Cell Organization & Membranes
The random movement of molecules within a solution is referred to as:
diffusion
The interior region of a phospholipid bilayer is characterized as:
hydrophobic
Molecules that are _____________ and _____________ are able to move across the cell membrane via simple diffusion.
hydrophobic; small
Which of the types of molecules depicted in the figure is amphipathic?
integral membrane proteins, cholesterol, and phospholipids
As molecules move down their concentration gradient, from a more ordered state to a less ordered state, entropy:
is increasing
The image illustrates our understanding of how typical cell membranes are structured. Which line is pointing at a protein?
line A
The image illustrates our understanding of how typical cell membranes are structured. Which arrow is pointing at the hydrophilic head group of a phospholipid?
line B
The image illustrates our understanding of how typical cell membranes are structured. Which arrow is pointing at a cholesterol?
line D
Which eukaryotic organelle is associated with the breakdown of macromolecules?
lysosome
A protein that is temporarily associated with a biological membrane is a(n):
peripheral membrane protein.
The lipid components of cellular membranes often include:
phospholipids and cholesterol.
Some plant cells create a high concentration of protons outside the cell to move solutes, such as sucrose, across the plasma membrane into the cell where the sucrose concentration is already relatively high. This type of transport is an example of:
secondary active transport
Why does active transport of molecules across a membrane require ATP?
An input of energy is needed to allow the movement of molecules from an area of low concentration to one of higher concentration.
What would happen in the FRAP experiment if proteins did not move in the plane of a membrane?
An experiment showing that proteins move in membranes uses the fluorescence recovery after photobleaching (FRAP) technique. First, the proteins embedded in the cell membrane are labeled with a fluorescent dye. A laser is then used to bleach a small area of the cell surface so that it no longer fluoresces. Eventually, the fluorescently labeled proteins from other parts of the cell move into the bleached area and cause it to fluoresce once again. If the proteins did not move in membranes, that area would stay bleached over time.
A beaker is divided by a membrane that is permeable to water and glucose, but not to sucrose. Equal volumes of solutions are added to side A and B with the initial concentrations as shown below. Initially, the liquid levels on both sides are the same. After the system described above reaches equilibrium, what will be the concentration of glucose on side B?
0.75 M
T/F: Simple diffusion of a molecule down its concentration gradient requires an input of energy to the system.
False
How do eukaryotic plant and animal cells differ from one another?
Animal cells do not have chloroplasts and cell walls, and plant cells do.
During osmosis, water moves from a region of _____ to a region of _____
Both "high solvent concentration; low solvent concentration" AND "low solute concentration; high solute concentration" are correct answers.
The plasma membrane is composed of a phospholipid bilayer and associated proteins. What else is commonly found in the plasma membranes of animal cells?
Cholesterol
Which of the answer choices correctly describes the movement of water across a selectively permeable membrane during osmosis?
Either of these descriptions is correct and equivalent: The water will move from low solute concentration to high solute concentration. The water will move from high water concentration to low water concentration.
How do lipids with hydrophilic and hydrophobic regions behave in an aqueous environment?
In an aqueous environment, the polar hydrophilic head group readily interacts with the polar water molecules. In contrast, the nonpolar hydrophobic tail does not readily interact with water, but instead interacts with other nonpolar tail groups or hydrophobic molecules. For example, a micelle forms when the polar head group of a lipid interacts with water and they hydrophobic tails of the lipids interact with each other, excluding the water. Lipids can also form bilayers and liposomes.
Why is the transporter in the figure considered to be an example of "secondary transport"?
It is driven by the proton gradient that was created by energy from ATP.
Compare the organization, degree of compartmentalization, and size of prokaryotic and eukaryotic cells.
Prokaryotic cells lack a nucleus and extensive internal compartmentalization. They contain plasmids that carry additional genes that can be transferred to other bacteria. Prokaryotic cells are small (usually 1-2 micrometers in diameter or smaller). Because of their small size, they have a large surface-area-to-volume ratio, which means they are able to absorb nutrients from the environment to meet their metabolic needs. Eukaryotic cells have a nucleus and specialized internal structures called organelles. They are 10 times larger in diameter and 1000 times larger in volume than a prokaryotic cell.
