Key Takeaways
- Eukaryotic cells have a nucleus and membrane-bound organelles; prokaryotic cells do not
- Mitochondria produce ATP; ribosomes synthesize proteins; nucleus contains DNA
- DNA bases pair A-T and G-C; RNA has U instead of T
- Mitosis produces 2 identical diploid cells; meiosis produces 4 different haploid cells
- Dominant alleles are expressed with one copy; recessive require two copies
Last updated: January 2026
Cell Biology and Genetics
Understanding cell structure, function, and genetics is fundamental to the TEAS Science section. This covers cells, DNA, cell division, and heredity.
Cell Structure
Prokaryotic vs. Eukaryotic Cells:
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | No membrane-bound nucleus | Membrane-bound nucleus |
| Size | Smaller (1-10 μm) | Larger (10-100 μm) |
| Examples | Bacteria, archaea | Plants, animals, fungi |
| Organelles | Few, no membrane-bound | Many membrane-bound |
Eukaryotic Cell Organelles
| Organelle | Function |
|---|---|
| Nucleus | Contains DNA, controls cell activities |
| Mitochondria | Produces ATP (cellular respiration) |
| Ribosomes | Synthesizes proteins |
| Endoplasmic reticulum (ER) | Protein (rough) and lipid (smooth) synthesis |
| Golgi apparatus | Modifies, packages, and ships proteins |
| Lysosomes | Digests waste and foreign materials |
| Cell membrane | Controls what enters/exits cell |
| Cytoplasm | Gel-like fluid containing organelles |
Plant cell only:
- Cell wall (cellulose)
- Chloroplasts (photosynthesis)
- Central vacuole (storage, structure)
Cell Membrane Structure
The fluid mosaic model describes the cell membrane:
- Phospholipid bilayer (hydrophilic heads, hydrophobic tails)
- Embedded proteins (transport, receptors)
- Cholesterol (membrane fluidity)
- Carbohydrates (cell recognition)
Transport Across Membranes
| Type | Energy | Direction | Examples |
|---|---|---|---|
| Passive diffusion | No | High → Low concentration | O₂, CO₂ |
| Facilitated diffusion | No | High → Low (with proteins) | Glucose |
| Osmosis | No | Water moves toward solute | Water balance |
| Active transport | Yes | Low → High concentration | Na⁺/K⁺ pump |
DNA and RNA
| Feature | DNA | RNA |
|---|---|---|
| Structure | Double helix | Single strand |
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Location | Nucleus | Nucleus and cytoplasm |
| Function | Stores genetic info | Protein synthesis |
DNA Replication
Process: DNA makes a copy of itself before cell division Key enzyme: DNA polymerase Result: Two identical DNA molecules
Base pairing rules:
- Adenine (A) pairs with Thymine (T)
- Guanine (G) pairs with Cytosine (C)
Protein Synthesis
| Step | Location | Process |
|---|---|---|
| Transcription | Nucleus | DNA → mRNA |
| Translation | Ribosome | mRNA → Protein |
Key players:
- mRNA: Carries genetic code from DNA
- tRNA: Brings amino acids to ribosome
- rRNA: Part of ribosome structure
Cell Division
Mitosis: Cell division for growth and repair
- Result: 2 identical daughter cells (diploid)
- Phases: Prophase → Metaphase → Anaphase → Telophase
Meiosis: Cell division for gamete (sex cell) production
- Result: 4 genetically different cells (haploid)
- Creates genetic diversity through crossing over
Genetics Terminology
| Term | Definition |
|---|---|
| Gene | Segment of DNA coding for a trait |
| Allele | Different versions of a gene |
| Genotype | Genetic makeup (e.g., Bb) |
| Phenotype | Observable trait (e.g., brown eyes) |
| Dominant | Expressed when one copy present (B) |
| Recessive | Expressed only when two copies present (bb) |
| Homozygous | Two identical alleles (BB or bb) |
| Heterozygous | Two different alleles (Bb) |
Punnett Squares
Used to predict offspring genotypes and phenotypes.
Example: Cross Bb × Bb
| B | b | |
|---|---|---|
| B | BB | Bb |
| b | Bb | bb |
- Genotype ratio: 1 BB : 2 Bb : 1 bb
- Phenotype ratio: 3 dominant : 1 recessive
Test Your Knowledge
Which organelle is responsible for producing ATP?
A
B
C
D
Test Your Knowledge
What is the result of meiosis?
A
B
C
D
Test Your Knowledge
If a parent has genotype Bb, what percentage of gametes will carry the B allele?
A
B
C
D