cell signalling

Question 1

Why is cell communication important?

Answer 1

Cell communication is crucial for maintaining proper cellular function and coordinating responses within multicellular organisms. Pathologies often involve dysregulation of chemical signals, and medications can target these pathways to either mimic or block their effects, highlighting the importance of understanding cell communication.

Question 2

Why do cells communicate with each other?

Answer 2

Cells communicate to respond to their immediate environment, including danger signals, as well as to central and local commands. By receiving and interpreting signals, cells can coordinate their responses, integrate signals from multiple sources, and adjust their behavior accordingly.

Question 3

What are the mechanisms of cell communication?

Answer 3

Cell communication involves various mechanisms, including chemical signals, receptors, and signaling pathways. Chemical signals, such as hormones, neurotransmitters, and growth factors, interact with specific receptors on the surface or inside cells, initiating signaling cascades that lead to cellular responses.

Question 4

What are cell receptors?

Answer 4

Cell receptors are proteins located on the surface or inside cells that bind to specific chemical signals. They transmit signals from the extracellular environment to the interior of the cell, initiating a cascade of molecular events that ultimately lead to a cellular response.

Question 5

What types of signals do cells respond to?

Answer 5

Cells can respond to a wide range of signals, including chemical signals, mechanical signals, and electrical signals. These signals can induce or decrease cell growth, division, differentiation, and other cellular responses based on the needs of the organism.

Question 6

What are chemical signals in cell communication?

Answer 6

Chemical signals are the most common type of signals involved in cell communication. They can be short-range, such as neurotransmitters acting between neighboring cells, or long-range, such as hormones that travel through the bloodstream to target distant cells.

Question 7

How are chemical signals synthesized and released?

Answer 7

Chemical signals are synthesized within cells and then released either by exocytosis (for neurotransmitters) or by secretion into the bloodstream (for hormones). The release of the signaling molecule allows it to travel to the target cells.

Question 8

How do cells detect chemical signals?

Answer 8

Cells detect chemical signals through specific receptors located on their surface or inside the cell. These receptors are designed to bind to specific signaling molecules and initiate a cellular response when the molecule is detected.

Question 9

What happens when a chemical signal binds to a receptor?

Answer 9

Binding of a chemical signal to its specific receptor triggers a series of intracellular signaling events. This can involve activation of second messengers, phosphorylation cascades, or gene expression changes, leading to a change in cellular behavior.

Question 10

How is the cellular response terminated?

Answer 10

The cellular response to a chemical signal is often terminated by removing the signal itself or by removing the receptor. This termination can involve degradation or clearance of the signaling molecule or downregulation of the receptor expression.

Question 11

What are physical signals in cell communication?

Answer 11

Physical signals involve direct physical interactions between cells. These interactions can occur through various intercellular junctions, such as tight junctions, adherens junctions, desmosomes, gap junctions, and hemidesmosomes. These junctions allow for cell-cell adhesion and communication.

Question 12

What are gaseous signals in cell communication?

Answer 12

Gaseous signals, such as oxygen, nitric oxide, and carbon monoxide, can also play a role in cell communication. These gases can diffuse through cell membranes and act as signaling molecules, affecting cellular responses and functions.

Question 13

What are receptors in cell communication?

Answer 13

Receptors are proteins that specifically bind to signaling molecules, called agonists or ligands, and initiate a cellular response. They can be transmembrane or cell surface receptors, located on the outer surface of the cell membrane. Different types of receptors, such as G protein-coupled receptors (GPCRs), ion channel-linked receptors, and enzyme-linked receptors, respond to specific signals.

Question 14

How do transmembrane receptors function?

Answer 14

Transmembrane receptors respond to signals on the outside of the cell by interacting with molecules on the inside. Ligand binding to the extracellular domain of the receptor causes conformational changes that activate the intracellular domains, initiating signaling cascades and cellular responses.

Question 15

Do signaling molecules need to enter the cell to activate receptors?

Answer 15

No, the signaling molecules themselves do not need to enter the cell. Transmembrane receptors can relay the signal from the extracellular environment to the intracellular space without the signaling molecule crossing the cell membrane.

