Cellular Signaling and Signal Transduction

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Questions and Answers

What role do steroid-receptor complexes play in cellular processes?

  • They act as signal amplifiers.
  • They act as transcription factors. (correct)
  • They deactivate protein kinases.
  • They inhibit gene transcription.

What is the primary function of the ras protein in cellular signaling?

  • It acts as a transcription factor.
  • It activates protein kinase cascades. (correct)
  • It inhibits tyrosine kinase activity.
  • It deactivates second messengers.

How do protein kinases contribute to signal transduction?

  • By phosphorylating target proteins. (correct)
  • By binding directly to ligand-gated channels.
  • By inhibiting calcium ion entry.
  • By generating second messengers.

What occurs if there is a mutation in the gene for the ras protein?

<p>Ras is activated without growth factor. (B)</p> Signup and view all the answers

Which of the following is a primary second messenger in cellular signaling?

<p>Calcium ion (Ca+2) (D)</p> Signup and view all the answers

What catalyzes the formation of cyclic AMP from ATP?

<p>G-protein activated adenylyl cyclase (B)</p> Signup and view all the answers

What happens to the concentration of calcium ions (Ca+2) in the cytoplasm during signaling?

<p>It increases through release from the endoplasmic reticulum. (B)</p> Signup and view all the answers

What is the consequence of deactivating protein kinases in the signaling pathway?

<p>Termination of the signaling cascade. (A)</p> Signup and view all the answers

What is the primary function of receptor tyrosine kinases when a signaling ligand binds to them?

<p>They transfer phosphate groups between macromolecules. (B)</p> Signup and view all the answers

What happens when a ligand binds to a ligand-gated ion channel?

<p>The channel opens, allowing specific ions to enter the cell. (D)</p> Signup and view all the answers

How does phosphorylation generally affect a protein's activity?

<p>It can change the protein's shape, affecting its function. (B)</p> Signup and view all the answers

What role does the Ras oncogene play in cell signaling?

<p>It acts as a G-protein that propagates signals. (A)</p> Signup and view all the answers

What is a common consequence of disruptions in receptor tyrosine kinase pathways?

<p>Development of various cancers. (A)</p> Signup and view all the answers

What distinguishes second messengers from primary signaling molecules?

<p>Second messengers act inside the cell after the primary signal. (A)</p> Signup and view all the answers

What occurs during the formation of a dimeric protein in receptor tyrosine kinases?

<p>Two protein monomers combine upon ligand binding. (A)</p> Signup and view all the answers

What is a characteristic of hydrophobic signaling molecules?

<p>They can cross the cell membrane to bind their receptor inside the cell. (A)</p> Signup and view all the answers

What occurs when a ligand binds to its receptor on a target cell?

<p>The receptor undergoes a change in shape. (C)</p> Signup and view all the answers

Which of the following is NOT a function of receptor tyrosine kinases?

<p>Activation of G-proteins. (D)</p> Signup and view all the answers

In signal transduction, what is the role of a phosphorylation cascade?

<p>It amplifies the signal within the cell. (A)</p> Signup and view all the answers

What is a common effect of second messengers in signal transduction pathways?

<p>They mediate the transmission of signals from receptors. (C)</p> Signup and view all the answers

Which mechanism allows cells to respond specifically to chemical signals?

<p>Expression of specific receptor proteins on target cells. (A)</p> Signup and view all the answers

How does the Ras oncogene contribute to cell signaling?

<p>It functions as a molecular switch in signaling pathways. (D)</p> Signup and view all the answers

What is the primary role of ligand-gated ion channels in cellular signaling?

<p>They facilitate rapid changes in ion concentrations. (B)</p> Signup and view all the answers

What typically happens in a cell when the ligand binds to a receptor in the process of signal transduction?

<p>The receptor triggers a series of intracellular responses. (A)</p> Signup and view all the answers

Flashcards

Steroid Hormone Action

Steroid hormones bind to receptors, forming complexes that regulate gene expression.

Signal Transduction Cascade

A series of protein activations, amplifying the effect of initial signals.

Protein Kinase

An enzyme that adds phosphate groups to other proteins, affecting their function.

Protein Phosphatase

An enzyme that removes phosphate groups from proteins, deactivating them.

