Most Things Biology

3.3 Organelles and the Scaffold

Case home  ·  Start at the beginning  ·  The Reveal

Time To Read

30–46 minutes

Date Last Modified

The Cell & Its Transport · Chapter 3 of 7

1989, age fourteen: “It’s my legs” — a deep, cramping ache in the calves and the thighs that starts the day her period starts and keeps her awake. “Two Tylenol take the edge off for about an hour, and then it comes back.” A year earlier the school nurse had asked whether she had her period and handed her an aspirin. When Mom offers the doctor, she says no: “They’ll say normal.” This chapter tours the rest of the cell — the soup, the surface, the scaffold, the power plant and the cleanup crew — to find out what those two pills could reach, and which structure inside a white cell neither of them ever touches.

The question you will answer

Two pills, two years, the same result: relief for about an hour. A pill can only change what it reaches. The question for the chapter: which parts of a cell do aspirin and acetaminophen act on — and which structure inside a white cell would a drug have to reach to quiet an alarm rather than the messenger that carries it?

Opener · Two Tylenol, One Hour · about 2¼ minutes

The opener is the same narrated animation you will watch in Scene 1.

Watch it in Scene 1 ↓

Watch the opener first. It sets the question; the chapter answers it.

1

Read the chart

Patient chart · Stina

1988 and 1989 · ages 13 and 14 · an aspirin from the school nurse, two Tylenol at bedtime

1988 · 13
Feet, shins, the backs of her knees and her back hurt, “from the ground up”: concrete floors “under a carpet as thin as a towel,” desks too tall, a twenty-pound backpack weighed twice on the bathroom scale. After gym she asks the school nurse for a note; the nurse asks whether she has her period. “I said that’s not what this is. She gave me an aspirin.”

1989 · 14
“It’s my legs”: a deep, cramping ache in the calves and thighs that “starts the day my period starts and keeps me awake.” “Two Tylenol take the edge off for about an hour, and then it comes back.” Mom asks about the doctor; she says no.

Ages 11-15 · the chart
“Her feet, shins, back and legs hurt – standing on the school’s concrete floors, sitting in desks too tall for her, carrying a twenty-pound backpack. Gym leaves her soaked, shaking and wrung out in a way the other kids are not.”

Told
“Growing pains.” “Deconditioned.” A school nurse asks whether she has her period. Her own forecast at fourteen (her words, not the chart’s): “growing pains, or cramps, or that it’s normal for some girls. They’ll say normal.”

Chart clues this module: 3 · this module (logged in Chapter 7) — undated, “Every workup”; this chapter adds no clue, and no lab value exists for these years

Before you go on · your prediction

Fourteen, and the same thing every month: an ache that starts the day her period starts, and two Tylenol that take the edge off for about an hour before it comes back. Before you tour the cell, what does an hour of relief most likely tell you?

Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.

It’s growing pains — “Mom says I’m growing”

Watch what a pain pill actually acts on, and ask whether growing would keep a calendar that starts on the first day of a period.

Relief from a step the pill reaches, while something it can’t reach keeps going

Watch where each pill stops inside a cell, which cell it stops in, and which structure none of the 1989 pills ever visits.

It’s ordinary period cramps — “that it’s normal for some girls”

Watch which chemistry Tylenol damps, and whether that chemistry is where a problem starts or only a step along the way.

From Stina’s diary

Age 14 · “Tylenol”

2

The story

Three short movements: the case, the anatomy and physiology, then the tie back to Stina. Each links to the scene where you’ll see it move.

I · About an hour

Fourteen, 1989, and it isn’t heavy bleeding, whatever the school nurse thinks she means. It’s her legs. The ache sits deep in the calves and the thighs, a cramping ache that starts the day her period starts and keeps her awake. She has a routine for it now. “Two Tylenol take the edge off for about an hour, and then it comes back.” After that she lies there pushing her heels into the mattress, trying to make the muscles give up. The year before, at thirteen, the pill had come from school. She had come out of gym red and soaked through and shaking and asked the nurse for a note, and the nurse asked whether she had her period. “I said that’s not what this is. She gave me an aspirin.” So by fourteen she has tried two pills, one handed to her at school and one she takes herself at home, and she has learned exactly what they are good for: about an hour. When Mom asks if she wants to see the doctor, she says no. She already knows the script — growing pains, or cramps, or that it’s normal for some girls. “They’ll say normal, and I’ll have spent a whole appointment being told I’m normal.” Look at what she is doing, alone, at night. She is timing the pill. She has noticed that the ache arrives on a date. Nobody has asked her either thing, and she isn’t going to volunteer them to people who have already chosen the word.

