Bio102 Problems
Membranes
1. A phospholipid may contain all of the following EXCEPT for a
A. glycerol molecule.
B. staurated fatty acid molecule.
C. unsaturated fatty acid molecule.
D. hydrophillic “head” group.
E. triglyceride molecule.
2. Which one statement is NOT true about phospholipids?
A. Phospholipids are found only in the cell membrane of a eukaryotic cell.
B. Phospholipids are amphipathic.
C. Phospholipids may contain double bonds.
D. Phospholipids contain a negatively charged phosphate.
E. Phospholipids contain two fatty acid ‘tails’.
3. Which one molecule is NOT a lipid?
A. Cholesterol
B. Triglyceride
C. Glucose
D. Phospholipid
E. Fatty acid
4. Steroids like cholesterol are found only in
A. the plasma membrane.
B. the inner mitochondrial membrane.
C. animal cells.
D. the nuclear membrane.
E. prokaryotic cells.
5. By definition, an amphipathic molecule is one that
A. has one region that is hydrophobic and one region that is hydrophillic.
B. folds into a specific three-dimensional structure.
C. contains a glycerol molecule.
D. has one region that is positively charged and one region that is negatively charged.
E. contains at least one -sheet.
6. If the environmental temperature increases, it can kill a bacterial cell (which is prokaryotic).
Increased temperature can cause many problems for cells, including problems with the cell membrane.
A) What problem would increased temperature cause for a membrane?
B) The bacterial cell responds to the warmer environment by changing the lipids in its
membrane. Name two lipid changes that the cell could make to help it survive higher
temperatures and explain why the changes help it survive.
7A. Palmitoleic acid is a fatty acid that is composed of 16 carbon atoms and contains a single site of
unsaturation. Its melting point is 30oC. Describe one change that would decrease the melting point.
Please explain your answer.
7B. If this palmitoleic acid were part of a membrane, how would the modifiction that you described in
part 7A affect the fluidity of that membrane?
7C. If this palmitoleic acid were part of a membrane, how would the modifiction that you described in
part 7A affect the ability of the membrane to block the movement of Na+ ions?
8. A phospholipid is made of a glycerol, a phosphate, a polar head group and two ______________.
9. Which of the three molecules shown below is most soluble in water? Why?
H
H
H
H
H
C C
C H
H
H
H
H
H
H
O
H
C C
C H
H
H
H
H
H
O O O
H
C C
C H
H
H
H
polar
‘head groups’
phosphates
glycerol
fatty acids
amines
10A. Several complex lipids are assembled from smaller pieces. For both lipids below, indicate how
many of the smaller molecules are needed. In some cases, ‘zero’ is an appropriate answer.
A phospholipid is build from
A triglyceride is built from
10B. These molecules are connected together by ___ __________ reactions.
10C. In a eukaryote, these lipids are assembeled in what organelle? _______________________
11A. Lauric acid is a saturated fatty acid containing a total of 12 carbon atoms. Linderic acid is a fatty
acid with 12 carbon atoms and one unsaturation. Draw possible structures for lauric acid and linderic
acid in the space below. Be sure your drawing illustrates how the shapes of these two molecules are
different.
11B. Imagine a membrane built of lauric acid molecules only. What two key attributes of the
membrane would change if it was only half lauric acid molecules and half linderic acid molecules? Be
sure to refer to your structures in part A when explaining how and why these attributes change.
11C. How would a membrane built only of lauric acid change if it was built only of palmitic acid
molecules? (Palmitic acid has 16 carbon atoms). Be sure to explain your answer.
12. McDonald’s makes their french fries by deep-fat frying, which means that they put potatoes into a
very hot oil bath. The oil they use is derived from plants and containings a mixture of triglycerides:
50% of the fatty acids in the triglycerides are saturated, 20% have one unsaturation (monounsaturated)
and 30% have multiple unsaturations (polyunsaturated). All of these fatty acids are 16 carbon atoms
long. As you probably know, if the french fries cool enough, the oil congeals, or becomes a solid.
Being the inquisitive type, you decide to make some measurements and find that the oil congeals at
35ºC.
12A. If we changed the oil so that 30% of the fatty acids are saturated, 30% are monounsaturated
and 40% are polyunsaturated, what will happen to the temperature at which the oil congeals?
Why?
12B. If we changed the oil so that all the fatty acids are 18 carbon atoms long (but the
saturated/unsaturated percentages are unchanged), what will happen to the temperature at
which the oil congeals? Why?
12C. What clue in the question makes you positive that this oil contains no cholesterol? If we
added a little cholesterol to the oil, what will happen to the temperature at which the oil
congeals? Why?
13. Which one molecule is a sterol?
14. Which molecule is NEVER found as part of a phospholipid?
A. phosphate
B. sterol
C. saturated fatty acid
D. polyunsaturated fatty acid
E. glycerol
15. Each of the following five molecules contains six carbon atoms. Put the molecules in order of
hydrophobicity, labeling the most hydrophobic molecule “1” and the most hydrophillic molecule “5”.
_____
_____
______
____
______
16. Chlamydomonas are single-cellular eukaryotic plants that are commonly found in ponds in the
midwest. As the water temperature increases during, the Chlamydomonas cells need to modify the
molecules present in their membranes to cope with the warmer environment.
16A. Name two changes to the molecules in the plasma membrane that you expect to occur as the
temperature increases and briefly explain your reasoning.
16B. If a cell fails to make these modifications, why might this lead to it’s death?