Question 1

Which of the following statements about a G protein signaling pathway is true?

Accepted Answer

A G protein signaling pathway involves a G protein-coupled receptor binding to a ligand, which activates the receptor and causes it to exchange GDP for GTP on the G protein. The G protein, now bound to GTP, is in its active state and can activate downstream effector molecules. Hydrolysis of the bound GTP by the G protein inactivates it and allows it to bind GDP again, returning it to its inactive state.

Question 2

Which of the following is a type of local signaling in which a cell secretes a signal molecule that affects neighboring cells?

Accepted Answer

Paracrine signaling involves the secretion of signal molecules that affect nearby cells. It is a local signaling method that allows cells to communicate with one another in a specific area. Hormonal signaling involves signal molecules being transported through the bloodstream to distant cells, while autocrine signaling involves cells signaling themselves. Synaptic signaling involves signal molecules being transmitted across a synapse between neurons.

Question 3

Scientists have found that extracellular matrix components may induce specific gene expression in embryonic tissues such as the liver and testes. For this to happen, there must be direct communication between the extracellular matrix and the developing cells. Which kind of transmembrane protein would most likely be involved in this kind of induction?

Accepted Answer

Integrins are transmembrane proteins that form a link between the extracellular matrix and the actin cytoskeleton of the cell. They are known to be involved in cell signaling and can activate intracellular signaling pathways, which can lead to changes in gene expression. Therefore, integrins are the most likely transmembrane protein involved in the induction of gene expression by extracellular matrix components in embryonic tissues like the liver and testes.

Question 4

Why does testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affect only target cells?

Accepted Answer

Testosterone affects only target cells because intracellular receptors for testosterone are present only in target cells. These receptors allow testosterone to bind and initiate a series of biochemical reactions that ultimately lead to changes in gene expression and cellular function. Non-target cells do not have these receptors, so they are not able to respond to testosterone in the same way.

Question 5

In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?

Accepted Answer

Cell signaling plays a crucial role in the aggregation of bacteria that can cause cavities, which is a key aspect of biofilm formation on unbrushed teeth.

Question 6

What is the most likely mechanism by which testosterone functions inside a cell?

Accepted Answer

Testosterone is a steroid hormone and is known to bind to intracellular receptors. These receptors are found in the cytoplasm and upon binding, they translocate to the nucleus and bind to specific DNA sequences called hormone response elements (HREs). Binding of the hormone-receptor complex to the HREs results in the activation of gene expression, leading to the biological effects of testosterone.

Question 7

Many G protein-coupled receptors contain seven transmembrane α-helical domains. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would you expect to find the carboxyl end of the protein?

Accepted Answer

Since the amino end of the protein is located at the exterior of the plasma membrane, it follows that the carboxyl end of the protein must be located at the cytosolic surface of the membrane, opposite to the amino end.

Question 8

Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. Which of the following conditions is required for the target organ to respond to a particular hormone?

Accepted Answer

The target organ must have receptors that recognize and bind the hormone molecule. This is because hormones act like keys that must fit into specific locks in order to have a physiological effect. Once the hormone binds to its respective receptor, it triggers a cascade of physiological responses within the target organ.

Question 9

In yeast signal transduction, a yeast cell releases a mating factor, which ________.

Accepted Answer

The yeast cell releases a mating factor that binds to receptors on the membranes of other types of yeast cells, initiating signal transduction and leading to the mating process. The other options are incorrect as they do not accurately describe the process of yeast signal transduction.

Question 10

Yeast cells of mating type a are genetically engineered to produce only mating factor α instead of the normal mating factor a. The gene for the mating factor receptor was unaltered. How will these engineered cells behave in terms of mating?

Accepted Answer

The engineered cells will still produce their own mating factor α, but their mating receptor remains unaltered, which means they can receive mating signals from both the normal mating type a cells and other engineered cells. However, they will not be able to respond to the mating factor α produced by normal mating type α cells, which means they will not mate with them. Therefore, option C is correct.

Question 11

Use the following figure to answer the question.

Which of the following types of signaling is represented in the figure?

Accepted Answer

The answer of Use the following figure to answer the...

Question 12

Many G protein-coupled receptors contain seven transmembrane α-helical domains. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would a coupled G protein most likely interact with this receptor?

Accepted Answer

The loop between helices 5 and 6 is usually the site of interaction for a coupled G protein. This is because it is longer and more flexible than the other loops, making it easier for the G protein to bind and initiate signaling.

Question 13

In which of the following ways do plant hormones differ from hormones in animals?

Accepted Answer

Plant hormones can travel through the air as gases, such as ethylene, which is a gaseous plant hormone. Animal hormones typically travel through the bloodstream rather than through gap junctions, and they are not limited to being local regulators.

Question 14

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?

Accepted Answer

G proteins rely on GTP for their activation, so if a cell loses the ability to produce GTP, it would not be able to activate G proteins on the cytoplasmic side of the plasma membrane. This would impair the signaling system of the cell.

Question 15

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?

Accepted Answer

Glycogen breakdown was observed only when epinephrine was administered to intact cells, suggesting that an intracellular second messenger was necessary for the effect.

Question 16

Which of the following statements describes a likely effect of a drug designed that inhibits the cellular response to testosterone?

Accepted Answer

Testosterone signaling plays a role in gene transcription. Inhibiting the cellular response to testosterone would decrease the transcription of certain genes that are regulated by testosterone.

Note: choices A, C, and D are not directly related to testosterone signaling and are unlikely effects of inhibiting the cellular response to testosterone.

Question 17

One of the major categories of receptors in the plasma membrane functions by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?

Accepted Answer

Receptor tyrosine kinases (RTKs) form dimers upon ligand binding, leading to autophosphorylation of its tyrosine residues. This activation allows the RTK to activate downstream relay proteins, initiating signal transduction in the cell.

Question 18

Use the following figure to answer the question.

In the figure, the dots in the space between the two structures represent which of the following?

Accepted Answer

The answer of Use the following figure to answer the...

Question 19

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

Accepted Answer

Ligand-gated ion channels directly open in response to the binding of a signaling molecule, allowing ions to flow across the membrane and changing the distribution of ions on opposite sides of the membrane. Receptor tyrosine kinases activate a signaling pathway through phosphorylation, G protein-coupled receptors activate second messenger systems, and steroid receptors directly affect gene expression.

Question 20

When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?

Accepted Answer

The neurotransmitter is serving as the signal molecule in this scenario, as it is the molecule that is transmitting the signal between neurons.

Quiz 11: Cell Communication