome pathway underlie the pathogenesis of many inherited as well as acquired human diseases, including :

cancer (colon carcinoma, lymphoma, …)
inflammatory diseases
neurodegenerative diseases
(Parkinson, Alzheimer, Huntington, …)
Likewise, the ubiquitin-proteasome pathway has been shown to be manipulated by many pathogens, including viruses, to circumvent cell defences.

• Ubiquitin ligases : arbiters of protein degradation

The degradation of proteins by the ubiquitin-proteasome pathway involves two successive steps. First, the proteins to be degraded are selected by specific enzymes called ubiquitin ligases. The ubiquitin ligases tag the selected proteins by attaching them a specific poly-ubiquitin chain. Then, after they have been tagged, these ubiquitinated proteins are recognized and degraded by the proteasome 26S. The proteasome is a large complex made up of many proteases that degrade ubiquitinated proteins to multiple small inactive pieces.

The ubiquitin ligases are thus the genuine arbiters of the proteins’ survival because they are responsible for both the efficiency and the selectivity of their degradation by the ubiquitin-proteasome pathway. Recent estimates indicate that the human genome is coding for at least 150 ubiquitin ligases belonging to several structural groups.

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UGI REACTION MultiComp. reaction, in which an amine, an aldehyde, a carboxylic acid, & an isonitrile (R-N=C) react to form an N-substituted amide of an N-acylated alpha-aminoacid. The advantage of the UGI is that varying the substituents on the 4 comp. lets chemists assemble many combinations quickly. But the prodts have acyclic peptidelike structures, while medicinal chemists want structural motifs that are more "druglike"
UHDE BAYER PROCESS Some industrial plants exist in the world (Germany, ex Soviet Union, China) that recover chlorine by means of the electrolysis of hydrochloric acid with diaphragm electrolysers.
Each one of the elementary cells which compose an electrolyser is constituted by an anodic compartment made of impregnated graphite, a separation diaphragm made of PVC or PVDF and a cathodic compartment which is made of impregnated graphite too. With this technology also the electrodes – anode and cathode - are made of graphite. Aqueous HCl is fed to the anodic chamber at approx. 21% concentration. At the anode the oxidation of the chloride ions takes place and chlorine is formed. At the outlet of the chamber we have the depleted acid (at approx. 17% concentration) and the produced chlorine. H+ ions migrate through the diaphragm towards the cathodic chamber. At the cathode the reduction of the hydrogen ions occurs and hydrogen is formed. The hydrochloric acid solution is fed to the cathodic chamber too. This process is known as Uhde-Bayer process.
The average power consumption that it is possible to achieve with the diaphragm technology is about 1700 kWh/t Cl2.
ULCERATIVE COLITIS is a chronic inflammatory disease of unknown aetiology afflicting only the large bowel and, except when very severe, limited to the bowel mucosa. The course of the disease may be continuous or relapsing, mild or severe. It is curable by total colectomy which may be needed for acute severe disease or chronic unremitting disease. Most patients with ulcerative colitis are managed medically rather than surgically
ULLMANN REACTION process in which iodobenzene breaks apart with the help of a copper powder catalyst, allowing liberated phenyl molecules to fuse into biphenyl
ULTRAFILTRATION Ultrafiltration, typically used for concentration and purification, employs membranes with smaller pore sizes than those used for microfiltration. The process, which uses pressures up to 145 psi, concentrates suspended solids and solutes with molecular weights greater than 1,000. Salts, sugars, organic acids, and small peptides permeate the membranes, leaving behind proteins, fats, and polysaccharides
ULTRASOUND an imaging technique that uses high frequency sound waves.
URICASE (URATE OXIDASE) enzyme that converts uric acid into a highly soluble and more easily excreted product
URICOSURIA The presence of excessive amounts of uric acid in urine
UV-A RADIATION 320-400 nm radiation, permitting skin natu
ral tanning.

Penetrate more deeply into the skin & do greater long-term damage
UV-B RADIATION 280-320 nm wavelength radiation causing skin burns & erythema, & may be harmful to natural tanning
UVEITIS Inflammatory Disease that Involves the Internal Parts of the Eye