Cell and Molecular Biology Lesson
Lesson Overview
- Atomic Structure and Elements in Biology
- Chemical Bonds and Water Properties
- Acids, Bases, and pH
- Organic Compounds in Cells
- Lipids: Saturated vs Unsaturated
- Enzymes and Activation Energy
- Energy in Reactions
- Photosynthesis and Respiration
- Cell Theory and Types
- Plant vs Animal Cells
- Organelles and Functions
- Transport Across Membranes
- Endocytosis and Exocytosis
- Receptors and Signaling
- Why Cells Stay Small
- Microscopy Magnification
- Homeostasis
- Key Takeaway
Imagine trying to build a functioning city without knowing how bricks, water pipes, and electric wires work. That's what learning life science without understanding cells and molecules would be like.
This lesson on Cell and Molecular Biology gives you the foundation to understand how life works at its smallest levels-from atoms to entire cells. Each concept is explained to align with quiz-style assessments and real classroom needs.
Atomic Structure and Elements in Biology
What makes one element different from another?
The number of protons in an atom's nucleus defines the element.
| Feature | Description |
| Proton | Determines atomic number and identity |
| Electron | Involved in chemical bonding |
| Neutron | Affects atomic mass and isotopes |
Chemical Bonds and Water Properties
Types of Bonds
- Ionic Bonds: Electrons are transferred; forms ions (e.g., Na⁺Cl⁻).
- Covalent Bonds: Electrons are shared (e.g., H₂O molecule).
Water's Special Features
- Polarity: Oxygen pulls electrons, making one side slightly negative, the other positive.
- Hydrogen Bonds: Weak attraction between water molecules.
| Water Property | Description |
| Cohesion | Water sticks to itself |
| Adhesion | Water sticks to other materials |
| Solvent | Water dissolves many substances |
Memory Tip: Cohesion = co- (with self), Adhesion = add (to other things).
Acids, Bases, and pH
pH Scale
| pH Range | Type | Description |
| 0–6 | Acidic | High H⁺ ion concentration |
| 7 | Neutral | Equal H⁺ and OH⁻ concentration |
| 8–14 | Basic | High OH⁻ ion concentration |
Acids have pH < 7, and bases have pH > 7. Cells require near-neutral pH to maintain homeostasis.
Organic Compounds in Cells
All organic molecules contain carbon, the backbone of life.
| Type of Biomolecule | Elements Present | Function |
| Carbohydrates | C, H, O | Short-term energy |
| Lipids | C, H, O | Long-term energy, cell membranes |
| Proteins | C, H, O, N | Enzymes, structure, signaling |
| Nucleic Acids | C, H, O, N, P | Genetic information (DNA/RNA) |
Lipids: Saturated vs Unsaturated
- Saturated Fatty Acids: Single bonds only; solid at room temperature.
- Unsaturated Fatty Acids: At least one double bond; liquid at room temperature.
| Fat Type | Structure | State at Room Temp |
| Saturated | No double bonds | Solid (e.g., butter) |
| Unsaturated | One/more double bonds | Liquid (e.g., oil) |
Enzymes and Activation Energy
Enzymes are protein catalysts that speed up chemical reactions by lowering activation energy.
Key Terms
| Term | Meaning |
| Enzyme | Biological catalyst made of protein |
| Substrate | Molecule enzyme acts upon |
| Active Site | Region where substrate binds |
| Products | Resulting molecules after reaction |
| Activation Energy | Energy required to start a reaction |
Lock-and-Key Model
The enzyme's shape fits its substrate exactly-like a lock and key. If the enzyme changes shape (due to heat or pH), it can't function.
Energy in Reactions
| Reaction Type | Energy Flow | Example |
| Endothermic | Absorbs energy | Photosynthesis |
| Exothermic | Releases energy | Cellular respiration |
Catalysts (like enzymes) lower activation energy, speeding up both types of reactions.
Photosynthesis and Respiration
- Photosynthesis: Converts CO₂ and H₂O into glucose and oxygen using sunlight.
- Respiration: Breaks down glucose to release energy (ATP).
Photosynthesis is endothermic; respiration is exothermic.
Cell Theory and Types
Cell Theory
- All organisms are made of cells.
- The cell is the basic unit of life.
- All cells come from existing cells.
Types of Cells
| Feature | Prokaryotic | Eukaryotic |
| Nucleus | Absent | Present |
| Organelles | No membrane-bound | Membrane-bound present |
| Example | Bacteria | Plant, Animal, Fungi cells |
Plant vs Animal Cells
| Feature | Plant Cell | Animal Cell |
| Cell wall | Present | Absent |
| Chloroplast | Present | Absent |
| Large Vacuole | Present | Small or absent |
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Organelles and Functions
| Organelle | Function |
| Nucleus | Stores DNA, controls cell activities |
| Ribosome | Protein synthesis |
| Mitochondria | Produces energy (ATP) |
| Chloroplast | Performs photosynthesis |
| Vacuole | Storage (large in plants) |
| Cell membrane | Controls entry/exit |
| Cell wall | Provides support (plants) |
Transport Across Membranes
The cell membrane is selectively permeable.
Passive Transport (No energy required)
| Type | Description |
| Diffusion | Movement from high to low concentration |
| Osmosis | Water diffusion through a membrane |
| Facilitated Diff. | Uses protein channels, still passive |
Tonicity
| Solution Type | Solute Concentration | Water Movement |
| Hypotonic | Lower outside cell | Water enters cell (swell) |
| Hypertonic | Higher outside cell | Water exits cell (shrink) |
| Isotonic | Equal inside and outside | No net water movement |
Active Transport (Requires energy)
- Moves substances from low to high concentration.
- Requires ATP and transport proteins.
Example: Sodium-potassium pump in nerve cells.
Endocytosis and Exocytosis
Bulk Transport
| Process | Description |
| Endocytosis | Cell engulfs materials into a vesicle |
| Exocytosis | Vesicle fuses with membrane to release items |
Both require energy and are forms of active transport.
Receptors and Signaling
| Receptor Type | Location | Works With |
| Membrane Receptor | On cell surface | Polar molecules (e.g., insulin) |
| Intracellular Receptor | Inside cell | Nonpolar molecules (e.g., estrogen) |
Why Cells Stay Small
- Small cells have a higher surface-area-to-volume ratio, which makes diffusion more efficient.
- If a cell grows too large, diffusion becomes inefficient-nutrients can't reach the center quickly.
Microscopy Magnification
Total magnification = Eyepiece × Objective Lens
Example:
Eyepiece (10×) × Objective (40×) = 400×
Homeostasis
Homeostasis is the cell's ability to maintain a stable internal environment despite changes. It's critical for:
- pH balance
- Temperature regulation
- Nutrient/waste exchange
Key Takeaway
Cell and Molecular Biology connects chemical and biological processes to explain life at a microscopic level. Whether you're identifying cell types, understanding how enzymes work, or predicting water movement in different solutions, these fundamentals are key to mastering life science.
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