Define Diffusion

1) Explain the significance of the equation for diffusion in the context of cell biology: t=x^2 / D

(a)  define diffusion in words and explain the symbols above

(b)  Explain what is important about the relationship in the equation and why this matters to how a cell works

2) Eukaryotic cells contain more complex intracellular structures than do many bacterial and archaeal cells. Using a specific example and explain how a cell structure helps eukaryotes overcome the challenges of diffusion limitation. For your specific example, describe how a “normal” ~1 um bacteria would accomplish that same function and predict how a giant bacteria (without this eukaryotic structure) could overcome diffusion issues.

3) Draw the outline of two spherical cells, a bacterial cell with a diameter of 1 μm and an animal cell with a diameter of 15 μm.

(a)  Which cell has a larger surface area to volume ratio? Calculate cell volume, cell surface area, and the surface area to volume ratio for each cell. Show your work.

(b)  List 3 important activities that happen at cellular membranes. Explain the importance of these activities to cellular physiology.

(c)  Calculate how the membrane surface area to volume ratio change if you included internal membranes in your calculation of the cell surface area? (Assume internal membranes have a surface area equivalent to 15x the area of the plasma membrane.)

(d) Explain and evaluate the following hypothesis: “Internal membranes allowed bigger cells to evolve,” using by integrating your answers to 4abc.

4) What is an active site? Are the key amino acids in the active site necessarily adjacent in the primary structure of the protein? Explain your answer.