cell communication
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Questions and Answers

What is the primary function of adenylyl cyclase in the signaling pathway described?

  • Transport glucose molecules
  • Convert ATP to cAMP (correct)
  • Phosphorylate receptor proteins
  • Degrade cAMP to AMP

Which of the following statements accurately reflects the role of EGF in its signaling pathway?

  • EGF is a peptide hormone that binds to a tyrosine kinase receptor. (correct)
  • EGF activates G-protein-coupled receptors directly.
  • EGF is a steroid hormone that crosses the membrane.
  • EGF initiates the process by deactivating adenylate cyclase.

What type of receptor does epinephrine bind to?

  • Ligand-gated ion channel
  • G-protein coupled receptor (GPCR) (correct)
  • Nuclear receptor
  • Receptor tyrosine kinase

What is the result of activating the EGF signaling pathway?

<p>Enhanced cell division and growth (B)</p> Signup and view all the answers

Which of the following best describes the amplification event in the transduction pathway?

<p>Each activated molecule leads to the activation of more molecules. (A)</p> Signup and view all the answers

What molecule is primarily responsible for the breakdown of glycogen into glucose 1-phosphate in response to epinephrine?

<p>Protein kinase A (PKA) (A)</p> Signup and view all the answers

In the context of cell signaling, what is the role of the ligand in the discussed pathways?

<p>To bind and activate the receptor (A)</p> Signup and view all the answers

Which of the following statements about peptide hormones, like EGF, is correct?

<p>They require specific receptors on the cell surface. (B)</p> Signup and view all the answers

What is the role of nitric oxide (NO) in signal transduction?

<p>It acts as a first messenger that starts the signal transduction. (C)</p> Signup and view all the answers

Which of the following is a secondary messenger involved in muscle relaxation?

<p>cGMP (B)</p> Signup and view all the answers

How does ginseng potentially affect nitric oxide levels?

<p>It enhances nitric oxide production. (C)</p> Signup and view all the answers

What is the primary function of PDE5 in the signaling pathway?

<p>It degrades cGMP, regulating its levels. (A)</p> Signup and view all the answers

What cellular response is triggered by the signaling cascade involving nitric oxide?

<p>Muscle relaxation (B)</p> Signup and view all the answers

What is the primary function of the sending cell in cell communication?

<p>Creates and releases the ligand (D)</p> Signup and view all the answers

What characterizes autocrine signaling?

<p>A cell releases a ligand that binds to its own receptors. (B)</p> Signup and view all the answers

How do target cells differ from non-target cells in cell signaling?

<p>Target cells have receptors for the ligand (D)</p> Signup and view all the answers

Why does the signaling pathway involve amplification?

<p>It allows for a small initial signal to lead to a larger cellular response. (B)</p> Signup and view all the answers

What role do chemical signals play in cell communication?

<p>Allow communication without physical contact (A)</p> Signup and view all the answers

What type of receptor does nitric oxide act on?

<p>Intracellular receptors (A)</p> Signup and view all the answers

What is the function of juxtacrine signaling?

<p>It requires direct contact between two cells. (A)</p> Signup and view all the answers

What effect would Viagra have on the activity of PDE5?

<p>It blocks the activity of PDE5. (D)</p> Signup and view all the answers

What role do cytokines play in direct signaling?

<p>They bind to complementary proteins on adjacent cells. (D)</p> Signup and view all the answers

What is the significance of a threshold concentration in cell signaling?

<p>It is required to trigger the communication pathway (A)</p> Signup and view all the answers

Which type of signaling is specifically identified as 'cell talking to itself'?

<p>Autocrine signaling (C)</p> Signup and view all the answers

What is quorum sensing in bacteria?

<p>Sensing population density through signaling molecules (D)</p> Signup and view all the answers

How do signal transduction pathways function in relation to environmental stimuli?

<p>They lead to programmed cellular responses (B)</p> Signup and view all the answers

What is one key characteristic of paracrine signaling?

<p>It allows a cell to signal nearby cells. (A)</p> Signup and view all the answers

Which type of cell communication is essential for distinguishing 'self from non-self'?

