Chapter 1, Problem 1.3PS

QUANTITATIVE Sizing Things Up. To appreciate the sizes of the subcellular structures shown in Figure 1-3b, consider the following calculations:

(a) All cells and many subcellular structures are surrounded by a membrane. Assuming a typical membrane to be about 8 nm wide, how many such membranes would have to be aligned side by side before the structure could be seen with the light microscope? How many with the electron microscope?

(b) Ribosomes are the cell structures in which the process of protein synthesis takes place. A human ribosome is a roughly spherical structure with a diameter of about 30 nm. How many ribosomes would fit in the internal volume of the human liver cell described in Problem 1-2 if the entire volume of the cell were filled with ribosomes?

(c) The genetic material of the Escherichia coli cell described in Problem 1-2 consists of a circular DNA molecule with a strand diameter of 2 nm and a total length of 1.36 mm. To be accommodated in a cell that is only a few micrometers long, this large DNA molecule is tightly coiled and folded into a nucleoid that occupies a small proportion of the cell’s internal volume. Approximating the DNA molecule as a very thin cylinder, calculate the smallest possible volume the DNA molecule could fit into, and express it as a percentage of the internal volume of the bacterial cell that you calculated in Problem 1-2a.