Chapter 5 Learning Curve

A cell membrane is associated with many types of proteins. Which type of protein would most easily be removed from the cell membrane using aqueous conditions in a laboratory technique?

Peripheral membrane proteins

The process of diffusion leads to

achieving equilibrium of solute and solvent molecules in a solution.

In the signal cascade triggered by epinephrine in liver cells, glycogen phosphorylase is

activated and releases glucose

If a cell is bathed in an extracellular solution high in calcium ions, it would use _______ to maintain a normal, low intracellular concentration of calcium ions.

active transport against the concentration gradient of Ca2+

Osmosis, the movement of water though specialized membrane channels, is a specific form of

diffusion

The cell membrane contains carbohydrates, which can serve as recognition sites for other molecules. The carbohydrates may be covalently bonded to

lipids and proteins.

The main components in biological membranes are

lipids, proteins, and carbohydrates

Osmosis involves movement of water across membranes in the direction from a _______ to a(n) _______.

low concentration of solutes; high concentration of solutes

Characteristics of three different vesicles isolated from a cell are summarized in the table above. Which vesicle(s) would you expect to contain receptor proteins lining their interior walls?

B and C

Suppose a new signal transduction pathway has been discovered that may involve either an ion channel receptor or a G protein-linked receptor. Which procedure could provide information that could help distinguish between these two possibilities?

Check to see whether signal transduction is correlated with cell uptake of a small polar substance labeled with a radioisotope.

Suppose you have two identical solutions of glucose, called A and B. Both solutions are placed in a dish separated by a membrane that will allow the movement of both glucose and water. You want to establish a concentration gradient so that the glucose in B will move into A. How could you manipulate this setup so that the glucose will move in the desired direction?

Add more water to compartment A

Experiments were performed using mammalian cells having the primary function of secreting insulin into the blood. Because these cells secrete so much insulin, they have a high exocytosis rate as shown in the table above. Also shown are rates of endocytosis under control conditions and the effect of adding a clathrin antibody, which binds and removes clathrin proteins from participating in vesicle formation. In addition, since the cell membrane surface area increases as a result of exocytosis and decreases as a result of endocytosis, the amount of cell membrane recovered over the time period of data collection was determined under each condition. Based on these results, what conclusion can be drawn about these insulin-secreting cells?

Both b and d

How does facilitated diffusion by channel proteins differ from facilitated diffusion by carrier proteins?

Channel proteins form a pore through the membrane to allow substances to pass, whereas carrier proteins bind to and change conformation as they transport substances through the membrane.

Which molecule acts as a second messenger in the cascade by which epinephrine stimulates the activation of the enzyme glycogen phosphorylase?

Cyclic AMP

Which is a function of the proteins lining the extracellular surfaces of coated pits involved in receptor-mediated endocytosis?

Forming the receptors that bind a specific molecule

What are two benefits of having a cascade of cellular events during signal transduction?

Increased amplification of the signal and increased distribution of the signal

Cell membranes of root cells from broccoli plants were analyzed following 15-day exposure to no-salt or added-salt conditions. The results are summarized in the table above. The plants grew normally under both control and added-salt conditions. What do the results imply about cell membrane composition in response to salt stress?

It shifts toward greater unsaturated fatty acid content in order to withstand salt stress.

How could you distinguish between a signal transduction pathway that leads to an alteration in gene expression and a pathway that leads to an alteration in enzyme activity?

Look at the timing of the cellular response to signal molecules to determine whether the response is very fast or relatively slow.

Which sequence of amino acids in an integral membrane protein would most likely be found in the internal region of the cell membrane?

Phenylalanine, leucine, valine

There are two basic types of active transport. A main difference between them is that only one uses

a concentration gradient established by a previous reaction to drive transport

A cell will use carrier proteins to transport a compound across its cell membrane because the compound is

a reactant in an essential metabolic reaction that runs at a rate greater than the rate of simple diffusion.

A protein that forms an ion channel in a membrane is most likely to be

a transmembrane protein

Second messengers

are found in the cytoplasm

Persons with the inherited disease familial hypercholesterolemia have very high levels of cholesterol because of

deficient LDL receptor proteins that bind cholesterol in the liver.

Cells secrete materials to the exterior environment through the process of

exocytosis.

In biological membranes the lipid bilayer contains phospholipids, each with a head and two fatty acid tails. They are arranged so that the

fatty acid tails point toward each other.

Active transport moves molecules

in a direction opposite to the one in which diffusion would move them.

In the signal cascade triggered by epinephrine within liver cells, glycogen synthase is

inactivated and does not produce glycogen.

Epinephrine stimulates a G protein-mediated cascade within liver cells, resulting in phosphorylation of two enzymes: glycogen synthase and glycogen phosphorylase. This results in _______ glucose moving into the blood and _______ glycogen storage in liver cells.

increased; decreased

Protein movement within a membrane may be restricted by

interactions with cytoskeletal proteins on the membrane's inner face.

When a severely dehydrated patient is brought to the hospital, an intravenous drip of saline is started immediately. Sterile deionized water is not used because

it would cause the patient's blood cells to swell and eventually burst.

