Cell Signaling I

Question 1

What do cells monitor and respond to?

Answer 1

Intracellular and extracellular environments

Cells respond to changes in their surroundings, including nutrients and toxins.

Question 2

What is quorum sensing?

Answer 2

A process that allows bacteria to coordinate their behavior based on chemical signals from neighboring cells

This includes motility, antibiotic production, and mating.

Question 3

What is paracrine signaling?

Answer 3

Signaling where secreted molecules act on neighboring cells

Usually involves different cell types but can also include autocrine signaling.

Question 4

What are effector proteins?

Answer 4

Proteins altered by incoming signals that implement changes in cell behavior

These can be transcription regulators, ion channels, or metabolic pathway components.

Question 5

How do contact-dependent signaling and paracrine signaling differ?

Answer 5

Contact-dependent signaling requires direct contact, while paracrine signaling involves local mediators acting on nearby cells

Contact-dependent signaling is crucial during development.

Question 6

What are the two main types of receptors for signal molecules?

Answer 6

Transmembrane receptors and intracellular receptors

Transmembrane receptors are on the cell surface, while intracellular receptors are inside the cell.

Question 7

What type of signaling do neurons use?

Answer 7

Synaptic signaling

Neurons transmit signals electrically and release neurotransmitters at chemical synapses.

Question 8

What role do hormones play in endocrine signaling?

Answer 8

Hormones are secreted into the bloodstream for long-range signaling

This allows them to act on target cells throughout the body.

Question 9

What is the significance of receptor specificity?

Answer 9

Receptors bind signal molecules with high specificity to ensure appropriate responses

This helps prevent cross-reactivity with other signaling molecules.

Question 10

What is the effect of acetylcholine on different cell types?

Answer 10

It has different effects: decreases action potential firing in heart cells, stimulates saliva production in salivary glands, and causes contraction in skeletal muscle

This is due to variations in intracellular signaling proteins and effector proteins.

Question 11

What is autocrine signaling?

Answer 11

A form of signaling where cells produce signals that act on themselves

This is often seen in cancer cells for survival and proliferation.

Question 12

What is the primary challenge in cell biology regarding extracellular signals?

Answer 12

Determining how a cell integrates multiple signaling inputs to make decisions

These decisions can include cell division, movement, and differentiation.

Question 13

What types of molecules can act as extracellular signals?

Answer 13

Proteins, small peptides, amino acids, nucleotides, steroids, retinoids, fatty acid derivatives, and gases

These molecules can be released through various mechanisms like exocytosis or diffusion.

Question 14

What is terminal differentiation?

Answer 14

A nondividing state that requires specific survival and differentiation signals

It often overrides signals to divide.

Question 15

What is the primary role of extracellular signals in cellular response?

Answer 15

Induce the cell to respond according to its predetermined state

This state is influenced by the cell’s developmental history and the specific genes it expresses.

Question 16

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

Answer 16

1. Ion-channel-coupled receptors
2. G-protein-coupled receptors
3. Enzyme-coupled receptors

Question 17

What is the function of ion-channel-coupled receptors?

Answer 17

Involved in rapid synaptic signaling

They mediate signaling by transiently opening or closing ion channels.

Question 18

How do G-protein-coupled receptors operate?

Answer 18

By indirectly regulating the activity of a target protein via a G protein

This target protein can be an enzyme or an ion channel.

Question 19

What do enzyme-coupled receptors typically do?

Answer 19

Function as enzymes or associate directly with enzymes

They often phosphorylate specific sets of proteins in the target cell when activated.

Question 20

What are second messengers?

Answer 20

Small chemicals generated in response to receptor activation

Examples include cyclic AMP and Ca2+.

Question 21

What is the role of protein phosphatases?

Answer 21

Remove phosphate groups from proteins

This action is crucial for returning proteins to their inactive state.

Question 22

What defines the activation state of GTP-binding proteins?

Answer 22

Binding of GTP for the ‘on’ state and GDP for the ‘off’ state

GTP-binding proteins have intrinsic GTPase activity to hydrolyze GTP to GDP.

Question 23

What accelerates the inactivation of GTP-binding proteins?

Answer 23

GTPase-activating proteins (GAPs)

They increase the rate of hydrolysis of bound GTP.

Question 24

What is the function of guanine nucleotide exchange factors (GEFs)?

Answer 24

Promote the release of GDP to activate GTP-binding proteins

This allows a new GTP to bind, activating the protein.

Question 25

What happens in a signaling pathway when two inhibitory steps occur?

Answer 25

Can have the same effect as one activating step ## Footnote This is common in signaling systems.

Question 26

What is a key factor for signaling specificity in intracellular signaling?

Answer 26

High affinity and specificity of interactions between signaling molecules and their correct partners. ## Footnote This ensures that signals are passed to the appropriate targets despite potential noise from other pathways.

Question 27

How do protein kinases enhance signaling specificity?

Answer 27

They contain active sites that recognize specific amino acid sequences around phosphorylation sites on target proteins, along with additional docking sites for high-affinity interactions. ## Footnote This mechanism increases the likelihood of effective signaling.

Question 28

What role do noise filters play in signaling systems?

Answer 28

They reduce or remove undesirable background signals, allowing for a strong response only when appropriate kinases are active enough to overcome phosphatase activity. ## Footnote This helps to ignore weak background signals.

Question 29

What is induced proximity in signaling pathways?

Answer 29

A mechanism where a signal triggers the assembly of a signaling complex, bringing proteins into close proximity for activation. ## Footnote This is a common way to relay signals from one protein to another.