See it move: Scene 1 · Two Tylenol, One Hour · Scene 6 · The Dam and the Janitor

II · A factory tour: shape, movement, power, cleanup

This is where a lot of courses lose people, because it turns into a scavenger hunt of names. Don’t let it. Walk the cell like a tiny factory and meet every department except the assembly line (that’s Chapter 4): shape first, then movement, then power, then cleanup. The plasma membrane is the property line; we studied it in Chapter 1, and now we step across it. Inside is the cytosol, the broth — water crowded with negatively charged proteins, amino acids and potassium, about 140 mM K⁺ inside against about 4 outside, with sodium the other way round. Add everything floating in it and you have the cytoplasm, the whole soup, chunks and all; “cytoplasm” is almost always the safe answer. At the surface, microvilli are the membrane itself pushed out into fingers about a micrometer long; villi are whole folds of the lining, many cells each; and lungs have neither for gas exchange — they have alveoli. Cilia are real hair-like extensions, a couple of hundred to a cell and millions across a patch of airway, beating bottom to top in the trachea: the mucus escalator. The sperm’s flagellum beats as a wave driven by dynein; spinning flagella are bacterial. Under it all is the cytoskeleton, first the cell’s bony skeleton and then its rails: actin microfilaments about 7 nm, intermediate filaments about 10 nm, and hollow tubulin microtubules about 25 nm, organized from the centrosome, built and torn down all day, with kinesin and dynein motors hauling cargo along them. Power is the mitochondrion: H⁺ stacked behind the inner membrane spins ATP synthase, a real turbine — the Hoover Dam in miniature. Cleanup is the lysosome, the janitor organelle, acid at pH 4.5 to 5 and born from the Golgi, and the peroxisome, which burns fatty acids, detoxifies and breaks its own hydrogen peroxide with catalase.

See it move: Scene 2 · Broth and the Whole Soup · Scene 3 · Fingers, Brushes and a Tail · Scene 4 · The Rails · Scene 5 · The Organizing Center · Scene 6 · The Dam and the Janitor

III · The rail no pill touched

Here is the reading nobody could have offered her in 1989. Aspirin and acetaminophen are honest drugs. Aspirin blocks COX, the enzyme on the endoplasmic reticulum’s membrane that turns a membrane fatty acid into prostaglandins, in many tissues (Module 2.4); acetaminophen dampens the same step mostly inside the brain, and exactly how is still being worked out. In the disease this course is building toward, familial Mediterranean fever, prostaglandins are the middle of the chain, not its start. The start is a sensor called pyrin, dissolved in the cytosol of white cells; when it fires, the alarm messenger IL-1β leaves, reaches the blood vessels at the edge of the brain’s thermostat, and orders the prostaglandin made there. So a pill can lower the last step in one cell while the alarm in another keeps ringing — one honest way to read “and then it comes back.” Honesty flag: the diary doesn’t say what made a fourteen-year-old’s legs ache on day one; calling those nights attacks is the course’s reading, not her record (Muscular 7.4 takes the cramp itself). The organelle that matters here is the one no 1989 pill visited: the neutrophil’s microtubules. They steer the cell as it crawls, and in ordinary cells pyrin’s inflammasome needs them intact to assemble (FMF variants lean on them less). Colchicine binds free tubulin and stops the rails being rebuilt, which is a large part of why it can quiet this alarm — how it prevents attacks is not fully settled — and why it does nothing for a headache. Forward flash, 2026, at fifty-one: “Colchicine is a small white pill that comes from the autumn crocus.” Thirty-seven years after the Tylenol.

See it move: Scene 1 · Two Tylenol, One Hour · Scene 4 · The Rails · Scene 5 · The Organizing Center

3

Watch · explore · think · check

6 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.

How to read the scenes

  • Animation (dark teal) — a short animated explainer, one idea each
  • Slide (dark teal) — a still to study: a micrograph, a diagram or a map
  • Explore (purple) — something to push on while you watch
  • Game (purple) — a quick challenge
  • Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
  • Check (gold) — a quick H5P that scores itself

Scene 1 of 6

Two Tylenol, One Hour

An hour of relief is a measurement — of what a pill can reach, and of what it can’t.

Animation · in production · 2 min 20 s

Two Tylenol, One Hour

1989, a bedroom at night: a bedside clock, two white tablets on the nightstand, a fourteen-year-old on her back with her heels pushed into the mattress. The clock runs one hour; a pain gauge beside the bed dips, holds, and climbs back. The camera drops into one round cell (an animal cell with its organelles) and a tour map unrolls over it in four stops — SHAPE · MOVEMENT · POWER · CLEANUP — with the plasma membrane drawn as a property line. Two pill tokens, ASPIRIN (1988, from the school nurse) and ACETAMINOPHEN (1989, two Tylenol), slip across the line, and a card reads WHERE EACH ONE STOPS — FOLLOW IT IN THE EXPLORE. An arrow from a membrane fatty acid to PROSTAGLANDINS thins to a trickle, with a tag: MODULE 2.4. The view pulls back to two cells joined by a dotted line marked IL-1β: on the left a white cell with a lobed nucleus, where a small bell marked 1β keeps ringing; on the right a vessel-lining cell at the edge of the brain’s thermostat, where the prostaglandin is made. A third token, a small white tablet stamped with an autumn-crocus flower and the date 2026 (a narrator’s card: not in her house in these years), slips across the white cell’s membrane, and the frame holds before it stops. Last frame: the tour map again, with one green thread drawn through all four stops — THE CYTOSKELETON, THE THREAD OF THIS CHAPTER — and a question card: WHICH STOP DID NO 1989 PILL REACH?

