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MODULE 4:
MAKING CELLS AND PROTEINS
PART 5 OF 7
One letter. The whole arc of her life turned on a single substituted amino acid — M694V, valine where methionine belongs — bending one protein just enough to break it.
Slide 1 Transcript
PATIENT CHART
STINA
Serositis, Pleural effusion, Self-limiting fever episodes
THIS PART
Age 30
PRESENTING WITH
Culture negative, self-limited fevers with serositis
ACTION TAKEN
Pharmacological
DRUGS ORDERED
Colchicine
CHART CLUES
COLLECTED AS YOU GO
A Full Family & Ancestry History
A Germline (Constitutional) Variant
An Actively Expressed Disease
MEFV Mutation, Misfolded Pyrin
?
?
?
Put your money down: How did a built-in error slip past every quality check?
Bet before the cycle turns. For years a private part of Stina wondered whether she had done this to herself — stress, food, some failure she couldn’t name. Two quick fact-checks on cell-cycle checkpoints; then the ask: should the cell’s quality-control guards have caught and removed her mutationA change in DNA sequence that can affect gene function. — or is it the kind of error they were never built to see?
Pick the answer you believe now. We’ll come back to it later!
It Was in Me Before I Was Born
It is hard to hold in your headRounded proximal end that fits into the acetabulum of the hip bone. that an entire life can pivot on one letter. But that is Stina’s story, told at the smallest possible scale. Decades of fevers, of missed school and missed work, of dismissals and confident wrong diagnoses, a knee that swelled on a hiking trip and a belly that sent her to the operating table — all of it traces back to a single substituted building block in a single protein. Not a tumor, not an infection, not a lifestyle, not a failure of will. One amino acidThe building blocks of proteins, consisting of an amino group, carboxyl group, and side chain. in the wrong seat. There is something almost vertiginous about it, and something clarifying too: the cause was always that specific, and that small.
An Ordered Sequence
A cell’s life in order — G1, S, G2, M: grow, copy, grow, divide.
Slide 2 Transcript
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Single Choice: What is the correct order of the cell cycleThe sequence of events in a cell’s life, including growth, DNA replication, and division. phases?
Growth, Twice — and Synthesis
The gap phases bookend the copy — growthAn increase in size and number of cells. before and after S-phase synthesis.
Slide 3 Transcript
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Drag the Words: Drop each phase beside its job.
A Schedule With Guards at Every Gate
Translation is where the message becomes a protein. The ribosome reads the mRNA three bases at a time — each three-letter codon specifying one amino acidA substance that releases hydrogen ions (H⁺) in solution. — while transfer RNAs (tRNAs) ferry in the matching amino acid for each codon, building the protein in sequence. It is a translationThe process of converting mRNA into a protein. in the truest sense: from the language of nucleic acids into the language of proteinsLarge molecules made of amino acids with various functions in the body., one codon at a time, faithfully.
M Phase & G0
Dividing — or opting out entirely: M splits the cell, G0 parks it (like a neuron).
Slide 4 Transcript
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Fill in the Blanks: Fill in what happens in M phase and in G0.
Quality Control
Guards between the steps — each checkpoint asks ‘is it right?’ and sends the unfixable to apoptosisProgrammed cell death, an essential process for growth and development..
Slide 5 Transcript
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Mark the Words: Mark the question each checkpoint asks.
The Flaw the Guards Were Never Built to See
In Stina’s MEFV message, the codon at position 694 has been altered, so the wrong tRNA is admitted and valine is inserted where methionine belongs — the substitution written M694V. That one swap bends pyrin into a misfolded shape that can no longer restrain the inflammasome it is meant to police. The entire disease — every fever, every effusion, every dismissed emergency — sits downstream of this single mistranslated codon. The whole arc of her life, in one amino acid: a sentence with one wrong letter, faithfully built into a protein that cannot do its job.
The Cycle Out of Control
When the guards are ignored — checkpoints skipped, apoptosis fails, mutations pile up over years.
Slide 6 Transcript
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Multiple Choice: What happens when checkpoints are disregarded and apoptosis fails?
FINDING!
A Constitutional Error the Checkpoints Can’t Catch — It’s the Sequence, Not Damage
Cell-cycle checkpoints catch damage, but Stina’s error is not damage — it is woven into the legitimate MEFV sequence itself, indistinguishable from a correct instruction. So every S phaseThe DNA synthesis phase of the cell cycle where chromosomes are replicated. duplicated it and every checkpoint waved it through as normal. That is why it was present before she was born and in every cell since: not something she caught, caused, or could have avoided. Chart entry: constitutional (germline) MEFV variant, invisible to normal quality control — not acquired, not preventable, not her fault.
Confirm or refute your bet: How did a built-in error slip past every quality check?
Having met interphaseThe phase of the cell cycle in which the cell grows, performs its functions, and replicates DNA. (G1, S, G2), M phase, and the checkpoints that send unfixable cellsThe basic structural and functional units of life. to apoptosis, return to the bet. Her error isn’t damage — it’s part of the legitimate sequence, so every S phase copied it and every checkpoint waved it through.
Slide 8 Transcript
NEXT PART
One bad protein in one lone cell would barely register. The tragedy is that this typo sits in every cell Stina has — and the next two pages explain exactly how it got everywhere.
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← Familial Mediterranean Fever — case home
All pages for Module 4 — Making Cells & Proteins
4.0 Module Overview
4.1 The First Doctor Who Asked
4.2 Copying the Code
4.3 Written in Me the Whole Time
4.4 One Letter — Translation and M694V
4.5 It Was in Me Before I Was Born — The Cell Cycle
4.6 One Typo, Every Cell
4.7 The Reveal – From MEFV to Diagnosis
4.8 Conclusion and Assessment
4.9 Evidence Behind the Case
All Modules
- Anatomical Language, Membranes & Homeostasis
- Just Enough Chemistry
- The Cell & Its Transport
- Making Cells & Proteins
- The Integumentary System
- The Skeletal System
- The Muscular System
- Nervous Tissue & the Senses
- The Spinal Cord
- The Brain & the Blood–Brain Barrier
- The Autonomic Nervous System
- Special Senses (in developmentThe process of growth and differentiation.)
- The Endocrine System
- Blood
- The Heart
- Blood Vessels
- The Digestive System
- The Respiratory System
- The Urinary System
- Fluids, Electrolytes & Acid–Base Balance
- The Reproductive System
- The Immune System
List of terms
- mutation
- head
- amino acid
- cell cycle
- growth
- acid
- translation
- proteins
- apoptosis
- S phase
- interphase
- cells
- development