Unit 2 - Cell Structure and Function Details

Cell Structure and Function Notes

Key Differences Between Cell Types

• Prokaryotes:

  • Single-celled organisms, such as bacteria.
  • Lack a nucleus.
  • Do not have membrane-bound organelles.

• Eukaryotes:

  • Can be single-celled or multi-celled organisms.
  • Have a nucleus.
  • Contain membrane-bound organelles such as:
  • Nucleus
  • Mitochondria
  • Chloroplasts
  • Endoplasmic reticulum
  • Golgi apparatus
  • Ribosomes
  • Lysosomes
  • Vesicles

Importance of Cell Size

• Cell size and efficiency:
  • Smaller cells have a larger surface area to volume ratio, making them more efficient.
  • Larger cells are less efficient due to lower surface area to volume ratio.

Cell Membrane Structure and Function

• The cell membrane serves as a barrier between internal and external environments of the cell.
• It controls the entry and exit of substances.
• Composition:
  • Phospholipid bilayer:
  • Hydrophilic head: Attracts water.
  • Hydrophobic tail: Repels water.
• Only small, nonpolar molecules can pass through the membrane unassisted.

Cell Transport Mechanisms

• Cell transport: Processes allowing molecules to enter or exit the cell.

Passive Transport

• Does not require energy (ATP).
• Moves substances from high concentration to low concentration.
  • Examples:
  • Simple Diffusion: Allows small nonpolar molecules to pass without energy.
  • Facilitated Diffusion: Necessary for large, charged, or polar molecules. Requires channel or carrier proteins but no energy.
  • Osmosis: Special form of facilitated diffusion dealing specifically with water.
    • Water moves from low tonicity (hypotonic) to high tonicity (hypertonic).
    • Additionally, moves from low osmolarity (hypoosmotic) to high osmolarity (hyperosmotic).
    • Also moves from high water potential to low water potential.

Active Transport

• Requires energy (often from ATP).
• Moves solutes from low to high concentration.
• Can involve secondary active transport:
  • Moves a solute down its concentration gradient to power the movement of another solute against its concentration gradient.

Origins of Cell Compartmentalization

• Evolution of small organelles in eukaryotic cells increases internal surface area to volume ratio.
• Allows specific chemical reactions to occur in designated areas, enhancing cellular efficiency.

Endosymbiotic Theory

• Origin of Mitochondria and Chloroplasts:
  • Evolved through endosymbiosis, whereby two prokaryotic cells formed a symbiotic relationship.
  • The smaller cell eventually became an organelle rather than an independent organism.
• Best evidence of endosymbiosis:
  • Double membrane: indicates engulfment of a smaller cell.
  • Own DNA: suggests it once lived independently.
  • Own ribosomes: implies ability to produce proteins independently.