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Follow the pill

A transit-style route map laid over two cells side by side, drawn as colored subway lines with stations. LEFT, a white cell (a neutrophil, its nucleus in lobes): stations PLASMA MEMBRANE (entry) · CYTOSOL · NUCLEUS · MITOCHONDRIA · GRANULES (LYSOSOMES) · and a green MICROTUBULE LINE running out from a hub near the nucleus (the centrosome); floating in the cytosol, a small bell labeled ALARM (pyrin → IL-1β, named only). RIGHT, a vessel-lining cell at the edge of the brain’s thermostat: stations PLASMA MEMBRANE · IL-1 RECEPTOR (where the messenger lands — Chapter 1) · ER MEMBRANE: COX · PROSTAGLANDIN E₂ OUT · NUCLEUS. A dotted line between the cells is labeled IL-1β, THE MESSENGER. Three pill tokens wait at a turnstile: ASPIRIN (1988 — the school nurse’s), ACETAMINOPHEN (1989 — “two Tylenol”) and COLCHICINE (stamped 2026, with a narrator’s tag: not in her house in these years). For each pill the student first predicts its stop by tapping a station, then rides it. All three cross the membrane on their own (small molecules; Module 2.6’s passport check, one line). Aspirin travels to COX on the ER membrane — in the vessel cell and in most tissues — and blocks it for the life of the enzyme; the prostaglandin arrow thins. A card adds that, since the mid-1980s, aspirin labels have warned against giving it to children and teenagers with flu-like illness or chickenpox because of Reye syndrome. Acetaminophen stops at COX too, but mostly inside the brain, and a card says honestly that its exact mechanism is still debated and that it does little for inflammation out in the tissues. Colchicine rides into the white cell and stops on the MICROTUBULE LINE, whose stations go gray one by one; the ALARM bell, which in ordinary cells needs intact microtubules to assemble, forms less readily, and the white cell crawls less well; a card says colchicine is not a painkiller and does nothing for a headache. A score strip compares each prediction with the real stop. The reveal lays the stops along one chain — ALARM (white cell) → MESSENGER (IL-1β in the blood) → PROSTAGLANDIN (vessel cell at the brain) → FEVER AND ACHE — and the student drags each pill to the link it cuts: the two 1989 pills land on the third link, colchicine on the first. A clock card plays “about an hour” against the chain: cut the third link and the first keeps sending; when the drug wears off, the ache is back — one honest reading of “and then it comes back,” labeled as the course’s reading, not a fact on her record. Last screen: the four-stop tour map (shape · movement · power · cleanup) with the one station no 1989 pill visited circled in green. Keyboard path: Tab moves station to station, Enter records a prediction, Space rides the selected pill; each ride is announced in a polite live region (“Aspirin: crossed the membrane; stopped at COX on the ER membrane”). A <details> text version gives every pill’s route, stop and effect as a table.

Think · not graded

“Two Tylenol take the edge off for about an hour, and then it comes back.” Suppose the ache is the far end of a chain that starts with an alarm inside a white cell. Draw the chain as three boxes — alarm, messenger, ache — and mark where acetaminophen acts. What does relief followed by a return tell you about which box is still running? And what would a drug have to reach to stop the first box?

The true/false spot-check for this prompt is in production.

Check · Single Choice

Colchicine, from the autumn crocus, has been used for swollen, inflamed joints since antiquity — the Egyptian Ebers papyrus of about 1500 BC describes the plant. What does that track record most strongly suggest?

This self-scoring check is in production.

Evidence card 1

Add it to your evidence board

Age fourteen: “Two Tylenol take the edge off for about an hour, and then it comes back.”

Scene 2 of 6

Broth and the Whole Soup

The cell’s interior has two names, and the chemistry lives in the broth.

Narrated slide · in production · 1 min 22 s

Broth and the Whole Soup

Three of Amy’s narrated slides. Slide 1, Non-Protein Organelles (a short lead-in): the part of the course where people get lost “because it turns into a scavenger hunt of names”; instead, “walking through a tiny factory and meeting every department except the assembly line itself.” Slide 2, Cell Membrane: “The membrane separates the inside of a cell from its external environment. That’s its job in a single sentence”; “the property line of our crime scene — we’ve studied it in detail already, and now we step across it.” Slide 3, Cytosol vs. Cytoplasm: “cytosol is the broth; cytoplasm is the whole soup, chunks and all”; “‘cytoplasm’ is almost always the safe answer”; one cell’s fluid is the cytosol, all cells’ together the intracellular fluid — “one cell versus all cells”; the cytosol “packed with negatively charged proteins, amino acids, and a great deal of potassium.” Caption lines under the player: (1) Timed cue in Slide 2 at about 0:29, as she says the membrane “loves that pinkish purple stain”: tissue processing for an H&E slide dissolves lipid, so a fat cell looks empty with a thin pink rim — the pink is cytoplasm and membrane protein taking the eosin, not lipid “loving” the stain. (2) Slide 3, in numbers (textbook values): K⁺ about 140 mM inside a cell vs about 4 mM outside; Na⁺ about 12–15 mM inside vs about 145 mM outside. The potassium’s later role is Chapter 6’s — when it floods out of a stressed white cell it trips NLRP3, a different alarm from pyrin.

