Unformatted text preview: Amino Acid Metabolism Problem Set Reading: Chapters 23 and 24 Problems: Chapter 23- 10, 11, 12, 13, 18 Then try these: 1. What is the function of leghemoglobin in plants with root noodles that contain nitrogen-fixing bacteria? Why is it not surprising that leghemoglobin has a structure similar to hemoglobin and myoglobin? Leghemoglobin binds O2 that would otherwise inhibit the bacterial nitrogenase that is required for nitrogen fixation. Leghemoglobin has a similar function as hemoglobin and myoglobin, so it is not surprising that it has a similar structure. 2. While the catabolic pathways differ, all 20 amino acids are converted to one of 7 metabolites: acetyl-CoA, acetoacetate, oxaloacetate, pyruvate, - ketogluterate, succinyl-CoA, or fumarate. What is the metabolic fate of each of these intermediates? Acetoacetate is a ketone body and can either be secreted from the liver and metabolized by other tissues or it can be converted to acetyl CoA and used for fatty acid synthesis. Under conditions of low energy charge, the rest will continue through the citrate cycle and be oxidized to CO2 and water. Under high-energy charge, acetyl CoA becomes a substrate for fatty acid synthesis or ketone body synthesis. The rest can be converted to oxaloacetate and be used to make glucose via gluconeogenesis. 3. What are the sources of the 2 nitrogens and the carbon in urea? One nitrogen comes from amino acid catabolism in the mitochondria (likely glutamate) and the other one comes from aspartate entering the urea cycle in the cytoplasm. The carbon comes from carbon dioxide (converted to biocarbonate ion) released during the citrate cycle. 4. Glyphosate, also known as Round-Up , is an herbicide that kills plants by inhibiting an enzyme in the amino acid biosynthetic pathway responsible for phenylalanine synthesis. Would it be safe to use glyphosate in areas where farm animals may accidentally eat plants that have been sprayed? Explain. Yes it would be safe because animals do not have the enzyme pathway to synthesize phenylalanine (unlike plants) and would therefore be unaffected by glyphosate (animals obtain phenylalanine from their diet). Phenylketonuriacs are not albinos because they obtain tyrosine from the diet and are not dependent on tyrosine production from phenylalanine. 5. Individuals with type 1 albinism have a mutation in gene encoding the tyrosinase enzyme and thus cannot convert tyrosine to melanin precursors. Individuals with phenylketonuria (PKU) cannot synthesize tyrosine from phenylalanine, do they also suffer from albinism? Explain. ...
View Full Document
This note was uploaded on 05/06/2010 for the course BIOC 460 taught by Professor Ziegler during the Spring '07 term at Arizona.
- Spring '07