Cell Structure: Prokaryotic vs Eukaryotic

Study Notes

Prokaryotic Cell Structure

Prokaryotic cells are simple, single-celled organisms lacking a nucleus and other membrane-bound organelles.
Typical prokaryotic cells are significantly smaller than eukaryotic cells.
Their genetic material (DNA) is located in a region called the nucleoid.
Key structures include:
- Cell wall: Provides structural support and protection.
- Plasma membrane: Regulates the passage of substances into and out of the cell.
- Ribosomes: Sites of protein synthesis.
- Capsule: A protective outer layer found in some prokaryotes.
- Flagella: Whip-like structures used for movement.
- Pili: Hair-like appendages used for attachment or conjugation (transfer of genetic material).

Eukaryotic Cell Structure

Eukaryotic cells are complex, typically larger than prokaryotic cells, and possess a nucleus and membrane-bound organelles.
Genetic material (DNA) is enclosed within a membrane-bound nucleus.
Organelles are specialized structures within the cell performing specific functions.
Key structures and their functions:
- Nucleus: Contains the cell's DNA and directs cellular activities. It contains the nucleolus, site of ribosome assembly.
- Endoplasmic reticulum (ER): A network of membranes involved in protein and lipid synthesis.
- Rough ER: Studded with ribosomes, responsible for protein synthesis.
- Smooth ER: Lacks ribosomes, involved in lipid synthesis and detoxification.
- Golgi apparatus: Processes, packages, and modifies proteins.
- Mitochondria: The "powerhouse" of the cell, responsible for cellular respiration and ATP production.
- Lysosomes: Contain digestive enzymes, breaking down waste and cellular debris.
- Vacuoles: Membrane-bound sacs involved in storage and transport.
- Cytoskeleton: A network of protein filaments supporting cell shape and movement.

Cell Membrane Structure and Function

The cell (plasma) membrane is a selectively permeable barrier separating the internal and external environments of the cell.
Fluid mosaic model describes the membrane structure: a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.
Phospholipids form a double layer. Hydrophilic (water-loving) heads face the intracellular and extracellular environments; hydrophobic (water-fearing) tails face each other within the bilayer.
Membrane proteins have various functions:
- Transport proteins: Facilitate the movement of molecules across the membrane (e.g., channels, carriers).
- Receptor proteins: Bind to signaling molecules.
- Enzymes: Catalyze specific reactions.
- Structural proteins: Maintain membrane structure.
Carbohydrates are attached to proteins or lipids on the outer surface, playing roles in cell recognition and communication.

Cell Transport Mechanisms

Passive transport: Movement of molecules across the membrane without energy input.
- Simple diffusion: Movement from high to low concentration.
- Facilitated diffusion: Movement with the help of transport proteins.
- Osmosis: Movement of water across the membrane.
Active transport: Movement of molecules against the concentration gradient requiring energy.
- Pumps: Use ATP to move molecules.
Endocytosis: Bulk transport into the cell.
Exocytosis: Bulk transport out of the cell.

Cellular Metabolism

Cellular metabolism encompasses all biochemical reactions occurring within the cell.
Catabolism: Breakdown of complex molecules to simpler ones, releasing energy.
Anabolism: Synthesis of complex molecules from simpler ones, requiring energy.
ATP (adenosine triphosphate): The main energy currency of the cell.
Cellular respiration: Process that breaks down glucose to produce ATP. Occurs in mitochondria.

Cell Signaling

Cells communicate with each other through signaling pathways.
Signaling molecules (ligands) bind to receptors on target cells.
This triggers a series of intracellular events, leading to a cellular response.
Different types of signaling mechanisms exist, including direct contact, paracrine, endocrine, and synaptic signaling.

Description

Explore the fundamental differences between prokaryotic and eukaryotic cell structures. This quiz covers key features of both cell types, including their genetic material organization and essential organelles. Test your knowledge on the unique characteristics that distinguish these two major classes of cells.