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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.