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生物化学试题标准答案(2005秋季,A卷)
05 1. With regard to amino acids, which statement is false? A) Amino acids can act as proton donors and acceptors. B) All amino acids discovered in organism are L enantiomers. C) An L amino acid can be Dextrorotary. D) Non-standard amino acids can be found in the hydrolysis product of a protein. 2. In a highly acidic solution, pH = 1.3, the dominant form of glycine is: A) NH2-CH2-COOH;B) NH3+-CH2-COOH; C) NH2-CH2-COO–;D) NH3+-CH2-COO–. 3. In the isoelectric form of a tetrapeptide: A) The amino and carboxyl termini are not charged. B) Two internal amino acids of the tetrapeptide cannot have ionizable R groups. C) The total net charge is zero. D) Only the amino and carboxyl termini contribute charge. 4. Which would elute first from a gel-exclusion chromatographic column? A) a negatively charged protein of MW=40,000 B) a positively charged protein of MW=40,000 C) a protein at its isoelectric point of MW=30,000 D) a polysaccharide of MW=100,000 5. In an aqueous solution, protein conformation is determined by two major factors. One is the formation of the maximum number of hydrogen bonds. The other is the: A) formation of the maximum number of hydrophilic interactions. B) maximization of ionic interactions. C) minimization of entropy by forming a water solvent shell around the protein. D) placement of all hydrophobic amino acid residues within the interior of the protein. 6. You can destabilize a duplex DNA molecule in an aqueous solution by A) Decreasing the concentration of salt. B) Decreasing the concentration of organic solvents. C) Adjusting the pH to a value near 7. D) Adding a detergent. 7. With regard to DNA, which statement is false? A) Triple helix and tetraplex tend to appear at sites where replication, recombination or transcription is initiated or regulated. B) Hydrogen bonds are the only force to stabilize DNA structure. C) The absorbance of DNA at 260 nm will rise when it is denatured. D) Z-DNA tracts may play an role in the regulation of the
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