Biological organisms humans

Biological organisms respond differently to the same dose of a toxicant. These differences are a result of age, sex, weight, diet, general health, and other factors. For example, consider the effects of an irritant vapor on human eyes. Given the same dose of vapors, some individuals will barely notice any irritation (weak or low response), whereas other individuals will be severely irritated (high response). 

Alexander, R. D. Noonan, K. M. 1979. Concealment of ovulation, parental care, and human social evolution. In Evolutionary biology and human social organization (Ed. by N. A. Chagnon W. G. Irons), pp. 436-453. Duxbury North Scituate. 

The most important pyrimidine derivatives are those upon which biological organisms depend. Cytosine 1018 and uracil 1019 are found in ribonucleic acid (RNA) in the form of their ribonucleotides, cytidine 1020 and uridine 1021, while in deoxyribonucleic acid (DNA), cytosine and thymine 1022 are found in the form of their 2 -deoxyribonucleotides, 2 -deoxycytidine 1023 and thymidine 1024. 5-Methylcytosine 1025 is also found to a small extent (c. 5%) in human DNA in the form of its 2 -deoxyriboside 1026, and 5-(hydroxymethyl)cytosine-2 -deoxyriboside 1027 has also been detected in smaller amounts <2005CBI1>. Many variants of cytosine and uracil can be found in RNA including orotic acid 1028 in the form of its ribonucleotide orotidine 1029. Other pyrimidine derivatives to have been isolated from various biological sources include 2 -deoxyuridine 1030, alloxan 1031, and toxopyrimidine (pyramine) 1032 (Figure 2). 

This means that development of a risk-based waste classification system must consider the events that could result in exposing biological organisms e.g., humans) to hazardous substances placed in a disposal facility, the probability that each event will occur, and the consequences of the event if it does occur. 

Characterize possible mechanisms of exposure to hazardous substances. The pathways by which hazardous substances released from a disposal facility can be transported through the biosphere and the resulting routes of human exposure are specified, often along with their respective probabilities. To estimate exposures of humans at assumed receptor locations, dilution of contaminants by transport in air or water as well as concentration by various means, such as precipitation and uptake by intermediate biological organisms consumed by humans, must be considered. An example of the potentially complex web of exposure pathways is shown in Figure 3.3. 

DNA (like in the human genome project), which codes all the proteins of the species, each protein given as a sequence of amino acids. The estimated number of proteins in the terrestrial biological organisms is of the order of 107, while the number of the 3D structures (in the atomic resolution) deposited in the Protein Data Bank (as of 24 June 2008) is 47,526. Thus, theoretical prediction of the 3D shape of proteins, being potentially much faster than the X-ray and NMR techniques, seems to be a must for contemporary biology. 

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