Bioenergetics and muscle metabolism I

Adenosine triphosphate (ATP)

ATP hydrolysis to ADP and phosphate ΔG = -31kJ mol-1

ATP is not a long-term energy store

The body must constantly synthesise new ATP

Three ATP synthesis pathways

1. ATP-phosphocreatine system (anaerobic metabolism)

2. Glycolytic system (anaerobic metabolism)

3. Oxidative system (aerobic metabolism)

1. ATP - phosphocreatine system

Phosphocreatine (PCr): ATP recycling

PCr energy cannot be used for cellular work

PCr energy can be used to reassemble ATP

Replenishes ATP stores during rest

Recycles ATP during exercise until used up

Glycolysis

1. Preparation phase:

Traps glucose in cell

Forms a compound that is readily converted into 3C molecules

2 molecules of ATP consumed

Glycolysis

2. Payoff phase:

Harvesting of some of the free energy of the intermediates

4 ATP produced

2 NADH produced

Anaerobic glycolysis - lactate dehydrogenase

Used when:

the supply of oxygen is inadequate

Allows formation of ATP by glycolysis by regenerating NAD via lactate dehydrogenase

Lactate The Cori Cycle

- lactate from muscle is converted to glucose in the liver (via the conversion to pyruvate)

- glucose returns to the muscle and is used in glycolysis

Aerobic metabolism

- Glycolysis

- Citric acid cycle

- Oxidative phosphorylation

Source of energy in the body

Carbohydrates

Fats

Proteins

Glycogen metabolism

Glycogen synthesis - glycogenesis - key enzyme = glycogen synthase

Glycogen breakdown- glycogenolysis- key enzyme = glycogen phosphorylase

Fat ( Triacylglycerol) metabolism

Hormonal signals control mobilisation/.storage of TAGs in adipose

Insulin- promotes TAG storage

Glucagon/adrenaline- promotes lipolysis

Common pathways used to provide energy

Interaction of different energy systems

Different pathways active at different times

Short sprint

PCr and Anaerobic Glycolysis

PCr carbohydrate

Long distance run – PCr, Aerobic metabolism (Ox Phos)

carbohydrate & lipid

Capacities of different energy systems

Changes in fuel use during prolonged, moderate exercise

Oxidative capacity in muscle

Different muscles exhibit different oxidative capacity

Determined by activity of oxidative enzymes

Muscle fibre types

Type I fibres during exercise:

High aerobic endurance

Can maintain exercise for prolonged periods

Require oxygen for ATP production

Efficiently produce ATP from fat, carbohydrate

Type II fibres during exercise:

Poor aerobic endurance, fatigue quickly

Produce ATP anaerobically