Cell Structure Overview

Cell Structure

1. Overview of Cells

• Basic unit of life.
• Two main types: prokaryotic and eukaryotic.

2. Prokaryotic Cells

• Definition: Simple, single-celled organisms without a nucleus.
• Key Features:
  • Cell Membrane: Phospholipid bilayer controlling entry and exit of substances.
  • Nucleoid: Region containing genetic material (DNA).
  • Ribosomes: Sites of protein synthesis, smaller than eukaryotic ribosomes.
  • Cytoplasm: Jelly-like fluid where cellular processes occur.
  • Cell Wall: Rigid structure providing shape and protection (made of peptidoglycan in bacteria).

3. Eukaryotic Cells

• Definition: Complex cells with a nucleus and membrane-bound organelles.
• Key Features:
  • Nucleus: Contains DNA, surrounded by a nuclear envelope.
  • Endoplasmic Reticulum (ER):
    • Rough ER: Studded with ribosomes; synthesizes proteins.
    • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies.
  • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport.
  • Mitochondria: Powerhouse of the cell, site of ATP (energy) production through cellular respiration.
  • Chloroplasts (in plant cells): Site of photosynthesis, contains chlorophyll.
  • Lysosomes: Digestive organelles containing enzymes to break down waste.
  • Peroxisomes: Break down fatty acids and detoxify harmful substances.
  • Cytoskeleton: Network of fibers providing structure and facilitating movement.

4. Additional Structures

• Cell Membrane: Selectively permeable, composed of a phospholipid bilayer with embedded proteins.
• Vacuoles: Storage organelles; larger in plant cells for storage of water and nutrients.
• Centrioles: Involved in cell division, found in animal cells.
• Cell Wall (in plant cells): Provides structural support and protection; made of cellulose.

5. Differences Between Plant and Animal Cells

• Plant Cells:
  • Have a cell wall and chloroplasts.
  • Larger central vacuole.
• Animal Cells:
  • Lack cell wall and chloroplasts.
  • Smaller, more numerous vacuoles.

6. Cell Theory

• All living organisms are composed of cells.
• The cell is the basic unit of life.
• All cells arise from pre-existing cells.

Overview of Cells

• Cells are the fundamental building blocks of life.
• Two primary categories exist: prokaryotic and eukaryotic cells.

Prokaryotic Cells

• Simple organisms, typically unicellular, lacking a nucleus.
• Cell Membrane: Comprises a phospholipid bilayer that regulates the movement of substances in and out.
• Nucleoid: Area in the cell where genetic material (DNA) is concentrated.
• Ribosomes: Function as protein synthesis sites, smaller compared to eukaryotic ribosomes.
• Cytoplasm: Viscous, gel-like substance hosting various cellular functions.
• Cell Wall: Rigid outer layer that maintains cell shape and provides protection; in bacteria, it's primarily made of peptidoglycan.

Eukaryotic Cells

• More complex structures with a defined nucleus and membrane-bound organelles.
• Nucleus: Houses the cell’s DNA, protected by a nuclear envelope.
• Endoplasmic Reticulum (ER):
  • Rough ER: Studded with ribosomes for protein synthesis.
  • Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for cellular transport.
• Mitochondria: Known as the cell’s powerhouse, responsible for ATP production via cellular respiration.
• Chloroplasts (exclusive to plant cells): Responsible for photosynthesis, containing the green pigment chlorophyll.
• Lysosomes: Contains digestive enzymes to breakdown waste materials.
• Peroxisomes: Involved in fatty acid breakdown and the detoxification of harmful substances.
• Cytoskeleton: A fibrous network that maintains cell shape and supports cellular movement.

Additional Structures

• Cell Membrane: Selectively permeable barrier made of phospholipid bilayer with embedded proteins.
• Vacuoles: Storage vesicles; typically larger in plant cells for maintaining water and nutrient stores.
• Centrioles: Organelles critical for cell division, primarily found in animal cells.
• Cell Wall (in plant cells): Provides structural support and is made of cellulose.

Differences Between Plant and Animal Cells

• Plant Cells: Possess a cell wall and chloroplasts, along with a large central vacuole.
• Animal Cells: Do not have a cell wall or chloroplasts, and generally contain smaller, more numerous vacuoles.

Cell Theory

• All living organisms consist of cells.
• The cell is recognized as the basic unit of life.
• New cells arise only from pre-existing cells.