Introduction to the Cell: Structure, Function, and Organelles

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Lesson 1 - Introduction to the Cell

Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life in all living organisms.

All living organisms are made up of cells.
All cells come from pre-existing cells.
Cells are the basic functioning unit of life.

Matthias Schleiden (Botanist): Discovered that plants were made up of cells. He believed in "free cell formation" but was later corrected by Rudolf Virchow.

Theodor Schwann (Zoologist): Discovered that animals were made up of cells.

Types of Cells

Cells are classified into two main types based on their structure and complexity: Prokaryotic and Eukaryotic cells.

Prokaryotic	Eukaryotic
Unicellular	Uni- and Multicellular
No nucleus	Has nucleus
DNA in unbound region (nucleoid)	DNA in nucleus, bounded by double membrane
No membrane-bound organelles	Has membrane-bound organelles
Cytoplasm bound by plasma membrane	Cytoplasm in region between plasma membrane and nucleus

Plant vs Animal Cells

Plant and animal cells share many features but also have key differences.

Plant	Animal
Chloroplast, Cell Wall, Central Vacuoles, Peroxisomes	Lysosomes, Centrioles
Autotrophs (produce own food)	Heterotrophs (get food from other plants/animals)
Photosynthesis	Cilia, Flagella, Multivilli
Bigger	Smaller

Lesson 2 - Cell Structures and Functions

Common Features of Cells

Genetic Material (DNA): Contains the genetic code for organisms. Found in nucleoid (prokaryotes) or nucleus, mitochondria, chloroplast, and cytoplasm (eukaryotes).
Plasma Membrane/Cell Membrane: Regulates entry and exit of materials; selectively permeable; made up of a phospholipid bilayer.
Cytosol: Fluid part of cytoplasm; all cells have cytosol but different components.
Ribosomes: "Protein factory of the cell"; not an organelle but a sub-cellular component. Found free in cytoplasm/cytosol or bound to endoplasmic reticulum.

Cell Organelles and Their Functions

Nucleus (The Control Center): Contains most of the cell's DNA in the form of chromosomes/chromatin. Most genes in eukaryotic cells are located here. The nucleus is the most conspicuous organelle.
- Nucleolus: Site where ribosomal RNA is synthesized using instructions from DNA.
- Nuclear Envelope: Double membrane composed of a lipid bilayer; encloses the nucleus and separates it from the cytoplasm.
- Nuclear Lamina: Netlike array of protein filaments that maintain the shape of the nucleus.
- Chromosomes: Structures that carry genetic information.
- Chromatin: Complex of DNA and proteins; uncondensed version of chromosomes.
Endoplasmic Reticulum (ER) - Biosynthesis Factory: Network of membranes involved in protein and lipid synthesis.
- Smooth ER: Synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons, stores calcium ions. Lacks ribosomes.
- Rough ER: Has bound ribosomes; synthesizes proteins and glycoproteins. Glycoproteins are important for cell-cell recognition. Distributes transport vesicles.
Golgi Apparatus/Body - Sorting Center: Modifies, sorts, and ships biomolecules. Has cis (receiving) and trans (shipping) faces.
Lysosomes - Bags: Contain hydrolytic enzymes that digest macromolecules and organelles. Functions include autophagy (recycling cell's own organelles) and phagocytosis (digesting food particles).
Vacuoles - Maintenance Compartments: Large vesicles derived from ER and Golgi apparatus. Types include:
- Food vacuoles: Formed by phagocytosis, capture food particles.
- Contractile vacuoles: Pump excess water out of cells (common in freshwater protists).
- Central vacuole: Found in many mature plant cells, holds organic compounds and water.
Mitochondria - Powerhouse: Site of cellular respiration, a process that uses oxygen to generate ATP (adenosine triphosphate).
- Cristae: Folds in the inner membrane, increasing surface area for ATP production.
- Mitochondrial Matrix: Contains enzymes, mitochondrial DNA, and ribosomes.

Endomembrane System

The endomembrane system regulates protein traffic and performs metabolic functions in the cell. It includes the nuclear envelope, endoplasmic reticulum, Golgi body, lysosomes, and vacuoles. These components are related either through direct continuity or by transfer of vesicles.

Regulates protein traffic
Performs metabolic functions
Consists of nuclear envelope, ER, Golgi body, lysosomes, vacuoles

Key Terms and Definitions

Autotroph: Organism that produces its own food (e.g., plants via photosynthesis).
Heterotroph: Organism that obtains food from other organisms (e.g., animals).
Phagocytosis: Process by which a cell engulfs particles to form an internal compartment known as a phagosome.
ATP (Adenosine Triphosphate): The main energy currency of the cell.

Example: Mitochondrial ATP Production

The mitochondrion uses oxygen to convert glucose into ATP through cellular respiration. The process can be summarized by the equation:

Summary Table: Major Eukaryotic Organelles and Functions

Organelle	Main Function
Nucleus	Stores genetic material, controls cell activities
Ribosome	Protein synthesis
Endoplasmic Reticulum (Rough/Smooth)	Protein and lipid synthesis
Golgi Apparatus	Modification, sorting, and shipping of proteins and lipids
Lysosome	Digestion and recycling of cellular waste
Vacuole	Storage and maintenance of cell turgor (plants)
Mitochondria	ATP production via cellular respiration

Additional info: The notes also reference a supplementary video for further study on the endomembrane system, which can be useful for visual learners.