Cell Structure

Basic Structure of a Cell

  • Characteristics of Living Organisms

    1. Made of CELLS

    2. Require ENERGY (food)

    3. REPRODUCE (species)

    4. Maintain HOMEOSTASIS

    5. Highly ORGANIZED

    6. RESPOND to the environment

    7. GROW and DEVELOP

    8. EXCHANGE materials with surroundings (water, wastes, gases)

Levels of Organization

  • Nonliving Levels:

    1. ATOM (element)

    2. MOLECULE (compounds like carbohydrates & proteins)

    3. ORGANELLES (nucleus, ER, Golgi …)

  • Living Levels:

    1. CELL (makes up ALL organisms)

    2. TISSUE (cells working together)

    3. ORGAN (heart, brain, stomach …)

    4. ORGAN SYSTEMS (respiratory, circulatory …)

    5. ORGANISM

    6. POPULATION (one species in an area)

    7. COMMUNITY (several populations in an area)

    8. ECOSYSTEM (e.g., forest, prairie …)

    9. BIOME (e.g., Tundra, Tropical Rainforest…)

    10. BIOSPHERE (all living and nonliving things on Earth)

History of Cells & the Cell Theory

  • First to View Cells

    • In 1665, Robert Hooke used a microscope to examine a thin slice of cork (dead plant cell walls) and saw small boxes, naming them CELLS after the small rooms that monks lived in.

  • Anton van Leeuwenhoek

    • In 1673, he was the first to view living organisms using a handheld microscope to examine pond water & teeth scrapings.

  • Cell Theory Beginnings:

    • In 1838, German botanist Matthias Schleiden concluded that all plants were made of cells, cofounding the cell theory.

    • In 1839, German zoologist Theodore Schwann concluded that all animals were also made of cells.

    • In 1855, German doctor Rudolph Virchow observed cells dividing, concluding that all cells come from pre-existing cells through cell division.

Cell Theory

  • Cell Theory Components:

    1. All living things are made of cells.

    2. Cells are the basic unit of structure and function in an organism.

    3. Cells arise from the reproduction of existing cells.

Endosymbiotic Theory

  • Proposed by Lynn Margulis in 1970, indicating that some organelles within cells (like chloroplasts and mitochondria) were once free-living cells. Evidence includes organelles with their own DNA.

Cell Size and Types

  • Observation: Cells can only be observed under a microscope.

  • Types of Cells:

    1. Animal Cells

    2. Plant Cells

    3. Bacterial Cells

  • Organism Composition:

    • Unicellular: Composed of one cell.

    • Multicellular: Composed of many cells organized into tissues and systems.

Cell Dimensions

  • Typical cells range from 5 – 50 micrometers (microns) in diameter.

  • Relative Size: Plant cells > Animal cells > Bacterial cells.

  • Micron Measurement:

    • 1 cm = 10,000 microns

    • 1 inch = 25,000 microns

Cell Specialization

  • Occurs in multicellular organisms where cells take on different shapes and functions through a process called DIFFERENTIATION.

Specialized Cells

  • Animal Cells:

    • Muscle cells, Red blood cells, Cheek cells.

  • Plant Cells:

    • Pollen, Xylem cells, Guard Cells.

Levels of Life Organization

  • Nonliving Levels:

    • ATOMS → MOLECULES → ORGANELLES

  • Living Levels:

    • CELLS → TISSUES → ORGANS → ORGAN SYSTEMS → ORGANISM

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotes:

    • Cells lacking a nucleus and membrane-bound organelles (e.g., bacteria).

    • Structure:

      • Nucleoid region contains DNA, surrounded by a cell membrane & cell wall (peptidoglycan), ribosomes present.

  • Eukaryotes:

    • Cells with a nucleus and membrane-bound organelles, including protists, fungi, plants, and animals.

    • Basic Structures: Nucleus, Cell Membrane, Cytoplasm with organelles.

Organelles

  • Small structures within cells performing various functions, found in the cytoplasm. Some are membrane-bound.

Types of Organelles

  • Animal Cell Organelles:

    • Nucleolus, Nucleus, Ribosomes, Cell Membrane, Rough & Smooth ER, Golgi apparatus, Mitochondria, Centrioles.

  • Plant Cell Organelles:

    • Include chloroplasts (absent in animal and bacterial cells).

Cell Membrane

  • Structure: Composed of a double layer of phospholipids and proteins, controlling entry and exit of substances.

  • Components:

    • Phospholipids (hydrophilic heads and hydrophobic tails), protein channels, glycoproteins for cell recognition.

Organelle Functions:

  1. Nucleus: Controls cell activities, contains genetic material (DNA).

  2. Mitochondria: Generates ATP through cellular respiration, contains its own DNA.

  3. Endoplasmic Reticulum (ER):

    • Rough ER: Studded with ribosomes, synthesizes proteins.

    • Smooth ER: Lacks ribosomes, synthesizes lipids, detoxifies drugs.

  4. Golgi Bodies: Modifies, sorts, and packages molecules for transport out of the cell.

  5. Lysosomes: Contain enzymes for digestion and recycling of cell parts.

  6. Vacuoles: Storage sacs for materials.

Conclusion

  • Cells vary in type and specialization, and their functions are critical for the survival of living organisms.