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Ras Oncogene

A gene that, when mutated, can cause uncontrolled cell growth.

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Second Messengers

Small, non-protein molecules that relay signals inside a cell, such as calcium and cAMP.

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Cyclic AMP (cAMP)

A second messenger produced from ATP, activating protein kinase A.

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Calcium Ions (Ca+2)

A second messenger that can be released from the ER to trigger intracellular responses.

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Signal types (short distance)

Paracrine and synaptic signals affect cells near the source of the signal.

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Signal types (long distance)

Endocrine signals travel through the bloodstream to distant cells.

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G protein-coupled receptors (GPCRs)

Membrane receptors that activate intracellular G-proteins upon ligand binding, initiating downstream signaling cascades.

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Receptor Tyrosine Kinases

Membrane receptors that phosphorylate tyrosines upon ligand binding, triggering multiple downstream signaling pathways.

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Ligand-gated ion channels

Membrane channels that open or close in response to ligand binding, allowing ion flow across the membrane.

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Intracellular receptors

Receptors located inside the cell that bind hydrophobic signals that can pass through the cell membrane directly.

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Phosphorylation

The addition of a phosphate group to a molecule, often altering its activity.

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Signal transduction

The process by which a signal from outside the cell is converted to a response within the cell.

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Cell-cell communication

Cells exchange signals to coordinate their activities.

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Gap junctions

Direct connection between animal cells that allows molecules to pass through.

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Plasmodesmata

Direct connection between plant cells that allows molecules to pass through.

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Signal transduction

The process by which a cell converts a signal into a cellular response.

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Target cells

Cells that have receptors specific to a signaling molecule / ligand

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Receptor protein

A protein on a cell surface that binds to a signaling molecule.

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Ligand

A signaling molecule that binds to a receptor.

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Yeast mating

Yeast cells release specific molecules to attract compatible mates.

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Study Notes

Cellular Signaling and Signal Transduction

  • Cell communication is crucial for cell function. Cells exchange key molecules directly.
  • Gap junctions facilitate communication between animal cells, and plasmodesmata do the same for plant cells.

Cell-Cell Recognition

  • Surface ligands on one cell bind to receptors on another cell, triggering a response in the target cell.

Cellular Communication by Released Molecular Signals

  • Yeast cells, for sexual reproduction, have different mating types ("A" and "alpha").

  • "A" cells release "A" mating factor (recognized by "alpha" cells), and vice versa.

  • Fusion of cells results in diploid cells and meiosis (genetic recombination).

  • Myxococcus bacteria, when nutrients are scarce, form structures to survive.

  • This involves chemical signaling between individual cells enabling their collective action.

  • Single-celled eukaryotes utilize similar mechanisms.

Signal Transduction

  • Cell membranes receive and absorb chemical signals from outside the cell.

  • These signals alter cellular functions and gene expression.

  • Signal transduction is essential for multicellular organisms.

  • Cells respond only if they have appropriate receptor proteins for the signal.

  • Ligand binding to a receptor changes the receptor's shape, triggering intracellular responses.

  • These responses lead to the appropriate cellular responses.

Types of Signals and Receptors

  • Signals can be short-range and long-range.
    • Short-range: paracrine, synaptic
    • Long-range: endocrine
  • G protein-coupled receptors (GPCRs) are transmembrane proteins that use GTP.
  • Important for embryonic development, sensory functions, and responses to infections.
  • Receptor tyrosine kinases are activated by dimerization (two monomers coming together).
  • Tyrosine kinases phosphorylate other proteins, triggering a cellular response, particularly involved in cancer.
  • Important for cell growth and division.
  • Ion channels are receptors that allow ion flow.
  • Steroid hormones are examples of hydrophobic signals that interact with intracellular protein receptors (intracellular signaling).

Signal Transduction Pathways

  • Signal transduction often uses a cascade of protein activations.

  • This amplifies the initial signal.

  • Protein kinases phosphorylate proteins, and phosphatases dephosphorylate them.

  • This allows reversible activation and responses.

  • Signal pathways use second messengers like calcium ions (Ca²⁺) and cyclic AMP (cAMP).

  • These second messengers amplify and distribute signals quickly.

  • The goal of signal transduction is often to alter gene expression.

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