Question 16

What are cytoplasmic and nuclear receptors?

Answer 16

Cytoplasmic and nuclear receptors are specialized receptors that can directly bind to small and hydrophobic signaling molecules. These signaling molecules, such as nitric oxide, steroid hormones, and thyroxine, can cross the cell membrane due to their size and hydrophobic nature. Once inside the cell, they bind to receptors located in the cytoplasm or nucleus.

Question 17

How do cytoplasmic and nuclear receptors function?

Answer 17

Cytoplasmic and nuclear receptors, once bound by their specific signaling molecule, undergo conformational changes that enable them to translocate into the nucleus. In the nucleus, they directly interact with DNA, influencing gene expression and regulating cellular responses.

Question 18

Can different cells express different receptors?

Answer 18

Yes, different cells can express different types and quantities of receptors. This differential receptor expression allows cells to respond selectively to specific signaling molecules, tailoring their responses to their specific functions and environmental cues.

Question 19

Can exposure to signals modify receptor expression or activity?

Answer 19

Yes, exposure to signaling molecules can lead to changes in receptor expression or activity. Cells can upregulate or downregulate the expression of specific receptors in response to the presence or absence of certain signals, thereby adjusting their sensitivity and responsiveness to those signals.

Question 20

Can cells respond to multiple signals?

Answer 20

Yes, cells have the ability to respond to multiple signals simultaneously. They can receive and process different signals from their environment, integrating and coordinating their responses accordingly.

Question 21

Can a single signal elicit multiple responses in a cell?

Answer 21

Yes, a single signal can trigger multiple cellular responses within the same cell. Different signaling pathways and intracellular machinery can be activated in response to the same signal, leading to diverse cellular outcomes.

Question 22

Do different cells respond differently to the same signal?

Answer 22

Yes, different cells can respond differently to the same signaling molecule. This can be due to variations in the sets of receptors expressed by different cells and the specific intracellular machinery they possess. These differences contribute to the diverse functional specialization of cells within an organism.

Question 23

How can the sets of receptors in a cell affect its response to signals?

Answer 23

The sets of receptors expressed by a cell determine which signals it can detect and respond to. Different receptors can activate distinct signaling pathways and initiate specific cellular responses, allowing cells to respond selectively to particular signals.

Question 24

Why can drugs sometimes have additional unwanted effects?

Answer 24

Drugs that target specific signaling pathways or receptors may have unintended effects because the targeted receptors can also interact with other signaling molecules. Activation of these receptors by the drug may lead to additional cellular responses beyond the intended therapeutic effect.

Question 25

What is endocrine signaling?

Answer 25

Endocrine signaling involves the release of hormones by endocrine glands into the bloodstream. These hormones circulate throughout the body and act on target cells located at distant locations. Endocrine signaling allows for long-distance communication between cells.

Question 26

How do hormones regulate cell reactions?

Answer 26

Hormones regulate cell reactions by affecting gene expression in target cells. When a hormone binds to its specific receptor on the surface or inside the target cell, it initiates signaling cascades that ultimately lead to changes in gene expression, altering cellular responses and functions.

Question 27

Can all cells respond to hormones?

Answer 27

No, only cells that express the specific receptors for a particular hormone can respond to it. Cells must possess the correct receptor to interpret the hormone’s signal and initiate the appropriate cellular response.

Question 28

What is paracrine signaling?

Answer 28

Paracrine signaling involves the release of signaling molecules from one cell that diffuse locally to neighboring cells. These signaling molecules, such as proteins (e.g., cytokines, platelet-derived growth factor), amino acid derivatives (e.g., histamine), or dissolved gases (e.g., nitric oxide), act on nearby cells to regulate their functions.

Question 29

How do paracrine signals function?

Answer 29

Paracrine signals act on cells in close proximity to the signaling cell. The released molecules diffuse through the extracellular space and interact with receptors on neighboring cells, triggering specific cellular responses.

Question 30

What is neurocrine signaling?

Answer 30

Neurocrine signaling, also known as neurocrine communication, involves the release of neurotransmitters from a nerve cell. These neurotransmitters travel across the synaptic gap to adjacent target cells, such as other nerve cells or muscle cells, to transmit signals. Neurocrine signaling is highly localized and specific to the synaptic connections between neurons.

