Question 1

Vascular endothelial growth factor (abbreviated VEGF and pronounced "Veg-F") is a peptide signaling molecule related to platelet-derived growth factor. VEGF is important in the formation of the circulatory system because its signaling pathway causes the formation of new blood vessels in developing embryos during normal development. Tumors also produce and secrete VEGF, causing the formation of new blood vessels that supply these tumors. Given what you know about the different kinds of cell signaling and about VEGF, is VEGF a paracrine or an endocrine-signaling molecule? Justify your answer.

Accepted Answer

The answer of Vascular endothelial growth factor (abbreviated VEGF and...

Question 2

Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors?

Accepted Answer

Large, nonpolar molecules are likely to be membrane impermeable and unable to enter eukaryotic cells to directly interact with components of the signal transduction pathway or affect transcription within the nucleus. They are, however, able to interact with the hydrophobic regions of cell surface receptors and interfere with receptor activation or signal-receptor binding, thus inhibiting the normal signaling pathway.

Question 3

You create a cell that has a mutation in a receptor protein that binds a signaling molecule, which is also produced by the same cell. When you overexpress the signaling molecule produced by this cell, nothing happens. What is defective in this cell?

Accepted Answer

The mutation in the receptor protein suggests that the signaling molecule produced by the cell is an autocrine signal that binds to receptors on the same cell. Overexpressing this signal should have an effect on the cell's behavior, unless the receptor is no longer functioning properly due to the mutation. This indicates a defect in autocrine signaling.

Question 4

Which of the following types of cell signaling generally occurs between cells that are distant from each other?

Accepted Answer

Endocrine signaling generally occurs between cells that are distant from each other, often through the release of hormones into the bloodstream. Paracrine signaling occurs between cells that are in close proximity to each other, while autocrine signaling occurs when a cell signals itself.

Question 5

Of the choices below, what is the MOST likely reason that paracrine signaling does not activate the cell that is producing the signaling molecule?

Accepted Answer

Paracrine signaling involves the secretion of signaling molecules that diffuse locally to nearby cells. For the signaling molecule to activate the cell that produced it, that cell would need to have receptors for that specific signaling molecule. However, it is more common for neighboring cells to have the appropriate receptors, while the cell producing the signal does not. Thus, choice C - the cell does not have the proper receptor - is the most likely reason that paracrine signaling does not activate the cell that is producing the signaling molecule.

Question 6

Which of the following is a type of cell communication where the signaling molecule is released by the same cell that responds to the signal?

Accepted Answer

Autocrine signaling involves a cell secreting a signaling molecule that binds to receptors on the same cell, causing the cell to respond to the signal.

Question 7

The differentiation of embryonic stem cells into neurons and glial cells is a consequence of which type of cell signaling?

Accepted Answer

The answer of The differentiation of embryonic stem cells into...

Question 8

Recall from the text the example of cell communication in Streptococcus pneumoniae: The rate of DNA uptake by pneumococcal cells increases sharply when they are at high density, due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor proteins, how would the rate of DNA uptake be affected when the cells reach high density?

Accepted Answer

The answer of Recall from the text the example of...

Question 9

A cell can only respond to signals from other cells, not from the physical environment.

Accepted Answer

Cells can respond to signals from both other cells and the physical environment. For example, skin cells can respond to physical stimuli such as touch or temperature, while immune cells can respond to signals from other cells in the body to fight off infection.

Question 10

Vascular endothelial growth factor (abbreviated VEGF and pronounced "Veg-F") is a peptide signaling molecule related to platelet-derived growth factor. VEGF is important in the formation of the circulatory system because its signaling pathway causes the formation of blood vessels in developing embryos during normal development. Tumors also produce and secrete VEGF, causing the formation of new blood vessels that supply these tumors. Given what you know about the different kinds of cell signaling and VEGF, which one of the following statements is TRUE?

