Anatomy and Physiology: The Cellular Level of Organization

Chapter 4: The Cellular Level of Organization

4.1 The Cell Membrane

  • Structure: Separates internal/external environments, regulates material movement, composed of phospholipids, cholesterol, carbohydrates, proteins.
  • Phospholipids: Major component; amphipathic with hydrophilic heads and hydrophobic tails arranged in a bilayer.
  • Membrane Proteins: Integral (transmembrane) and peripheral proteins facilitate various functions like transport and cell recognition.

4.2 Transport Across the Cell Membrane

  • Selective Permeability: Only small, nonpolar molecules pass freely; movement is from high to low concentration.
  • Passive Transport: Includes simple diffusion (direct across membrane) and facilitated diffusion (via proteins).
  • Osmosis: Water movement from low solute to high solute concentration.
  • Active Transport: Requires energy to move substances against concentration gradient (e.g., sodium-potassium pump).

4.3 The Cytoplasm and Cellular Organelles

  • Cytoplasm: Gel-like interior containing cytosol and organelles.
  • Organelles: Include endoplasmic reticulum (rough ER for protein synthesis, smooth ER for lipid synthesis), Golgi apparatus (modifies and sorts proteins), mitochondria (ATP production), lysosomes (digests waste).

4.4 The Nucleus and DNA

  • Nucleus: Houses the cell's DNA, has a nuclear envelope and nucleolus for ribosome production.
  • DNA Structure: Double-helix with four bases (A, T, C, G); packaged into chromatin and chromosomes.

4.5 Protein Synthesis

  • Process: Begins in the nucleus with transcription (DNA to mRNA) and proceeds to translation (mRNA to protein) in the cytoplasm, involving ribosomes and tRNA.

4.6 Cell Replication

  • Cell Cycle: Comprises interphase (G1, S, G2 phases) and mitosis, resulting in two identical daughter cells.
  • Mitosis Phases: Prophase, Metaphase, Anaphase, Telophase, followed by cytokinesis.

4.7 Cellular Differentiation

  • Differentiation: Development of specialized functions from a single cell; stem cells can differentiate into specific types based on gene expression regulated by transcription factors.