BackCellular Transport and the Cell Cycle: Study Notes for Anatomy & Physiology
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Cellular Transport Mechanisms
Intracellular and Extracellular Fluid
The body’s cells are surrounded by and contain fluids that are essential for physiological processes. Understanding the location and movement of these fluids is fundamental in Anatomy & Physiology.
Intracellular Fluid (ICF): The fluid found inside cells. It constitutes the majority of the body’s total water content.
Extracellular Fluid (ECF): The fluid located outside the cells. This includes interstitial fluid (between cells) and plasma (in blood vessels).
Key Ions: K+ (potassium) is primarily found in the intracellular fluid, while Na+ (sodium) is mainly in the extracellular fluid.
Example: The sodium-potassium pump maintains these gradients by moving Na+ out of and K+ into the cell.
Sodium-Potassium Pump
The sodium-potassium pump is a vital membrane protein that uses ATP to transport ions against their concentration gradients.
Function: Moves 3 Na+ ions out of the cell and 2 K+ ions into the cell per ATP molecule hydrolyzed.
Importance: Maintains resting membrane potential and cell volume.
Equation:
Example: Essential for nerve impulse transmission and muscle contraction.
Endocytosis: Pinocytosis vs. Phagocytosis
Endocytosis is the process by which cells internalize substances from their external environment. There are two main types: pinocytosis and phagocytosis.
Process | Main Function | Vesicle Type | Example |
|---|---|---|---|
Pinocytosis | "Cell drinking"; uptake of fluids and dissolved solutes | Small vesicles filled with extracellular fluid | Absorption of nutrients by cells lining the intestines |
Phagocytosis | "Cell eating"; uptake of large particles or cells | Large vesicles called phagosomes | White blood cells engulfing bacteria |
Pinocytosis: The cell membrane invaginates to form vesicles containing extracellular fluid.
Phagocytosis: The cell engulfs large particles, forming a phagosome that fuses with lysosomes for digestion.
Energy Requirement: Both processes require ATP.
The Cell Cycle
Overview of the Cell Cycle
The cell cycle is the series of events that cells go through as they grow and divide. It ensures that DNA is accurately replicated and distributed to daughter cells.
Main Phases: Interphase and Mitosis (M phase).
Interphase: The period of cell growth and DNA replication, preparing the cell for division.
Phases of Interphase
Interphase is subdivided into three distinct phases, each with specific functions:
G1 Phase (First Gap): The cell grows, synthesizes proteins, and carries out normal metabolic functions. Preparation for DNA synthesis begins.
S Phase (Synthesis): DNA replication occurs, resulting in two identical copies of each chromosome.
G2 Phase (Second Gap): The cell continues to grow and prepares for mitosis. Organelles may duplicate, and the cell checks for DNA errors.
Note: During interphase, chromosomes are not visible under a light microscope because DNA is in a relaxed, uncondensed state.
Importance of the Cell Cycle
Ensures genetic continuity: Each daughter cell receives an exact copy of the parent cell’s DNA.
Regulation: Checkpoints exist to ensure errors are corrected before the cell proceeds to the next phase.
Example: Rapid cell division occurs in skin cells to replace those lost due to abrasion.
Additional info: The cell cycle is tightly regulated by proteins such as cyclins and cyclin-dependent kinases (CDKs), which ensure proper timing and fidelity of cell division.
