Question 1

What is an autocrine signal?

Accepted Answer

A signal that is sent and received by the same or similar nearby cells.

Question 2

What is a cell-surface receptor?

Accepted Answer

A cell-surface protein that transmits a signal from the exterior of the cell to the interior, even though the ligand does not enter the cell. AKA transmembrane receptor.

Question 3

What is a chemical synapse?

Accepted Answer

A small space between axon terminals and dendrites of nerve cells where neurotransmitters function.

Question 4

What is an endocrine cell?

Accepted Answer

A cell that releases ligands involved in endocrine signaling (hormones).

Question 5

What is an endocrine signal?

Accepted Answer

A long-distance signal that is delivered by ligands (hormones) traveling through an organism's circulatory system from the signaling cell to the target cell.

Question 6

What is an enzyme-linked receptor?

Accepted Answer

A cell-surface receptor with intracellular domains that are associated with membrane-bound enzymes.

Question 7

What is an extracellular domain?

Accepted Answer

A region of a cell-surface receptor that is located on the cell surface.

Question 8

What is a G-protein-linked receptor?

Accepted Answer

A cell-surface receptor that activates membrane-bound G-proteins to transmit a signal from the receptor to nearby membrane components.

Question 9

What is intercellular signaling?

Accepted Answer

Communication between cells.

Question 10

What is an internal receptor?

Accepted Answer

A receptor protein that is located in the cytosol of a cell and binds to ligands that pass through the plasma membrane. AKA intracellular receptor.

Question 11

What is an intracellular mediator?

Accepted Answer

A small molecule that transmits signals within a cell. AKA second messenger.

Question 12

What is intracellular signaling?

Accepted Answer

Communication within cells.

Question 13

What is an ion channel-linked receptor?

Accepted Answer

A cell-surface receptor that forms a plasma membrane channel, which opens when a ligand binds to the extracellular domain (ligand-gated channels).

Question 14

What is a ligand?

Accepted Answer

A molecule produced by a signaling cell that binds with a specific receptor, delivering a signal in the process.

Question 15

What is a neurotransmitter?

Accepted Answer

A chemical ligand that carries a signal from one nerve cell to the next.

Question 16

What is a paracrine signal?

Accepted Answer

A signal between nearby cells that is delivered by ligands traveling in the liquid medium in the space between the cells.

Question 17

What is a receptor?

Accepted Answer

A protein in or on a target cell that binds to ligands.

Question 18

What is a signaling cell?

Accepted Answer

A cell that releases signal molecules that allow communication with another cell.

Question 19

What is a synaptic signal?

Accepted Answer

A chemical signal (neurotransmitter) that travels between nerve cells.

Question 20

What is a target cell?

Accepted Answer

A cell that has a receptor for a signal or ligand from a signaling cell.

Question 21

What is the specificity of ligands and receptors?

Accepted Answer

Ligands and receptors exist in several varieties; however, a specific ligand will have a specific receptor that typically binds only that ligand.

Question 22

What are the categories of chemical signaling found in multicellular organisms?

Accepted Answer

There are four categories: paracrine signaling, endocrine signaling, autocrine signaling, and direct signaling across gap junctions. The main difference between the different categories of signaling is the distance that the signal travels through the organism to reach the target cell. Not all cells are affected by the same signals.

Question 23

How are paracrine signals propagated?

Accepted Answer

Paracrine signals move by diffusion through the extracellular matrix. These types of signals usually elicit quick responses that last only a short amount of time. In order to keep the response localized, paracrine ligand molecules are normally quickly degraded by enzymes or removed by neighboring cells. Removing the signals will reestablish the concentration gradient for the signal, allowing them to quickly diffuse through the intracellular space if released again.

Question 24

What is an example of paracrine signaling?

Accepted Answer

One example of paracrine signaling is the transfer of signals across synapses between nerve cells.

Question 25

What is a nerve cell?

Accepted Answer

A nerve cell consists of a cell body, several short, branched extensions called dendrites that receive stimuli, and a long extension called an axon, which transmits signals to other nerve cells or muscle cells.

Question 26

How how are signals in nerve cells propagated?

