Biological Essentials

4 Hormonal regulation of female sexual functions and two Images showing a sperm cell fertilizing an egg cell and a human blastocyst five days after conception. 

The decreasing oestradiol level enhances a negative feedback. The FSH- and LH-production is inhibited by progesterone and their concentrations return to the initial levels. This ensures that during the second half of the cycle and likewise during pregnancy another ovulation and conception does not occur. 

If the egg is fertilised and has been implanted, the Corpus luteum - stimulated by the chorionic-gonadotropin (CG), a hormone of the uterine mucous membrane - develops into the Corpus luteum graviditatis and raises the production of progesterone, which is subsequently taken over by the placenta. For pregnancy tests, nowadays immunoassays are used, which allow the detection of CG in the blood stream or urine already within a few days after fertilisation. 

Most hormonal contraceptives contain progesterone derivatives, which prevent mid-cycle release of the maximal amoimt of FSH and LH, and thereby ovulation, but consequently simulate a mock pregnancy. [6] Birth control piUs can be devided into several groups  

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Humans can synthesize 12 of the 20 common amino acids from the amphiboHc intermediates of glycolysis and of the citric acid cycle (Table 28-1). While nutritionally nonessenrial, these 12 amino acids are not nonessential. AH 20 amino acids are biologically essential. Of the 12 nutritionally nonessential amino acids, nine are formed from amphibolic intermediates and three (cysteine, tyrosine and hydroxylysine) from nutritionally essential amino acids. Identification of the twelve amino acids that humans can synthesize rested primarily on data derived from feeding diets in which purified amino acids replaced protein. This chapter considers only the biosynthesis of the twelve amino acids that are synthesized in human tissues, not the other eight that are synthesized by plants. 

Pool concentration of a substance that exceeds the threshold - for example megadose vitamin C - or substances that are excreted unchanged because they cannot be metabolised, such as sugar alcohols, or compounds that are not biologically essential, such as carcinogens, bacterial toxins and some minor plant constituents, are also bioavailable (and thus bioactive) in that they have a metabolic impact, even if this is only the stimulation of detoxification processes, or the use of energy for their excretion. 

The relationship between the rate constant for ligand-metal binding kf) and the concentration of free metal ion [M"+] in oceanic surface waters for the biologically essential trace metals. Data plotted from Table 1 in Hudson, J. M and F. M. M. Morel (1993). Deep Sea Research, 40, 129-150. 

Administration of 1 and 3 mg Sn/kg body weight to rats resulted in inhibition of various enzymes, including hepatic succinate dehydrogenase and the acid phosphatase of the femoral epiphysis. Tin also appears to interact with the absorption and metabolism of biological essential metals such as copper, zinc, and iron and to influence heme metabolism. ... 

Moss SJ, Bai L, Toelzer S, Carroll BJ, Mahmud T, Yu T-W, Floss FIG (2002) Identification of Asml9 as an Acyltransferase Attaching the Biologically Essential Ester Side Chain of Ansamitocins Using W-Desmethyl-4,5-desepoxymaytansinol, Not Maytansinol, as Its Substrate. J Am Chem Soc 124 6544... 

Biologically essential tetrapyrrolic macrocycles of two main types exist the porphyrins, the prosthetic group of heme proteins, and the corrins, most representative among which is the coenzyme of Vitamin B12. 

Figure 6. Biologically essential and inessential parts of e -transfer between flavin and iron (proposal connecting Figures 2 and 4).

Figure 7. Structure and decay of 5-deazaflavin radicals. The 5-protonated tautomer, which would be analogous to the biologically essential blue flavo-semiquinone, is not formed, and disproportionation, which is characteristic for the flavin system, does not happen.

Examination of the genealogical mimicry involved in the construction and synthesis of Starburst/cascade dendrimers places this activity at the interface between chemistry and biology. Essentially all genealogical phenomena in biological systems involve and evolve around two generic classes of compositions, namely (a) nucleic acids and (b) proteins. The nucleic acids, DNA and RNA are estimated to be over three billion years old by radioactive carbon dating (see Ref. 206) (see Fig. 45). 

The employed computational methodology allowed us to explain the PES spectra of AT- and MAMT- in the gas phase. Simultaneously, we demonstrated that PT induced by electron attachment, important for the unconstrained AT complexes, is irrelevant for the biologically essential Watson-Crick configuration as modeled by the MAMT complex. Nevertheless, the Watson-Crick MAMT structure binds an excess electron that localizes on thymine, by 7.7 kcal/mol (see structure aMA% °MT in Table 21-1 and Figure 21-23). 

Other Remarks. In general, selenium and tellurium compounds are toxic. On the other hand selenium, in trace quantities, is biologically essential and may have anticancer properties. 

Eicosanoids, also referred to as icosanoids, are so named because of the 20-carbon constituency that identifies this class of oxygenated lipid molecules. A primary synthetic pathway for these molecules involves the phospholipase-mediated cleavage of a membrane phospholipid to produce arachidonic acid [(all-Z)-ik osa-5,8,ll,14-tetraenoic acid]. From this biologically essential intermediate fatty acid, two major subclasses of eicosanoids can be produced 1) leukotrienes, via the action of lipooxygenases, and 2) prostanoids, via the action of cyclooxygenases (COX-1 and COX-2). Examples of chemical structures for a leukotriene (Fig. la) and three types of prostanoids (Fig. Ib-d) underscore their shared arachidonate origin. 

R380 M. Inouye, Synthetic Hydrogen-Bonding Receptors for Biologically Essential Monosaccharides , Yuki Gosei Kagaku Kyokaishi, 2000, 58, 1077... 

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