Accepted Answer

VEGF is a paracrine signaling molecule because it acts locally on cells at the site where new blood vessels are needed, rather than circulating through the bloodstream like an endocrine signaling molecule.

Question 11

Which of the following CORRECTLY lists the types of cellular communication from shortest to longest distance traveled by the signaling molecule to reach its responding cell?

Accepted Answer

Autocrine signaling involves cells targeting themselves, paracrine signaling targets nearby cells, and endocrine signaling involves hormones traveling through the bloodstream to distant cells, thus from shortest to longest distance: autocrine, paracrine, endocrine.

Question 12

Platelet-derived growth factor (PDGF) is a signaling molecule that functions in which of the following types of cell signaling?

Accepted Answer

PDGF primarily functions in paracrine signaling, where it is released by cells to affect nearby target cells.

Question 13

Many diseases are the result of a problem with cell signaling. Which of the following diseases BEST exemplifies this fact?

Accepted Answer

Cancer cells often have mutations in cell signaling pathways, including receptors and their downstream effectors. A truncated receptor that becomes stuck in the activated form would result in constant signaling, leading to uncontrolled cell growth and division. The other options involve problems with membrane transport (cystic fibrosis), cardiovascular function (congestive heart failure), or receptor function (familial hypercholesterolemia), but are not caused specifically by cell signaling abnormalities.

Question 14

The first event that happens after a signaling molecule binds to a receptor is:

Accepted Answer

The first event that happens after a signaling molecule binds to a receptor is that the receptor becomes activated. It then undergoes a conformational change that allows it to transmit the message to the inside of the cell, where signal transduction pathways can take place and ultimately lead to a cellular response. The termination of the signal comes later in the process.

Question 15

Which type of cell signaling does not rely on the diffusion of a chemical signal molecule?

Accepted Answer

Contact-dependent signaling involves direct physical contact between cells, rather than the diffusion of a chemical signal molecule. Paracrine signaling involves the diffusion of molecules over short distances. Autocrine signaling involves cells responding to signals they themselves produced, which requires some diffusion. Endocrine signaling involves the release of hormones into the bloodstream for distribution throughout the body, which also requires diffusion. Therefore, only contact-dependent signaling does not rely on the diffusion of a chemical signal molecule.

Question 16

Which of the following is TRUE about the Delta protein?

Accepted Answer

Delta is a transmembrane protein found in embryonic brain cells (A), produced by embryonic stem cells as they differentiate into neurons in the brain (B), and directly signals to a Notch transmembrane protein in adjacent cells (C). Delta directs adjacent cells to differentiate into glial cells (D).

Question 17

Types of steroids include:

Accepted Answer

All of these choices are correct. Steroids include sex hormones such as estrogen and testosterone, glucocorticoids that regulate blood glucose levels, insect molting hormones, and lipid-soluble hormones derived from cholesterol.

Question 18

In many signaling pathways, once a signaling molecule binds to a receptor, the receptor becomes phosphorylated. This initial phosphorylation step BEST demonstrates:

Accepted Answer

Phosphorylation of the receptor is the first step in activating the receptor, allowing it to initiate the downstream signaling pathway. This is known as receptor activation.

Question 19

A researcher introduces a signal produced by bacteria to eukaryotic cells that she is culturing in the laboratory. Remarkably, she notices that this signal results in an increase in eukaryotic gene expression. How is this possible?

Accepted Answer

It is likely that the signal produced by bacteria is similar in structure to a ligand used by eukaryotes or that the signaling pathway is used by both prokaryotes and eukaryotes. This would allow the prokaryotic signal to bind to eukaryotic receptors and activate gene expression pathways in the eukaryotic cells.

Question 20

Communication between neurons is an example of which type of cell signaling?

Accepted Answer

Communication between neurons is primarily an example of paracrine signaling, where neurotransmitters are released from one neuron and affect nearby neurons.

Quiz 9: Cell Signaling