Accepted Answer

Signals within the nerve cells are propagated by fast-moving electrical impulses. When these impulses reach the end of the axon, the signal continues on to a dendrite of the next cell by the release of chemical ligands called neurotransmitters by the presynaptic cell (the cell emitting the signal). The neurotransmitters are transported across the very small distances between nerve cells, which are called chemical synapses. When the neurotransmitter binds the receptor on the surface of the postsynaptic cell, the electrochemical potential of the target cell changes, and the next electrical impulse is launched. The neurotransmitters that are released into the chemical synapse are degraded quickly or get reabsorbed by the presynaptic cell so that the recipient nerve cell can recover quickly and be prepared to respond rapidly to the next synaptic signal.

Question 27

Where are endocrine cells found?

Accepted Answer

In the body, many endocrine cells are located in endocrine glands, such as the thyroid gland, the hypothalamus, and the pituitary gland.

Question 28

What is the effect of endocrine signals?

Accepted Answer

Endocrine signals usually produce a slower response but have a longer-lasting effect.

Question 29

What is a hormone?

Accepted Answer

The ligands released in endocrine signaling are called hormones, signaling molecules that are produced in one part of the body but affect other body regions some distance away.

Question 30

How do hormones move through the body?

Accepted Answer

Hormones travel the large distances between endocrine cells and their target cells via the bloodstream, which is a relatively slow way to move throughout the body. Because of their form of transport, hormones get diluted and are present in low concentrations when they act on their target cells. This is different from paracrine signaling, in which local concentrations of ligands can be very high.

Question 31

What is the target of autocrine signals?

Accepted Answer

Autocrine signals are produced by signaling cells that can also bind to the ligand that is released. This means the signaling cell and the target cell can be the same or a similar cell.

Question 32

What are some examples of autocrine signaling?

Accepted Answer

Autocrine signaling often occurs during the early development of an organism to ensure that cells develop into the correct tissues and take on the proper function. Autocrine signaling also regulates pain sensation and inflammatory responses. Further, if a cell is infected with a virus, the cell can signal itself to undergo programmed cell death, killing the virus in the process.

Question 33

What is an example of autocrine signals targeting neighbor cells?

Accepted Answer

In some cases, neighboring cells of the same type are also influenced by the released ligand. In embryological development, this process of stimulating a group of neighboring cells may help to direct the differentiation of identical cells into the same cell type, thus ensuring the proper developmental outcome.

Question 34

How are gap junctions used for cell signaling?

Accepted Answer

Gap junctions in animals and plasmodesmata in plants are connections between the plasma membranes of neighboring cells. These water-filled channels allow small signaling molecules, called intracellular mediators, to diffuse between the two cells. Small molecules, such as calcium ions (Ca2+), are able to move between cells, but large molecules like proteins and DNA cannot fit through the channels. The specificity of the channels ensures that the cells remain independent but can quickly and easily transmit signals. The transfer of signaling molecules communicates the current state of the cell that is directly next to the target cell; this allows a group of cells to coordinate their response to a signal that only one of them may have received. In plants, plasmodesmata are ubiquitous, making the entire plant into a giant, communication network.

Question 35

What are the types of receptors?

Accepted Answer

There are two types of receptors, internal receptors and cell-surface receptors.

Question 36

What is gene expression?

Accepted Answer

Gene expression is the cellular process of transforming the information in a cell's DNA into a sequence of amino acids.

Question 37

How can internal signals be used to moderate gene expression?

Accepted Answer

When a ligand binds to an internal receptor, a conformational change is triggered that exposes a DNA-binding site on the protein. The ligand-receptor complex moves into the nucleus, and binds to specific regulatory regions of the chromosomal DNA and promotes the initiation of transcription. Internal receptors can directly influence gene expression without having to pass the signal on to other receptors or messengers.

Question 38

What do cell-surface receptors do?

Accepted Answer

A cell-surface receptor spans the plasma membrane and performs signal transduction, in which an extracellular signal is converted into an intercellular signal. Ligands that interact with cell-surface receptors do not have to enter the cell that they affect. Cell-surface receptors are also called cell-specific proteins or markers because they are specific to individual cell types.

Question 39

What are some risks of cell-surface receptor failure?

