Q23 - Geometry and Gradients Set Calcium Flow at the Muscle Membrane

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Muscle Physiology Cell Signaling & Communication

Jean Hanson (1919-1973) discovered how muscles contract. Contraction is triggered by a build up of calcium in the cytoplasm, which is actively removed during relaxation. Calcium diffuses through plasma membrane channels (1), or endoplasmic reticulum membrane channels (2). (1, purple) Plasma membrane channels, opened by depolarisation, pore width = 1 atom (2, orange) ER channels, open by binding calcium on cytoplasmic face, pore width = 100s of atoms The concentrations of the major biological ions in different compartments are shown.

Figure for Q23: Geometry and Gradients Set Calcium Flow at the Muscle Membrane

Using the information and data, determine which of the statements are true or which are false.

A. Peak calcium flow into the cytoplasm is greater from the intracellular than extracellular stores.

B. Cytosolic calcium has to be moved against an electrical and chemical gradient to be returned to the endoplasmic reticulum.

C. Muscle performance is improved by artificially expressing channel (2) on the plasma membrane.

D. Peak calcium flow is greater in high frequency muscle than to low frequency muscle.

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Question reproduced from IBO 2017, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key & worked solutions