A molecule that binds to the particular three-dimensional structure of a receptor site is known as a(n)

ligand

The main difference between osmosis and diffusion is that

osmosis refers specifically to the movement of water across a membrane, whereas diffusion refers to the movement of any particles.

White blood cells can defend the body against invaders through

phagocytosis

The fluid mosaic model of a biological membrane suggests that the membrane is made up of discrete units that can move freely. Which components determine the fluidity of the membrane?

phospholipids and cholesterol

The function of the clathrin molecules that coat vesicles in receptor-mediated endocytosis is to

provide strength and stability

Mice having a genetic mutation that prevents the production of a protein called megalin were compared to healthy mice that produce normal amounts of megalin. Using the data shown in the table, it is likely that megalin is a(n)

receptor protein in kidney cells that binds and takes up vitamin B12 in receptor-mediated endocytosis to prevent its excretion in urine.

An important difference between phagocytosis and receptor-mediated endocytosis is that

receptor-mediated endocytosis is more specific.

Mammalian cells acquire specific macromolecules from their environment by the process of

receptor-mediated endocytosis.

A transmembrane protein may contain a long sequence of hydrophilic amino acids. If these were removed, the rest of the protein molecule would

remain inside the membrane.

If hydrolysis of ATP is temporarily blocked, the sodium-potassium pump will

remain unphosphorylated and unable to move Na+ out of the cell.

All of the following are ways that cells change in response to signals except

signal activation

Membrane fragments from different areas of a cell are constantly breaking down, moving, and in some cases fusing with other parts of a membrane. This is possible because of

the ability of lipids to spontaneously associate with one another.

If aquaporins are injected into the membranes of a cell that does not normally contain them,

the membranes will become more permeable to water.

All of the following affect the rate of diffusion of a substance except

the presence of other solutes in the solution

All of the following may be involved in facilitated diffusion except

ATP, which is used as an energy source

Which type of cellular response represents a long-term response to an external signal?

Activation of a gene expressing an enzyme

In the fluid mosaic model, some proteins are able to move freely within the membrane, while others, such as proteins in a muscle cell membrane, are anchored or restricted in their movement. What is the best explanation for a cell's restriction of some proteins to a specific region of the cell membrane?

A protein's function may depend on its presence in a specific location.

Which of the following statements about diffusion is false?

During diffusion, the cell membrane becomes increasingly less permeable to the diffusing substance.

If a person becomes dehydrated and needs to acquire dissolved solutes rapidly, which cellular process would likely be accelerated?

Pinocytosis

Acetylcholine is a small molecule involved in the transmission of nerve impulses from one neuron to another. Inside a neuron, acetylcholine moves from the cytoplasm into secretory vesicles, which then move to the cell membrane for release of acetylcholine into the extracellular medium. While investigating this process, a biologist observed that a hydrogen ion gradient was associated with acetylcholine secretory vesicles. In a series of experiments, the biologist tested both the formation of this hydrogen ion gradient and the uptake of acetylcholine into vesicles under various conditions. The conditions used and their corresponding results are summarized in the table above. Which acetylcholine transport mechanism is consistent with these data?

Secondary active transport

Cytoskeletal proteins are important for maintaining the structure of the cell, but some of their components also have other functions affecting the cell membrane. If cytoskeletal proteins were temporarily disrupted, what might take place in the cell membrane?

Some attached membrane proteins would detach and move freely.

The fatty acid composition of the intestinal cell membranes from three different fish species were analyzed. One species lives in Antarctic Ocean waters, another in the northern Atlantic, and the third in the Mediterranean Sea. Use the data to match each species with its native waters.

Species 1: northern Atlantic; Species 2: Mediterranean; Species 3: Antarctic

A cell requires movement of Substances 1, 2, and 3 from the extracellular medium into the cell to sustain life functions. Based on the information given in the table, which mechanisms would enable the cell to transport each substance, while maximizing conservation of its energy resources?

Substance 1: active transport; substance 2: facilitated diffusion; substance 3: simple diffusion

Which occurs during both endocytosis and exocytosis?

The cell membrane undergoes compositional change.

Suppose a shallow pan is filled with water and a drop of red ink is placed in one end of the pan and a drop of green ink is placed in the other end. Which condition can be predicted to exist once the system has reached equilibrium?

The red and green inks will be uniformly distributed throughout the pan.

Which statement is true about signal molecules?

The same signal molecule can target different cells in different ways.

Which can occur during both endocytosis and exocytosis?

The vesicle membrane is continuous with the plasma membrane.

Receptors bind noncovalently to their ligands according to the law of mass action. This means that

binding is reversible and dependent on ligand concentration.

Which of the following is the correct order of the molecules that are activated by a single molecule of epinephrine in liver cells, from lowest number of molecules to highest number of molecules?

cAMP, protein kinase A, phosphorylase kinase, glycogen phosphorylase

Channel proteins

can allow movement of substances either into or out of the cell.

Cell-to-cell adhesion often occurs through the interactions of

carbohydrates