What did I learn? Score Your Quiz (Module 5)

Alkaloids are found most commonly in the subclass of Angiosperms known as the dicots. Which of the following best describes the characteristics of a dicot?
1. Embryos bearing one cotyledon, parallel-veined leaves, 3-petaled leaves, and scattered vascular bundles
  Sorry, this is incorrect – this answer describes the characteristics of a monocot, such as the wild yam that produces a steroid-like compound that is used as the starting material to make progesterone used in birth control pills.
2. Embryos bearing one cotyledon, net-veined leaves, 4- or 5-petaled leaves, and vascular cylinders arranged in concentric rings
  Oops! Monocots have one cotyledon; the remaining characteristics describe a dicot.
3. Embryos bearing two cotyledons, parallel-veined leaves, 3-petaled leaves, and scattered vascular bundles
  Wrong. Although a dicot does have two cotyledons, the remaining characteristics describe a monocot.
4. Embryos bearing two cotyledons, net-veined leaves, 4- or 5-petaled leaves, and vascular cylinders arranged in concentric rings
  You are correct! Dicots, such as the opium poppy, tomatoes, and the oak tree, have two cotyledons, net-veined leaves, 4- or 5-petaled leaves, and vascular cylinders arranged in concentric rings within the plant stem. Remember, it is the dicots that most commonly produce alkaloids.
When extracting alkaloids from plants (either chemically or by smoking), why does the extraction process usually require an alkaline environment?
1. It shifts the equilibrium of the alkaloid molecule to favor the polar, charged form.
  Sorry, you got it backwards. The polar, charged form of alkaloids exists inside the watery and acidic environment of the vacuole.
2. It shifts the equilibrium of the alkaloid molecule to favor the non-polar, free base form.
  Good job – you are correct! Alkaloids exist predominantly in their polar or charged form inside the acidic environment of the vacuole. When the alkaloid is mixed in an alkaline solution (or environment), the equilibrium shifts the other way, in favor of the free base, which is non-polar or uncharged.
3. It shifts the equilibrium of the alkaloid molecule to favor the polar, free base form.
  Well, you’re partly correct. When the alkaloid is mixed in an alkaline solution (or environment), the equilibrium shifts in favor of the free base, which is non-polar or uncharged.
4. It shifts the equilibrium of the alkaloid molecule to favor the non-polar, charged form.
  You’re partly correct. When the alkaloid is mixed in an alkaline solution (or environment), the equilibrium shifts in favor of the free base, which is non-polar or uncharged.
Tobacco companies add ammonium hydroxide to the tobacco as it is prepared in the production of cigarettes. Why do they do this?
1. It makes the inhaled smoke taste better.
  No, the tobacco companies add other compounds (like menthol) to make the smoke taste better.
2. It keeps nicotine from degrading.
  Incorrect. Nicotine becomes degraded when it gets oxidized (especially if it is exposed to air).
3. It shifts nicotine into its more polar form, helping it to volatilize.
  You are partly correct. The base does help nicotine volatilize because it shifts it into its nonpolar form, which has a lower boiling point.
4. It shifts nicotine into its more non-polar form, helping it to volatilize.
  Great! Nicotine is an alkaloid, and addition of a base shifts the nicotine into its free base or nonpolar form, which has a lower boiling point. Thus it is easily volatilized.
Drugs have several targets with which they interact in the body to produce their effects. These targets include enzymes, receptors and transporters. They belong to the family of:
1. Lipids
  Sorry. This isn’t correct. Some lipids can interact with drugs, but these targets do not have the structure of lipids.
2. Carbohydrates
  Incorrect. Some carbohydrates can interact with drugs, but the chemical structure of these targets is much larger than that of a carbohydrate.
3. Proteins
  Hooray! Yes, enzymes, receptors and transporters are all macromolecular structures called proteins.
4. Nucleic Acids
  Well, you’re only right for the receptor. Actually, some nucleic acids in DNA can serve as a receptor for certain drugs. However, nucleic acids do not act as enzymes or chemical transporters.
Several forces enable the reversible binding of a charged drug to its receptor (or target). Which of the following describes the forces involved in 1) the initial attraction of a charged drug to its target and 2) the strengthening of the drug-target interaction?
1. electrostatic; hydrogen bonds
  Great! The initial attraction between a charged drug and its target is electrostatic, pulling the molecules together. Hydrogen bonds, the strongest form of van der Waals forces, help to strengthen and stabilize the interaction between the drug and its target, especially at close range.
2. hydrogen bonds; van der Waals forces
  Sorry, this is not entirely correct. The initial attraction between a charged drug and its target is electrostatic, pulling the molecules together. Van der Waals forces (hydrogen and dipole-dipole) help to strengthen and stabilize the interaction between the drug and its target, especially at close range.
3. van der Waals forces; electrostatic
  Sorry, this is backwards. The initial attraction between a charged drug and its target is electrostatic, pulling the molecules together. Van der Waals forces (hydrogen and dipole-dipole) help to strengthen and stabilize the interaction between the drug and its target, especially at close range.
4. electrostatic; covalent
  You’re partly right. The initial attraction between a charged drug and its target is electrostatic, pulling the molecules together. However, a covalent bond that might form by sharing a pair of electrons would prevent reversible binding between the drug and receptor.