Key Points on Cell Structure and Function

Introduction to Cells

• Cells are the smallest living units of an organism.
• All cells share three common features:
  • Cell Membrane: Separates the cell's interior from the environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Types of Cells

1. Eukaryotic Cells

• More advanced and complex.
• Contain organelles, including:
  • Nucleus: Control center; contains DNA.
  • Other specialized parts.
• Examples: Cells in plants and animals.

2. Prokaryotic Cells

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

Organelles Overview

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

Nucleus

• Contains DNA; dictates cell function and behavior.
• Chromatin: Tangled form of DNA inside the nucleus.
• DNA condenses into chromosomes when the cell is ready to divide.
• Contains a nucleolus where ribosomes are produced.

Ribosomes

• Synthesize (make) proteins.
• Can be free in cytoplasm or attached to the Endoplasmic Reticulum (ER).

Endoplasmic Reticulum (ER)

• Membrane-enclosed passageway for transport.
• Rough ER: Has ribosomes attached.
• Smooth ER: No ribosomes attached.

Golgi Apparatus (Golgi Body)

• Receives proteins from the ER.
• Modifies proteins into usable forms (folding, adding materials).

Vacuoles

• Sac-like structures for storing materials.
• Central Vacuole in plant cells stores water.

Lysosomes

• Act as garbage collectors; break down damaged cell parts using enzymes.

Mitochondria

• Powerhouse of the cell; produces ATP through cellular respiration.
• More mitochondria are found in energy-demanding cells.

Cytoskeleton

• Maintains cell shape.
• Composed of:
  • Microfilaments: Thread-like, made of protein.
  • Microtubules: Thin hollow tubes.

Chloroplasts (Plant Cells Only)

• Site of photosynthesis; contains chlorophyll (green pigment).

Cell Wall (Plant Cells Only)

• Provides shape, support, and protection; absent in animal cells.

Unique Cell Structures

• Cilia: Hair-like projections that help trap and expel particles in the respiratory tract (in humans).
• Flagella: Tail-like structure that aids in cell movement; present in some bacteria and sperm cells in humans.

Summary

• Eukaryotic Cells: Have a nucleus and membrane-enclosed organelles (plants and animals).
• Prokaryotic Cells: Unicellular with no nucleus or organelles (e.g., bacteria).
• All cells have a cell membrane, cytoplasm, and genetic material.
• Plant cells have chloroplasts; both plant and animal cells have mitochondria.