A.2.3.1 Different energy systems

Metabolism

Metabolism - all the chemical processes in living organisms required for the maintenance of life. It consists of two phases:

• Anabolism - the constructive phase of metabolism where smaller molecules are converted into bigger molecules, e.g. glucose molecules converted to glycogen

• Catabolism - the destructive phase of metabolism where larger molecules are converted to smaller molecules, e.g. triglycerides convert to glycerol and fatty acids

The role of the mitochondria

Mitochondria are cell components that accommodate the biochemical processes of aerobic metabolism, including the Krebs cycle and electron transport chain

• Krebs cycle - a series of chemical reactions that produce a large quantity of ATP

ATP (Adenosine Triphosphate)

In cells, catabolic reactions convert biochemical energy from organic molecules into ATP. The controlled release of energy in the form of ATP is called cell respiration.

ATP can be synthesised by adding a phosphate group to the compound ADP (adenosine diphosphate)

Muscle contraction

1. Muscular contraction needs energy

2. Energy is synthesised in the mitochondria and stored in the cytoplasm of the muscle cells as ATP

3. ATPase is the enzyme that breaks off the last phosphate

4. Creates an inorganic phosphate and releases a high amount of energy

5. There is a limited amount of ATP in the muscles, which lasts 3-5 seconds

6. For exercise to be continued, ATP has to be regenerated from ADP using energy obtained from other sources

7. ATP synthase aids the anabolic reaction by allowing inorganic phosphate to reconnect with ADP, resynthesizing ATP

8. This keeps occurring to give us a release of energy and then resynthesize to produce stored energy

For a muscle contraction to occur, energy is required. It is synthesised in the mitochondria

Carbohydrate metabolism

To release energy from carbohydrates in our food, they’re digested down to monosaccharides: glucose, fructose and galactose. They are then sent to the liver after being absorbed into the bloodstream. These monosaccharides are then converted into glucose.

1. Breakdown of glucose to pyruvate

• Glycolysis - the breakdown of glucose in all cells in the cytosol

• Glycolysis leads to the metabolism (breakdown) of glucose to pyruvate and the production of ATP

• When oxygen is available = pyruvate enters the mitochondria = is oxidised, producing CO₂ and water

• Under anaerobic conditions (high-intensity exercise), pyruvate is converted into lactate

• Gluconeogenesis - lactate is transported back into the liver, where it is reformed into glucose

2. Conversion of glucose to glycogen for storage

• Glycogenesis - the process where glucose is converted into glycogen specifically for storage, many glucose molecules are linked to form glycogen

• This is done in liver/muscle cells when the diet provides more glucose than the tissue requires

• Glycogenolysis - the process where glycogen is broken down into glucose in the liver and glucose-6-phosphate in the muscles

• This is done when the body needs more glucose than is ingested

• Muscle glycogen is only used to deliver an immediate energy source for the muscle, liver glycogen provides glucose for all other organs

Fat metabolism

Fatty acids are broken down through a process called beta-oxidation

• Occurs in the mitochondria, to which fatty acids are transported

• Supports carnitine

  • An enzyme that transports fatty acids to the mitochondria

• Fatty acids gradually break down into acetyl-Coa = releasing ATP energy

• Fatty acids contribute to reactions that form cholesterol = which can lead to narrow arteries, heart attack/stroke risks