Bio102 Problems
Fluid Mosaic Model
1. A peptide bond is formed by a(n) ___________.
A. dehydration reaction
B. equilibrium reaction
C. hydrogen bond
D. hydrolysis reaction
E. disulfide bond
2. Which one of the following is an example of a secondary structure?
A. Beta Sheet
B. Triglyceride
C. Double Helix
D. Disulfide Bridge
E. Peptide Bond
3. Which one statement accurately describes condensation reactions?
A. Condensation reactions are used to break down polymers into monomers.
B. Water is consumed during condensation reactions.
C. A condensation reaction is the same thing as a hydrolysis reaction.
D. Condensation reactions can be used to connect amino acids with peptide bonds.
E. Condensation reactions are used to connect phospholipids together to make a cell membrane less
permeable.
4. Which one force does NOT contribute to the tertiary structure of a protein?
A. Hydrogen bonding
B. Micelle interactions
C. van der Waals interactions
D. Disulfide bridges
E. Ionic interactions
5. Which one of the following forces does NOT contribute to tertiary structure?
A. Hydrogen bonds
B. Amphipathic bonds
C. Disulfide bonds
D. Van der Waals (hydrophobic) interactions
E. Ionic bonds
6. Which one of the following does NOT contribute to the secondary structure of a protein?
A. Hydrogen bonding
B. Activation energy interactions
C. Hydrophobic interactions
D. Ionic bonding
E. Disulfide bridges
7. Not all proteins have quaternary structure. This is because not all proteins
A. contain peptide bonds.
B. have quaternary amines.
C. contain at least one disulfide bridge.
D. contain the amino acid quaternine.
E. bind another protein.
8. The fluid mosaic model of membrane structure predicts that the plasma membrane
A. prevents the destruction of the cell by osmosis.
B. is more fluid than the cell membrane.
C. restricts the lateral movement of phospholipids.
D. forms a rigid structure to prevent the loss of important molecules.
E. contains proteins.
9. Which of the following might have a secondary structure?
A. Phospholipid
B. Cholesterol
C. Amino Acid
D. Tyrosinase
E. Peptide Bond
10. If a protein is amphipathic it is likely
A. to be made of many amino acids.
B. found in a membrane.
C. to have quaternary structure.
D. to be an enzyme.
E. to be at or near it’s Vmax value.
11. Protein fill-in-the-blank:
A. The “back” end of a protein is better called the ___Carboxy terminus_______.
B. Individual units are held together by this special type of covalent bond: __Peptide bond__.
C. A protein is a polymer of many __amino acids__________.
D. An -helix is one type of ___secondary structure_.
12. We’ve drawn biological membranes as two layers of phospholipid molecules (shown as a circle
with two tails) with large protein blobs (shown below as a striped ‘T’).
Protein
This membrane has an aqueous (or water-based) solution on both sides. Imagine that we took this
membrane and instead of having it in water, we placed a hydrophobic liquid on both sides. How
would the membrane structure change? Include both phospholipids and the protein shown above in
your drawing.
13 Show the chemical structures of the three groups attached to the central carbon of an amino acid.
H
H
H-N-
O
C
-C-OH
Side
Group
13B The ‘front’ end of a protein is better known as the _ Amino- (or N-) terminus __.
13C An -helix (alpha-helix) is an example of a type of __Secondary_________ structure.
13D. Two amino acids are joined together with what type of bond? ___Peptide Bond_______
13E. On what cellular structure are these bonds synthesized? _____Ribosome_______
14. In a fully functional hemoglobin molecule, four individual proteins are associated with one
another. If we increase the sodium concentration to 0.5M, the four proteins separate into individual
proteins. Which type of structure has been disrupted?
A. Primary
B. Secondary
C. Tertiary
D. Quaternary
15. Each of the following four forces helps to stabilize the secondary and tertiary structure of a
protein. Which one is the strongest force?
A. Ionic interaction
B. Disulfide bond
C. Hydrophobic interaction
D. Hydrogen bond
16. The image on the right is Figure 7.2 from your textbook, with some additional
labels added.
16A. Would the G value for moving the circled phospholipid from its
current position to “position A” be positive, negative or zero? Why?
Zero. The phospholipid is equally stable (and thus has the same
level of free energy) at either position
16B. Would the G value for moving the circled phospholipid from the
innerlayer (position A) to the outer layer (position B) of the membrane be
positive, negative or zero? Why?
Zero. The phospholipid is equally stable (and thus has the same level of free energy) at
position.