<p>Juxtacrine signaling (C)</p> Signup and view all the answers

What are autoinducers in the context of bacterial communication?

<p>Signaling molecules produced by bacteria (D)</p> Signup and view all the answers

What does the presence of conserved signaling mechanisms in bacteria and eukaryotes suggest?

<p>Ancestral signaling molecules evolved in prokaryotes (C)</p> Signup and view all the answers

What is a potential outcome of autocrine signaling during development?

<p>Stabilization of cell identity (C)</p> Signup and view all the answers

What system uses plasmodesmata for signaling between cells?

<p>Plant cell signaling (B)</p> Signup and view all the answers

What will occur when a killer T-cell binds to an infected cell but cannot kill it?

<p>The killer T-cell will detach and target another cell. (C)</p> Signup and view all the answers

How does quorum sensing (QS) impact the expression of virulence genes in microbes?

<p>It requires a high concentration of signaling molecules to enhance virulence. (A)</p> Signup and view all the answers

Which method is most effective to decrease the virulence of a microbe that utilizes quorum sensing?

<p>Develop a drug that decreases the cell density of the microbial infection. (A)</p> Signup and view all the answers

What is the nature of communication implied in the scenario with a signal-emitting cell and a nearby receptor cell?

<p>They utilize local regulators released into the surrounding environment. (C)</p> Signup and view all the answers

What effect does breaking down the T-cell receptor have on the humoral immune response?

<p>B-cells will not be activated if T-cell binding is compromised. (B)</p> Signup and view all the answers

What role do signaling molecules play in quorum sensing?

<p>They enable microbes to coordinate behavior based on population density. (C)</p> Signup and view all the answers

If a microbe's ability to communicate via quorum sensing is disrupted, what is likely to occur?

<p>The expression of virulence genes may be diminished. (C)</p> Signup and view all the answers

What is the primary consequence when the helper T-cell cannot bind to the B-cell?

<p>The B-cell produces fewer antibodies due to lack of activation. (A)</p> Signup and view all the answers

What occurs when a signal molecule binds to a GPCR?

<p>The G-protein is activated. (B)</p> Signup and view all the answers

Which component is necessary for the activation of a G-protein?

<p>GTP (A)</p> Signup and view all the answers

What happens to a G-protein when it is attached to GDP?

<p>It becomes inactive. (D)</p> Signup and view all the answers

Which of the following statements about GPCRs is true?

<p>GPCRs are transmembrane proteins. (B)</p> Signup and view all the answers

What does the alpha subunit of the G-protein do upon activation?

<p>It activates adenylate cyclase. (A)</p> Signup and view all the answers

What is the role of cAMP in GPCR signaling?

<p>It acts as a secondary messenger. (D)</p> Signup and view all the answers

What initiates the process where a GPCR activates a G-protein?

<p>Ligand binding to the GPCR. (A)</p> Signup and view all the answers

Why is GTP important in the context of GPCR signaling?

<p>It transitions the G-protein to an active state. (D)</p> Signup and view all the answers

Flashcards

Signal amplification in transduction pathways

A signaling pathway where the binding of a single signal molecule triggers a cascade of events, amplifying the signal at each step.

G-protein coupled receptor (GPCR)

A type of receptor that binds to a signaling molecule and activates a G protein, which in turn activates another molecule, triggering a signal cascade.

Second messenger

A small intracellular molecule that acts as a messenger to relay and amplify signals within the cell.

Epinephrine signaling pathway in glycogen breakdown

A signaling pathway triggered by epinephrine binding to its GPCR, leading to the breakdown of glycogen into glucose 1-phosphate.

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Peptide hormone

A type of hormone that binds to receptors on the cell surface, not passing through the membrane.

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Ligand

A molecule that binds to a receptor and initiates a signaling pathway.

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Tyrosine kinase receptor

A type of receptor that binds to a ligand and activates a protein kinase, triggering a phosphorylation cascade.

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Target (end) proteins

The final proteins in a signaling pathway that carry out the cellular response.

