plasma membrane

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Boundary: Provides a separation between the cell and its environment.
Cellular Transport: Facilitates selective permeability, determining what enters/exits the cell.
Biochemical Reactions: Site for metabolic processes, especially respiration in prokaryotes.

Composed of phospholipids, contributing to the fluid mosaic model where various components exist.
Fluidity: Increased by cholesterol, affecting membrane properties.
Unsaturated Fats: Enhance membrane fluidity due to the presence of kinked tails.
Hydrophobic Interactions: Tail regions of phospholipids prevent membrane separation.
Integral Membrane Proteins: Span the entire membrane, maintaining structure through interactions with hydrophobic residues and Van der Waals forces.

Osmosis: Diffusion of water across the membrane influenced by solute concentration.
- Hypertonic Solution: High solute concentration outside the cell; water exits, causing cell to shrivel (animal cells).
- Isotonic Solution: Equal solute concentrations; no net water movement, cell maintains shape.
- Hypotonic Solution: Low solute concentration outside; water enters cell, causing it to swell, potentially burst.

Animal Cells: Optimal in isotonic solutions, can shrivel in hypertonic solutions, and may burst in hypotonic solutions.
Plant Cells: Prefer hypotonic solutions (turgid state) for optimal pressure, can experience plasmolysis in hypertonic environments.

Passive Transport: Movement of solutes from high to low concentration without energy.
Active Transport: Movement of solutes from low to high concentration requiring energy (ATP).
- Primary Active Transport: Directly uses ATP to move ions, e.g., Na+/K+ pump.
- Secondary Active Transport: Uses the movement of one ion down its gradient to power another ion moving against its gradient. Example: Sodium-glucose pump.

Exocytosis: Exporting materials out of the cell via vesicles (e.g., protein secretion).
Endocytosis: Importing materials into the cell.
- Phagocytosis: Engulfing large particles or organisms.
- Pinocytosis: Ingesting small particles or liquids.
- Receptor-mediated endocytosis: Specific binding of molecules to receptors facilitates entry.

Importance of communication for growth, survival, and recognition of neighboring cells.
Types of Signaling:
- Direct Contact: Cells physically touching via gap junctions.
- Local Signaling: Nearby cell communication.
- Endocrine Signaling: Communication over distances via the bloodstream (e.g., hormones).
- Synaptic Signaling: Communication between neurons.

Three Main Steps of Signal Transduction: Reception, Transduction, Response.
- Reception: First messenger binds to cell surface receptors, initiating signaling.
- Transduction: Activation of proteins in a cascade (phosphorylation cascade) leading to signal amplification.
- Response: Cellular actions such as transcription and translation are initiated based on the signal.

G-Protein Coupled Receptors: Interacts with GTP and produces second messengers initiating responses.
Intracellular Receptors: For nonpolar molecules that easily cross the plasma membrane; these receptors are located inside the cell.