10. Cell Signaling

Types of Cell Signaling

Active, Passive, and Bulk Cell Transport

 No. Thromboxane is not a neurotransmitter. 

 No. Synthesis of mRNA is being neither promoted nor inhibited. 

 No. A protein kinase transfers a phosphate group from ATP to a protein. 

No. Thromboxane A2 is not a G protein.

Consider the site of the secretion relative to the site of action.

When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example, thromboxane A2 is acting as a __________.

Intracellular Signaling / Second Messenger System

 numerous cells can receive and respond to a signal produced in their vicinity 

 No. The type of signal described is called a local regulator. 

 the signal can be directed to a very specific target because a narrow space separates the target cell from the transmitting cell 

 No. This type of signal is common in the nervous system, where cells are separated by a synapse. 

 a concentration gradient between the signaling cell and its target cells is established, causing cells along the gradient to respond in different ways 

 No. Hormonal recognition requires a specific receptor, which is activated when the appropriate hormone is present. 

 special molecules are passed through cell junctions 

 No. Although this type of communication occurs, the molecules passed in this fashion are not hormones. 

 specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected 

Consider how hormonal signaling differs from other signaling modes such as paracrine signaling.

Cells use different signaling strategies to achieve different goals. In hormonal signaling, __________.

You have been hired as a field assistant for a researcher interested in the evolution of flower characteristics in orchids. Design an experiment to determine whether color, size, shape, scent, or amount of nectar is the most important factor in attracting pollinators to a particular species. Assume that you can change any flower’s color with a dye and that you can remove petals or nectar stores, add particular scents, add nectar by injection, or switch parts among species by cutting and gluing.

Indirect Cell Signaling: Paracrine vs Endocrine

 No. Nitric oxide does not enter the cell via a protein channel. 

 No. Nitric oxide activates an enzyme that produces a second messenger (cGMP). 

 binds to membrane receptors and cytoplasm receptors 

 activates proteins by removing phosphate 

Consider how nitric oxide differs from other signal molecules discussed in the chapter.

Nitric oxide is unusual among animal signal molecules in that it __________.

 In a typical cell, calcium ions are far more abundant in the cytoplasm than in the blood and other extracellular fluid. 

 No. Actually, the cytosolic concentrations of calcium are generally very low. 

 In a typical cell, calcium ions are rapidly transported into the endoplasmic reticulum in response to G-protein-mediated signals. 

 No. In fact, calcium is often released from the endoplasmic reticulum in response to G-protein-mediated signals. 

 In a typical cell, calcium ions are not very widely used as second messengers. 

 No. Actually, just the opposite is true. 

 All of the listed responses are correct. 

 No. Only one of the choices is correct. 

 In a typical cell, calcium ions are often concentrated within the endoplasmic reticulum. 

Calcium concentrations in the cytosol are typically very low.

Which of the following statements about calcium ions in a typical cell is true?

 kill other yeast cells nearby, which may be competing for access to food 

 No. The &alpha; factor molecule is a signal molecule. 

 kill bacteria nearby, which may be competing for access to food 

 attract other yeast cells of the same mating type to assemble 

No. The &alpha; factor is a signal molecule that causes yeast cells of the opposite mating type, a, to grow toward &alpha; cells.

 enzymatically process food into a form that can be easily absorbed 

stimulate cells of the opposite mating type, a yeast cells, to grow toward the &alpha; cell

This molecule is involved in a type of mating.

Certain yeast cells secrete a molecule called the &alpha; factor. The purpose of this molecule is to __________.

Video 1: Intercellular Signalling

 Apoptosis typically involves only a single signaling pathway. 

 No. Apoptosis typically involves multiple signaling pathways. 

 Apoptosis occurs randomly during embryonic development of a nematode. 

 No. Apoptosis occurs at defined times during the embryonic development of a nematode. 

 Apoptosis is triggered only by signals from outside the cell. 

 No. Apoptosis can be triggered by signals from outside or inside the cell. 

 No. Only one of the listed responses is correct. 

 Apoptosis is essential for normal development of the nervous system. 

Apoptosis is controlled cell suicide.

Which of the following statements about apoptosis is true?

Cell Physiology: Cell Signaling

Produced and secreted by the target cell. 

Secreted by cells close to the target cell.

Secreted by nerve cells across a synapse.

Secreted by cells far from the target cell.

Paracrine signaling is characterized by signaling molecules (ligands) that are _______:

Direct Cell Signaling

Cell Signaling Types (Paracrine, Endocrine, Juxtacrine, ...)

Which of the following types of signaling is represented in the figure?<img src="https://static.studychannel-prd.pearsonprd.tech/courses/biology/thumbnails/images/8dbb76f4" alt="" />

 causes the ion channel to phosphorylate an amino acid on a target molecule 

 results in the formation of ion-channel dimers 

 No. Dimers are formed when ligands bind to receptor tyrosine kinases. 

 promotes the binding of a steroid hormone to its receptor in the cytoplasm 

 No. Ligand-gated ion channels are found as integral membrane proteins in membranes. 

 alters the expression of genes, especially in neurons 

 No. In neurons, ligand-gated ion channels are important for the propagation of signals from one cell to the next. 

Review the basic mechanisms of the three types of cell-surface transmembrane receptors.

The binding of a signal molecule to a ligand-gated ion channel __________.

Synaptic Cell Signaling

 Some apoptotic signals originate from outside a cell. 

 No. Although this is true, it is not the best choice. 

 Some apoptotic signals come from the nucleus, when DNA has suffered irreparable damage. 

 Some apoptotic signals come from the endoplasmic reticulum when excessive protein misfolding occurs. 

 Some apoptotic signals come from mitochondria. 

Apoptotic signals can come from more than one location.

Which of the following statements is correct?

Cell Signaling in ONE MINUTE! Autocrine, Paracrine, Juxtacrine and Endocrine Signaling | MCAT |

Cortisol travels through the blood stream.

Cortisol travels through the nervous system.  

Cortisol is unable to affect cells far from the adrenal glands.

Cortisol is a stress hormone created by the adrenal glands which can affect many tissues throughout the body. How is cortisol able to reach target cells that are far from the adrenal glands?

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