Introduction to Cell Structures

Introduction to Cell Structures

• Cells are the fundamental units of life, exhibiting diverse structures and functions.
• All cells share common features, such as a plasma membrane, cytoplasm, and genetic material (DNA).
• Different cell types possess specialized structures that perform unique tasks.
• Cells are classified into prokaryotic (lacking a nucleus) and eukaryotic (possessing a nucleus).

Prokaryotic Cell Structures

• Prokaryotic cells are generally simpler and smaller than eukaryotic cells.
• They lack membrane-bound organelles.
• Key structures include:
  • Cell wall: Provides structural support and protection.
  • Plasma membrane: Regulates the passage of substances into and out of the cell.
  • Cytoplasm: The jelly-like substance filling the cell, containing ribosomes and other cellular components.
  • Ribosomes: Synthesize proteins.
  • Nucleoid: Region where the genetic material (DNA) is located.
  • Capsule (sometimes): An outer layer protecting the cell.
  • Flagella (sometimes): Whip-like structures for movement.
  • Pili (sometimes): Hair-like structures for attachment or conjugation.

Eukaryotic Cell Structures

• Eukaryotic cells are more complex and larger than prokaryotic cells.
• They possess membrane-bound organelles.
• Key structures include:
  • Nucleus: Contains the cell's genetic material (DNA).
  • Plasma membrane: Regulates the passage of substances into and out of the cell.
  • Cytoplasm: The jelly-like substance filling the cell, containing various organelles.
  • Endoplasmic reticulum (ER): Involved in protein synthesis, folding, and transport. Rough ER has ribosomes, smooth ER lacks them.
  • Golgi apparatus: Processes and packages proteins and lipids.
  • Mitochondria: Generate energy (ATP) through cellular respiration.
  • Ribosomes: Synthesize proteins.
  • Lysosomes: Contain enzymes to break down waste materials and cellular debris.
  • Vacuoles: Storage compartments for water, nutrients, or waste products; especially large in plant cells.
  • Peroxisomes: Contain enzymes that detoxify harmful substances.
  • Cytoskeleton: Provides structural support and facilitates cell movement.
  • Chloroplasts (plant cells): Conduct photosynthesis.
  • Cell wall (plant cells): Provides structural support and protection.

Cell Membrane Structure and Function

• The cell membrane is a selectively permeable barrier that encloses the cell's contents.
• It is composed primarily of a phospholipid bilayer with embedded proteins.
• Functions include:
  • Regulating transport of molecules into and out of the cell.
  • Providing a structural boundary for the cell.
  • Maintaining cell shape and integrity.
  • Facilitating cell signaling and communication.

Cellular Processes

• Various processes occur within cells, including:
  • Protein synthesis: The process of creating proteins using genetic information from DNA. Involves transcription and translation.
  • Cellular respiration: The process of breaking down glucose to produce ATP, the cell's energy currency.
  • Photosynthesis (in plant cells): The process of converting light energy into chemical energy in the form of glucose.
  • Cell division: The process by which cells reproduce. Includes mitosis (eukaryotic) and binary fission (prokaryotic).

Specialized Cell Structures

• Different cell types possess specialized structures to perform specific functions. For example:
  • Nerve cells have long axons for transmitting signals.
  • Muscle cells have contractile proteins for movement.
  • Red blood cells transport oxygen.
  • Sperm cells have flagella for movement.

Comparison of Prokaryotic and Eukaryotic Cells

• Prokaryotic cells are simpler, smaller, and lack membrane-bound organelles. Eukaryotic cells are more complex, larger, and contain membrane-bound organelles.
• Bacteria and archaea are examples of prokaryotic cells. Animals, plants, fungi, and protists are examples of eukaryotic cells.

Organelle Interactions

• Cellular processes often involve the interaction of multiple organelles.
• For example, proteins synthesized in the ribosomes are processed and packaged in the Golgi apparatus, before being transported to other locations.