The ATP-PC and glycolytic systems

Overview

Phosphocreatine and creatine kinase, the ATP-PC system's yield, duration, advantages and drawbacks, the stages of anaerobic glycolysis in the sarcoplasm, its net ATP yield and duration, what limits it, and the events that rely on each.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is phosphocreatine, and where is it stored?

   Model answer

   Phosphocreatine (PC) is a high-energy compound stored in the sarcoplasm of muscle cells. Muscle PC stores are small, enough for only a few seconds of maximal work.

2. 2

   Describe how the ATP-PC system resynthesises ATP.

   Model answer

   The enzyme creatine kinase breaks phosphocreatine into phosphate and creatine, releasing energy. The energy rejoins ADP and a phosphate to rebuild ATP.

3. 3

   What activates creatine kinase at the start of exercise?

   Model answer

   A rise in ADP concentration as ATP is used activates creatine kinase. The ATP-PC system therefore responds almost instantly when exercise begins.

4. 4

   How much ATP does one molecule of phosphocreatine produce?

   Model answer

   One molecule of phosphocreatine resynthesises one molecule of ATP. The yield is small, but the reaction is very fast.

5. 5

   For how long can the ATP-PC system be the dominant energy provider?

   Model answer

   The ATP-PC system dominates for up to about 10 seconds of maximal exercise. PC stores are then largely depleted.

6. 6

   Give two advantages of the ATP-PC system.

   Model answer

   The ATP-PC system resynthesises ATP very rapidly, so it supports maximal force. The system produces no fatiguing by-products.

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