Cell Membrane Mechanisms

Passive Transport: Movement of molecules without energy input.
- Diffusion: Movement from high to low concentration.
- Facilitated Diffusion: Uses transport proteins for molecules that cannot directly cross the membrane.
- Osmosis: Diffusion of water through a selectively permeable membrane.
Active Transport: Requires energy (ATP) to move substances against their concentration gradient.
- Primary Active Transport: Directly uses ATP (e.g., Sodium-Potassium pump).
- Secondary Active Transport: Uses the energy from the movement of one molecule to drive another molecule against its gradient (cotransport).
Vesicular Transport: Involves the formation of vesicles to transport larger molecules.
- Endocytosis: Process of taking materials into the cell.
  - Phagocytosis: "Cell eating"; uptake of large particles.
  - Pinocytosis: "Cell drinking"; uptake of fluids and small solutes.
- Exocytosis: Release of materials from the cell.

Phospholipid Bilayer: Basic structure comprising hydrophilic heads and hydrophobic tails.
Cholesterol: Interspersed among phospholipids; maintains fluidity and stability.
Proteins: Integral and peripheral proteins perform various functions.
Carbohydrates: Attached to proteins and lipids, forming glycoproteins and glycolipids; involved in cell recognition.

Describes the cell membrane as a dynamic and flexible structure.
Fluidity: Lipids and proteins can move laterally within the layer, allowing for flexibility and adaptability.
Mosaic: Membrane is composed of various proteins that float in or on the fluid lipid bilayer.

Integral Proteins: Span the membrane; involved in transport and communication.
Peripheral Proteins: Loosely attached to the membrane surface; play roles in signaling and maintaining cell shape.
Functions:
- Transport: Channels and carriers facilitate molecule movement.
- Enzymatic Activity: Catalyze reactions on the membrane surface.
- Signal Transduction: Receive and transmit signals from outside to inside the cell.
- Cell Recognition: Glycoproteins serve as markers for cell identity.

Involves communication between cells through signaling molecules (ligands).
Receptors: Proteins on the cell membrane that bind to ligands, initiating a response.
- Types of Receptors:
  - G-protein Coupled Receptors (GPCRs): Activate intracellular signaling pathways upon ligand binding.
  - Tyrosine Kinase Receptors: Trigger phosphorylation cascades affecting cellular responses.
Signal Transduction Pathways: Series of molecular events that lead to a cellular response; often involve secondary messengers (e.g., cAMP, calcium ions).
Cellular Responses: Can include changes in gene expression, cellular metabolism, and cell behavior (growth, apoptosis).

Passive Transport: Movement of substances across membranes without energy; relies on concentration gradients.
Diffusion: Natural movement of molecules from an area of high concentration to low concentration.
Facilitated Diffusion: Utilizes specific transport proteins to aid the movement of large or polar molecules across the membrane.
Osmosis: Movement of water molecules through a selectively permeable membrane, balancing solute concentrations.
Active Transport: Energy-requiring process (ATP) that moves substances against their concentration gradient.
Primary Active Transport: Direct use of ATP, exemplified by the Sodium-Potassium pump, crucial for maintaining cellular ion balances.
Secondary Active Transport: Utilizes energy derived from the transport of one substance to drive the transport of another (e.g., glucose coupled to Na+ transport).
Vesicular Transport: Mechanism for moving large quantities of materials in and out of cells via vesicles.
Endocytosis: Cellular uptake process for materials; includes recognition and engulfment of substances.
Phagocytosis: A type of endocytosis that involves the ingestion of large particles or cells.
Pinocytosis: A form of endocytosis that involves the uptake of liquid and small solute molecules.
Exocytosis: Process for expelling materials from the cell, crucial for secretion functions.

Phospholipid Bilayer: Fundamental structure, consisting of hydrophilic heads facing outward and hydrophobic tails facing inward, creating a barrier to water-soluble substances.
Cholesterol: Embedded within the bilayer, plays a critical role in maintaining membrane fluidity and structural integrity.
Proteins: Divided into integral (spanning the membrane) and peripheral (attached to the surface) proteins, each fulfilling distinct roles in functionality.
Carbohydrates: Associated with proteins and lipids to form glycoproteins and glycolipids, essential for cell recognition and signaling.

Describes the cell membrane's structure as a flexible and dynamic assembly of various proteins and lipids.
Fluidity: Allows lateral movement of lipids and proteins, promoting flexibility and adaptability to cellular environments.
Mosaic Nature: Highlights the diversity of membrane proteins that float within or on the lipid bilayer, contributing to varied functions.

Integral Proteins: Span the lipid bilayer and are critical for transport processes and cellular communication.
Peripheral Proteins: Associate loosely with the surface; involved in signaling pathways and structural support.
Functions:
- Transport: Channels and carrier proteins allow selective passage of molecules.
- Enzymatic Activity: Certain proteins catalyze reactions directly at the membrane surface, enhancing metabolic processes.
- Signal Transduction: Proteins receive extracellular signals and transmit them into the cell, initiating responses.
- Cell Recognition: Glycoproteins participate in identifying and differentiating cell types.

Communication: Involves the release and reception of signaling molecules known as ligands.
Receptors: Membrane proteins responsible for binding ligands, causing a conformational change leading to a cellular response.
Types of Receptors:
- G-protein Coupled Receptors (GPCRs): Trigger intracellular signaling when ligands bind, activating G-proteins for diverse messaging pathways.
- Tyrosine Kinase Receptors: Involved in phosphorylation cascades that drive cellular responses to growth signals.
Signal Transduction Pathways: Series of molecular processes, including the involvement of secondary messengers (e.g., cAMP, calcium ions), leading to a specific cellular activity.
Cellular Responses: Outcomes may include alterations in gene expression, metabolic activity, and changes in cellular behavior such as growth or programmed cell death (apoptosis).