Question

) Describe how skeletal muscle derives ATP over a period of prolonged activity.  Use these subheadings as a guide to start your thinking.  Do this out loud in lab and by hand later:

• Creatine Phosphate

• Oxidative Phosphorylation

• Glycolysis

• Glycogen

• Circulating Glucose

• Circulating Fatty Acids

• Amino Acids

• Lactic Acid

• High Oxygen Levels

• Low Oxygen Levels

• Gluconeogenesis

Answer 1

ATP is the energy source for muscle contractions and Production of ATP in muscles takes place in three different ways.

From creatine phosphate: ATP is synthesized in skeletal muscles, but it is not stable, it should be utilized within 3 seconds. After this time the excess ATP is combined with creatine and produces creatine phosphate along with ADP. Whenever the excess ATP is needed (during prolonged muscle activity), the process is reversible; means the ATP is synthesized from creatine phosphate stores and ADP.

ATP + Creatine ↔ ADP + Creatine phosphate

Low oxygen levels:

Glycolysis: If oxygen levels are low or absent glycolysis is used for synthesis of ATP. So glycolysis is an anaerobic process for production of ATP. In glycolysis glucose is converted into pyruvic acid during which ATP is produced.

The steps are as follows:

Using glycogen: The large amount of glycogen is present in muscles. This glycogen is converted into glucose and this glucose will produce ATP by glycolysis process.

Gluconeogenesis: When more amount of ATP is required, it is synthesized using glycolysis process. For this process glucose is the beginning substance, so it should be produced either from glycogen stores as indicated above or from gluconeogenesis. Here puruvic acid (pyruvate) produced in glycolysis will be used for production of glucose. Pyruvic acid is converted into lactic acid and then to glucose. The steps are mentioned in figure provided.

High oxygen levels:

Aerobic respiration: During prolonged exercise muscles are provided with high amounts of oxygen.

Glucose from different sources is used for production of ATP. The sources of glucose in aerobic respiration are:

Circulating glucose from food

Glycogen in liver

Circulating fattyacids

Oxidative phosphorylation in mitochondria

Oxidative phosphorylation: By using this about 30 ATP molecules are synthesized. In this process ATP is produced from NADH and FADH2 molecules which are produced during glycolysis and citric acid cycle.

During prolonged muscle activity the following sequence of steps takes place in body to meet the requirements of ATP as energy source.

Step 1: ATP present in muscles is used (first 3 seconds).

Step 2: ATP produced from creatine phosphate

Step 3: From glycogen stores (low oxygen levels)

Step 4: From aerobic respiration (high oxygen levels)