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Ladle the soup

A cutaway soup pot labeled ONE CELL (a neutrophil), a ladle, and two bowls on the counter: BROTH (CYTOSOL) and CHUNKS (ORGANELLES AND SCAFFOLD). Fourteen tokens float in the pot: water · K⁺ · a few Na⁺ · dissolved enzymes · ATP · glucose · amino acids · pyrin (a sensor protein) · pro-IL-1β (the alarm messenger before it is cut) · a mitochondrion · a granule (a lysosome) · a ribosome · a microtubule · the nucleus. Before each ladle the student predicts BROTH or CHUNK; the bowl accepts it or tips it back with a one-line reason. Four traps teach the categories. A ribosome has no membrane, but it is a particle, not a fluid — a chunk, counted in the cytoplasm. A microtubule is part of the scaffold — a chunk. Pyrin and pro-IL-1β are dissolved proteins — broth: the alarm sensor of the disease this course follows lives in the soup, not in the membrane, which is why nothing that tests the outside of a cell can see it. The nucleus is the trick card: it goes in neither bowl, because its own double envelope keeps it out of the cytoplasm (its fluid is the nucleoplasm, Chapter 4). When both bowls are full, a label slides across them: CYTOPLASM = BROTH + CHUNKS — “almost always the safe answer.” A ZOOM OUT button pours the broth of every cell in the body into one enormous glass: INTRACELLULAR FLUID, about two-thirds of the body’s water — one cell versus all cells. A chemistry panel then opens on the broth, labeled with textbook values: K⁺ about 140 mM inside vs about 4 mM in the fluid outside; Na⁺ about 12–15 mM inside vs about 145 mM outside; inside, many negatively charged proteins and phosphates that can’t leave. The student predicts which way each ion would move if the membrane let it, then reads a card: holding that difference costs ATP, and the pump that pays is Chapter 6’s; when K⁺ floods out of a stressed white cell it trips NLRP3 — a different alarm from pyrin, which is set off another way (Chapter 7). A last card shows an H&E fat cell: the lipid was dissolved in processing, so the cell looks empty with a thin pink rim — the pink is protein, not fat. Keyboard path: Tab to a token, Enter to ladle it, arrow keys choose a bowl, Space confirms; each placement is announced (“Pyrin — broth: a dissolved protein in the cytosol”). A <details> text version lists every token, its bowl and the reason, and the ion table.

Think · not graded

Both pills in Stina’s diary had to get inside cells to work. Using broth and the whole soup, explain why “cytoplasm” is almost always the safe answer but “cytosol” is the precise one when you mean where a dissolved enzyme or a sensor protein floats. Then answer the trick question: is the nucleus in the cytoplasm?

The true/false spot-check for this prompt is in production.

Check · Drag the Words

Sort the soup from the broth, and the ions to their sides. Two distractors are on the bank.

This self-scoring check is in production.

Evidence card 2

Add it to your evidence board

Age thirteen: “I asked the nurse for a note and she asked if I had my period. I said that’s not what this is. She gave me an aspirin.”

Scene 3 of 6

Fingers, Brushes and a Tail

Three ways a cell reaches past its own edge — and one that’s been taught wrong for years.

Narrated slide · in production

Fingers, Brushes and a Tail

Amy’s narrated slide, Cilia — “Tiny Sweepers”: unlike villi, “these genuinely are hair-like extensions,” sitting on the cells of mucous membranes, “the linings of every opening to the outside world”; the singular is cilium, the plural cilia; flagella are “much longer, tail-like.” “Cilia are short, thin, and they never act alone — there are thousands of them carpeting the apical surface, the top.” “In your trachea every cilium waves from inferior to superior — bottom to top — sweeping mucus upward so you swallow it into your esophagus without ever noticing… It’s a conveyor belt” you run every second of your life: the mucus escalator. Caption lines under the player: (1) Not every mucous membrane is ciliated — the airways and the uterine tubes are; the stomach and intestine are not. (2) A cilium beats by dynein motors on a 9+2 core of microtubules. Two corrections for the slides this chapter does not play: (3) Microvilli are projections of one cell’s plasma membrane (the brush border); villi are multicellular folds of the intestinal lining, each covered by many cells; the lungs exchange gas across alveoli, not villi. (4) The human sperm flagellum is a 9+2 microtubule axoneme wrapped in the plasma membrane, beating as a dynein-driven wave; rotary, spinning flagella belong to bacteria.