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Cell signaling

The process by which cells communicate with each other through signaling molecules, triggering a cascade of reactions.

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Receptor

A protein that binds to a specific ligand, initiating a signal transduction pathway.

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Signal transduction pathway

A series of steps that a cell takes to change its activity in response to an external signal, involving a chain of molecules that amplify the signal.

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Signal amplification

A process in which a single signaling molecule triggers a cascade of events, amplifying the signal at each step.

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Threshold concentration

The concentration of a signaling molecule required to trigger a specific cellular response.

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Quorum sensing

A signaling pathway where cells release signaling molecules that are detected by other cells within a population, leading to coordinated behavior, such as biofilm formation.

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Cellular response

The process by which cells modify their internal environment, including their growth, development and behavior, in response to external stimuli.

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How to decrease virulence with quorum sensing?

A drug that reduces the number of bacteria present, which in turn decreases the concentration of signaling molecules, making it harder for the bacteria to activate virulence genes.

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Local Communication in Cells

Signal-emitting cells release local regulators that communicate with nearby target cells through diffusion.

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Impact of T-cell receptor breakdown

The T-cell receptor is essential for activating B-cells. When the receptor breaks down, the T-cell can no longer bind to the B-cell, preventing its activation.

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Role of helper T-cells in humoral immunity

Helper T-cells are crucial for activating B-cells in the humoral immune response. Without these cells, B-cells cannot be activated.

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Signal Transduction

The process where a signal molecule binds to a receptor and triggers a chain of events inside the cell, amplifying the signal.

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Humoral Immune Response

Antibodies produced by activated B-cells, targeting specific pathogens, are released into the bloodstream to fight infections.

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Impact of a faulty T-cell receptor on killer T-cells

Killer T-cells are responsible for directly destroying infected cells. When a T-cell receptor fails, the killer T-cell can still bind to the infected cell, but it can't kill it.

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Autocrine signaling

A cell sends signals to itself using ligands that bind to receptors on its own surface or inside the cell.

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Juxtacrine signaling

Signaling substances move directly between adjacent cells through gap junctions or plasmodesmata.

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Cell to cell recognition

Immune cells communicate directly by recognizing antigens (sugars) on each other's surfaces.

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Contact inhibition

Some cells prevent other cells from dividing by making direct contact with them.

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Direct signaling through binding proteins

Two cells may bind together because they have complementary proteins on their surfaces. When these proteins bind, they change shape, sending a signal.

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Cytokines

Small proteins released by cells that regulate the growth and activity of immune cells.

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Paracrine signaling

Cells may release signals that affect nearby cells.

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Endocrine signaling

Signaling molecules travel through the bloodstream to reach target cells.

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First Messenger

A molecule that initiates a signal transduction pathway within a cell.

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Cyclic GMP (cGMP)

A type of second messenger that is important for regulating many cellular processes, including muscle contraction and relaxation.

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What is a G-protein coupled receptor (GPCR)?

A type of transmembrane receptor that binds to signaling molecules (like hormones or neurotransmitters) and activates a G-protein, leading to a cascade of intracellular events.

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What is a G Protein?

A protein that acts as an 'on-off' switch in signal transduction pathways. It binds to guanine nucleotides, with GTP activating the protein and GDP inactivating it.

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What are heterotrimeric G proteins?

A type of G protein composed of three subunits (alpha, beta, and gamma). These proteins are often associated with GPCRs.

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What is signal transduction?

The process by which a signal molecule binds to a receptor, triggering a series of intracellular events that amplify and relay the signal.

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What is a ligand?

A signal molecule that binds to a receptor, initiating a signaling pathway.

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What is a second messenger?

A small intracellular molecule that relays and amplifies signals within the cell. It's generated in response to the initial signal and can activate various downstream targets.

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What is signal amplification?

The process of amplifying a signal, where a small initial signal triggers a cascade of events that produce a much larger response.

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Describe the steps in a G-protein coupled receptor signaling pathway.

A process involving a series of steps, where a signal molecule binds to a receptor and triggers a cascade of events, ultimately leading to a specific cellular response.

