BackCell Structure and Function: Prokaryotic and Eukaryotic Cells, Microscopy, and Organelles
Study Guide - Smart Notes
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Microscopy and the Study of Cells
Introduction to Microscopes
Microscopes are essential tools in biology, allowing scientists to visualize structures too small to be seen with the naked eye, such as cells and their components. There are two main types of microscopes commonly used in biology: light microscopes and electron microscopes.
Light Microscopes: Use visible light to magnify small objects, typically up to 1000x magnification. Suitable for viewing live cells and tissues.
Electron Microscopes: Use beams of electrons for much higher magnification and resolution, allowing visualization of subcellular structures.
Example: The range of the human eye, light microscopes, and electron microscopes covers different scales, from atoms to multicellular organisms.
Types of Electron Microscopes
Scanning Electron Microscope (SEM): Visualizes cell surfaces in great detail, producing three-dimensional images.
Transmission Electron Microscope (TEM): Visualizes internal cell structures by passing electrons through thin sections of specimens.
Application Example: To measure the size of a ribosome inside a eukaryotic cell, a transmission electron microscope would be used due to its high resolution.
Cell Types: Prokaryotic and Eukaryotic Cells
Domains of Life
All living organisms are classified into three domains based on cellular structure:
Bacteria (Prokaryotic)
Archaea (Prokaryotic)
Eukarya (Eukaryotic)
Domain | Cell Type | Nucleus | Organelles | Cell Size | Cellularity |
|---|---|---|---|---|---|
Bacteria | Prokaryotic | Absent | Absent | Small (<10 μm) | Unicellular |
Archaea | Prokaryotic | Absent | Absent | Small (<10 μm) | Unicellular |
Eukarya | Eukaryotic | Present | Present | Large (10–100 μm) | Unicellular or Multicellular |
Features of Bacterial (Prokaryotic) Cells
Abundance: Bacteria are the most abundant and diverse organisms on Earth.
DNA: Bacterial DNA is circular and found in a region called the nucleoid.
Ribosomes: Bacteria have small (70S) ribosomes and reproduce by binary fission.
Features of Eukaryotic Cells
Organelles: Eukaryotic cells contain several membrane-bound organelles, including a nucleus.
DNA: Eukaryotic DNA is linear and found within the nucleus.
Ribosomes: Eukaryotic cells have large (80S) ribosomes and divide by mitosis and cytokinesis.
Comparison: Prokaryotic vs. Eukaryotic Cells
Prokaryotic Cells | BOTH | Eukaryotic Cells |
|---|---|---|
|
|
|
Eukaryotic Cell Organelles
Overview of Eukaryotic Organelles
Eukaryotic cells contain several membrane-bound organelles, each with specialized functions. Some organelles are unique to animal or plant cells, while others are shared.
Nucleus: Stores genetic material (DNA) and controls cellular activities.
Mitochondria: Site of cellular respiration and energy (ATP) production.
Chloroplasts: Site of photosynthesis in plant cells.
Endoplasmic Reticulum (ER): Rough ER is involved in protein synthesis; Smooth ER in lipid synthesis and detoxification.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes: Contain digestive enzymes to break down waste (mainly in animal cells).
Central Vacuole: Large storage organelle in plant cells for water, nutrients, and waste.
Cell Wall: Provides structural support in plant cells (composed of cellulose).
Animal vs. Plant Cells
Animal Cells: Contain lysosomes and centrioles; lack a cell wall and chloroplasts.
Plant Cells: Contain chloroplasts, a central vacuole, and a cell wall; lack lysosomes and centrioles.
Ribosomes
Definition: Ribosomes are molecular "machines" that build proteins by translating messenger RNA (mRNA).
Location: Ribosomes can be free in the cytoplasm or attached to the rough ER.
Function: Ribosomes synthesize proteins in all types of cells.
Map of Eukaryotic Cell Organelles
The following is a logical map of eukaryotic cell organelles and their functions:
System | Organelles | Main Functions |
|---|---|---|
Endomembrane System | Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Vesicles | Protein synthesis, modification, and transport |
Energy-Related Organelles | Mitochondria, Chloroplasts (plants) | ATP production, photosynthesis |
Cytoskeleton | Microtubules, Microfilaments, Intermediate Filaments | Cell shape, movement, and division |
Cell Junctions | Tight Junctions, Desmosomes, Gap Junctions | Cell-to-cell communication and adhesion |
Cytoskeleton Components
Microtubules: Hollow tubes that maintain cell shape and facilitate movement of organelles.
Microfilaments: Thin filaments involved in cell movement and muscle contraction.
Intermediate Filaments: Provide mechanical support for the cell.
Summary Table: Prokaryotic vs. Eukaryotic Cells
Feature | Prokaryotic Cells | Eukaryotic Cells |
|---|---|---|
Nucleus | Absent | Present |
Organelles | Absent | Present |
Cell Size | Small (<10 μm) | Large (10–100 μm) |
DNA Structure | Circular | Linear |
Ribosomes | 70S | 80S |
Cell Division | Binary Fission | Mitosis/Cytokinesis |
Key Terms and Definitions
Microscope: An instrument used to magnify and visualize small objects.
Prokaryote: A cell lacking a nucleus and membrane-bound organelles (Bacteria and Archaea).
Eukaryote: A cell with a nucleus and membrane-bound organelles (Eukarya).
Organelle: Specialized structure within a cell that performs a specific function.
Ribosome: A complex that synthesizes proteins from amino acids using mRNA as a template.
Cytoskeleton: A network of protein filaments that provides structural support and facilitates movement.
Practice Questions (Examples)
Which type of microscope would you use to view the internal structure of a mitochondrion?
What are the main differences between prokaryotic and eukaryotic cells?
Which organelle is responsible for packaging genetic material in eukaryotic cells?
What biomolecule do ribosomes synthesize in all types of cells?