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Zoom the surface

A zoom bar runs down the right edge of the screen from 1 mm to 10 nm, marked at 1 mm · 100 µm · 10 µm · 1 µm · 100 nm. Six cards wait to be placed: VILLUS · MICROVILLUS · CILIUM · SPERM FLAGELLUM · BACTERIAL FLAGELLUM (a decoy, stamped NOT HUMAN) · ALVEOLUS (for the lung question). For each card the student sets three things. SCALE, by sliding it onto the zoom bar: villus about 0.5–1 mm tall; microvillus about 1 µm long and 0.1 µm wide; cilium about 5–10 µm; sperm flagellum about 50 µm; bacterial flagellum several µm long but only about 20 nm thick; alveolus about 0.2 mm across. MADE OF, from a menu: MANY CELLS · ONE CELL’S MEMBRANE OVER AN ACTIN CORE · A 9+2 MICROTUBULE CORE BENT BY DYNEIN · A PROTEIN FILAMENT TURNED BY A ROTARY MOTOR · A THIN-WALLED AIR SAC. JOB AND ADDRESS: absorb — small intestine · absorb — kidney tubule · sweep — trachea and uterine tubes · swim — the sperm cell · exchange gas — the lungs · swim — a bacterium. As each card snaps into place, a zoom window renders that magnification: at 1 mm a villus fills the frame with columnar cells along its edge; slide to 1 µm and one of those cells’ brush border appears; slide again and a single microvillus shows its actin core under the membrane. Predict-first prompts before each placement: “Which of these is made of many cells?” · “Which two beat by dynein?” · “Which one spins?” Feedback corrects the classic slips: a villus is not a membrane projection; the lungs have no villi for gas exchange — they use some 300–500 million alveoli, about 50–100 m² of surface (Amy: “I would dearly love to meet whoever unrolled it to measure”), while the small intestine’s lining, actually measured, is about 30 m², not a tennis court; the human sperm flagellum beats as a wave inside its own membrane, and only bacteria spin; the flat mesothelial cells lining the belly carry microvilli too (Chapter 2’s cell). A last card, “Structure is never arbitrary”: the testes sit outside the body cavity, about 2–4 °C cooler than the core, because heat impairs sperm production — not because a warm tail would spin wrong. A closing card, in Amy’s words: “Cells are not passive blobs — they crawl and sweep and haul.” Keyboard path: Tab to a card, arrow keys move it along the zoom bar, Enter opens its MADE OF and JOB menus; each placement is announced (“Microvillus, 1 micrometer: one cell’s membrane over actin; absorbs in the small intestine”). A <details> text version gives the full table: structure · scale · made of · job · where.

Think · not graded

A villus and a microvillus both add surface area, but one is built of many cells and the other is part of one cell’s membrane. How would you tell them apart under a microscope? Then explain why the lungs, which need even more surface than the gut, use neither one.

The true/false spot-check for this prompt is in production.

Check · Single Choice

How does the human sperm flagellum move?

This self-scoring check is in production.

Evidence card 3

Add it to your evidence board

Age fourteen: the leg ache “starts the day my period starts and keeps me awake.”

Scene 4 of 6

The Rails

The cell’s rails are torn down and relaid all day — which is exactly why a drug that only blocks the relaying works.

Animation · in production · 2 min 20 s

The Rails

A round cell lit like a fluorescence micrograph: bright green microtubules radiate from a hub beside the nucleus, fine pink and purple filaments around them. A scale bar sorts the three kinds of filament by width — ACTIN MICROFILAMENT ~7 nm (pushing the front edge of a crawling cell; the core of a microvillus) · INTERMEDIATE FILAMENT ~10 nm (tough cables; keratin in skin) · MICROTUBULE ~25 nm (hollow). Zoom onto one microtubule: two-colored tubulin pairs (α and β) click onto the growing end under a glowing cap; the cap blinks out, the end frays and the tube collapses (a label: CATASTROPHE); a new cap catches and it grows again (RESCUE). Two motor proteins walk the rail in opposite directions with vesicles on their backs: KINESIN (1985) outward, DYNEIN (1963) inward — a stamp corrects “21st century” to 20th. A four-panel strip: shape · rails · steering a crawling white cell · pulling chromosomes apart. Then a narrator’s card, COLCHICINE: small molecules bind loose tubulin pairs in the cytosol; a drug-bound pair adds to the tip and nothing clicks on after it; with the rebuilding stopped, catastrophes keep coming and the green rails shrink back toward the hub while a kinesin cart stalls at the new end of the line. Last frame: a neutrophil with its rails dimmed, and two labels — CRAWLS LESS WELL · PYRIN’S ALARM ASSEMBLES LESS READILY (CHAPTER 7).

