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Unit Overview

  • Unit 4: Cell Communication & Cell Cycle

    • Lesson 1: Cell Communication & Signal Transduction

    • Lesson 2: Feedback Mechanisms

    • Lesson 3: Cell Cycle

    • Lesson 4: Mitosis

    • Lesson 5: Checkpoints & Regulatory Proteins

    • Lesson 6: Cancer

Lesson 1: Aim

  • Aim: How do cells communicate with each other?

  • Importance of cell communication

Importance of Cell Communication

  • Think-Pair-Share Question: Why is it important for cells to communicate?

  • Consider examples to illustrate the concept.

Topic 4.1: Cell Communication

  • Learning Objectives:

    • IST-3.A: Describe ways that cells communicate.

    • IST-3.B: Explain short and long-distance communication.

  • Describe vs Explain:

    • Describe: note characteristics.

    • Explain: delve into the "why" or "how".

Topic 4.2: Reception and Transduction Basics

  • Learning Objectives:

    • IST-3.C: Describe components of signal transduction pathways.

    • IST-3.D: Explain role of components in cellular response.

Topic 4.3: Cell Response to Transduction

  • Learning Objectives:

    • IST-3.E: Role of environment in cellular response.

    • IST-3.F: Types of cellular responses from signal transduction pathways.

Cell Signaling Defined

  • Definition: Series of steps allowing cells to respond to environmental signals.

  • Responses can initiate cellular activities (e.g., cell cycle initiation).

  • Involves ligand secretion and receptor interaction.

Overview of Cell Signaling

  • Three stages:

    1. Reception: Ligand binds to receptor.

    2. Transduction: Signal conversion occurs.

    3. Response: Alteration of cellular processes.

How Cells Respond to Signal Transduction

  • Initiation of transcription of target genes leads to protein synthesis that elicits responses.

Reception Process

  • Reception: Detection of ligand by receptor in target cell.

  • Receptor Characteristics:

    • Binds signal molecules (ligands).

    • Involves specificity in binding.

Activation of Receptors

  • Ligand binding induces conformational change, facilitating interaction with other cellular molecules.

  • May occur at plasma membrane or intracellularly.

Types of Receptors

  • Plasma Membrane Receptors:

    • Most common type; bind to polar and large ligands.

    • Examples: G protein coupled receptors, ligand-gated ion channels.

  • Intracellular Receptors:

    • Found in cytoplasm/nucleus; bind to hydrophobic molecules like steroid hormones.

Mechanisms of Ligand Delivery

  • Cell-to-Cell Contact:

    • Physical contact between cells for signal transmission.

  • Paracrine Signaling:

    • Short-range signaling via ligands.

  • Autocrine Signaling:

    • Cell acts on itself via secreted ligands.

  • Endocrine Signaling:

    • Hormones released into circulation for long-distance signaling.

Cell-to-Cell Contact Mechanisms

  • Fastest signaling method; using gap junctions in animal cells or plasmodesmata in plant cells for rapid signal diffusion.

Transduction Process

  • Transduction: Conversion of extracellular signals to intracellular signals, forming a signal transduction pathway.

Protein Regulation in Transduction

  • Regulated by phosphorylation (activation) and dephosphorylation (deactivation) of proteins.

  • Shape change impacts protein function.

Second Messengers in Transduction

  • Amplifies the signaling response.

  • Common second messenger: cyclic AMP (cAMP).

Response Mechanism

  • Final signaling pathway molecule translates signal into a cellular response:

    • Alters membrane permeability.

    • Impacts metabolic processes.

    • Modifies gene expression.

Signal Transduction Pathways

  • Influence gene expression and cell function, modifying phenotypes or inducing cell death.

Changes in Signal Transduction Pathways

  • Mutations in signaling molecules/receptors can disrupt normal cellular responses, leading to diseases.

Practice Question

  • Identify the three stages of cell signaling and the nature of the signal transduced.

    • Answer: Reception, transduction, response; signal is a ligand.

Important Receptors in Eukaryotes

  • Two main categories of membrane receptors:

    1. G protein-coupled receptors (GPCRs)

    2. Ion channels

G Protein Coupled Receptors (GPCRs)

  • Ligand binding activates GPCR and phosphorylates G proteins, initiating transduction.

  • Functions in sensory systems; largest receptor category.

Ion Channels

  • Ligand-gated ion channels act as gates allowing ion diffusion, triggering cellular responses.

Chemical Compounds & Interference

  • Medicines/toxins can modulate signaling pathways (e.g., Botox interferes with neurotransmitter release).

Review: Thyroid-Stimulating Hormone (TSH)

  • TSH initiates signal transduction in the thyroid gland;

    • Implications of mutations in TSH receptors in various health conditions (e.g., hypothyroidism).

Review Questions: Signal Transduction Events

  • Correct order of signal transduction events.

Quorum Sensing in Bacteria

  • Communication among bacteria that affects gene expression based on population density.

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