Problem 784
A chemist has an \(\mathrm{E}\). coli bacterium cell of cylindrical shape. It is \(2 \mu\) (microns) long and ly in diameter and weighs \(2 \times 10^{-12} \mathrm{~g}\). (a) How many lipid molecules are present, assuming their average molecular weight to be 700 and lipid content to be \(2 \%\) ? (b) If the cell contains 15,000 ribosomes, what percent of the volume do they occupy? You may assume them to be spherical with a diameter of \(180 \AA\); also \(10_{4} \AA=1\) micron.
Problem 789
An \(\mathrm{E}\). coli cell is \(1.0 \mu\) in diameter and \(2.0 \mu\) long and may be assumed to be cylindrical. It contains \(80 \%\) water. If the intracellular \(\mathrm{pH}\) is \(6.4\), calculate the number of \(\mathrm{H}^{+}\) ions in a single cell.
Problem 791
At \(\mathrm{pH}\) values of 4 to 9 , natural amino acids exist as polar or zwitter ions: \(\mathrm{H}_{2} \mathrm{~N}^{+} \mathrm{CHZCO}^{-}{ }_{2}\). At a pH of 12 , what would be the predominant ionic type? What would it be at a \(\mathrm{pH}\) of 2? Can the uncharged molecular form, \(\mathrm{H}_{2} \mathrm{NCHZCO}_{2} \mathrm{H}\) ever predominate at any \(\mathrm{pH}\) ?
Problem 793
Paper electrophoresis at \(\mathrm{pH} 6.0\) was carried out on a mixture of glycine, alanine, glutamic acid, lysine, arginine and serine, (a) Which compound moved toward the anode? (b) Which moved toward the cathode? (c) Which remained at the origin?
Problem 794
To \(1.0\) liter of a \(1.0 \mathrm{M}\) solution of glycine at the isoelectric \(\mathrm{pH}\) is added \(0.3\) mole of \(\mathrm{HCl}\), What will be the \(\mathrm{pH}\) of the resultant solution? What would be the \(\mathrm{pH}\) if \(0.3\) mole of \(\mathrm{NaOH}\) were added instead?
Problem 800
In the Citric Acid Cycle (also known as the Krebs Cycle), citrate is converted to isocitrate. From the algebraic sign of \(\Delta \mathrm{G}^{\circ}\) for the isomerization, what is the favored or spontaneous direction of the reaction? Calculate \(\Delta \mathrm{G}^{\circ}\) for the following reaction and explain what bearing this reaction will have on the isomerization of citrate and the operation of the Krebs Cycle: Isocitrate \(^{3-}+(1 / 2) \mathrm{O}_{2}(\mathrm{~g})+\mathrm{H}^{\mathrm{f}} \rightleftarrows\) a ketoglutarate \(^{2-}+\mathrm{H}_{2} \mathrm{O}(\ell)+\) (g) \(\Delta \mathrm{G}_{\mathrm{f}}\) in \((\mathrm{Kcal} / \mathrm{mole})\) are for citrate \({ }^{3-}=-279.24\); \(\mathrm{CO}_{2}(\mathrm{~g}\) isocitrate \(^{3-}=-277.65 ; \mathrm{H}^{\mathrm{f}}=0, \mathrm{O}_{2}=0\) \(\alpha\) -ketoglutarate \(^{2-}=-190.62 ; \mathrm{H}_{2} \mathrm{O}(\ell)=-56.69\) \(\mathrm{CO}_{2}(\mathrm{~g})=-94.26\)
Problem 803
Cytochrome \(\mathrm{C}\) is a molecule with an iron-porphyrin head connected to a protein tail. Analysis shows the molecule is \(0.45\) percent iron by weight. Calculate the molecular weight of cytochrome \(\mathrm{C}\).
Problem 804
The hard shell of crustaceans (lobsters, etc,) and insects (roaches, etc.) is a polysaccharide called chitin. On enzymatic hydrolysis of chitin, \(\mathrm{N}\) -acetylglucosamine is obtained. This molecule resembles glucose except that at \(\mathrm{C}-2 \mathrm{a}-\mathrm{N}-\mathrm{C}^{\mathrm{O}}-\mathrm{CH}_{3}\) is attached instead of \(-\mathrm{OH}\). (a) Write an open chain formula for N-acetylglucos amine. (b) The structure of chitin is analogous to that of cellulose. Draw a formula containing two joined \(\mathrm{N}\) -acetyl- glucosamine units, (c) If the molecular weight of chitin is 150,000 , how many units are in the polymer?
Problem 806
If a membrane contains \(40 \%\) by weight of lipids and \(60 \%\) protein, calculate the molar ratio of lipids to proteins. Assume that the lipid molecules have an average molecular weight of 800 and the proteins an average molecular weight of 50,000
Problem 807
Most membranes of animal cells contain about \(60 \%\) protein and \(40 \%\) phosphoglycerides. (a) Calculate the average density of a membrane, assuming that protein has a density of \(1.2\left(\mathrm{~g} / \mathrm{cm}^{3}\right)\) and phosphoglyceride a density of \(0.92\) \(\left(\mathrm{g} / \mathrm{cm}^{3}\right)\). (b) If a sample of membrane material were centrifuged in \(\mathrm{NaCl}\) solution of \(1.05\) specific gravity, would it sediment or float?