Question 31

Can you give an example of neurocrine signaling?

Answer 31

An example of neurocrine signaling is the release of noradrenaline from sympathetic nerve terminals. Noradrenaline acts on adrenoceptors in nearby target cells, such as smooth muscle cells in blood vessels, to cause vasoconstriction.

Question 32

What is autocrine signaling?

Answer 32

Autocrine signaling occurs when cells secrete signaling molecules that bind to their own receptors, generating changes in their own behavior. These molecules act on the same cell type that produced them, allowing cells to regulate their own functions.

Question 33

Can you provide an example of autocrine signaling?

Answer 33

A well-known example of autocrine signaling is the cytokine interleukin-1 produced by monocytes. Interleukin-1 is released in response to external stimuli and binds to cell-surface receptors on the same monocyte that produced it, influencing the cell’s behavior and immune responses.

Question 34

How can autocrine signaling impact molecule production?

Answer 34

Autocrine signaling can lead to positive or negative feedback on molecule production. Binding of the signaling molecule to its own receptor can increase (positive feedback) or decrease (negative feedback) the production of the molecule, providing self-regulation of cellular responses.

Question 35

What is juxtracrine signaling?

Answer 35

Juxtracrine signaling, also known as contact-dependent signaling, involves immediate neighbors signaling to each other through membrane-bound molecules. This form of signaling does not require the release of a signaling molecule into the extracellular space.

Question 36

Can you provide an example of juxtracrine signaling?

Answer 36

An example of juxtracrine signaling is contact-dependent receptor-ligand binding, where direct cell-to-cell communication occurs through interactions with membrane-bound molecules or the extracellular matrix (ECM). An important example is antigen presentation, which requires contact between cells involved in the immune response.

Question 37

What are communication junctions and how do they function?

Answer 37

Communication junctions, such as gap junctions, provide a direct communication link between neighboring cells. Gap junctions are channels that can be opened or closed in response to the cell environment, similar to ion channels. These channels allow the diffusion of small molecules, including ions, nucleotides, and sugars, between the connected cells.

Question 38

How are gap junctions formed and what do they enable?

Answer 38

Gap junctions are formed by pore-forming proteins called connexins, which create narrow pores (2-4nm) between cells. These junctions provide rapid metabolic and electrical coupling between cells, allowing for the coordinated transfer of molecules and electrical signals. For example, gap junctions between heart muscle cells enable the quick passage of waves of electrical excitation, facilitating synchronized contractions.

Question 39

Where are gap junctions particularly important?

Answer 39

Gap junctions play a crucial role in the myometrium of the uterus toward the end of pregnancy. They help coordinate uterine contractions during childbirth, allowing for effective and synchronized muscle contractions.

Question 40

What are the classes of transmembrane receptors?

Answer 40

The classes of transmembrane receptors include G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), ion channel-linked receptors, and enzyme-linked receptors.

Question 41

What is the mechanism that initiates intracellular signaling in transmembrane receptors?

Answer 41

The mechanism of intracellular signaling initiation in transmembrane receptors involves ligand binding to the extracellular domain of the receptor, leading to conformational changes in the receptor’s intracellular domain. This conformational change activates the receptor, allowing it to interact with intracellular signaling molecules and initiate signaling cascades.

Question 42

What are G protein-coupled receptors (GPCRs)?

Answer 42

GPCRs are transmembrane receptors that interact with heterotrimeric G proteins. Upon ligand binding, GPCRs undergo conformational changes, activating the associated G protein. The activated G protein then initiates downstream signaling cascades by regulating the activity of effector proteins or ion channels.

Question 43

What are receptor tyrosine kinases (RTKs)?

Answer 43

RTKs are transmembrane receptors that have intrinsic kinase activity. Ligand binding to RTKs leads to receptor dimerization and autophosphorylation of tyrosine residues. The phosphorylated tyrosine residues serve as docking sites for signaling proteins, initiating intracellular signaling pathways.

Question 44

How do ion channel-linked receptors function?

