Cell Biology Lecture Notes

Basic Characteristics of Cells

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

Categories of Cells

• Eukaryotic Cells:
  • Contain organelles, including a nucleus.
  • More complex and advanced.
  • Found in plants and animals.
• Prokaryotic Cells:
  • Do not have a nucleus or membrane-enclosed organelles.
  • Genetic material is not contained within a nucleus.
  • Always unicellular (e.g., bacteria).

Organelles and Their Functions

• Organelles: Specialized parts of a cell with unique jobs.

Nucleus

• Control center of the cell.
• Contains DNA, dictating cell functions and activities.
• Chromatin: Tangled form of DNA inside the nuclear membrane.
• Chromosomes: Condensed form of DNA during cell division.
• Nucleolus: Structure where ribosomes are made.

Ribosomes

• Synthesizing proteins.
• Located in the cytoplasm or attached to the endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

• Rough ER: Has ribosomes attached.
• Smooth ER: No ribosomes attached.
• Transports materials like proteins.

Golgi Apparatus

• Receives vesicles from ER.
• Customizes proteins by folding them or adding lipids/carbohydrates.

Vacuoles

• Sac-like structures for storing materials.
• E.g., Central vacuole in plant cells stores water.

Lysosomes

• Garbage collectors: Take in damaged/worn-out cell parts.
• Filled with enzymes to break down cellular debris.

Mitochondria

• Powerhouse of the cell for animal and plant cells.
• Produce ATP through cellular respiration.
• Cells needing more energy have more mitochondria.

Cytoskeleton

• Maintains cell shape.
• Composed of microfilaments (protein threads) and microtubules (thin hollow tubes).

Chloroplasts

• Present in photoautotrophic organisms (e.g., plants).
• Site of photosynthesis.
• Contains chlorophyll (green pigment).

Cell Wall

• Present in plant cells.
• Provides shape, support, and protection.
• Absent in animal cells.

Unique Cell Structures

• Cilia: Microscopic hair-like projections in respiratory tract cells, trapping particles and expelling them during coughing.
• Flagella: Tail-like structure for movement. Present in some bacteria and human sperm cells.

Summary

• Eukaryotic Cells: Plant and animal cells with nuclei and organelles.
• Prokaryotic Cells: Unicellular organisms without nuclei and membrane-enclosed organelles.
• All cells have a membrane, cytoplasm, and genetic material.
• Plant cells have chloroplasts but both plant and animal cells have mitochondria.