Cell Structure, Function, and Microscopy: Study Notes for General Biology

Cell Structure and Function

Fundamental Unit of Life: The Cell

The cell is the basic structural and functional unit of all living organisms. Cells can vary greatly in size, shape, and function, but all share certain fundamental characteristics.

• Definition: A cell is the smallest unit of life that can carry out all life processes.

• Types of Cells: Prokaryotic and Eukaryotic

• Example: Escherichia coli (prokaryote), human skin cell (eukaryote)

Microscopy and Cell Study Tools

Microscopes in Biology

Microscopes are essential tools for studying cells and their components. Different types of microscopes allow scientists to observe cells at various levels of detail.

• Light Microscope: Uses visible light to magnify objects up to ~1000x. Suitable for viewing live cells.

• Electron Microscope (EM): Uses electron beams for much higher resolution. Includes Transmission EM (TEM) and Scanning EM (SEM).

• Fluorescence Microscope: Uses fluorescent markers to visualize specific cell components.

• Super-resolution Microscopy: Allows visualization of molecules at nanometer scale.

Microscope Type	Resolution	Application
Light Microscope	~200 nm	Live cells, tissues
Electron Microscope	~0.1 nm	Cell organelles, viruses
Fluorescence Microscope	~20-200 nm	Specific proteins, structures
Super-resolution	<20 nm	Molecular complexes

Cell Fractionation

Cell fractionation is a laboratory technique used to separate cellular components for detailed study.

• Process: Cells are broken open (homogenized), and components are separated by centrifugation.

• Purpose: To isolate organelles such as nuclei, mitochondria, and ribosomes.

• Example: Differential centrifugation separates cell parts based on size and density.

Prokaryotic and Eukaryotic Cells

Comparison of Cell Types

Cells are classified as prokaryotic or eukaryotic based on their structural features.

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	No (nucleoid region)	Yes (membrane-bound)
Organelles	Few, not membrane-bound	Many, membrane-bound
DNA	Circular, in cytoplasm	Linear, in nucleus
Examples	Bacteria, Archaea	Plants, Animals, Fungi

• Prokaryotes: Simpler structure, no nucleus, domains Bacteria and Archaea.

• Eukaryotes: Complex structure, nucleus present, includes plants, animals, fungi, and protists.

Cellular Compartmentalization

Internal Membranes and Organelles

Eukaryotic cells contain internal membranes that create compartments for specialized functions.

• Plasma Membrane: Encloses the cell, regulates entry and exit of substances.

• Organelles: Specialized structures (e.g., nucleus, mitochondria, endoplasmic reticulum) with distinct functions.

• Advantages: Compartmentalization allows for higher concentrations of molecules, specialized environments, and efficient metabolic processes.

The Nucleus and Ribosomes

Nucleus: Genetic Control Center

The nucleus houses the cell's genetic material and coordinates activities such as growth and reproduction.

• Structure: Surrounded by a double membrane (nuclear envelope) with pores for transport.

• Contains: Chromatin (DNA + proteins), nucleolus (site of ribosome synthesis).

• Function: Stores genetic information, directs protein synthesis.

Ribosomes: Protein Factories

Ribosomes are molecular machines that synthesize proteins by translating messenger RNA (mRNA).

• Structure: Composed of ribosomal RNA (rRNA) and proteins; found free in cytoplasm or attached to endoplasmic reticulum.

• Function: Site of protein synthesis.

• Equation: $\text{mRNA} \rightarrow \text{Protein}$

Endomembrane System

Components and Functions

The endomembrane system is a group of interconnected organelles that manage protein and lipid synthesis, transport, and degradation.

• Components:

  • Endoplasmic Reticulum (ER)

  • Golgi Apparatus

  • Lysosomes

  • Vacuoles

  • Plasma Membrane

• Function: Protein trafficking, metabolic processes, and cellular compartmentalization.

Endoplasmic Reticulum (ER)

The ER is a network of membranes involved in protein and lipid synthesis.

• Types:

  • Rough ER: Studded with ribosomes; synthesizes proteins for secretion or membrane insertion.

  • Smooth ER: Lacks ribosomes; synthesizes lipids, detoxifies chemicals.

• Example: Liver cells have abundant smooth ER for detoxification.

Golgi Apparatus, Lysosomes, and Vacuoles

These organelles further process, sort, and store cellular materials.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for breaking down macromolecules.

• Vacuoles: Storage organelles, prominent in plant cells.

Additional info: Some content was inferred and expanded for completeness, including definitions, examples, and the table comparing cell types and microscopes.