Module 5 Cell Signaling: 1 Principles of Cell Signaling

Question 1

It’s a process by which cells respond to physical and chemical changes in their environment through mechanisms that allow them to communicate with each other.

Answer 1

Cell signaling

Question 2

It’s a process where bacteria secrete chemical signals to coordinate behavior, such as motility, antibiotic production, and spore formation, based on population density.

Answer 2

quorum sensing

Question 3

Yeast cells secrete a __ that signals opposite mating-type cells to stop proliferating and prepare for mating, leading to zygote formation.

Answer 3

mating factor peptide

Question 4

These are molecules that communicate signals between cells, including proteins, peptides, amino acids, nucleotides, steroids, and gases like nitric oxide and carbon monoxide.

Answer 4

extracellular signal molecules

Question 5

an extracellular signal molecule that binds specifically to a receptor to initiate a cellular response.

Answer 5

ligand

Question 6

cells produce signals that they themselves respond to.

Answer 6

autocrine signaling

Question 7

occurs in neurons, where chemical synapses allow neurotransmitter release to communicate with target cells.

Answer 7

synaptic signaling

Question 8

uses hormones released into the bloodstream to target distant cells throughout the body.

Answer 8

endocrine signaling

Question 9

a protein, often a transmembrane protein, that specifically binds to a ligand and initiates an intracellular signaling cascade.

Answer 9

receptor protein

Question 10

the final targets in signaling pathways, which are altered by the signal to bring about a change in cell behavior, such as gene expression or ion channel activity.

Answer 10

effector proteins

Question 11

Each cell is programmed to respond to specific combinations of extracellular signals that may __ or __ different cellular actions.

Answer 11

• stimulate
• inhibit

Question 12

Cells respond selectively to certain signals, ensuring that they integrate relevant signaling information to make specific decisions, such as when to divide, move, or differentiate.

Answer 12

Signal selectivity

Question 13

Cells integrate multiple signaling inputs to determine appropriate responses, which may include __, __, __, or __(__).

Answer 13

• division
• movement
• differentiation
• programmed cell death (apoptosis)

Question 14

the programmed death of a cell, which is a controlled process essential for removing damaged or unnecessary cells.

Answer 14

Apoptosis

Question 15

the process by which cells divide and multiply, essential for growth, tissue repair, and regeneration.

Answer 15

Cell proliferation

Question 16

the final stage of cell differentiation, where a cell becomes specialized to perform a specific function and typically loses its ability to divide.

Answer 16

Terminal differentiation

Question 17

A signal molecule can have varied effects on different target cells due to differences in their __, __, and __.

Answer 17

• intracellular signaling proteins
• effector proteins
• gene expression

Question 18

An example of a signal molecule that can elicit different responses in various target cells and give three (3) target cells and its response.

Answer 18

Acetylcholine
- heart pacemaker cell > decreased heart rate of firing
- salivary gland cell > secretion
- skeletal muscle cell > contraction

Question 19

A __ can have varied effects on different target cells due to differences in their intracellular signaling proteins, effector proteins, and gene expression.

Answer 19

signal molecule

Question 20

The response of a target cell to a signal molecule is guided by its __, meaning that it will react according to its specific cellular context and signaling pathways.

Answer 20

predetermined state

Question 21

What are the three major classes of cell-surface receptor proteins? (3)

Answer 21

• ion-coupled-channel receptors
• G-protein coupled receptors
• enzyme-coupled receptors

Question 22

__ proteins act as signal transducers, converting an extracellular ligand-binding event into intracellular signals that alter the behavior of the target cell.

Answer 22

Cell-surface receptor

Question 23

What are ion-channel coupled receptors also known as? (2)

Answer 23

transmitter-gated ion channels or ionotropic receptors

Question 24

__ cells, such as neurons and muscle cells, commonly utilize ion-channel coupled receptors.

Answer 24

Electrically excitable

Question 25

Neurotransmitters bind to __, causing the channels to open and allowing ions to flow across the cell membrane, thus altering the cell’s electrical potential.

