Denaturation: what heat breaks in a protein and what it leaves, a protein's melting point, one mutation that lowers it, and a protein that survives a hot spring.
Step 1 of 5 · Heat it
Step 1 of 5
Heat it
A protein’s fold is held by many weak bonds: hydrogen bonds (the dots between the strands of the sheet and along the helix), attraction between opposite charges, and the oily side chains’ urge to hide from the water. Each of them is very weak next to the peptide bonds that hold the chain itself, but together they hold the shape.
Step 2 of 5
What is left
When a protein loses its shape, we say it has denatured. That is what happens to egg white when you cook it: it was clear and runny, and turns white and solid, because the unravelled chains tangle together. In an egg, as in the Scene, denaturation is usually not reversible.
Step 3 of 5
One swap
A protein’s melting point is the temperature at which half its molecules are folded and half unfolded. For the natural protein it is 60 °C. The Mutant is almost identical: only one amino acid, at the heart of the fold (marked with a red ring), was swapped. In place of an oily one that hid in the middle there is a charged one, which has no comfortable place there.
Step 4 of 5
A fever
At body temperature most of the mutant’s molecules are still folded. But it sits close to its melting point, and every extra degree counts.
Step 5 of 5
Hot springs
Some bacteria live in hot springs, at 80 °C and more. Their proteins do the same jobs as ours, and fold into the same shapes, but they do not unravel at that heat. Temperature and Protein are free: compare the three versions.
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Each step sets up the Scene for you, and a control marked “fixed” stays put for that step.
Practice · Predict, then look
In the folded protein, at body temperature, 28 hydrogen bonds hold the helix and the sheet. We will heat it to Boiling. How many will be left?
Practice · Predict, then look
In the folded protein, at body temperature, 28 hydrogen bonds hold the helix and the sheet. We will heat it to Boiling. How many will be left?
Practice · Calculate
The protein is at boiling, fully unfolded. How many peptide bonds are left in its chain of 56 amino acids?
Practice · Calculate
The protein is at boiling, fully unfolded. How many peptide bonds are left in its chain of 56 amino acids?
Practice · Reach the target
This is the Mutant: one oily amino acid at the heart of the fold was swapped for a charged one. Find the Temperature at which exactly half its molecules are folded, then press Check.
Practice · Reach the target
This is the Mutant: one oily amino acid at the heart of the fold was swapped for a charged one. Find the Temperature at which exactly half its molecules are folded, then press Check.
Practice · Calculate
The mutant has a fever of 41 °C. What percentage of its molecules are still folded? Read it off the chart.
Practice · Calculate
The mutant has a fever of 41 °C. What percentage of its molecules are still folded? Read it off the chart.
Practice · Choose
The Heat-loving version comes from a microbe that lives in a hot spring. At 80 °C it is still folded. What holds it together?
Practice · Choose
The Heat-loving version comes from a microbe that lives in a hot spring. At 80 °C it is still folded. What holds it together?
Lesson complete. Every practice question here is done.