Cell Structure & Function: MDCAT Notes and MCQs
Plant vs animal cell
| Plant cell | Animal cell |
|---|---|
| Cellulose cell wall present | No cell wall |
| Chloroplasts / plastids | No plastids |
| Large central vacuole | Small, temporary vacuoles |
| Centrioles absent (higher plants) | Centrioles present |
| Stores starch | Stores glycogen |
Prokaryotic vs eukaryotic
| Prokaryote (bacteria) | Eukaryote |
|---|---|
| No nuclear membrane — nucleoid | True nucleus with envelope |
| Single circular DNA, no histones | Linear chromosomes with histones |
| 70S ribosomes | 80S ribosomes (70S in mitochondria/chloroplasts) |
| No membrane-bound organelles | ER, Golgi, mitochondria, lysosomes |
| Cell wall of peptidoglycan (murein) | Cellulose (plants) / chitin (fungi) / none |
Organelles
- Nucleus: double-membrane envelope with nuclear pores; contains chromatin and nucleolus (makes rRNA/ribosome subunits). Controls cell activities and heredity.
- Endoplasmic reticulum: Rough ER (ribosomes) → protein synthesis & transport; Smooth ER → lipid/steroid synthesis, detoxification (liver), Ca2+ storage (sarcoplasmic reticulum in muscle).
- Golgi apparatus (Camillo Golgi, 1898): stack of cisternae with cis (forming) and trans (maturing) faces; modifies, packages and secretes proteins/lipids, adds carbohydrates (glycoproteins), forms lysosomes and cell plate.
- Mitochondria: "powerhouse"; double membrane, inner one folded into cristae bearing ETC and ATP synthase (F1 particles); matrix contains Krebs enzymes, circular DNA and 70S ribosomes (semi-autonomous).
Chromosomes
- Composition: DNA + histone proteins (≈ 1:1) + some RNA and non-histone proteins. DNA wraps around 8 histones → nucleosome.
- Structure: two chromatids joined at the centromere (primary constriction, kinetochore attaches spindle). Ends = telomeres.
- Types by centromere: metacentric, sub-metacentric, acrocentric, telocentric.
- Euchromatin (loose, active) vs heterochromatin (condensed, inactive).
- Humans: 46 chromosomes (23 pairs: 22 autosomes + 1 pair sex chromosomes). Function: carry genes, transmit hereditary information.
PMDC learning outcomes for this unit
- Cell structure: 4.1 Compare the structure of typical animal and plant cell
- Prokaryotic and Eukaryotic cell: 4.2 Compare and contrast the structure of prokaryotic cells with eukaryotic cells
- Cytoplasmic Organelles: 4.3 Outline the structure and function of the following organelles: nucleus, endoplasmic reticulum, Golgi apparatus and mitochondria
- Chromosomes: 4.4 Describe the structure, chemical composition and function of chromosomes.