Answer 25

ion-channel coupled receptors

Question 26

a cell-surface receptor protein that activates plasma-membrane-bound target proteins, such as enzymes or ion channels, through the intermediary of a trimeric GTP-binding protein (G protein).

Answer 26

G-protein-coupled receptors (GPCRs)

Question 27

G-protein-coupled receptors (GPCRs) activate plasma-membrane-bound target proteins, such as enzymes or ion channels, through the intermediary of a __.

Answer 27

trimeric GTP-binding protein (G protein).

Question 28

• a cell-surface receptor protein that functions as enzymes themselves or are directly associated with enzymes that they activate upon ligand binding.
• typically single-pass transmembrane proteins, with ligand-binding sites located outside the cell and enzyme-binding sites inside the cell.

Answer 28

Enzyme-coupled receptors

Question 29

__ are enzymes that catalyze the transfer of phosphate groups to specific substrates, thereby modifying the activity of proteins and playing a crucial role in signaling pathways.

Answer 29

Protein kinases

Question 30

molecules that are often referred to as second messengers.

Answer 30

Intracellular signaling

Question 31

• typically small chemicals or water-soluble molecules, or lipid-soluble, that bind to and alter the behavior of selected signaling or effector proteins.
• act as molecular switches by changing their state or concentration, which influences the activity of downstream signaling proteins.

Answer 31

Second messengers

Question 32

the addition of a phosphate group to a protein, typically carried out by kinases, which can activate or deactivate the protein’s function.

Answer 32

phosphorylation

Question 33

What types of kinases are involved in phosphorylation? (2)

Answer 33

• serine-threonine kinases
• tyrosine kinases

Question 34

__ remove phosphate groups from proteins, reversing the effects of kinases and thus modulating protein activity.

Answer 34

Phosphatases

Question 35

How many kinases and phosphatases are present in human cells?

Answer 35

• 520 kinases
• 150 phosphatases

Question 36

GTP-binding proteins are in the “__” state when bound to GTP and in the “__” state when bound to GDP.

Answer 36

• on/active
• off/inactive

Question 37

What are the two types of GTP-binding proteins?

Answer 37

• trimeric GTP-binding proteins (G proteins)
• monomeric GTP-binding proteins (small monomeric GTPases).

Question 38

activate the “off” state by promoting the hydrolysis of GTP to GDP.

Answer 38

GTPase-activating proteins (GAPs)

Question 39

activate GTP-binding proteins by releasing bound GDP, allowing GTP to bind and switch the protein to the “on” state.

Answer 39

Guanine nucleotide exchange factors (GEFs)

Question 40

refers to a series of activation steps where the inhibition of a negative regulator leads to the activation of a signaling pathway.

Answer 40

Double-negative activation

Question 41

An activated intracellular signaling molecule should interact only with appropriate downstream targets, ensuring __ and __ for effective signaling.

Answer 41

• high affinity
• specificity

Question 42

can ignore signals unless the upstream signal reaches a high concentration or activity level, allowing for precise regulation of cellular responses.

Answer 42

Downstream target proteins

Question 43

What are the three types of intracellular signaling complexes?

Answer 43

• Performed signaling complex on a scaffold protein
• Assembly of signaling complex on an activated receptor
• Assembly of signaling complex on a phosphoinositide docking sites

Question 44

localize signaling proteins into complexes, enhancing specificity and reducing background noise by holding them in close proximity for rapid interaction.

Answer 44

Scaffold proteins

Question 45

• hold proteins at high local concentrations, allowing for rapid, efficient, and selective activation in response to extracellular signals.
• often form transiently in response to an extracellular signal and rapidly disassemble when the signal is gone.

Answer 45

Signaling complexes

Question 46

The __ of an activated enzyme-coupled receptor is phosphorylated, creating docking sites for other signaling proteins to assemble.