Answer 44

Ion channel-linked receptors are transmembrane receptors that directly control the opening and closing of ion channels. Ligand binding to these receptors induces conformational changes that alter the ion channel’s activity, leading to changes in membrane potential and intracellular signaling.

Question 45

What are enzyme-linked receptors?

Answer 45

Enzyme-linked receptors are transmembrane receptors that have intrinsic enzymatic activity. Ligand binding to these receptors induces conformational changes, activating the receptor’s enzymatic activity. This enzymatic activity initiates intracellular signaling cascades by phosphorylating downstream signaling molecules.

Question 46

What happens during the reception step of cell signaling?

Answer 46

During reception, a chemical message, also known as a signaling molecule or ligand, binds to a specific protein receptor on the cell surface. This binding event initiates the cell signaling process.

Question 47

What occurs during the transduction step of cell signaling?

Answer 47

In the transduction step, the binding of the signaling molecule to the receptor induces conformational changes in the receptor protein. These conformational changes activate intracellular signaling pathways, leading to a cascade of reactions. This cascade often involves the activation or modulation of various proteins and second messengers, amplifying the initial signal.

Question 48

What happens during the response step of cell signaling?

Answer 48

The transduction pathway triggered by the binding of the signaling molecule leads to a specific cellular response. The response can vary depending on the type of signaling pathway and the target cell. Examples of cellular responses include gene expression changes, activation or inhibition of enzymes, rearrangement of the cytoskeleton, or altered cell behavior.

Question 49

How does cell signaling affect gene expression?

Answer 49

In some cases, cell signaling pathways can activate transcription factors, which are proteins that control gene expression. Transcription factors can bind to specific regions of DNA, turning on or off the expression of target genes. This regulation of gene expression allows cells to respond to external signals and adapt their behavior accordingly.

Question 50

How are signaling molecules controlled?

Answer 50

Signaling molecules can be controlled through post-translational modifications, such as phosphorylation, which can activate or deactivate them. Additionally, the binding of guanosine diphosphate (GDP) or guanosine triphosphate (GTP) to G proteins can regulate their activity and signaling function. Other molecules, such as calcium ions (Ca2+) and cyclic adenosine monophosphate (cAMP), can act as activators or modulators of signaling pathways.

Question 51

What are the three main types of cell surface receptors?

Answer 51

The three main types of cell surface receptors are ion channel receptors, G-protein coupled receptors (GPCRs), and enzyme-linked receptors.

Question 52

What are ion channel receptors?

Answer 52

Ion channel receptors act like gates that open or close to allow ions to enter or exit the cell. They can be further classified into voltage-gated ion channels, which respond to changes in membrane potential, and ligand-gated ion channels, which open or close in response to the binding of specific ligands, such as neurotransmitters.

Question 53

What are G-protein coupled receptors (GPCRs)?

Answer 53

GPCRs are cell surface receptors that are coupled to intracellular G proteins. When a ligand binds to the extracellular domain of a GPCR, it induces conformational changes that activate the associated G protein, initiating intracellular signaling cascades. GPCRs are involved in a wide range of physiological processes and are targets for many drugs.

Question 54

What are enzyme-linked receptors?

Answer 54

Enzyme-linked receptors are cell surface receptors that have intrinsic enzymatic activity. Ligand binding to these receptors activates their enzymatic function, leading to the initiation of intracellular signaling pathways. Examples of enzyme-linked receptors include receptor tyrosine kinases (RTKs) and receptor guanylyl cyclases.

Question 55

What are G-protein coupled receptors (GPCRs)?

Answer 55

GPCRs are a diverse group of cell surface receptors that use specific proteins called G proteins to participate in cell signaling. They have a transmembrane region that spans the cell membrane seven times, and their downstream effects are mediated via their associated G-proteins.

Question 56

What are enzyme-linked receptors?

Answer 56

Enzyme-linked receptors are cell surface receptors that have a catalytic site on their intracellular domain. They can be associated with an enzyme or have intrinsic enzymatic activity. Binding of a ligand to the extracellular domain of an enzyme-linked receptor activates the associated enzyme, leading to the initiation of specific intracellular signaling pathways.