Question 30

What are scaffold proteins?

Answer 30

Proteins that bring together groups of interacting signaling proteins into complexes to enhance specificity and reduce noise. ## Footnote They often preassemble signaling complexes before a signal is received.

Question 31

What are phosphoinositides?

Answer 31

Modified phospholipid molecules produced in the plasma membrane that serve as docking sites for intracellular signaling proteins. ## Footnote They are involved in the signaling pathway after receptor activation.

Question 32

What is the function of modular interaction domains in signaling proteins?

Answer 32

They mediate specific interactions between signaling proteins, facilitating the assembly of signaling complexes. ## Footnote This modularity allows for the evolution of new signaling pathways.

Question 33

Name two types of interaction domains found in signaling proteins.

Answer 33

* Src homology 2 (SH2) domains * Phosphotyrosine-binding (PTB) domains ## Footnote These domains bind to phosphorylated tyrosines in specific peptide sequences.

Question 34

How does the concentration of activated receptors and signaling proteins affect signaling?

Answer 34

It enhances the strength and specificity of the receptor signal while reducing interference from other pathways. ## Footnote This is often achieved through the formation of protein matrices.

Question 35

What is the dynamic range of a signaling system?

Answer 35

The range of extracellular signal concentrations over which a signaling system can respond effectively. ## Footnote Some systems are responsive over a narrow range, while others can handle a broader range.

Question 36

How does response timing vary in different signaling systems?

Answer 36

Response timing can range from milliseconds in synaptic signaling to hours or days in developmental signaling. ## Footnote This variation is based on the speed required for the response.

Question 37

What is signal amplification?

Answer 37

A mechanism where a small number of activated receptors can evoke a large intracellular response by producing large amounts of a second messenger or activating many downstream proteins. ## Footnote This is crucial for increasing sensitivity in signaling systems.

Question 38

What determines the sensitivity of a signaling system?

Answer 38

The range of extracellular signal concentrations that it is responsive to.

Question 39

What is a broad dynamic range in signaling systems often achieved by?

Answer 39

Adaptation mechanisms that adjust responsiveness according to the prevailing amount of signal.

Question 40

What mechanisms can alter the duration and reversibility of a response?

Answer 40

Positive and negative feedback.

Question 41

What does signal processing convert?

Answer 41

A simple signal into a complex response.

Question 42

What is an example of a gradual increase in an extracellular signal leading to?

Answer 42

An abrupt, switchlike response.

Question 43

What is integration in signaling systems?

Answer 43

Governance of a response by multiple inputs.

Question 44

What can coordination of multiple responses in one cell be achieved by?

Answer 44

A single extracellular signal.

Question 45

What does branching in signaling pathways allow?

Answer 45

One extracellular signal to modulate the strength of responses to other signals.

Question 46

What does the speed of a signaling response depend on?

Answer 46

The nature of the intracellular signaling molecules.

Question 47

What type of response can occur rapidly?

Answer 47

Responses that depend on changes in proteins already present in the cell.

Question 48

What happens when a signal is withdrawn in many signaling pathways?

Answer 48

The response fades and often becomes transient.

Question 49

What is the relationship between turnover rate and response speed?

Answer 49

Higher turnover rates lead to quicker responses to signal changes.

Question 50

What type of response is characterized by a sigmoidal curve?

Answer 50

A response that rises steeply at intermediate stimulus levels.

Question 51

What is an all-or-none response?

Answer 51

A response that switches on completely when a threshold concentration is reached.

Question 52

What can positive feedback in a signaling pathway produce?

Answer 52

An all-or-none response.

Question 53

What does bistability in a system mean?

Answer 53

The system can exist in either a 'switched-off' or 'switched-on' state.

Question 54

How can positive feedback induce long-term changes in cells?

Answer 54

By triggering the transcription of genes that promote muscle-cell specification.

Question 55

What is the effect of positive feedback in cell signaling?

Answer 55

Promotes an all-or-none response and can convert a short-lasting signal into a long-lasting response. ## Footnote Positive feedback loops amplify the response, making it more pronounced.

Question 56

What does negative feedback do in signaling systems?

Answer 56

Counteracts the effect of a stimulus and limits the response, making the system less sensitive to perturbations. ## Footnote Negative feedback can lead to oscillatory responses if the delay is long.

Question 57

What phenomenon allows cells to respond to changes in signal strength?

Answer 57

Adaptation or desensitization. ## Footnote This enables cells to adjust their sensitivity to a wide range of signal levels.

Question 58

What is one mechanism of adaptation involving receptor inactivation?

Answer 58

Phosphorylation of the receptor leading to association with arrestins. ## Footnote Arrestins interfere with G-protein activation and reduce the response.

Question 59

What are some mechanisms that can inactivate cell-surface receptors?

Answer 59

* Internalization into endosomes * Destruction in lysosomes * Phosphorylation leading to arrestin binding ## Footnote These mechanisms reduce the cellular response to signals.

Question 60

What is the significance of studying single cells in signaling research?

Answer 60

It reveals all-or-none responses that may be masked in population studies. ## Footnote This helps in understanding the variability in responses among individual cells.

Question 61

What is the primary function of cell-surface receptor proteins?

Answer 61

Act as signal transducers converting extracellular signals into intracellular responses. ## Footnote They initiate signaling cascades within target cells.

Question 62

What happens to the response of a signaling system when the input signal stops?

Answer 62

The response declines unless sustained by positive feedback. ## Footnote This is characteristic of many signaling pathways.