Dimensions of an E. coli cell: a cylinder 2 m long and 1 m in diameter Under opt
ID: 207629 • Letter: D
Question
Dimensions of an E. coli cell: a cylinder 2 m long and 1 m in diameter Under optimal conditions for growth, an E. coli cell will divide around every 20 minutes. If no cell died, how long would it take a single E. coli cell, under optimal conditions in a 10L culture flask, to reach its maximum cell density of 1010 cells/mL (a "saturated" culture)? Assuming that optimum conditions could be maintained, how long would it take for the same 1010 cells/mL density to be reached in a 200,000L fermenter (this is the size of the large fermentation processes)? 1. 2. Many proteins in E. coli are normally present at concentrations of 2 molecules per cell. What is the molar concentration of such a protein? The DNA of an E. coli chromosome measures 1.6 mm in length, when extended, and 20A in diameter. What fraction of an E. coli cell is occupied by its DNA? 3. 4. Draw the hydrogen bonding pattern that water forms with acetamide (CH3CONH2) and with pyridine (benzene with a CH group replaced by N) "Inverted" micelles are made by dispersing amphipathic molecules in a nonpolar solvent, such as benzene, together with a small amount of water (counter-ions are also provided if the head groups are ionic). Draw the structure of an inverted micelle and describe the forces that stabilize it 6. Explain why the mobility of H in ice is only about an order of magnitude less than that in liquid water, whereas the mobility of Na* in solid NaCl is zero 7. The volume of a typical bacterial cell is on the order of 1.0 . At pH 7, how many hydrogen ions are contained inside a bacterial cell? A bacterial cell contains thousands of macromolecules, such as proteins and nucleic acids, that each bear multiple ionizable groups. What does your result indicate about the common notion that ionizable groups are continuously bathed with H and OH ions? 8. Many soil bacteria have GC rich genomes. When cloning genes from these GC-rich bacteria, higher DNA melting temperatures and higher primer annealing temperatures must be used. Why do you think this would be the case compared to template DNA that is not as GC predominant? 9. Explain why it is critical that both A-T and G-C basebairs are both 10.85A wide.Explanation / Answer
1. Under optimal conditions for growth, an E. coli cell will divide around every 20 minutes. If no cell died, how long would it take a single E. coli cell, under optimal conditions in a 10L culture flask, to reach its maximum cell density of 10 10 cells/mL (a “saturated” culture)? Assuming that optimum conditions could be maintained, how long would it take for the total volume of the cells alone to reach a 200,000L fermenter (this is the size of the large fermentation processes)?
10L*1000mL/L*10 10 cells/mL=10 14 cells 2 n =10 14 cells n=14/log2=46.5 doublings 46.5 doublings*20min/doubling = 930min * 1hr/60min = 15.5hrs 2000,000L * 100mL/L * 10 10 cells/mL=10 17 cells 2 n =10 17 cells n=17/log2=56.5 doublings*20min/doubling = 1130min * 1hr/60min = 18.8hrs
2. Many proteins in E. coli are normally present at concentrations of 2 molecules per cell. What is the molar concentration of such a protein?
Volume of E. coli cell = (1 × 10 –6 m/2) × 2 × 10 –6 m × 10 3 L·m –3 = 1.57 × 10 –15 L
Number of moles of the protein in an E. coli = 2 molecules/6.02 × 10 23 molecules·mol –1 = 3.32 × 10 –24 mol
The molar concentration of such a protein = 3.32 × 10 –24 mol /1.57 × 10 –15 L = 2.11 × 10 –9 M
3. The DNA of an E. coli chromosome measures 1.6 mm in length, when extended, and 20Å in diameter. What fraction of an E. coli cell is occupied by its DNA?
Volume of E. coli cell = × (1 × 10 –6 /2) 2 × 2 × 10 –6 m 3 = 1.57 × 10 –18 m 3
Volume of DNA = × (20 Å × 10 –10 m·Å –1 /2) 2 × 1.6 mm × 10 –3 m/mm = 5.03 × 10 –21 m 3
Fraction of an E. coli cell is occupied by its DNA= 5.03 × 10 –21 m 3 /1.57 × 10 –18 = 3.20 × 10 –3
6. Explain why the mobility of H + in ice is only about an order of magnitude less than that in liquid water, whereas the mobility of Na + in solid NaCl is zero.
In NaCl, Na + and Cl – ions are rigidly held in a crystalline lattice, so they are immobile in an electric field. The same case is with water molecules in a crystal of ice. As water molecules in ice are oriented with their OH bonds pointing at neighboring water molecules and the protons can easily jump from molecule to molecule. The apparent mobility of protons in ice is comparable to that in liquid water due to same mechanism of proton migration in both phases....