Download Bio102 Problems

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?
The membrane becomes too permeable because the additional heat causes faster motion of the
molecules.
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.
More saturated phospholipid tails (which is the same as fewer unsaturations).
Longer fatty acid tails on the phospholipids.
Either change reduces fluidity which thus reduces permeability.
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.
Either make it more unsaturated (or increase the number of double bonds) or make it shorter. Either
one decreases the London Dispersion Forces that hold the molecules together. Since they are held
together less well, it takes less energy (i.e. a lower temperature) to separate them.
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?
Increases Fluidity
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?
Blocks the sodium ion less well (or increases the permeability).
8. A phospholipid is made of a glycerol, a phosphate, a polar head group and two __fatty acids___.
9. Which of the three molecules shown below is most soluble in water? Why?
Glycerol (the one on the right) is most soluble as it has the most oxygen molecules and thus the
largest number of polar bonds.
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
amines
fatty acids
glycerol
phosphates
polar
‘head groups’
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
0
2
1
1
1
A triglyceride is built from
0
3
1
0
0
10B. These molecules are connected together by ___ condensation (or dehydration)_ reactions.
10C. In a eukaryote, these lipids are assembeled in what organelle? ____Smooth ER_________
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.
O
O
||
||
C-OH
C-OH
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.
Adding the unsaturated linderic acid would increase both the fluidity and permeability of the
membrane. This is because the greater bend or kink in the linderic acid means that the fatty acid tails
of the phospholipids will pack together less efficiently and thus have a lower density.
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.
Using longer fatty acid tails on the phospholipids would decrease both the fluidity and permeability of
the membrane. This is because adjacent fatty acids will weakly adhere to each other better by Van der
Waals interactions.
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?
By decreasing the amount of saturated fatty acids, the lipids will pack together less well and thus
increase their fluidity. Being more fluid means that they‟ll be a liquid to lower temperatures. Thus
the congealing temperature will fall.
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?
By lengthening the fatty acids, the lipids will stick together better and thus decrease their fluidity.
Being less fluid means that they‟ll be a solid to higher temperatures. Thus the congealing
temperature will rise.
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?
The question states that the oil is from plants and cholesterol is found only in animals. Cholesterol
makes the lipids less fluid, but raising the congealing temperature.