뒤로Chapter 7: Inside the Cell – Structure and Function of Prokaryotic and Eukaryotic Cells
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Inside the Cell
Introduction to Cell Types
Cells are the fundamental units of life and are divided into two major types based on the presence or absence of a membrane-bound nucleus: eukaryotes and prokaryotes. Understanding the differences between these cell types is essential for studying cell biology.
Eukaryotes: Cells that possess a membrane-bound nucleus. Examples include protists, fungi, plants, and animals.
Prokaryotes: Cells that lack a membrane-bound nucleus. Examples include bacteria and archaea.
Prokaryotic Cell Structures and Their Functions
Overview of Prokaryotic Cell Structure
Prokaryotic cells are generally smaller and simpler than eukaryotic cells. They are usually unicellular and have specialized structures that allow them to survive in diverse environments.
Plasma Membrane: A lipid bilayer that encloses the cell, controlling the movement of substances in and out.
Cell Wall: An "exoskeleton" barrier composed mainly of carbohydrates (such as peptidoglycan in bacteria) that provides structural support and protection.
Chromosome (Nucleoid Region): Genetic material is typically a single, supercoiled DNA molecule located in the nucleoid region, not surrounded by a membrane.
Plasmids: Small, circular DNA molecules that can confer advantages such as antibiotic resistance.
Ribosomes: Sites of protein synthesis; composed of RNA and protein. Ribosomes are present in both prokaryotic and eukaryotic cells.
Specialized Structures in Prokaryotes
Some prokaryotes possess additional structures that enhance their survival and functionality.
Internal Photosynthetic Membranes: Found in photosynthetic bacteria; these membranes convert energy from sunlight into chemical energy through photosynthesis.
Flagella: Long, whip-like appendages that rotate to propel the cell through its environment.
Fimbriae: Hair-like structures that help cells adhere to surfaces and to each other.
Eukaryotic Cell Structures and Their Functions
Overview of Eukaryotic Cell Structure
Eukaryotic cells are typically much larger than prokaryotic cells and may be unicellular or multicellular. Their internal structure is highly organized, with membrane-bound organelles that compartmentalize cellular functions.
Nucleus: Contains the cell's genetic material (DNA) and is surrounded by a double membrane called the nuclear envelope.
Organelles: Specialized compartments such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes, each with distinct functions.
Cytoskeleton: A network of protein filaments that provides structural support, facilitates cell movement, and organizes organelles within the cell.
Examples of eukaryotes include protists, fungi, plants, and animals. Eukaryotic cells can range in size from microscopic algae to large multicellular organisms like redwood trees.
Compartmentalization in Eukaryotic Cells
Membrane-bound organelles allow eukaryotic cells to compartmentalize different biochemical reactions, increasing efficiency and specialization.
Mitochondria: Site of cellular respiration and energy (ATP) production.
Chloroplasts: Found in plant cells and some protists; site of photosynthesis.
Endoplasmic Reticulum (ER): Rough ER is involved in protein synthesis; smooth ER synthesizes lipids and detoxifies chemicals.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes: Contain digestive enzymes to break down macromolecules and cellular debris.
Comparison Table: Prokaryotic vs. Eukaryotic Cells
Feature | Prokaryotic Cells | Eukaryotic Cells |
|---|---|---|
Nucleus | Absent | Present (membrane-bound) |
Organelles | Few, non-membrane-bound | Many, membrane-bound |
Size | Generally small (1-10 μm) | Larger (10-100 μm or more) |
Examples | Bacteria, Archaea | Protists, Fungi, Plants, Animals |
Key Terms
Prokaryote: A unicellular organism lacking a membrane-bound nucleus.
Eukaryote: An organism whose cells contain a nucleus and other organelles enclosed within membranes.
Organelle: A specialized subunit within a cell that has a specific function.
Plasma Membrane: The biological membrane that separates the interior of all cells from the outside environment.
Ribosome: A molecular machine for protein synthesis, composed of RNA and protein.
Example Application
Photosynthetic bacteria use internal photosynthetic membranes to convert sunlight into chemical energy, demonstrating the adaptation of prokaryotic cells to specific environments.
Additional info: Eukaryotic cells' compartmentalization allows for greater complexity and specialization, which is essential for multicellular life forms.
