Reticulum Videos

Professor George Wolfe discusses endoplasmic reticulum in this video from Thinkwell's online Biology series.

Author: dabbetularz1400 Keywords: cell living darwin dqrwin structure orannels organels organnels organells mitochondry mt mitokondri gorgi endoplasmatic reticulum Added: July 8, 2009

Author: dabbetularz1400 Keywords: cell living darwin dqrwin structure orannels organels organnels organells mitochondry mt mitokondri gorgi endoplasmatic reticulum Added: July 8, 2009

Author: dabbetularz1400 Keywords: cell living darwin dqrwin structure orannels organels organnels organells mitochondry mt mitokondri gorgi endoplasmatic reticulum Added: July 8, 2009

Author: dabbetularz1400 Keywords: cell living darwin dqrwin structure orannels organels organnels organells mitochondry mt mitokondri gorgi endoplasmatic reticulum Added: July 8, 2009

Author: Coene Added: Fri, 15 Dec 2006 18:33:32 -0800 Duration: 23 The name P450 refers to the "pigment at 450 nm", so named for the characteristic Soret peak formed by absorbance of light at wavelengths near 450 nm when the heme iron is reduced (with sodium dithionite) and complexed Animal CYPs are primarily membrane-associated proteins, located either in the inner membrane of mitochondria or in the endoplasmic reticulum of cells. CYPs metabolise thousands of endogenous and exogenous compounds. Most CYPs can metabolize multiple substrates, and many can catalyze multiple reactions, which accounts for their central importance in metabolizing the potentially endless variety of endogenous and exogenous molecules. In the liver, these substrates include drugs and toxic compounds as well as metabolic products such as bilirubin (a breakdown product of hemoglobin). Cytochromes P450 are present in many other tissues of the body including the mucosa of the gastrointestinal tract, and play important roles in hormone synthesis and breakdown (including estrogen and testosterone synthesis and metabolism), cholesterol synthesis, and vitamin D metabolism. In most animals, including humans, hepatic cytochromes P450 are the most widely studied of the P450 enzymes. The Human Genome Project has identified 63 human genes (57 full genes and 5 pseudogenes) coding for the various cytochrome P450 enzymes [1]. Drug Metabolism In drug metabolism, cytochrome P450 is probably the most important element of oxidative metabolism (also known as Phase I metabolism) in animals (metabolism in this context being the chemical modification or degradation of chemicals including drugs and endogenous compounds). Many drugs may increase or decrease the activity of various CYP isozymes in a phenomenon known as enzyme induction and inhibition). This is a major source of adverse drug interactions, since changes in CYP enzyme activity may affect the metabolism and clearance of various drugs. For example, if one drug inhibits the CYP-mediated metabolism of another drug, the second drug may accumulate within the body to toxic levels, possibly causing an overdose. Hence, these drug interactions may necessitate dosage adjustments or choosing drugs which do not interact with the CYP system. In addition, naturally occurring compounds may also cause a similar effect. For example, bioactive compounds found in grapefruit juice and some other fruit juices, including bergamottin, dihydroxybergamottin, and paradisin-A, have been found to inhibit CYP3A4-mediated metabolism of certain medications, leading to increased bioavailability and thus the strong possibility of overdosing. Because of this risk, avoiding grapefruit juice and fresh grapefruits entirely while on drugs is usually advised. [edit] P450s in Plants Plant cytochrome P450s are involved in a wide range of biosynthetic reactions, leading to various fatty acid conjugates, plant hormones, defensive compounds, or medically important drugs. Terpenoids, which represent the largest class of characterized natural plant compounds, are often metabolic substrates for plant CYPs

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