(Turn in your answers on these pages. Hard copies only.
Electronically submitted papers will not be graded.)
You may consult with other students on these problems but the work you present
must
be your own. You may use calculators on the homework , but they will not be
allowed on
exams. (Get used to adding and subtracting exponents .)
Note: when doing chemical calculations show the equations used and include the
cancelled units. (ex. 3 X 102 g/ X 10-3 /l = 3 X 10-1
g)
If you don’t show the
equations and units you will not get credit.
Remember 1 μM = 10-3 mM = 10-6 M.
1) The smallest known living organisms are eubacteria
known as mycoplasma. Some are only 0.3 μm
in diameter. To appreciate their size answer the following. (Volume of sphere =
4/3 π r3 and cylinder = π
r2 h.) Remember 1 cm3 = 1 cc = 1 ml. You may assume π = 3
for your calculations.
a) What is the internal volume of a mycoplasma in ml? How does this compare to
the common
cylindrical intestinal bacterium E. coli which has a diameter of 1 μm and a
length of 2 μm?
b) Bacterial (and organellar) ribosomes are roughly
spherical and 25 nm in diameter. E. coli has about
35,000 ribosomes. Assuming ribosomes can occupy no more than 20% of the internal
volume of cell,
how many ribosomes could fit in a mycoplasma?
c i) Assuming the glucose concentration in a typical mycoplasma is 1.0 mM, how
many molecules of
glucose are present in a mycoplasma cell? (Hint, if you can use 3 for π, what
should you use for
Avogadro’ s number ?)
cii) Most compounds are present in cells at much lower
concentrations than glucose. NAD, for example,
is typically present at about 2 μM. How many molecules of NAD are present in a
mycoplasma cell?
d) If there were 80 protons in the cytoplasm of a mycoplasma what would be the
approximate pH?
e) The genetic information to build a mycoplasma is
encoded in a single DNA molecule with a molecular
weight of 2 X 108. What fraction of the weight of a mycoplasma does
the DNA molecule represent?
(Assume the density of a mycoplasma cell to be 1.1 g/cm3.)
f) The MW of a base pair of DNA is about 640. About how many base pairs of DNA
are in a mycobacterial
genome?
g) “Nanobes” are tiny structures first found in rock
samples in deep
sea beds off Australia. Their sizes are quite variable , but they can be
as small as 20 nm in diameter and 100 nm in length. Some
investigators believe them to be living things, while others think them
mineral growths.
The discoverers of nanobes reported that they contain DNA based on
their ability to react with chemicals that bind DNA (The chemicals are
not terribly specific for DNA). Consider the size of the nanobes. Do
you think the claim that they have DNA strengthens the case they are
living things, or does it cause you to question the thinking of the
investigators? Explain your reasoning and express your opinion
about whether nanobes are plausible life forms?
For fun, not for credit, you may want to
consider the case of the reputed
microfossils present in the Martian meterorite ALH84001. These are
similar in size to nanobes and have been touted by some as compelling
evidence of extra-terrestrial life. Most biologists reject the claim.
Prominent among the myriad reasons--they are simply too small.
Dr. Neil deGrasse Tyson, a prominent and able public advocate of
science, has dismissed the size argument with something akin to, ‘if it’s an
ALIEN life form, how can they know what’s too small?’ Do you think Tyson’s
point was carefully considered or was it a knee-jerk reaction? Think about what
kinds of problems alien
cells would have to confront and what kinds of “things” such cells could be made
up of. Would the
problems be similar or different from those confronting terrestrial organisms.
What might be similar or
different between the structural/functional components of the cells.
2) Milk sugar or lactose is a disaccharide consisting of
one molecule of galactose joined to glucose by a
β-1,4 linkage. Draw the structure of lactose. (Consult Panel 2-3 for structures)
3) Which of the following organisms will have the highest
percentage of unsaturated fatty acids in the
phospholipid membranes? Circle one answer and briefly explain your
choice. (Careful...)
a) freshwater eel in Lake Superior
b) Mohave desert rattlesnake
c) human
d) polar bear
e) Antarctic dwelling archaea