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Grow, collapse, rescue

A single microtubule track runs horizontally from a centrosome hub on the left (the minus end) toward the cell’s edge on the right (the plus end), drawn as stacked two-tone tubulin pairs. Above it, a FREE TUBULIN reservoir gauge; at the growing tip, a CAP indicator that glows while fresh pairs are on the end. Controls: ADD TUBULIN (raise or lower the free pool), RUN CLOCK, and a dropper marked COLCHICINE. Round 1, grow: the student predicts whether a fuller reservoir makes the track grow faster, then runs the clock — pairs click on, the cap stays lit, the track lengthens. Round 2, catastrophe: lower the pool until the cap flickers out; the tip frays and the track shortens fast (CATASTROPHE), and sometimes a fresh cap catches and growth resumes (RESCUE). A counter tallies both: DYNAMIC INSTABILITY — rails relaid all day, which is how a cell can redraw its tracks in minutes. Round 3, traffic: a kinesin cart (discovered 1985) and a dynein cart (1963) each carry a vesicle; the student routes one outward and one home and sees that they share the rails in opposite directions. Round 4, the drug — predict first: as the rails shrink, which fails first, the kinesin cart’s trip to the edge or a dividing cell’s spindle — and why? Drop it in: colchicine molecules bind loose pairs in the reservoir; a drug-bound pair adds to the tip and nothing can click on after it; growth stops, catastrophes keep coming, and over the clock run the track shrinks back toward the hub. The kinesin cart stalls at the new end of the line. A side panel shows the three filaments to scale — actin microfilament ~7 nm, intermediate filament ~10 nm, microtubule ~25 nm — with one job each (actin pushes a crawling cell’s front edge and cores the microvilli; intermediate filaments, such as keratin, take strain; microtubules carry, steer and divide) and asks which one the drug hit. A narrator card closes the bench: in a neutrophil, microtubules hold the crawling cell’s front and back steady while actin pushes, and in ordinary cells pyrin’s inflammasome needs them intact to assemble (Chapter 7; FMF variants depend on them less) — so stopping the rebuild slows the crawl and makes the alarm form less readily; neutrophils also take up and hold colchicine more than most cells do. Keyboard path: Tab to each control, Enter to act, Space runs the clock; the track’s state is announced in a live region (“growing, cap on” · “catastrophe” · “colchicine bound — growth stopped”). A <details> text version gives the four rounds and their outcomes in a table.

Think · not graded

Colchicine never cuts a microtubule; it only blocks new tubulin being added. Explain why that is enough to make a cell’s microtubules disappear within hours. Then predict which two jobs of a neutrophil would suffer first — and which job of a dividing cell.

The true/false spot-check for this prompt is in production.

Check · Single Choice

Which part of the cytoskeleton is colchicine’s target?

This self-scoring check is in production.

Evidence card 4

Add it to your evidence board

Age fourteen: Mom asks if she wants to see the doctor, and she says no — “They’ll say normal.”

Scene 5 of 6

The Organizing Center

One small spot beside the nucleus organizes every rail in the cell, from the resting neutrophil to the dividing one.

Narrated slide · in production · 2 min 08 s

The Organizing Center

Amy’s narrated slide, Centrosomes & Centrioles — “Spindle Builders”: “A centrosome is a pair of centrioles — little barrel-shaped structures sitting near the nucleus.” Quiet until mitosis, “when microtubules extend out from the centrosomes and reach clear across the cell to grab the chromosomes at their kinetochores, right at the center”; they “pull the sister chromatids apart,” one complete copy to each side, “without a single error most of the time.” Then the through-line: “Microtubules aren’t a one-off vocabulary word… They give the cell its shape, they lay down its transport rails, they crawl it toward danger, and they divide it. And a drug that interferes with them — colchicine — therefore reaches into a lot of a cell’s life at once, which is exactly why it can calm an overactive neutrophil.” Caption lines under the player: (1) Timed cue at about 0:25, as she says “It dies and makes two new cells”: the parent cell doesn’t die when it divides — it becomes the two daughter cells. (2) The centrosome is the cell’s microtubule-organizing center: a pair of centrioles at right angles inside a cloud of protein (pericentriolar material). (3) Centrioles don’t pull; the spindle microtubules do, shortening at the kinetochores — protein plates on each centromere — and many cells can build a spindle without centrioles. (4) “Central mirrors” in the opening ad-lib means centromeres. (5) Colchicine here is the narrator’s science: it is the drug used for this disease, not one Stina takes in these years.

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Hook the kinetochores

A dividing cell in prometaphase: two centrosomes at opposite poles (each drawn as a pair of centrioles at right angles in a soft cloud of protein) and four condensed chromosomes in the middle, each two sister chromatids joined at a centromere with a kinetochore plate on either face — labeled “4 shown; a human cell has 46.” The student drags spindle microtubules out from each pole and hooks them onto kinetochores. A CHECKPOINT light stays red until every chromosome has one sister hooked to each pole; hook both sisters to the same pole and a card explains the error before letting the student fix it. Predict first: “Press ANAPHASE now — what happens?” With the light green, anaphase plays: the microtubules shorten at the kinetochores and the sisters move apart; telophase draws two nuclei; cytokinesis pinches the cell into two daughters, and a caption fixes the old ad-lib — the parent cell doesn’t die, it becomes the daughters. If the student overrides the red light, one daughter ends up with five chromosomes and the other with three, and the card names aneuploidy, with trisomy 21 (Down syndrome) as the familiar human example. Two corrections stay pinned at the side: the centrioles don’t pull — spindle microtubules do, and many cells can build a spindle without centrioles; the hook is the kinetochore, a protein plate on the centromere. Then the COLCHICINE dropper, predict first: the spindle’s microtubules can’t be rebuilt, the light never turns green, and the cell stalls with its chromosomes condensed and unseparated — the trick labs use to catch chromosomes for a karyotype (Module 4.5 counts them), and the reason an overdose of colchicine hits fast-dividing tissues such as the gut lining and the bone marrow first. Last screen, interphase: the same centrosome now organizes the resting cell’s rails as a starburst, and a neutrophil panel shows a crawling white cell with its centrosome behind the nucleus, toward the tail, its microtubules holding front and back steady while actin pushes the leading edge. Keyboard path: Tab to a pole, Enter to grab a microtubule, arrow keys to a kinetochore, Enter to hook; the checkpoint state is announced (“3 of 4 chromosomes attached to both poles”). A <details> text version gives each phase, the override outcome and the colchicine outcome.

