Concept of Cell Structure

Cell Types

• Cells can be categorized into unicellular and multicellular organisms
• Bacteria, protozoa, and unicellular fungi are examples of unicellular organisms without a nucleus
• Human, plants, and animals are multicellular organisms with more than one cell, containing a nucleus and plasma membrane

Characteristics of Red Blood Cells

• Red blood cells are unicellular and lack a nucleus
• They are typically biconcave in shape and responsible for carrying oxygen in the blood

Characteristics of Neurons

• Neurons are long and thin cells responsible for propagating nerve impulses for signaling
• They have subcellular parts attached to the end of the cell

Common Features of All Cells

• Cells contain four major macromolecules: carbohydrates, proteins, lipids, and nucleic acids
• These macromolecules are polymers formed from smaller units called monomers
• All cells have a plasma membrane, cytoplasm, ribosomes, and DNA molecules

Prokaryotic Cells

• Prokaryotic cells are unicellular and lack a nucleus and membrane-bound organelles
• They have a simple intracellular organization and a rigid cell wall composed of peptidoglycans in bacteria
• Components of prokaryotic cells include:
  • Cell membrane (regulates entry and exit of materials)
  • Cytoplasm (rigid gel-like substance within the cell membrane)
  • Ribosomes (70S, responsible for protein synthesis)
  • Nucleoid (contains genetic material, single circular bacterial DNA chromosome)
  • Plasmids (small circular DNA molecule that can replicate independently)
• Prokaryotic cells have protective coating layers: glycocalyx, cell wall, and cell membrane
• External structures include sex pili (facilitate genetic material transport), fimbriae (enable bacteria to adhere to surfaces), and flagella (used for locomotion)

Eukaryotic Cells

• Eukaryotic cells are multicellular and contain a nucleus and membrane-bound organelles
• They have a simple intracellular organization and are larger in size compared to prokaryotic cells
• Components of eukaryotic cells include:
  • Cell membrane
  • Cytoplasm (occupies everything outside the nucleus, including cytosol, microtubules, and other organelles)
  • Ribosomes (80S, composed of ribosomal protein and rRNA)
  • Lysosomes (only in animal eukaryotic cells)
  • Chloroplasts (only in plant cells, responsible for photosynthesis)
  • Peroxisome
  • Nucleolus (chromatin)
  • Nuclear membranes
  • Nuclear pore
  • Smooth and rough endoplasmic reticulum
  • Mitochondria
  • Golgi apparatus
  • Centrioles

Cytoskeleton

• The cytoskeleton is a three-dimensional structure of protein in the cytoplasm
• It regulates cell shape and orientation, providing strength and rigidity, and facilitates organelle movement and cellular processes
• The cytoskeleton is composed of three filamentous protein polymers: microfilaments, intermediate filaments, and microtubules
• These protein filamentous polymers are involved in muscle contraction, cell signaling, and other cellular processes