23.Theifern(btwn DNAand RNA is (re) deoxyribose sugars rather than ribose DNA RNA D) Two of the above are t uses uraci All of the above are true Ans:E 2AAahnian2anmmeasonehEaceseadnm6tvs natura s on Ear R Amino acids are of the(R)configuration Amino acids are of the(S)configuration. 9 Amino acids are not chiral. Amino acids are meso compounds. Amino acids easily change configuration. Ans:B 25.Which attractive force is responsible for maintaining the tertiary structure of proteins? lvgen Disulfide linkages D) hobic interactions C) Salt bridges Ans:E .Which then nown as(PKU) ryptophan B) D)Proline E) valin Ans:C 27.Which of the following statements is not true of amino acids? A) They are less acidic than carboxylic acids. 2) ney are so w would show an IR absorption near 3300 cm Ans:D Page7Page 7 23. The difference(s) between DNA and RNA is (are): A) DNA incorporates 2-deoxyribose sugars rather than ribose. B) RNA is smaller than DNA. C) DNA uses thymine, RNA uses uracil. D) Two of the above are true. E) All of the above are true. Ans: E 24. Although traces of racemic amino acids have been found in meteorites, nearly all naturally occurring amino acids on Earth have the stereochemistry shown. What is true of this stereochemistry? (Assume R = alkyl) R C H CO2H NH2 A) Amino acids are of the (R) configuration. B) Amino acids are of the (S) configuration. C) Amino acids are not chiral. D) Amino acids are meso compounds. E) Amino acids easily change configuration. Ans: B 25. Which attractive force is responsible for maintaining the tertiary structure of proteins? A) Disulfide linkages D) Hydrophobic interactions B) Hydrogen bonds E) All of these C) Salt bridges Ans: E 26. Which amino acid is responsible for the condition known as phenylketonuria (PKU) which occurs in a small fraction of the population? A) Tryptophan B) Histidine C) Phenylalanine D) Proline E) Valine Ans: C 27. Which of the following statements is not true of amino acids? A) They are less acidic than carboxylic acids. B) In acid solution (pH ~ 2) they would show an IR absorption near 1720 cm-1 . C) They are soluble in water but not in non-polar organic solvents. D) They are more basic than amines. E) In basic solution (pH ~ 12) they would show an IR absorption near 3300 cm-1 . Ans: D