Accepted Answer

Because cell-surface receptor proteins are fundamental to normal cell functioning, malfunctions in any one of these proteins could have severe consequences. Errors in the protein structures of certain receptor molecules have been shown to play a role in hypertension (high blood pressure), asthma, heart disease, and cancer.

Question 40

How are cell-surface receptors structured?

Accepted Answer

Each cell-surface receptor has three main components: an external ligand-binding domain, a hydrophobic membrane-spanning region, and an intracellular domain inside the cell. The ligand-binding domain is also called the extracellular domain. The size and extent of each of these domains vary widely, depending on the type of receptor.

Question 41

How do viruses survive and reproduce?

Accepted Answer

Unlike living cells, many viruses do not have a plasma membrane or any of the structures necessary to sustain life. Some viruses are simply composed of an inert protein shell containing DNA or RNA. To reproduce, viruses must invade a living cell, which serves as a host, and then take over the hosts cellular apparatus.

Question 42

How does a virus recognize its host?

Accepted Answer

Viruses often bind to cell-surface receptors on the host cell. Chemical differences in the cell-surface receptors among hosts mean that a virus that infects a specific species cannot infect another species.

Question 43

Which receptors does the flu virus bind to?

Accepted Answer

The virus that causes human influenza (flu) binds specifically to receptors on membranes of cells of the respiratory system.

Question 44

How do viruses spread between species?

Accepted Answer

Viruses have very small amounts of DNA or RNA, and, as a result, viral reproduction can occur rapidly. Viral reproduction invariably produces errors that can lead to changes in newly produced viruses; these changes mean that the viral proteins that interact with cell-surface receptors may evolve in such a way that they can bind to receptors in a new host. Such changes happen randomly and quite often in the reproductive cycle of a virus, but the changes only matter if a virus with new binding properties comes into contact with a suitable host. Once a virus jumps to a new host, it can spread quickly.

Question 45

Where do flu viruses originate?

Accepted Answer

In the case of influenza, the virus can spread to humans in settings where animals and people are in close contact, such as poultry and swine farms.

Question 46

Why is it important to monitor emerging viruses?

Accepted Answer

Scientists watch newly appearing viruses (called emerging viruses) closely in the hope that such monitoring can reduce the likelihood of global viral epidemics.

Question 47

What are the categories of cell-surface receptors?

Accepted Answer

There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.

Question 48

How do ion channel-linked receptors work?

Accepted Answer

To form a channel, this type of cell-surface receptor has an extensive membrane-spanning region. In order to interact with the phospholipid fatty acid tails that form the center of the plasma membrane, many of the amino acids in the membrane-spanning region are hydrophobic in nature. Conversely, the amino acids that line the inside of the channel are hydrophilic to allow for the passage of water or ions. When a ligand binds to the extracellular region of the channel, there is a conformational change in the proteins structure that allows ions such as sodium, calcium, magnesium, and hydrogen to pass through.

Question 49

How are G-protein-linked receptors activated?

Accepted Answer

G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein. The activated G-protein then interacts with either an ion channel or an enzyme in the membrane. All G-protein-linked receptors have seven transmembrane domains, but each receptor has its own specific extracellular domain and G-protein-binding site.

Question 50

How do G-protein-linked receptors work?

Accepted Answer

Cell signaling using G-protein-linked receptors occurs as a cyclic series of events. Before the ligand binds, the inactive G-protein can bind to a newly revealed site on the receptor specific for its binding. Once the G-protein binds to the receptor, the resultant shape change activates the G-protein, which releases GDP and picks up GTP. The subunits of the G-protein then split into the α subunit and the βγ subunit. One or both of these G-protein fragments may be able to activate other proteins as a result. After awhile, the GTP on the active α subunit of the G-protein is hydrolyzed to GDP and the βγ subunit is deactivated. The subunits reassociate to form the inactive G-protein and the cycle begins anew.

9: Cell Communication Flashcards

Signaling Molecules and Cellular Receptors, Propagation of the Signal, Response to the Signal, Signaling in Single-Celled Organisms

Brainscape's Knowledge GenomeTM

9: Cell Communication Flashcards

Signaling Molecules and Cellular Receptors, Propagation of the Signal, Response to the Signal, Signaling in Single-Celled Organisms

Brainscape's Knowledge Genome^TM