Internal Organization of Eukaryotic Cells

Overview of Eukaryotic Cell Structure and Function

Eukaryotic cells are highly organized structures that contain membrane-bound organelles, each performing specific functions necessary for life. The compartmentalization within eukaryotic cells allows for specialization and efficiency in cellular processes.

• Energy and Matter Acquisition: Organelles such as mitochondria and chloroplasts (in plants) are responsible for energy conversion and synthesis of biomolecules.

• Genetic Information: The nucleus houses DNA, which contains the genetic instructions for cell function and reproduction.

• Interactions with the Environment: The plasma membrane regulates the movement of substances into and out of the cell, maintaining homeostasis.

Example: Mitochondria generate ATP through cellular respiration, providing energy for cellular activities.

Microscopy and Cell Size

Comparing Cell and Organelle Sizes

Cells and their components vary greatly in size, from atoms and molecules to entire cells. Understanding these size differences is crucial for selecting appropriate microscopy techniques.

• Atoms: ~0.1 nm

• Ribosomes: ~20-30 nm

• Small Bacteria: ~0.5-1 μm

• Mitochondria: ~1-10 μm

• Animal Cells: ~10-30 μm

• Chicken Eggs: Several centimeters

Types of Microscopes and Their Uses

Different microscopes are used to visualize structures of varying sizes and properties:

• Light Microscope: Uses visible light to observe living cells and tissues; suitable for structures larger than ~200 nm.

• Fluorescence Microscope: Uses fluorescent dyes to label and visualize specific cell components; allows observation of dynamic processes in living cells.

• Electron Microscope: Uses electron beams for much higher resolution; includes:

  • Scanning Electron Microscope (SEM): Provides detailed 3D images of cell surfaces.

  • Transmission Electron Microscope (TEM): Reveals internal structures at the molecular level.

Example: Ribosomes are visible only with electron microscopes due to their small size.

Table: Types of Microscopes and Their Applications

Cell Size and Surface Area-to-Volume Ratio

Importance of Surface Area-to-Volume Ratio

The surface area-to-volume ratio is a key factor limiting cell size. As a cell grows, its volume increases faster than its surface area, making it more difficult to exchange materials with the environment efficiently.

• Formula for Surface Area of a Cube:

• Formula for Volume of a Cube:

• Surface Area-to-Volume Ratio:

Example: Smaller cells have a higher surface area-to-volume ratio, facilitating efficient nutrient uptake and waste removal.

Basic Unit of Life: The Cell

Essential Cell Features

All cells share certain features that are essential for life:

• Plasma Membrane: Encloses the cell, regulates entry and exit of substances, and provides a barrier between the cell and its environment.

• DNA: Contains genetic information necessary for controlling cellular processes.

• Ribosomes: Sites of protein synthesis.

• Cytoplasm: Gel-like substance where cellular components are suspended and metabolic reactions occur.

Prokaryotic vs. Eukaryotic Cells

Major Features of Prokaryotes

Prokaryotic cells, such as bacteria, are simpler and smaller than eukaryotic cells. They lack membrane-bound organelles and a true nucleus.

• Size: Typically about 1/10th the size of eukaryotic cells.

• Cell Wall: Provides structure and rigidity; contains peptidoglycan in bacteria.

• Genetic Material: DNA is circular and located in the nucleoid region, not enclosed by a membrane.

• Ribosomes: Smaller than those in eukaryotes; site of protein synthesis.

• Other Features: May have flagella for movement, pili for attachment, and a capsule for protection.

Example: Escherichia coli is a common prokaryotic bacterium.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Antibiotics and Cell Structure

How Antibiotics Kill Bacterial Cells but Not Human Cells

Antibiotics target features unique to bacterial cells, such as the peptidoglycan cell wall or specific enzymes involved in DNA replication. Human cells lack these structures, making antibiotics selectively toxic to bacteria.

• Penicillin: Inhibits synthesis of peptidoglycan, weakening bacterial cell walls and causing cell lysis.

• Other Antibiotics: May inhibit bacterial ribosomes or DNA replication enzymes.

Example: Penicillin is effective against Gram-positive bacteria due to their thick peptidoglycan layer.

Cell Organelles and Their Functions

Major Eukaryotic Organelles

Eukaryotic cells contain specialized organelles, each with distinct functions:

The Cytoskeleton

Structure and Function of the Cytoskeleton

The cytoskeleton is a dynamic network of protein filaments that provides structural support, maintains cell shape, and facilitates movement of organelles and the cell itself.

• Microtubules: Hollow tubes that maintain cell shape, enable chromosome movement during cell division, and serve as tracks for organelle movement.

• Microfilaments (Actin Filaments): Thin filaments involved in cell movement, muscle contraction, and cytokinesis.

• Intermediate Filaments: Provide mechanical strength and help anchor organelles.

Example: Microtubules form the mitotic spindle during cell division.

Plant vs. Animal Cells

Key Differences Between Plant and Animal Cells

While both plant and animal cells are eukaryotic, they have several distinct features:

• Plant Cells: Have a cell wall (cellulose), chloroplasts, and a large central vacuole.

• Animal Cells: Lack a cell wall and chloroplasts; have smaller vacuoles and centrioles.

Example: Only plant cells can perform photosynthesis due to the presence of chloroplasts.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard biology textbooks.