Think · not graded

When a cell divides, does the parent cell die? Explain what happens to it, what actually pulls the sister chromatids apart, and what you would expect to see under a microscope in a dividing cell soaked in colchicine. Why does that last answer explain where colchicine’s side effects show up first?

The true/false spot-check for this prompt is in production.

Check · Dialog Cards

Centrosomes and the spindle: say each answer out loud, then flip to check.

This self-scoring check is in production.

Evidence card 5

Add it to your evidence board

Ages 11–15, what the chart said: “Growing pains.” “Deconditioned.” A school nurse asks whether she has her period.

Scene 6 of 6

The Dam and the Janitor

A dam that makes ATP, a janitor that digests, and a detox crew long mistaken for a killer.

Narrated slide · in production

The Dam and the Janitor

Two of Amy’s narrated slides. Slide 9, Mitochondria — “The Powerhouse”: the organelle that makes ATP, “the energy currency your cells spend on absolutely everything.” “Let me bust a myth right away”: mitochondria are in plants as well as animals — plants make glucose by photosynthesis and their own mitochondria burn it. “Folded internal membranes set up gradients, and the energy stored in those gradients gets harnessed to build ATP — much like the Hoover Dam converting falling water into electricity” (“That’s the process of making ATP, not the process of the Hoover Dam”). Muscle cells “are absolutely packed with mitochondria.” “Hold onto that Hoover Dam image… it is going to pay off twice more in this very module” — every pump spends ATP a mitochondrion made. Slide 10, Lysosomes — “Little Stomachs”: “little stomachs that float around inside the cell, digesting things — especially the worn-out organelles the cell wants to recycle”; “lyso” means to split, and “rumor has it that’s the origin of the brand name Lysol”; born from the Golgi, “preloaded with digestive enzymes.” Caption lines under the player: (1) The gradient is a proton (H⁺) gradient across the inner membrane, and it drives ATP synthase — a real rotary turbine, so the Hoover Dam is even better than it sounds. (2) Timed cue in Slide 9 at about 1:14, as she says the process “consumes oxygen and glucose”: glucose is split to pyruvate in the cytosol first; the mitochondrion takes in pyruvate and fatty acids with oxygen and gives off CO₂ and water. (3) Lysosomes are acid, pH about 4.5–5, and they digest swallowed microbes as well as worn-out parts. (4) The deck’s example of a lysosome that fails, Tay-Sachs, is in the Explore: the HEXA gene isn’t missing — it is changed, so the enzyme β-hexosaminidase A doesn’t work and a lipid (GM2 ganglioside) piles up in neurons’ lysosomes. (5) Peroxisomes, which the deck’s next slide calls “vesicles of death,” don’t kill microbes: they oxidize fatty acids and detoxify, breaking their own hydrogen peroxide down with catalase. Neutrophils kill in the phagolysosome, with granule enzymes such as myeloperoxidase and the respiratory burst (Explore).

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Dispatch the cleanup crew

A dispatch board like a city public-works office, with three crews parked in numbered bays: LYSOSOME (acid at pH 4.5–5, acid hydrolase enzymes, built from the Golgi), PEROXISOME (oxidase enzymes and catalase) and NEUTROPHIL GRANULE (azurophil granules — specialized lysosomes carrying myeloperoxidase, elastase and defensins — plus specific granules). Along the top runs a POWER meter fed by a mitochondrion drawn as a dam: H⁺ stacked behind the inner membrane, ATP synthase as the turbine, and a footnote that glucose is split in the cytosol first, so the dam’s intake is pyruvate and fatty acids with oxygen, and its outflow CO₂ and water. Eight work orders print one at a time: a worn-out mitochondrion · a bacterium swallowed by a neutrophil · a very-long-chain fatty acid · hydrogen peroxide left over from the cell’s own reactions · part of the alcohol reaching a liver cell · a GM2 lipid that should have been broken down · an old red blood cell swallowed by a spleen macrophage · a drug molecule in a liver cell (a decoy: that order is routed to the smooth ER’s CYP enzymes, Chapter 4). For each order the student predicts the crew, then dispatches it; the truck animates to the job and a card explains. The lysosome takes the worn mitochondrion (autophagy, “the janitor organelle”), the red cell inside the macrophage, and the GM2 lipid — and in a Tay-Sachs cell its truck arrives without the right tool: the HEXA gene is present but changed, β-hexosaminidase A doesn’t work, and the lipid piles up in neurons’ lysosomes (“one missing enzyme, one un-recycled molecule, an entire cell overwhelmed”). The peroxisome takes the fatty acid, the hydrogen peroxide (catalase turns it into water and oxygen) and a share of the alcohol. The bacterium goes to the granule crew: the phagosome fuses with granules and lysosomes into a phagolysosome, NADPH oxidase fires the respiratory burst, and myeloperoxidase turns its peroxide into hypochlorous acid — bleach. The power meter reads differently for each crew: the lysosome’s ATP-powered proton pump keeps it acid, while the neutrophil’s respiratory burst runs on NADPH made from glucose in the cytosol — a neutrophil has few mitochondria and makes most of its ATP by glycolysis, so its dam is a small one. The reveal moves an old label: “vesicles of death” belongs to the phagolysosome, not the peroxisome, which is a fat-burning, detoxifying organelle. A narrator card ends the shift: “Her disease isn’t a failure to fight invaders; it’s a failure to stop fighting an invisible threat” — the same armed cell “keeps sounding the alarm when there’s nothing to kill.” Keyboard path: Tab to an order, arrow keys choose a bay, Enter dispatches; each outcome is announced. A <details> text version lists every order, its crew and the reason.