Question 57

What are tyrosine kinase receptors?

Answer 57

Tyrosine kinase receptors are a subtype of enzyme-linked receptors. They contain a kinase enzyme that transfers phosphate molecules to the amino acid tyrosine. Ligand binding to the extracellular domain of a tyrosine kinase receptor leads to receptor dimerization and phosphorylation of tyrosine residues, initiating downstream signaling cascades involved in processes such as cell division and wound healing.

Question 58

What is the structure of G-proteins?

Answer 58

G-proteins are proteins associated with GPCRs. They consist of three subunits: alpha, beta, and gamma. When a ligand binds to a GPCR, it induces conformational changes that allow the GPCR to interact with and activate the associated G-protein. The activated G-protein then dissociates into the alpha subunit and the beta-gamma dimer, which can regulate various intracellular signaling pathways.

Question 59

What are G-proteins?

Answer 59

G-proteins are heterotrimeric proteins consisting of three subunits: alpha (α), beta (β), and gamma (γ). In their inactive state, GDP is bound to the alpha subunit. They are involved in transmitting signals from GPCRs to intracellular signaling pathways.

Question 60

What are G-protein coupled receptors (GPCRs)?

Answer 60

GPCRs are a large family of cell surface receptors that interact with G-proteins. They can be activated by various signals such as neurotransmitters, hormones, ions, peptides, and photons. Examples include adrenoreceptors, muscarinic acetylcholine receptors, and opioid receptors.

Question 61

How does ligand binding to G-proteins lead to a cascade response?

Answer 61

When a ligand binds to a GPCR, it induces conformational changes that allow the GPCR to interact with the associated G-protein. This results in the exchange of GDP for GTP on the alpha subunit, leading to the activation of the G-protein. The activated G-protein can then initiate a cascade of intracellular signaling events by interacting with various secondary messengers, amplifying the signal and catalyzing multiple reactions.

Question 62

What is signal amplification in the context of G-proteins?

Answer 62

Signal amplification refers to the ability of one agonist binding to a GPCR to trigger multiple downstream cellular reactions. This is achieved through the activation of multiple enzymes and catalysis of many reactions by secondary messengers, leading to a robust and amplified cellular response.

Question 63

How is GPCR activity switched off?

Answer 63

GPCR activity is switched off through the action of GTPase, which catalyzes the hydrolysis of GTP on the alpha subunit of the G-protein into GDP and inorganic phosphate (Pi). This results in the dissociation of the alpha subunit from the effector molecule, allowing the reformation of the heterotrimeric complex of the G-protein. The G-protein can then reassociate with the transmembrane receptor, ready for the next ligand binding.

Question 64

What are the types of G-proteins?

Answer 64

G-proteins can be categorized based on their alpha (α) subunits. Different alpha subunits can stimulate different effector molecules, which can either increase or decrease the concentration of a secondary messenger. This ultimately leads to the activation or inhibition of downstream effectors, resulting in specific cellular responses. The specific type of G-protein and its associated alpha subunit determine the nature of the cellular response.

Question 65

What is the role of the GS alpha subunit?

Answer 65

The GS alpha subunit stimulates adenylyl cyclase, which catalyzes the conversion of ATP to cyclic AMP (cAMP). This leads to an increase in cAMP levels, which in turn activates protein kinase A (PKA). PKA phosphorylates target proteins, resulting in various cellular responses.

Question 66

What is the role of the Gi alpha subunit?

Answer 66

The Gi alpha subunit inhibits adenylyl cyclase, which reduces the production of cAMP. This leads to a decrease in cAMP levels, inhibiting the activation of protein kinase A (PKA) and modulating cellular responses.

Question 67

What is the role of the GQ or G11 alpha subunit?

Answer 67

The GQ or G11 alpha subunit stimulates phospholipase C, which cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) in the cell membrane into inositol trisphosphate (IP3) and diacylglycerol (DAG). This results in an increase in IP3 and DAG levels. IP3 opens calcium channels, leading to a release of calcium ions into the cytoplasm. DAG activates protein kinase C (PKC), which phosphorylates target proteins, contributing to cellular responses.