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Beta-Amyloid Production and Aggregation

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Learning Objective

Understand how beta-amyloid is produced from APP and how it aggregates into toxic forms (Bloom Level 2 - Understand).

Overview

Beta-amyloid is a small protein fragment that plays a central role in Alzheimer's disease. It starts out as part of a much larger, harmless protein called Amyloid Precursor Protein (APP), which sits in the membranes of neurons. When APP is cut by two enzymes in just the wrong way, it releases a sticky peptide (Aβ42) that can clump together into oligomers, protofibrils, and finally into the large amyloid plaques that are a hallmark of Alzheimer's.

This interactive diagram walks through all seven stages of this process along a single neuron cell membrane, so you can see how a normal protein is transformed into a pathological plaque step by step.

How to Use This Diagram

Explore Mode — Hover over any numbered marker or label to see a description of that stage and how it connects to Alzheimer's disease.

Quiz Mode — Click "Quiz" to test your knowledge. Read the hint, then click the correct marker on the diagram. Your score is tracked, and a celebration plays when you answer all seven correctly.

The Seven Stages

  1. APP in the Membrane (blue) — Amyloid Precursor Protein sits embedded in the neuron's cell membrane, where it normally helps with neuron growth and signaling.
  2. Beta-Secretase Cut (green) — The enzyme beta-secretase makes the first cut in APP, starting the harmful pathway. This happens in seconds.
  3. Gamma-Secretase Cut (darker green) — A second enzyme cuts at the membrane, releasing the small Aβ42 peptide fragment into the space between neurons.
  4. Free Aβ42 Monomers (orange) — Single Aβ42 peptides drift freely in the extracellular space. In a healthy brain, they are cleared away before causing harm.
  5. Oligomer Formation (burnt orange) — When clearance fails, 2-10 monomers stick together into small clusters called oligomers. These soluble clumps are now thought to be the most toxic form of beta-amyloid.
  6. Protofibrils (red-orange) — Oligomers grow into longer, thread-like aggregates over days to weeks.
  7. Mature Amyloid Plaque (dark red) — Over months to years, protofibrils pile up into dense, insoluble plaques that disrupt communication between neurons — the hallmark feature of Alzheimer's disease.