Think · not graded

Amy’s Hoover Dam: water stacked behind a wall, released through turbines to make electricity. Name what is stacked behind the mitochondrion’s inner membrane, what the turbine is, and what comes out the other side. Then explain why a lysosome needs an ATP-powered pump of its own just to stay at pH 4.5–5 — and what would happen to its enzymes if the pump stopped.

The true/false spot-check for this prompt is in production.

Check · Drag the Words

Power, cleanup and the killing compartment: drag each word into place. Two distractors are on the bank.

This self-scoring check is in production.

Evidence card 6

Add it to your evidence board

Age thirteen: “Mom says I’m growing. Dad says everybody’s backpack is heavy… If this is growing, it’s growing something other than me.”

4

Your evidence board

Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: A cause upstream of the pills, Neither on its own, or Growing pains, “normal for some girls”. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.

Evidence board · drag and drop · in production

The sorting board for this chapter’s cards is being built. Until it arrives, sort your evidence cards on paper into the three columns above.

5

Your verdict

Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.

Look back at your prediction

A deep leg ache that starts the day her period starts, and two Tylenol that take the edge off for about an hour — read through the cell’s organelles and scaffold, the reading that fits best is…

Find the one you chose at the top. Does the evidence support it, refute it, or revise it?

  • It’s growing pains — “Mom says I’m growing”
  • Relief from a step the pill reaches, while something it can’t reach keeps going
  • It’s ordinary period cramps — “that it’s normal for some girls”

Build your verdict · no writing

Choose the statement that holds in each set. The ones you keep become your argument.

This activity is in production.

6

The finding

Finding · organelles and the scaffold

An Hour of Relief, a Rail Untouched

1988 and 1989, ages thirteen and fourteen: an aspirin from the school nurse, then “Two Tylenol take the edge off for about an hour, and then it comes back,” and a girl who won’t see the doctor because “They’ll say normal.” Chart entry: aspirin and acetaminophen act on COX, the prostaglandin-making enzyme on the ER membrane, a step after a white cell’s alarm; a structure that alarm’s assembly leans on in ordinary cells — the neutrophil’s microtubules, hollow tubulin rails organized from the centrosome and relaid all day — is one neither pill touches, and it is colchicine’s target. An hour of relief and a return is what a pill acting downstream of a running cause would look like. Held open: whether her day-one aches were attacks (the diary doesn’t say; Muscular 7.4 takes the cramp), how the alarm protein leaves its cell (Chapter 4), and Chart Clue #3, “Every workup” (Chapter 7).

Next · Chapter 4

The Protein Factory and Its Two Exits

Fifteen, a Tuesday in 1990: “textbook: fever, pain low on the right, white count up,” and the appendix comes out. That morning two kinds of protein were leaving cells by two different doors — the liver’s by the factory’s loading dock, the white cells’ alarm through pores in the membrane — and a pathologist’s slide could show neither.

Continue to Chapter 4 →

Reliable information on rare diseases

NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation

Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.

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← Familial Mediterranean Fever — case home

All pages for Module 3 — The Cell & Its Transport

3.0 Module Overview
3.1 The Membrane
3.2 Meet the Cells
3.3 Organelles and the Scaffold
3.4 The Protein Factory and Its Two Exits
3.5 Osmosis, Tonicity, Effusion
3.6 Pumps, Channels and Voltage
3.7 Inside the Neutrophil
3.8 Conclusion and Assessment
3.9 The Evidence Behind the Case

All Modules
  1. Anatomical Language, Membranes & Homeostasis
  2. Just Enough Chemistry
  3. The Cell & Its Transport
  4. Making Cells & Proteins
  5. The Integumentary System
  6. The Skeletal System
  7. The Muscular System
  8. Nervous Tissue & the Senses
  9. The Spinal Cord
  10. The Brain & the Blood–Brain Barrier
  11. The Autonomic Nervous System
  12. Special Senses (in development)
  13. The Endocrine System
  14. Blood
  15. The Heart
  16. Blood Vessels
  17. The Digestive System
  18. The Respiratory System
  19. The Urinary System
  20. Fluids, Electrolytes & Acid–Base Balance
  21. The Reproductive System
  22. The Immune System

List of terms