B
A
either
16C. Which of these two movements happens faster? Why?
The movement to “A” happens faster because it has a much lower activation energy
17. Using a very clever labeling technique, cell biologists can covalently modify the proteins in one
region of a cell’s plasma membrane. Shown on the right is a
human white blood cell. Suppose that we use this technique to
‘label’ all the plasma membrane proteins in the circle shown on
the diagram. Those proteins now glow red under a special type
of microscope. Immediately after labeling, only the circle
glows bright red. Five minutes after labeling, all of the left half
of the cell glows a dim red. Thirty minutes after labeling, the
entire cell glows pink.
17A. Please briefly explain why the red glow slowly spreads
across the surface of the cell.
The red-labeled proteins diffuse away from this spot as
predicted by the fluid mosaic model
17B. The major fatty acid found in the phospholipids of this
cell is oleic acid, which is 18 carbon atoms long and has one unsaturation. If the major fatty acid
was instead linoleic acid (18 carbon atoms, two unsaturations), how would this have changed the
outcome of the experiment? Specifically, what do you think the cell would
minutes after labeling one spot? Please explain your reasoning.
look
like
five
The red label would diffuse away from the one spot more rapidly. Thus, after five minutes the
entire cell may be pink
18A. Shown below are the structures of three amino acids. Draw the structure of the small protein:
N terminus – Leucine – Serine – Aspartic Acid – C terminus
H O
H O
H
| ||
| ||
|
H2N—C—C—NH—C—C—NH—C—COOH
|
|
|
CH2
CH2OH
CH2COOH
|
CH3-CH-CH3
Aspartic Acid
Leucine
Serine
18B. Which of these three amino acids is most hydrophobic? ____Leucine___
19. Which of the following molecules is an amino acid? Circle all that apply.
20. A region of a protein that contains lots of amino acids with hydrophobic side chains is likely…
A. a -sheet.
B. a transmembrane domain.
C. an allosteric site.
D. a triacylglyceride.
E. an active site.
21. In the lab, we’ve been studying the Fluid Mosaic Model by using living yeast cells. Using some
sophisticated instruments, we determine that integral membrane proteins move at a rate of
10m/second at room temperature (25oC).
21A. What would happen to the rate of movement of this integral membrane protein if we
increased the the temperature to 37oC? Please briefly explain your answer.
It’s rate of lateral movement would increase because at higher temperatures the membrane
becomes more fluid
21B. -sitosterol is a molecule made by most plants and it’s
structure is shown on the right. If we simply add sitosterol to the liquid around the yeast cells, it becomes
part of the cell membrane. Why doesn’t it stay in the liquid
outside of the cells?
Nearly all of this molecule is highly hydrophobic and thus
very unstable in the aqueous liquid outside of the cells. It
is much more stable when dissolved in the hydrophobic zone of the cell membrane.
21C. What effect will the addition of -sitosterol to the membrane have on the rate of movement of
the integral membrane proteins at room temperature? Please briefly explain your answer.
It should decrease it.  -sitosterol is a sterol (like cholesterol) and thus it decreases the fluidity of
membranes.
21D. We can also measure the rate at which ethanol (CH3-CH2-OH) crosses the cell membrane.
Will adding  -sitosterol increase or decrease the rate at which ethanol moves? Why?
It will decrease ethanol’s movement across the membrane since decreases in fluidity are always
associated with decreases in permeability.
21E. Name two modifications of the fatty acids present in the phospholipids that would decrease
the rate at which the integral membrane proteins moves. For both modifications, what effect would
this have on the rate of movement of ethanol across the membrane? You do not need to explain
your reasoning for this answer.
Modification
Effect on ethanol movement rate
longer fatty acids
decrease
more saturated fatty acids
decrease
22. The three dimensional structure of a functional hemoglobin protein is shown below.
22A. Four different proteins are held together in this
structure. Because of that, we know that this protein
has __quaternary____ structure.
22B. Name the four types of molecular forces that may
contribute to holding these proteins together.
 Disulfide bonds
 Ionic interactions


Hydrogen bonds
Hydrophobic interactions
22C. Which one of the four forces from 22B is a covalent bond?
Disufide bons
22D. The structure of hemoglobin contains many spiral or spring-like structures that I’ve magnified
and isolated below the big structure. What is the name of this structure? It’s an example of what
level of protein structure?
-helix. Secondary structure
22E. The ‘back’ end of a protein is better known as the ______Carboxyl terminus_______.