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The exam is divided into 2 sections: Section A, essay answers, and section B, short answers.
Note that the topics covered in this exam may vary from term to term.
The following instructions are given in the preamble to the exam. Please read the questions carefully and try to organize your answer before you start to write. Please try to be concise and limit your remarks to the question asked.
60 points (15 points each). Each of these answers is restricted to about 1/2 page.
Answer 4 of the following 5 questions (1-5):
1. Explain what secondary compounds are, and differentiate between the terpenoids, alkaloids and phenolics.
2. Explain, in chemical terms, the difference between white rot and brown rot and why the white-rot organisms are of special interest in phytoremediation efforts.
3. Explain how toxic lectins such as abrin or ricin work.
4. Name at least 3 antinutritional factors that occur in plant food materials and describe how they work.
5. Take 2 of the alkaloids considered so far and explain how they work (what they do) at the molecular level.
40 points (8 points each). Each of these answers is restricted to about 4 lines.
6. Briefly, explain the meaning (and if appropriate, give an example) of any 3 of the following terms:
7. Briefly, explain the function of 2 of the following terms:
2. Explain, in chemical terms, the difference between white rot and brown rot and why the white-rot organisms are of special interest in phytoremediation efforts.
In white rot, the microorganisms breakdown the lignin first leaving the other constituents of wood, e.g., cellulose, which are white. Brown rot organisms break down the cellulose first leaving lignin, which is brownish.
The white rot organisms are able to attack and breakdown lignin which resembles many industrial waste chemicals, so it is hoped they can be used directly or modified to decompose some industrial wastes.
Go back to question 2 or go on to question 3.
6d. Glycoside and aglycone. A glycoside is a derivative of a sugar, where the second molecule, usually an alcohol, has combined with the OH in a hemiacetal produced from the carbonyl group. See the diagram below. If this second molecule is not a sugar, it is called an aglycone.
Go back to question 6d or go on to question 7.
3. Explain how toxic lectins such as abrin or ricin work.
Abrin and ricin are made up of two subunits, A (effectomer) and B (haptomer). The B chain binds to sugars in the glycocalyx on the cell membrane causing the membrane to become fluid and allow the A chain to enter the cell. The A chain then inhibits protein synthesis
Some students noted that lectins are proteins, other than antibodies, that specifically recognize and bind to sugars. This is good, but not required.
Go back to question 3 or go on to question 4.
5. Take 2 of the alkaloids considered so far and explain how they work (what they do) at the molecular level.
Obviously, there are huge number of possibilities here, but some examples are:
Morphine - acts as an endorphin analog and stimulates the pleasure centers of the brain
Colchicine - binds to tubulin and disrupts cell division
Nicotine - binds to certain acetycholine receptors (nicotinic) and opens K+ channels in the cell membrane in certain nerve cells.
Pyrrolizidine alkaloids - after bioactivation in the liver, these bind to DNA causing mutations, cancer and even cell death at high doses.
Go back to question 5 or go on to question 6.
6c. Phytolith. A silicate deposit on plant surfaces, especially leaves. These "plant stones" have very characteristic forms, and they are very persistant.
Go back to question 6c or go on to question 6d.
7b. Pheromones are chemical signals/communications used between different individuals of the same species. For example, the female gametes of the marine alga Ectocarpus release a pheromone that attracts the male gametes.
Go back to question 7b or go on to question 7c.
4. Name at least 3 antinutritional factors that occur in plant food materials and describe how they work.
Plants produce a wide variety of factors that decrease their nutritional quality or make their nutrients unavailable when they are released during feeding by herbivores.
Examples: Thiaminase, which breaks down the B vitamin thiamin, occurs in the ferns bracken and nardoo.
Protease inhibitors, such as the Kunitz inhibitor, occur in soybean and many other seeds.
Tannins are also antinutritional factors, because they bind to proteins and make them more difficult to digest.
Go back to question 4 or go on to question 5.
7a. Oxalates serve to protect plant tissues from herbivores. They are stored in vacuoles as crystals or solubilized. The crystals may act as spears and physically damage cells. The soluble forms bind to divalent cations such as Ca+2 and make them available for use in cell metabolism.
Go back to question 7a or go on to question 7b.
6a. Cuticle. The cuticle is a waxy covering over plant surfaces, especially leaves. It is made up mainly of long chain, hydrophobic alcohols and fatty acids which may be linked together as esters.
Go back to question 6a or go on to question 6b.
1. Explain what secondary compounds are, and differentiate between the terpenoids, alkaloids and phenolics.
Secondary compounds are formed outside primary metabolism (e.g., glycolysis).
Terpenoids, alkaloids and phenolics are major classes of secondary compounds, and they are primarily secondary compounds. The terpenoids are constructed from 5C units (isoprenes or isopentane). Phenolic compounds contain a six-membered aromatic ring with at least one OH group. The alkaloids contain a heterocyclic ring with an N; the N makes them weakly alkaline.
Go back to question 1 or go on to question 2.
6b. Dietary fiber consists of soluble components (e.g., pectins and gums) and insoluble components which are very diverse (e.g., microfibrils, lignin and cuticle).
Go back to question 6b or go on to question 6c.
7c. Gibberellins are plant hormones (chemical signals between cells within a plant), and they often regulate stem elongation or the formation of digestive enzymes in seeds.
Go back to question 7c or go back to question 1 or return to the Biology 415 Home Page.