Loading...
Please wait while the page loadsNursing · Cell Biology
How cells are built, how they communicate and divide, and why understanding the cell helps you make sense of disease, drugs, and what you see on placement.
Save for later
Student note
Organelles are the tiny structures inside a cell that each have a specific job. ATP is adenosine triphosphate, the molecule cells use as energy. The phospholipid bilayer is the double layer of fat molecules that forms the cell membrane. Mitosis means cell division for growth and repair. Meiosis is division that makes eggs and sperm.
Energy
Mitochondria make ATP. No ATP, no cellular work. Think of them as the batteries inside every cell.
Membrane rule
The phospholipid bilayer decides what gets in and out. It is selectively permeable, not freely open.
Central dogma
DNA makes RNA, RNA makes protein. Almost every disease and drug connects back to this chain.
Division
Mitosis = 2 identical cells (growth). Meiosis = 4 unique cells (gametes). Cancer = mitosis gone wrong.
What are the basic building blocks inside every human cell?
Nucleus
Cytoplasm & ribosomes
ER & Golgi
Mitochondria & lysosomes
Clinical pearl
Mitochondria have their own DNA because they were once free-living bacteria that became part of our cells. This is why mitochondrial diseases are always inherited from the mother, and why some antibiotics that target bacterial ribosomes can also affect mitochondria.
How does the cell control what gets in and out?
Membrane structure
Passive transport
Active transport
Bulk transport
Clinical pearl
Osmosis is why IV fluid choice matters so much. Give a hypotonic fluid and water moves into cells, causing them to swell. Give a hypertonic fluid and water moves out of cells, causing them to shrink. Isotonic fluids like 0.9% saline match cell concentration, so water stays balanced.
How does the cell read its genetic instructions and build what it needs?
DNA basics
Transcription
Translation
Why it matters
Clinical pearl
The central dogma in plain terms: DNA makes RNA, RNA makes protein. Almost every drug, every disease process, and every lab test you encounter in nursing connects back to this chain somewhere. A faulty gene means a faulty protein, and a faulty protein means a body system that does not work as expected.
How do cells copy themselves and why does it matter when it goes wrong?
The cell cycle
Mitosis
Meiosis
When division goes wrong
Red flags
Clinical pearl
Chemotherapy works by targeting cells that divide quickly, which is why it hits cancer cells hard. But it also damages other rapidly dividing healthy cells like hair follicles, gut lining, and bone marrow. That is the reason behind hair loss, nausea, and low blood counts as side effects.
How do cells organise into tissues, and why are different cell types shaped differently?
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Clinical pearl
Every cell in your body has exactly the same DNA, yet a nerve cell looks and works completely differently from a skin cell. The difference is which genes are switched on. Cell specialisation (differentiation) is the process of activating certain genes and silencing others to create a cell with a specific job.
How does cell biology connect to what you see on placement?
Inflammation
Wound healing
Infection & immunity
Medications & the cell
Red flags
Clinical pearl
When you give a drug, it does not just "work". It binds to a specific receptor or enzyme at the cell level. Understanding this helps you predict side effects, drug interactions, and why timing and dose matter. The cell is where pharmacology actually happens.
| Organelle | Structure | Function |
|---|---|---|
| Nucleus | Double membrane with pores, contains chromatin | Stores DNA and controls cell activity |
| Mitochondria | Double membrane with inner folds (cristae) | Aerobic respiration — produces ATP (energy) |
| Rough ER | Membrane network studded with ribosomes | Synthesises proteins for export |
| Smooth ER | Membrane network without ribosomes | Makes lipids, detoxifies drugs and alcohol |
| Golgi apparatus | Stack of flattened membrane sacs | Modifies, packages, and sorts proteins |
| Lysosomes | Membrane-bound sacs with digestive enzymes | Breaks down waste, worn-out organelles, and pathogens |
| Ribosomes | Small granules of RNA and protein | Site of protein synthesis (translation) |
| Cell membrane | Phospholipid bilayer with embedded proteins | Controls entry and exit of substances |
| Cytoskeleton | Network of protein filaments and tubules | Maintains cell shape, enables movement |
| Centrioles | Paired cylindrical structures near the nucleus | Organise spindle fibres during cell division |
| Mechanism | Type | How it works | Example |
|---|---|---|---|
| Simple diffusion | Passive | Small non-polar molecules move down the concentration gradient | O₂ and CO₂ across alveolar membrane |
| Facilitated diffusion | Passive | Larger or charged molecules use channel or carrier proteins | Glucose entering cells via GLUT transporters |
| Osmosis | Passive | Water moves across a semi-permeable membrane from dilute to concentrated | Water reabsorption in kidney tubules |
| Active transport | Active (ATP) | Substances pumped against their concentration gradient | Na⁺/K⁺ pump in nerve and muscle cells |
| Endocytosis | Active (ATP) | Cell membrane folds inward to engulf material | Phagocytes engulfing bacteria |
| Exocytosis | Active (ATP) | Vesicles fuse with cell membrane to release contents | Neurotransmitter release at synapses |
Clinical pearl
When you hang an IV bag, you are manipulating osmosis and diffusion at the cellular level. The concentration of the fluid you give determines which way water moves across cell membranes throughout the body.