Answer 46

cytoplasmic tail

Question 47

modified phospholipid molecules produced upon receptor activation that recruit specific intracellular signaling proteins to the membrane for activation.

Answer 47

Phosphoinositides

Question 48

What are the key features of an effective signaling response in terms of timing and sensitivity? (7)

Answer 48

1. response timing
2. sensitivity to extracellular signals (through number or affinity and amplification)
3. dynamic range (responsiveness)
4. persistence (transient response; prolonged or permanent)
5. signal processing (switchlike response; oscillatory response)
6. integration of multiple inputs
7. coordination of multiple responses.

Question 49

The speed of __ is influenced by whether the changes involve rapid alterations in existing proteins or slower changes in gene expression and new protein synthesis.

Answer 49

response

Question 50

The __ of the cell typically fades when the signaling molecule is no longer present, highlighting the transient nature of many signaling pathways.

Answer 50

response

Question 51

refer to the series of signals or processes that occur within a cell after an initial signaling event. These signals are the result of the activation of signaling pathways following the binding of an extracellular signal (such as a hormone, neurotransmitter, or growth factor) to a receptor on the cell surface.

Answer 51

downstream signals

Question 52

What type of response is characterized by a smoothly graded reaction as the concentration of a signaling molecule increases?

Answer 52

Hyperbolic response

Question 53

What occurs when the concentration of a signaling molecule rises beyond a certain threshold value?

Answer 53

Abrupt responses occur

Question 54

What type of response curve shows a gradual increase in response at low concentrations, a steeper increase at intermediate concentrations, and a plateau at high concentrations?

Answer 54

Sigmoidal response

Question 55

A discontinuous or switch-like response where the cell completely switches between low and high response levels.

Answer 55

all-or-none response

Question 56

Rapid responses occur when existing __ change, while responses involving __ and new __ take longer (minutes to hours).

Answer 56

• proteins
• gene expression
• protein synthesis

Question 57

What happens to a signaling pathway when the extracellular signal is withdrawn?

Answer 57

The response often fades, especially if it depends on short-lived intracellular molecules.

Question 58

mechanisms where the output of a process regulates that same process.

Answer 58

Feedback loops

Question 59

A feedback that occurs when the output stimulates its own production, enhancing the response.

Answer 59

Positive feedback

Question 60

How does positive feedback affect the response curve?

Answer 60

It can steepen the response, resulting in sigmoidal or all-or-none responses.

Question 61

What does it mean for a system to be bistable in the context of positive feedback?

Answer 61

can exist in either a “switched-off” or a “switched-on” state, often becoming self-sustaining after activation.

Question 62

It can induce long-term changes in cells, such as muscle-cell specification, which can persist beyond the initial signal.

signal

Answer 62

transient extracellular signal

Question 63

A feedback that makes the system less sensitive to perturbations by abbreviating and limiting responses.

Answer 63

negative feedback

Question 64

What is the effect of long delays in negative feedback?

Answer 64

Long delays can produce oscillatory responses that may persist as long as the stimulus is present.

Question 65

In the context of negative feedback, this occurs when a system generates a brief response to a stimulus that quickly decays, even while the stimulus persists.

Answer 65

Adaptation

Question 66

the process where prolonged exposure to a stimulus decreases the cell’s response to that level of stimulus.

Answer 66

Adaptation or desensitization

Question 67

Prolonged exposure to stimulus modifies the signaling machinery, resetting it to become __ responsive to that stimulus.

Answer 67

less

Question 68

A strong response can lead to modifications in the signaling machinery that results in decreased __ to the same stimulus.

Answer 68

• sensitivity

Question 69

Cells can adjust their responsiveness based on the __ of the extracellular signal molecule, which may involve adaptation.

Answer 69

concentration

Question 70

It prevents overstimulation and allows cells to fine-tune their responses to fluctuating levels of signals.

Answer 70

desentization