Lecture Notes on Cells

Introduction

• Cells are the smallest living units of an organism.
• All cells share three common components:
  • 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

1. Eukaryotic Cells

• Characteristics:
  • Have organelles, including the nucleus.
  • More complex, found in plants and animals.

2. Prokaryotic Cells

• Characteristics:
  • Lack nucleus and membrane-enclosed organelles.
  • Always unicellular organisms (e.g., bacteria).
  • Genetic material not contained within a nucleus.

Organelles

• Definition: "Little organ" – specialized parts of a cell with unique functions.

Key Organelles:

Nucleus

• The control center of the cell containing DNA.
• DNA Function: Dictates cell functions.
• Contains Chromatin (spread out DNA) and Chromosomes (condensed DNA during cell division).
• Houses the Nucleolus: Area for ribosome production.

Ribosomes

• Function: Synthesize proteins.
• Location: Can float in cytoplasm or attach to the endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

• Types:
  • Rough ER: Has ribosomes attached.
  • Smooth ER: No attached ribosomes.
• Function: Membrane-enclosed passageway for transporting materials, especially proteins.

Golgi Apparatus (Golgi Body)

• Function: Receives proteins from ER and customizes them into usable forms through folding and adding materials (lipids, carbohydrates).

Vacuoles

• Sac-like structures that store materials.
• Example: Central vacuole in plant cells stores water.

Lysosomes

• Function: Garbage collectors that digest damaged or worn-out cell parts using enzymes.

Mitochondria

• The powerhouse of the cell.
• Function: Produce ATP during cellular respiration, providing energy for activities.
• More energy-demanding cells have more mitochondria.

Cytoskeleton

• Maintains cell shape.
• Composed of microfilaments (thread-like proteins) and microtubules (thin, hollow tubes).

Chloroplasts (in plant cells)

• Function: Site of photosynthesis.
• Contains chlorophyll (green pigment).

Cell Wall (in plant cells)

• Structure that shapes, supports, and protects plant cells.
• Animal cells do not have a cell wall.

Unique Cell Features

• Cilia: Microscopic projections in respiratory tract cells for trapping particles.
• Flagella: Tail-like structures for movement in some bacteria; present in sperm cells in humans.

Summary

• Eukaryotic Cells: Have a nucleus and membrane-enclosed organelles (plant and animal cells).
• Prokaryotic Cells: Unicellular organisms without a nucleus or membrane-bound organelles.
• All cells possess a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells contain mitochondria, but only plant cells have chloroplasts.