| Tissue | Structure | Function | Where found |
|---|---|---|---|
| Simple squamous epithelium | Single layer of thin flat cells | Diffusion and filtration | Alveoli, blood vessel lining |
| Simple cuboidal epithelium | Single layer of cube-shaped cells | Secretion and absorption | Kidney tubules, gland ducts |
| Simple columnar epithelium | Single layer of tall cells, often with goblet cells | Absorption and mucus secretion | Stomach and intestinal lining |
| Stratified squamous epithelium | Multiple layers of flat cells | Protection against abrasion | Skin, mouth, oesophagus |
| Connective tissue (loose) | Scattered fibres in gel-like ground substance | Cushioning and support | Under skin, around organs |
| Connective tissue (dense) | Tightly packed collagen fibres | Strong attachment and support | Tendons, ligaments |
| Phase | What happens | Duration |
|---|---|---|
| G1 (Gap 1) | Cell grows, makes proteins, carries out normal functions | Hours to days |
| S (Synthesis) | DNA is replicated so each chromosome is copied | 6–8 hours |
| G2 (Gap 2) | Cell checks the DNA copy and prepares for division | 3–4 hours |
| Mitosis | Nucleus divides: prophase, metaphase, anaphase, telophase | ~1 hour |
| Cytokinesis | Cytoplasm splits, producing two daughter cells | Minutes |
| G0 (Quiescence) | Cell exits the cycle and stops dividing | Indefinite (e.g. neurones) |
Clinical pearl
Some cells like neurones spend most of their life in G0 and rarely divide. This is why brain and spinal cord injuries are so difficult to recover from. Other cells like gut epithelium divide every few days, which is why the gut lining is so sensitive to chemotherapy.
| Condition | Cell biology | Clinical effect |
|---|---|---|
| Sickle cell disease | Single DNA base mutation changes one amino acid in haemoglobin | Red blood cells become rigid and sickle-shaped, blocking small vessels |
| Cystic fibrosis | Mutation in CFTR gene on chromosome 7 | Chloride channel does not work properly, leading to thick sticky mucus |
| Type 1 diabetes | Autoimmune destruction of insulin-producing beta cells | No insulin production; cells cannot take up glucose properly |
| Cancer | Mutations in tumour suppressor genes or oncogenes | Uncontrolled cell division bypassing normal checkpoints |
| Down syndrome | Trisomy 21 — three copies of chromosome 21 instead of two | Extra genetic material affects development and organ function |
| Oedema | Fluid shifts due to osmotic or hydrostatic pressure imbalance | Excess fluid in interstitial spaces causing visible swelling |
ATP
Phospholipid bilayer
Osmosis
Mitosis
Meiosis
Differentiation
Organelle order
Naughty Mice Run Smoothly, Getting Lively — Nucleus, Mitochondria, Rough ER, Smooth ER, Golgi, Lysosomes.
DNA → protein
DNA → mRNA (Transcription) → Protein (Translation). "T before T" — transcription before translation.
Transport
Passive = no energy, downhill. Active = ATP, uphill. Think of passive as rolling downhill for free.
Tissues
ECMN — Epithelial, Connective, Muscle, Nervous. "Every Cell Must Need" a tissue type.