Chapter 9 Biology

Which one of the answer choices would be found inside the cell and not on the cell surface?

a steroid receptor

Recall from the text in the example of cell communication in Streptococcus pneumoniae that 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 protein, how would the rate of DNA uptake be affected when the cells reach high density?

There would be no increase in the rate of DNA uptake.

What happens to the α (alpha) subunit of a G protein when bound GTP is replaced with GDP?

All of these When GTP bound to G proteins is hydrolyzed to GDP, the G protein loses its ability to activate its target and returns to binding with the other G proteins and the receptor. It re-associates with the G protein-coupled receptor. It reassembles with the β (beta) and γ (gamma) subunits. It no longer activates an effector protein.

Nicotine from cigarette smoke acts as a ligand and associates with the acetylcholine receptor on specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. The listed statements are descriptions of the events that happen in the cellular response to nicotine. Place the events in the correct order to describe the steps in the signaling pathway. A) The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens. B) An influx of ions carries the signal to the reward areas of the brain. C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. D) The signal causes release of dopamine in the brain, which causes good feelings. E) Nicotine is quickly eliminat

C; A; B; D; E

According to the figure, what is a key difference between cell signaling by a cell-surface receptor and cell signaling by an intracellular receptor?

Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.

Most ligands form covalent bonds with their associated receptors; these complexes are more or less permanent and can only be broken through the hydrolysis of ATP.

False

How is a G protein classified?

It is a peripheral membrane protein.

In cell communication, which one of the answer choices is a requirement of the responding cell?

It must express receptor proteins.

In cell communication, which of these is a requirement of the responding cell?

It must have receptor proteins.

Which statement is true regarding neurotransmitters?

Neurotransmitters are typically dispersed over small distances.

According to the figure shown, which of the answer choices is responsible for amplifying the signal in a cell responding to adrenaline? Select all that apply.

One molecule of protein kinase A (PKA) can phosphorylate and activate many target proteins. One activated receptor can activate many G proteins. One molecule of adenylyl cyclase can activate many molecules of protein kinase A (PKA).

How do mitogen-activated protein (MAP) kinases get deactivated?

Phosphatases remove phosphate groups.

What is the role of signal transduction in cell signaling?

Signal transduction connects the activation of the receptor to the cellular response.

Why don't steroid hormones bind to transmembrane cell-surface receptors?

Steroid hormones are nonpolar and therefore are able to cross the cell's plasma membrane, binding to receptors inside the cell.

During the signal transduction process, the signal often triggers a signal transduction cascade. For example, a single activated receptor can activate hundreds of protein A molecules. Each activated protein A molecule activates hundreds of protein B molecules, and so on, until a cellular response occurs. What purpose does this cascade serve?

The cascade serves to amplify the signal so one activated receptor can have a significant response.

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

The cell does not have the proper receptor.

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?

These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.

Which is a true statement about receptors that are localized to the nucleus?

They move through a nuclear pore. They carry a nuclear-localization signal. They bind nonpolar ligands. They are synthesized in the cytosol.

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

This signal is likely similar in structure to ligands utilized by eukaryotic cells.

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 nearby blood vessels to branch and grow to form new blood vessels that supply these tumors.Given what you know about the different kinds of cell signaling and VEGF, which statement is true?

VEGF is a paracrine-signaling molecule because it binds to VEGF receptors on cells at the site where new blood vessels are needed.

What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus?

a change in gene expression

Signal amplification relies on:

a sequential increase in the different components, wherein a single, activated component can activate many copies of the next component in the pathway.

Ligand binding to a receptor kinase results in:

binding of cytoplasmic signaling molecules. receptor dimerization. phosphorylation of the cytoplasmic domain of the receptor.

Cell signaling over a long distance is known as:

endocrine signaling

The presence of excess epidermal growth factor (EGF) receptors can result in:

excessive cell division.

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

false

Based on the data provided in the two graphs shown, which method of culturing resulted in the greatest number of fibroblast cells on day 6? Click to view full size.

fibroblasts cultured with serum

Which type of protein adds a phosphate group to another molecule?

kinases

Growth factors such as platelet-derived growth factor (PDGF) function in:

paracrine signaling.

According to the figure shown, phosphate groups play a key role in receptor kinase activation by:

providing binding sites to recruit and activate signal-transduction proteins.

Cyclic AMP (cAMP) is an example of a(n):

second messenger.

Which components of cell signaling is involved in only some types of cell communication?

signal transduction molecules

Which signaling molecule would you expect to travel the longest distance in the human body?

testosterone

Which signaling molecules would you expect to travel the longest distance in the human body?

testosterone

GTP binding occurs on which subunit of a G protein?

the α (alpha) subunit

Ras is most similar to:

the α (alpha) subunit of three-subunit G proteins. Challenge

How does an "activated" receptor transfer information into the cell?

through a conformational change of the receptor

Signaling molecules involved in paracrine and autocrine signaling:

travel by diffusion

Cancer is a disease of cell division.

true

G proteins of G protein-coupled receptors are often made up of three subunits: alpha, beta and gamma.

true