Cell Structure & Function

Why This Matters for Nursing: Cells are the basic units of life. Understanding cell structure helps you understand how medications work (crossing cell membranes), how diseases affect the body, and how tissues heal.

What You Need to Know

Cells are the smallest units of life that can perform all life functions. The human body contains approximately 37 trillion cells.

Two Types of Cells

Human cells are eukaryotic — they have a nucleus and other membrane-bound organelles.

🧠 Memory Trick

"The cell is like a factory"

• Nucleus = Boss's office (contains instructions/DNA)
• Mitochondria = Power plant (makes energy)
• Ribosomes = Assembly line workers (make proteins)
• Cell membrane = Security fence (controls what enters/exits)
• ER = Packaging department (processes products)
• Golgi = Shipping department (sends products out)

Cell Membrane

The cell membrane (plasma membrane) is a phospholipid bilayer that: - Controls what enters and exits the cell - Has a fluid mosaic structure (proteins embedded in lipids) - Contains channel proteins for transport - Is selectively permeable (allows some substances through, not others)

Membrane Transport

Major Organelles

Nucleus

• Function: Contains DNA; controls cell activities
• Key features: Nuclear membrane, nucleolus (makes ribosomes)
• Think: "The brain of the cell"

Mitochondria

• Function: Produces ATP (cellular energy) through cellular respiration
• Key features: Has its own DNA; double membrane
• Think: "The powerhouse of the cell"
• Formula: Glucose + Oxygen → ATP + CO₂ + H₂O

Ribosomes

• Function: Synthesizes proteins
• Key features: Found free in cytoplasm OR attached to rough ER
• Think: "Protein factories"

Endoplasmic Reticulum (ER)

Golgi Apparatus

• Function: Modifies, packages, and ships proteins
• Think: "Shipping and receiving department"

Lysosomes

• Function: Contains digestive enzymes; breaks down waste
• Think: "Recycling center" or "garbage disposal"

Cytoplasm

• Function: Gel-like fluid that fills the cell; holds organelles
• Contains: Water, salts, organic molecules

✏️ Worked Examples

Example 1: Function Identification

Question: Which organelle would be most active in a muscle cell that needs lots of energy?

Step 1 — Identify what the question is really asking. "Most active" in a cell that "needs lots of energy." So we need the organelle responsible for making energy.

Step 2 — Match energy production to an organelle. ATP is the energy currency of the cell — it's basically the cell's battery. The organelle that manufactures ATP is the mitochondria (think: "the powerhouse of the cell" — that phrase actually means something here).

Step 3 — Confirm the logic. Muscle cells contract constantly. Contracting requires energy. More energy needed = more mitochondria working overtime. Heart muscle cells and leg muscle cells have massive numbers of mitochondria because they never stop working.

Answer: Mitochondria

🏥 Nursing connection: When a patient has a heart attack, heart muscle cells are cut off from oxygen. Without oxygen, mitochondria can't make ATP. No ATP = cells die. That's why time-to-treatment matters so much in cardiac events.