Chapter 5 Mastering Biology

What are the functions of signal transduction pathways?

- Signal transduction pathways convert a signal on a cell's surface to a specific cellular response. - Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. - Signal transduction pathways amplify the effect of a signal molecule.

Which of the following sequences is/are correct?

- binding of a growth factor to its receptor → phosphorylation cascade → activation of transcription factor → transcription - binding of a signaling molecule to its receptor → G protein activation → adenylyl cyclase activation → cAMP production → protein phosphorylation - diffusion of a signaling molecule across the plasma membrane → binding of the signaling molecule to its receptor → movement of the signaling molecule-receptor complex into the nucleus → transcription

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature

Which of the following statements is TRUE with regard to this animation of active transport?

Both sodium and potassium ions are transported against their concentration gradients. (Both ions are transported from where their concentration is low to where their concentration is high, and the cell expends energy in the form of ATP to do it.)

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur. - Solution A: 3.21% (m/v) NaCl - Solution B: 1.65% (m/v) glucose - Solution C: distilled H2O - Solution D: 6.97% (m/v) glucose - Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl

Crenation: A, D, E Hemolysis: B, C

Why are there often so many steps between the original signal event and the cell's response?

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

Which of the following correctly describes some aspect of exocytosis or endocytosis?

Exocytosis and endocytosis change the surface area of the plasma membrane.

Following activation of a receptor, which sequence below represents the correct order in which components will be involved in a signaling pathway that utilizes the second messenger cAMP?

G protein → adenyl cyclase → cAMP → protein kinase

What kind of solution is a cell in if there is a greater concentration of solute outside of the cell?

Hypertonic

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic (The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.)

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

It exhibits a specificity for a particular type of molecule.

How can a lipid be distinguished from a sugar?

Lipids are mostly nonpolar.

Select the correct statement about osmosis.

Osmosis is the diffusion of water molecules across a selectively permeable membrane.

Which of the following particles could diffuse easily through a cell membrane?

Oxygen (O2)

Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways.

Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.

Which statement is correct?

The contents of a red blood cell are hyperosmotic to distilled water. A solution of seawater is hypertonic. (The red blood cell has a greater solute concentration than distilled water, which means that its contents are hypertonic to distilled water.)

How do unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

The double bonds form kinks in the fatty acid tails that prevent adjacent lipids from packing tightly together.

A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water equal to the volume of blood lost − is transferred directly into one of his veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells.

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids

In facilitated diffusion, what is the role of the transport protein?

Transport proteins provide a hydrophilic route for the solute to cross the membrane.

True or false? Osmosis is a type of diffusion.

True.

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True.

Which of the following molecular movements is due to diffusion or osmosis?

When a plant cell is placed in concentrated salt water, water moves out of the cell.

Which of the following factors would tend to increase membrane fluidity?

a greater proportion of unsaturated phospholipids

Which of the following would increase the electrochemical gradient across a membrane?

a proton pump

Immediately following binding of a growth factor, an activated receptor would most likely stimulate ________.

activation of a protein kinase.

What is the function of a transport protein?

allow solute molecules to enter the cell.

An integral membrane protein would have to be ________.

amphipathic, with at least one hydrophobic region.

The fluid mosaic model of the membrane proposed that membranes ________.

consist of protein molecules embedded in a fluid bilayer of phospholipids.

The sodium-potassium pump is called an electrogenic pump because it _______.

contributes to the membrane potential.

The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?

cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis

Which of the following is least likely to be important in holding the components of a biological membrane together?

covalent interactions between the phospholipid and protein components of the membrane

A primary function of cholesterol in the plasma membranes of some animals is to ________.

enable the membrane to stay fluid more easily when the temperature drops.

What is the function of cholesterol?

helps to stabilize the structure of the plasma membrane (phospholipids)

Which of the following is a substance that acts at a long distance from the site at which it is secreted?

hormone

You know that this cell is in a(n) _______ solution because it _______.

hypertonic ... lost water (A cell will lose water when placed in a hypertonic solution.)

You know that a cell is in a(n) _______ solution because the cell _______.

hypotonic ... swelled (A cell will gain water when placed in a hypotonic solution.)

Endocytosis moves materials _______ a cell via _______.

into ... membranous vesicles

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect ONLY target cells because __________.

intracellular receptors are present only in target cells

Water passes quickly through cell membranes because _______.

it moves through aquaporin channel proteins.

Which of the following enzymes adds a phosphate group to target proteins?

kinase

A signal molecule is also known as a(n) _______.

ligand

What is the voltage across a membrane called?

membrane potential

What name is given to the process by which water crosses a selectively permeable membrane?

osmosis

A white blood cell engulfing a bacterium is an example of _______.

phagocytosis

The difference between pinocytosis and receptor-mediated endocytosis is that _______.

pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis is highly selective.

A signal transduction pathway is initiated when a _______ binds to a receptor.

signal molecule (The binding of a signal molecule to a receptor initiates a signal transduction pathway.)

You can recognize the process of pinocytosis when _______.

the cell is engulfing extracellular fluid

Submerging a red blood cell in a hypertonic solution will result in _______.

the cell wall shriveling.

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________.

they amplify the original signal manifold

Which of these is the second of the three stages of cell signaling?

transduction

Which of the following best describes the structure of a biological membrane?

two layers of phospholipids with proteins either crossing the layers or on the surface of the layers

Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?

water, glucose, hydrogen ion