What are two ways in which proteins associate with membranes?
Proteins can associate with membranes in the following ways. First, integral membrane proteins are permanently associated with the membrane and cannot be removed without destroying the membrane itself. Most integral membrane proteins span the cell membrane, so they have both hydrophilic and hydrophobic regions. Second, peripheral membrane proteins are temporarily associated with the membrane and can easily be experimentally separated. These proteins can be associated with either the internal or external side of the membrane. They are mostly hydrophilic and interact with the polar heads of the lipid bilayer, or the hydrophilic regions of integral membrane proteins.
Like cell membranes, many fats and oils are made up in part of fatty acids. Most animal fats (like butter) are solid at room temperature, whereas plant fats (like canola oil) tend to be liquid. Can you predict which type of fat contains saturated fatty acids, and which type contains unsaturated fatty acids?
Saturated fatty acids are less mobile within the membrane compared to unsaturated fatty acids. As a result, saturated fatty acids tend to be solid at room temperature, whereas unsaturated fatty acids tend to be liquid. Butter and many other animal fats contain saturated fatty acids and are solids, whereas many plant (and fish) oils contain unsaturated fatty acids and are liquids at room temperature.
A container is divided into two compartments by a membrane that is fully permeable to water and small ions. Water is added to one side of the membrane (side A), and a 5% solution of sodium chloride (NaCl) is added to the other (side B). If allowed to reach equilibrium, which of the answer choices would you predict?
The NaCl concentration on side A and side B will each be 2.5%
Although the phospholipid molecules can be in constant lateral movement, they very rarely flip from one side of the bilayer to the other. Which of the answer choices could explain this?
The head groups are repelled by the hydrophobic membrane interior
In the experiment that showed membrane fluidity, what was the purpose of shining a laser on the membrane?
The laser light destroys the dye fluorescence
A container is divided into two compartments by a membrane that is fully permeable to water but not to larger molecules. Water is added to one side of the membrane (side A), and an equal volume of a 5% solution of glucose is added to the other (side B). What would you predict will happen?
The water level on side B will increase and on side A will decrease.
A beaker is divided by a membrane that is permeable to water and glucose, but not to sucrose. Equal volumes of solutions are added to side A and B with the initial concentrations as shown below. Initially, the liquid levels on both sides are the same. After the system described above reaches equilibrium, what can you predict about the water levels?
The water will be higher on side A than on side B
A beaker contains two solutions of salt dissolved in water. The two solutions have different concentrations of salt (measured by molarity, M) and are separated by a membrane that is permeable to both salt and water. The salt and water will move through the membrane by diffusion. Which statement is true about the diffusion of these solutions?
There will be a net movement of salt from side B to side A and net movement of water from side A to side B.
If cells had single-layer membranes like micelles, how would the structures of transmembrane proteins be affected?
Transmembrane proteins would possess a hydrophobic region in the cell interior and a hydrophilic region in the extracellular space.
Which of the answer choices would be the best analogy for an electrochemical gradient across a cellular membrane? a water pump a light bulb a waterfall an electric generator a battery
a battery
A bacterial cell, a plant cell, and an animal cell have which structure in common?
a cytoplasm
In the image, an active transport proton pump drives protons out of the cell using energy from ATP. Under some circumstances pumps like this can be run in reverse. If this pump could be reversed, what would be the result in the cytoplasm?
a decrease in pH and an increase in ATP
The plasma membranes of some plant cells use transport proteins to move protons out of the cell against their concentration gradient. This is an example of
active transport
In the example illustrated here, a substance is moved _______ its concentration gradient using the energy of ______________
against; an electrochemical gradient
The defining characteristics of active transport are that this category of transport moves substances _________ their concentration gradient and requires ___________.
against; energy
Which molecules can easily diffuse across a plasma membrane?
gases like O2 and CO2
All cells have
genetic information
Which eukaryotic cell structure plays a role in protein trafficking and sorting?
the Golgi apparatus
Diffusion is best described as the random movement of molecules influenced by:
the thermal energy of the environment and energy transferred from molecular collisions in the cell.
T/F: At equilibrium, there will be no net movement of molecules across the cell membrane.
true
