Hemoglobin vs Myoglobin: Affinity and Curves

Hemoglobin vs Myoglobin: Structure, Oxygen Affinity and Curves

By StudyStore · Published 2026-11-04 · 1 min read · 260 words

Myoglobin stores oxygen in muscle. Hemoglobin transports oxygen in blood. Their different structures give them different binding curves.

Comparison

	Myoglobin	Hemoglobin
Location	Muscle	Red blood cells
Structure	Monomer, one heme	Tetramer (2 alpha, 2 beta), four hemes
Curve	Hyperbolic	Sigmoidal
Cooperativity	None	Positive
O₂ affinity	Higher (lower P50)	Lower (higher P50)
Regulated by H⁺, CO₂, 2,3-BPG	No	Yes
Role	Storage and release in working muscle	Loading in lungs, unloading in tissues

Why the curves differ

Hemoglobin shifts between a low-affinity T state and a high-affinity R state. Binding one O₂ favors the R state, so the next oxygens bind more easily. That cooperativity gives the S shape.

Myoglobin has a single binding site, so each molecule binds oxygen independently, giving a hyperbola.

Why it makes sense physiologically

In the lungs, high pO₂ loads hemoglobin nearly fully.
In tissues, hemoglobin gives up oxygen over a range of pO₂.
Myoglobin holds oxygen more tightly and releases it mainly when pO₂ falls very low, as in exercising muscle.

Fetal hemoglobin

Fetal hemoglobin has a higher O₂ affinity than adult hemoglobin because it binds 2,3-BPG less strongly. Oxygen therefore moves from maternal to fetal blood.

Common traps

Giving myoglobin a sigmoidal curve.
Saying myoglobin is lower affinity. It binds oxygen more tightly.
Applying Bohr or 2,3-BPG effects to myoglobin.

One-minute recap

Myoglobin: monomer, hyperbolic, higher affinity, storage.
Hemoglobin: tetramer, sigmoidal, cooperative, transport.

Check yourself: 5-question mini-quiz

Try each question first, then click it to reveal the answer.

1. What is the shape of the myoglobin binding curve?

Hyperbolic.

2. Why is the hemoglobin curve sigmoidal?

Positive cooperativity as binding shifts the protein from the T state toward the R state.

3. Which has the higher oxygen affinity, myoglobin or hemoglobin?

Myoglobin.

4. How many heme groups does hemoglobin carry?

Four.

5. Why does fetal hemoglobin bind oxygen more tightly than adult hemoglobin?

It binds 2,3-BPG less strongly.

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Written by StudyStore from standard scientific facts. Study aid only. Always check values against the reference your exam provides.