C2005/F2401 '06 Answers to Recitation Problems #2 1. Hint: Consider which molecules (or parts thereof) are hydrophobic or hydrophilic.

Answer: Phospholipid: the glycolipid has the same structure as a phospholipid except that it has a different hydrophilic (polar) group. It has 3 groups attached to glycerol as in a P-lipid. The polar group attached to the glycerol is (galactose) instead of the phosphate or phosphate ester group of the phospholipid; the nonpolar groups attached to the glycerol (2 fatty acids) are the same as in a phospholipid.

2. Hints:
A. What differences in properties are exploited by each of these methods?
B. How do the properties of asp (aspartic acid) and gln (glutamine) compare? Which method is most likely to take advantage of these differences?
C. Where does the carbon in aspartate (aspartic acid)* come from (in minimal medium)?

* The terms 'aspartate' and 'aspartic acid' are used interchangeably by most biochemists. Strictly speaking, 'aspartate' is the ionized form and 'aspartic acid' is the un-ionized form. In solution, at most pH values, you have a mixture of the two.

Answers:
2A. Method of Fingerprinting (meaning a 2D separation, using chromatography in one direction and electrophoresis in the other). This is the best bet because it combines the separation power of both paper chromatography and paper electrophoresis. Next best: paper chromatography, since it separates on the basis of small differences among the amino acids in their solubility in organic solvents.

Note: The term "fingerprinting" usually refers to the 2D separation of peptide fragments, that is, the separation of the products of partial hydrolysis of a protein. "Fingerprinting" usually does not refer to the separation of amino acids.
Why? If you hydrolyze proteins completely to amino acids, and separate the amino acids, almost every protein will give the same pattern or "fingerprint" -- almost every protein will give the same 20 spots corresponding to the same 20 amino acids. On the other hand, if you partially hydrolyze a protein and separate the peptide products, each protein will usually give a unique pattern of spots corresponding to a unique mixture of peptides.
What is meant by "method of fingerprinting," in this case, is the application of the fingerprinting procedure (that is, a 2D separation) to a mixture of amino acids.

2B. Paper electrophoresis at pH 12, since asp will have a net charge of -2 while gln will have a net charge of -1, OR paper chromatography using a different pH and or organic solvent than the first paper chromatographic separation. Paper electrophoresis at pH 2 would not work because both molecules would have a net charge of +1.

2C. 20. All the carbons of aspartate are derived from glucose (the only source of C in the minimal medium). The glucose contained 30 units per mole, and had 6 carbons, all equally labeled, so there are 30/6 = 5 radioactivity units per carbon atom (per mole of each carbon atom) in glucose. Aspartate has 4 carbon atoms, or 4 moles of carbon atoms per mole of aspartate. Each carbon derived from glucose has 5 units of radioactivity. Four carbons, at 5 units each, yields 5 X 4 = 20 radioactivity units per mole of aspartate.

3. Hints:
A. Is the glucose L or D? If the picture shows an alpha glucose, what does a beta glucose look like?
B. Would the sugar-sugar connects be straight across or at an angle?
C. What determines the overall shape of a polysaccharide chain?
D. What are the products of complete hydrolysis? Will any of them isomerize?

Answers:
3A. Equatorial to equatorial. C1 is equatorial in beta glucose (axial in alpha). All the other OH’s are equatorial in glucose, as can be seen in the structure of D glucose, the natural isomer.

3B. A helix but not like starch. The 1.3 connection, while allowing the connected monomer sugar chairs to occupy the same plane, nevertheless forces the polymer to turn a corner at each connection, since carbons 3,1, 3 (or 1, 3, and 1) do not lie in a straight line. The polymer will thus curve and turn on itself, forming a helix. The alpha 1,4 turn in starch is more
extreme, not allowing the sugars to exist in the same plane, and starch has the 1,6 branches, which make it even more compact. The inability to form straight chains that can line up with each other to form a bundle of polymers makes curdlan unlike cellulose. Thus it has an intermediate physical character.

3C. Carbon #5. The C5 OH is positioned so that when it swings around and approached C1, it can form a bond to the C1 carbon. The C1 double bond opens up and a hydroxyl is formed on the C1 O.
Another way to reason it without having to remember that it is the C5 OH that attacks: Inspection of the ring structure
shows that the ring O lies between carbons 1 and 5, so the O must have come from either C1 or C5. The anomeric carbon is number 1, which has a carbonyl (C=O) in the straight chain form. It is this double bond that is attacked by a hydroxyl to form the ring. After this attack, the carbonyl O becomes a hydroxyl, so that is not the one in the ring, so it must be the C5 OH that becomes the ring O.

3D. A carbonyl, beta-D-glucose, alpha-D-glucose, carbon with tetrahedral bonds, monomers. The free D-glucose would be comprised of an equilibrium mixture of the straight chain form (containing an aldehyde, which has a carbonyl), and the alpha and beta anomer ring forms. No L-glucose would form: one would have to break and reform the bonds between the hydroxyls and carbons at positions 2, 3 and 4 for that transformation to occur. No dimers or glycosidic bonds would be left as these are what is destroyed by the hydrolysis. The D-glucose monomers would be the products.

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