Biology: Cell Structure I Nucleus Medical Media

Scientific concepts, discoveries, and nature phenomena presented

Core cell theory / cell components

• Cells are the smallest living units of organisms.
• All cells share three common features:
  • Cell membrane: separates the cell’s internal environment from outside.
  • Cytoplasm: jelly-like fluid where cellular components are found.
  • DNA (genetic material): contains instructions for cell function.

Two major cell categories

• Eukaryotic cells (more complex; found in plants and animals)
  • Have membrane-enclosed organelles, including a nucleus.
• Prokaryotic cells (found in bacteria)
  • No nucleus and no membrane-enclosed organelles.
  • Genetic material is not contained within a nucleus.
  • Described as always unicellular.

Major organelles and their functions (as described)

• Nucleus (“control center”)

  • Contains DNA.
  • DNA regulates what the cell does and how it does it.
  • Chromatin: tangled, spread-out DNA inside the nuclear membrane.
  • Chromosomes: formed when DNA condenses during cell division.
  • Nucleolus: where ribosomes are made.

• Ribosomes

  • After leaving the nucleus, they help synthesize proteins.
  • Can be:
    • Free in cytoplasm, or
    • Attached to the endoplasmic reticulum (ER).

• Endoplasmic reticulum (ER): membrane-enclosed transport network

  • Rough ER: has ribosomes attached.
  • Smooth ER: does not have ribosomes attached.
  • Transports proteins (including those produced by ribosomes).

• Golgi apparatus (Golgi body)

  • Receives materials (e.g., proteins) from the ER (via vesicles).
  • Modifies/customizes proteins into usable forms (e.g., by adding other materials such as lipids or carbohydrates).

• Vacuoles

  • Sac-like storage structures.
  • In plant cells: central vacuole stores water.

• Lysosomes (animal cells)

  • “Garbage collectors” containing enzymes that break down damaged/worn cellular components.

• Mitochondria

  • Powerhouse organelles.
  • Produce ATP via cellular respiration, supplying energy for cell activities.
  • Cells needing more energy have more mitochondria.

• Cytoskeleton

  • Maintains cell shape.
  • Includes:
    • Microfilaments (thread-like; made of protein)
    • Microtubules (thin hollow tubes)

Plant-specific vs animal-specific structures

• Chloroplasts (plants; photoautotrophs capture sunlight)

  • Site of photosynthesis.
  • Green due to chlorophyll.

• Cell wall (plants only)

  • Exists outside the cell membrane.
  • Provides shape, support, and protection.

• Animal cells are described as lacking a cell wall.

Specialized structures in some cells

• Cilia (in human respiratory tract cells)

  • Microscopic, hair-like projections.
  • Beat in waves to move inhaled particles, helping expel them (e.g., via coughing).

• Flagella

  • Present in some bacteria (for movement/propulsion).
  • In humans, the sperm cell is stated to be the only human cell with a flagellum.

Researchers or sources featured

• None explicitly mentioned in the provided subtitles.