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Study Notes

Cell Communication Overview

  • Cells communicate using chemical signals.
  • These signals are often proteins or other molecules.
  • The sending cell secretes these molecules into the extracellular space.
  • These signals can then float to neighboring cells.
  • This process is like sending messages in a bottle.

Types of Cell Signaling

  • Autocrine: A cell signals to itself.
  • Juxtacrine: Cells connected by gap junctions exchange signaling substances directly. Animal cells using gap junctions and plant cells using plasmodesmata.
  • Paracrine: A cell targets a nearby cell. Examples include neurotransmitters in synapses, quorum sensing in bacteria, and yeast mating. Paracrine signals are short-range.
  • Endocrine: A cell targets a distant cell through the bloodstream. Specialized cells release hormones into the bloodstream, which carries them to their target cells throughout the body.

Signal Transduction

  • A signal molecule binds to a receptor protein, changing the receptor's shape.
  • Chemical messengers relay the signal.
  • This leads to a specific cellular response.
  • This process is an example of a cascade because one signal triggers many more downstream effects.
  • The receptor activation triggers subsequent proteins and messengers.
  • Ultimately, the pathway results in a specific cellular response.

Phosphorylation

  • Phosphorylation is the addition of a phosphate group to a molecule.
  • This process often activates or deactivates proteins, acting as a sort of "switch."
  • The transfer of a phosphate group is catalyzed by an enzyme called a kinase.
  • Another type of enzyme, a phosphatase, removes phosphate groups.

Important Things to Know

  • Chemical signals allow cells to communicate.
  • The distance between signaling and responding cells can vary (small or large).
  • There is often a gradient response.
  • Threshold concentrations are needed to trigger a communication pathway.

Quorum Sensing

  • Bacteria produce autoinducers (signaling molecules).
  • When enough bacteria are present (a quorum):
  • The concentration of signaling molecules increases.
  • Bacteria sense the local population density.
  • All bacteria turn on specific functions (eg. bioluminescence, formation of biofilms, or toxin production).

Types of Receptors

  • Cell-surface receptors: Embedded in the plasma membrane.
  • Intracellular receptors: Located inside the cell (cytoplasm or nucleus). Generally for hydrophobic hormones that can cross the membrane.

G-Protein Coupled Receptors (GPCR)

  • A common type of membrane receptor.
  • Consists of a receptor protein associated with a G protein.
  • G-proteins are proteins involved in relaying chemical signals from outside the cell to inside the cell.
  • G-proteins exist in three subunits (alpha, beta, and gamma).

How does a GPCR work?

  • The signal molecule binds to the receptor's binding site on the outside of the cell.
  • The GPCR undergoes a conformational change. This activates the G protein. . The activated G protein activates a cascade of further compounds, resulting in a change downstream in the cell.

Hormones

  • Hormones are signals that travel through the circulatory system.
  • Hormones act on distant target cells.
  • Hormones are crucial for long-distance communication.

Paracrine Signaling

  • Used for short-distance communication between nearby cells.
  • Diffusing chemical messengers carry signals.

Synaptic Signaling

  • Direct relay of signaling between neurons (a type of paracrine signaling).
  • Neurotransmitters carry information across synapses.

Receptor Tyrosine Kinases (RTKs)

  • Signal receptors that activate a cascade of reactions.
  • Involved in regulating various cellular activities.

Secondary Messengers

  • Small, non-protein, water-soluble molecules or ions.
  • Diffuse rapidly through a cell to amplify a signal.
  • Include cAMP, calcium ions (Ca2+), and inositol triphosphate (IP3).

Positive and Negative Feedback loops

  • Positive feedback loops amplify a response by increasing the stimulus.
  • Negative feedback loops reduce a response.

Apoptosis

  • Programmed cell death, a necessary process for development and homeostasis.
  • Triggered by molecular signals activating a cascade of suicide” proteins.

Other Topics

  • Different types of plant hormones.
  • How antidepressants work.
  • Cell signaling in the immune system
  • Signal transduction pathways
  • The role of ligands in cell signaling.
  • Importance to maintaining homeostasis

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