Bioc385i-W17-Discussions-Module7-KEY.pdf

Bioc385i-W17-Discussions-Module7-KEY.pdf - Roger L Miesfeld...

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Unformatted text preview: Roger L. Miesfeld Bioc 385i Winter 2017 Bioc 385 online: Discussion Questions Module TOPIC 7 20 Amino Acid Degradation Question Q7.1: The standard change in free energy for the glutamate dehydrogenase reaction is +30 kJ/mol. The reaction shown in figure 17.11 would therefore be unfavorable. Under what conditions + might the assimilation of NH4 into glutamate be favorable? Explain your answer by referring to the mass action ratio. Answer Crop plants often are exposed to very high levels of (NH4)2SO4 (ammonium sulfate), which will lead to a more favorable DGº’ because the mass action ratio [P]/[S] will be a number much less than 1. The natural log (ln) of a small number, is a (-­‐) number, making the actual change in free energy (DG) more favorable even with an unfavorable DGº’ of 30 kJ/mol. (see page 844). 21 Amino Acid Biosynthesis Q7.2: Describe the biochemistry behind RoundUp Ready crops, i.e., what is a RoundUp Ready plant, why does it yield more crop per acre, and what are the potential problems with such a strategy with regard to overuse of glyphosate? 22 Synthesis of Amino Acid Derivatives Q7.3: What explains the observation that individuals with phenylketonuria have pigmented skin and hair considering that phenylalanine hydroxylase catalyzes the conversion of phenylalanine to tyrosine and tyrosine is the precursor to melanin pigments? RoundUp Ready crops are resistant to the herbicide RoundUp (glyphosate) because they carry a bacterial gene encoding a variant of the enzyme EPSP synthase, a required enzyme in amino acid biosynthesis. RoundUp Ready crops can be sprayed with the herbicide and survive, but encroaching weeds will die, thus leading to higher crop yields. Some data suggest that excessive use of glyphosate could be harmful to animals and moreover, glyphosate-­‐ resistant native plants will emerge (See pages 879-­‐881) Individuals with phenylketonuria (PKU) have pigmented skin and hair because they obtain tyrosine in the diet. This dietary tyrosine is converted to melanin pigments. It is true however that children with PKU are often light skinned and have a higher risk of skin cancer because dietary tyrosine my not be sufficient (see pgs 870-­‐871) 1 ...
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