Understanding Cell Biology: Structure, Function, and Processes
Cell Theory: The Foundation of Biology
Key Concepts
All living things are composed of cells, and all cells arise from earlier cells.
Cell Structures and Their Functions
Prokaryotic Cells
Prokaryotic cells are simple cells without a nucleus or membrane-bound organelles. They belong to the domains Bacteria and Archaea.
Eukaryotic Cells
Eukaryotic cells are more complex cells with a nucleus and membrane-bound organelles. They belong to the domain Eukarya and include plant and animal cells.
Organelles
Cell Wall
A rigid structure that surrounds the cell membrane of plants and most bacteria.
Chloroplasts
Organelles found in plant cells and some other organisms that capture energy from sunlight and convert it into chemical energy.
Cilia
Short, numerous appendages that aid in movement, moving the cell via coordinated beating.
Cytoplasm
The region within the cell membrane that includes the fluid, the cytoskeleton, and all organelles except the nucleus.
Cytoskeleton
A network of protein filaments that helps the cell maintain its shape and is involved in cell movement.
Endoplasmic Reticulum (ER)
A network of passageways where proteins and other materials are transported within the cell.
- Rough ER: Studded with ribosomes and involved in protein synthesis.
- Smooth ER: Lacks ribosomes and involved in lipid synthesis and detoxification.
Eukaryote
A cell that contains a nucleus and membrane-bound organelles.
Flagella
Long, often single appendages that aid in movement, propelling the cell with whip-like movements.
Golgi Apparatus
Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes
Sacs containing digestive enzymes that break down waste materials and cellular debris.
Mitochondria
The powerhouse of the cell, responsible for producing ATP (energy) through cellular respiration.
Nucleus
Contains the cell’s genetic material (DNA) and controls cellular activities.
Plasma Membrane
A selectively permeable membrane that regulates the passage of molecules into and out of the cell.
Prokaryote
A single-celled organism that lacks a nucleus and membrane-bound organelles.
Ribosomes
Responsible for protein synthesis.
Vacuoles
Storage organelles that can contain water, nutrients, and waste products.
Cell Membrane Structure
Fluid Mosaic Model
The fluid mosaic model describes the cell membrane as a flexible and dynamic structure composed of a phospholipid bilayer with embedded proteins.
Functions of the Plasma Membrane
- Protects the cell
- Regulates transport of substances
- Receives chemical messengers
- Acts as a receptor
- Facilitates cell mobility, secretion, and absorption
Plant vs. Animal Cells
Key Differences
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present | Absent |
| Vacuole | Large, central vacuole | Small or absent |
| Chloroplasts | Present | Absent |
| Flagella | Only in gametes | Present in some cells |
Nuclear Components
Nucleolus
Produces ribosomes.
Chromatin/Chromosomes
Contain the cell’s genetic material (DNA).
Nuclear Envelope
A double membrane that surrounds the nucleus and regulates the passage of molecules between the nucleus and cytoplasm.
Cytoskeleton
Function
Provides structural support and facilitates cell movement.
Composition
Composed of protein fibers.
Cilia vs. Flagella
| Feature | Cilia | Flagella |
|---|---|---|
| Number | Numerous | Often single |
| Length | Short | Long |
| Function | Coordinated beating for movement | Whip-like movements for propulsion |
Cell Division and the Cell Cycle
Cell Division
The process by which a cell divides into two daughter cells.
Functions of Cell Division
- Growth
- Development
- Repair
Chromosomes
Gene-carrying structures found in the nucleus.
Human Chromosome Number
Humans have 46 chromosomes (23 pairs).
Chromosome Variation
Chromosome number and shape vary among organisms.
Chromosome Location
Chromosomes are located within the nucleus.
Cell Cycle Stages
- G1 (Gap 1): Cell growth and normal functions.
- S (Synthesis): DNA replication.
- G2 (Gap 2): Preparation for cell division.
- M (Mitosis): Nuclear division.
Mitosis
The process of nuclear division that produces two identical daughter nuclei.
Importance of Mitosis
Essential for growth, development, and repair.
Phases of Mitosis
- Prophase: Chromosomes condense, nuclear envelope breaks down.
- Metaphase: Chromosomes align at the center of the cell.
- Anaphase: Sister chromatids separate and move to opposite poles.
- Telophase: Nuclear envelope reforms, chromosomes decondense.
- Cytokinesis: Cytoplasm divides, forming two daughter cells.
Key Terms
- Asexual Reproduction: Reproduction without the involvement of gametes.
- Sexual Reproduction: Reproduction involving the fusion of gametes.
- Histone: Protein that helps package DNA.
- Centromere: Region where sister chromatids are joined.
- Sister Chromatid: One of two identical copies of a replicated chromosome.
- Benign Tumor: Non-cancerous tumor.
- Malignant Tumor: Cancerous tumor.