生化习题及答案.doc

1. The artificial sweeteners Equal and Nutrasweet contain aspartame, which has the structure:What are the two amino acids that are components of aspartame? What kind of bond links these amino acids? What do you suppose might happen if a solution of aspartame was heated for several hours at a pH near neutrality? Suppose you wanted to make hot chocolate sweetened only with aspartame, and you stored it in a thermos for several hours before drinking it. What might it taste like?2. Individuals with phenylketonuria must avoid dietary phenylalanine because they are unable to convert phenylalanine to tyrosine. Look up this condition and find out what happens if phenylalanine accumulates in the body. Would you advise a person with phenylketonuria to consume foods sweetened with aspartame? Why or why not?3. Separation of Amino Acids by Ion-Exchange Chromatography Mixtures of amino acids can be analized by first separating the mixture into its components through ion exchange chromatography。 Amino acids placed on a cation exchange resin containing sulfonate (-SO3-) groups flow down the column at different rates because of two factors that influence their movement: (1) ionic attraction between the sulfonate residues on the column and positively charged functional groups on the amino acids, and (2) hydrophobic interactions between amino acid side chains and the strongly hydrophobic backbone of the polystryrene resin. For each pair of amino acids listed, determine which will be eluted first from the cation-exchange column at pH 7.0 buffer.(a) Asp and Lys(b) Arg and Met(c) Glu and Val(d) Gly and Leu(e) Ser and Ala4. Identify. Examine the following four amino acids (AD):What are their names, three-letter abbreviations, and oneletter symbols?5. Match each amino acid in the left-hand column with the appropriate side-chain type in the right-hand column.6. Solubility. In each of the following pairs of amino acids, identify which amino acid would be most soluble in water:(a) Ala, Leu; (b) Tyr, Phe; (c) Ser, Ala; (d) Trp, His.7. Which of the following amino acids have R groups that have hydrogen-bonding potential? Ala, Gly, Ser, Phe, Glu, Tyr, Ile, and Thr.8.Name those components. Examine the segment of a protein shown here.(a) What three amino acids are present?(b) Of the three, which is the N-terminal amino acid?(c) Identify the peptide bonds.(d) Identify the -carbon atoms.1（1）由天冬氨酸和苯丙氨酸构成。 （2）两个氨基酸有肽键相连。 （3）如果加热，该蛋白质会变性。 （4）若将其加入到热咖啡，热咖啡不会变甜，因为加热会使该蛋白质变性，使其内部结构受到破坏，生物活性丧失。2.该病人不能吃。因为上面的糖精中含有苯丙氨酸