Homework set #2
BENG 100
Spring 2008
Due:
January 31, 2008
From Chapter 5
1.
A spherical cell with the diameter of 10
μ
m has a protein concentration of 20 mg/ml.
Determine the number of protein molecules within the cell if the molecular weight of
an average protein is 50,000 Daltons(g/mol).
Recall that Avogadro’s number is N
A
=
6.0221367 x 10
23
molecules/mol.
2.
The sphere, cylinder and rectangular parallelepiped are common shapes that could be
used to model different living cells.
Assume that you have 3 cells, a sphere, a
cylinder, and a rectangular parallelepiped.
Each cell has the same volume (1
μ
m
3
),
and the radius of the sphere and the cylinder are equal to the width of the two sides of
the rectangular cell.
a.
What are the surface / volume ratios for these shapes?
b.
Which shape is better? Why?
c.
Why might a given weight of small cells be more metabolically active than the
same weight of large cells?
(Assume the density is constant)
d.
Does the answer in (c) change if you compared an equal number of cells (rather
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 Spring '08
 MarkSaltzman
 Bacteria, DNA

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