Cell Biology Lecture Notes

Fundamental Characteristics of Cells

• Cells are the smallest living units of an organism.
• Common features of all cells:
  • Cell Membrane: Separates the inside of the cell from its environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

Eukaryotic Cells

• Have organelles including a nucleus and other specialized parts.
• Considered more advanced and complex.
• Found in plants and animals.

Prokaryotic Cells

• Lack a nucleus or membrane-enclosed organelles.
• Contain genetic material not enclosed within a nucleus.
• Always unicellular organisms, e.g. bacteria.

Organelles and Their Functions

Nucleus

• Control center of the cell.
• Contains DNA, which dictates cell function and structure.
• Chromatin: Tangle of DNA within the nuclear membrane.
• Chromosomes: Condensed DNA structures when a cell is ready to divide.
• Nucleolus: Site where ribosomes are made.

Ribosomes

• Essential for protein synthesis.
• Located in cytoplasm or attached to the endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

• Rough ER: Has ribosomes attached.
• Smooth ER: Lacks ribosomes.
• Acts as a passageway for materials such as proteins.

Golgi Apparatus (Golgi Body)

• Receives proteins from the ER.
• Modifies proteins into usable forms by folding or adding elements like lipids or carbohydrates.

Vacuoles

• Sac-like structures for storage.
• Central Vacuole in plants: Stores water.

Lysosomes

• Serve as garbage collectors for the cell.
• Contain enzymes to break down cellular debris.

Mitochondria

• Powerhouse of the cell.
• Site of cellular respiration, producing ATP for energy.
• Energy-demanding cells have more mitochondria.

Cytoskeleton

• Maintains cell shape.
• Composed of microfilaments and microtubules.

Chloroplasts

• Found in photoautotrophic organisms like plants.
• Site of photosynthesis.
• Contain chlorophyll, giving the green color.

Unique Cell Structures

• Cell Wall: Present in plant cells for support and protection; absent in animal cells.
• Cilia: Microscopic hair-like projections in the respiratory tract; help in trapping and expelling particles.
• Flagella: Tail-like structure in some bacteria and human sperm cells for movement.

Summary

• Eukaryotic cells (plants and animals) have a nucleus and membrane-enclosed organelles.
• Prokaryotic cells are unicellular without a nucleus or membrane-bound organelles.
• All cells share a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells contain mitochondria, but only plant cells have chloroplasts.