SEHS UNIT 3 ENERGY SYSTEMS - 3.3 NUTRITION AND ENERGY SYSTEMS

Golgi apparatus

Folded membranes within the cytoplasm, involved in secretion and intra-cellular transportation.

Mitochondria

Powerhouse of the cell, responsible for cellular respiration and resynthesis of most ATP within the cell

Lysosome

Breaks down waste

Ribosomes

Site of protein synthesis

Nucleus

Contains cell DNA and coordinates all cell activity

Rough Endoplasmic Reticulum

Responsible for the production, processing and transportation of proteins within the cell.

Label the mitochondria

Outer smooth membrane. Inner matrix. Cristae

Cell Respiration

The controlled release of energy in the form of ATP from organic compounds in cells.

How adenosine can gain and lose a phosphate molecule

ATP is only usable form of energy in the body.

The energy we get from the foods that we eat has to be converted into ATP before the energy in them can be used.

Energy is released from ATP by breaking the bonds that hold the molecules together.

The role of ATP in muscle contraction (1 of 4 steps)

Many chemical reactions in the cell use the energy from stored ATP, which is released when the phosphate bonds of ATP are broken.

The role of ATP in muscle contraction (2 of 4 steps)

Myosin filaments have small projections called myosin heads.

These extend out to the actin but do not touch.

A protein called tropomyosin is bound to the active sites of the myosin.

Tropomyosin prevents the actin heads and the myosin forming an attachment.

Another protein called troponin is bound to the actin.

This protein can neutralise the effects of tropomyosin in the presence of calcium ions

The role of ATP in muscle contraction (3 of 4 steps)

There is a limited store of ATP in the muscle fibres, which is used up very quickly (in about 3 seconds) and therefore needs to be replenished immediately. There are three energy systems that regenerate ATP:

The role of ATP in muscle contraction (4 of 4 steps)

ATP changes to ADP + P, causing the myosin heads to change their angle. The heads are now 'cocked' in their new position, where they store potential energy for muscle contraction from the ATP

The ATP-PC System

Phosphocreatine (PC) is an energy-rich phosphate compound found in the sarcoplasm of the muscles. It's important for providing contraction of high power.

There is only enough PC to last for up to 10 seconds and can only be replenished when the intensity of the activity is submaximal.

ATP-PC system regeneration

Regenerates ATP when the enzyme creatine kinase detects high levels of ADP. It breaks down the phosphocreatine to phosphate and creatine, releasing energy in an exothermic reaction.

This energy is then used to convert ADP back into ATP (an endothermic reaction)

Advantages of ATP-PC system

ATP can be regenerated rapidly using the ATP-PC system.

Phosphocreatine stores can be regenerated quickly (30seconds = 50% replenishment - 3minutes = 100% replenishment)

There are no fatiguing by-products

It is possible to extend the time the ATP-PC system can be utilised through the use of creatine supplement.

Disadvantages of ATP-PC system

There is only a limited supply of phosphocreatine in the muscle cells, (eg. it can only last for 10seconds).

Only one molecule of ATP can be regenerated for every molecule of PC

PC regeneration can only take place in the presence of oxygen (eg. when the intensity of exercise is reduced)

The lactic acid system (anaerobic glycolosis)

Once PC is depleted, the lactic acid system takes over and ATP is regenerated for the breakdown of glucose.

Glucose is stored in the muscles and liver as glycogen. Before glycogen can be used to provide energy to make ATP, it has to be converted into glucose. This process is called glycolosis and the lactic acid system is sometimes referred to as anaerobic glycolosis, due to the absence of oxygen.

How glucose molecule is broken down in the lactic acid system

The glucose molecule is broken down into two molecules of pyruvic acid.

In the absence of oxygen, pyruvic acid is then converted to lactic acid.

The main enzyme responsible for the anaerobic breakdown of glucose in phosphofructokinase (PFK), which is activated by low levels of phosphocreatine and increased levels of calcium (released from the sarcoplasmic reticulum during muscle contraction).

The energy released from the breakdown of each molecule of glucose is used to make two molecules of ATP.

Advantages of lactic acid system

ATP can be regenerated quickly.

In the presence of oxygen, lactic acid can be converted back into glycogen or used as fuel through oxidation into CO2 and H20.

Good for extra bursts of energy.

Disadvantages of lactic acid system

Is a by-product and accumulation in the body stops enzymes working effectively.

Only a small amount of energy is released from glycogen when oxygen is not present.

Oxygen deficit

Is the difference between the amount of oxygen consumed during exercise and the amount that would have been consumed if aerobic respiration occurred immediately.

Oxygen debt

Known as (EPOC) excess post-exercise oxygen consumption

The amount of oxygen "owed" to the body in order to recover.

The Aerobic System

This system breaks down glucose in the presence of oxygen into carbon dioxide and water. It is much more efficient than the anaerobic systems - the complete oxidation of glucose produces 34 molecules of ATP in the three stages.

Aerobic glycolysis

In the presence of oxygen the pyruvates enter the mitochondria.

Pyruvates are converted into acetyl CoA

Krebs cycle

Hydrogen ions liberate electrons for the electric transport chain

Electric Transport Chain

Electrons resynthesise ATP.

34ATP can be resynthesised pre glucose molecule

Advantages of aerobic system

More ATP produced

No fatiguing by-products

Glycogen and fat stores are large, so produces energy over a long period.

Disadvantages of aerobic system

Complicated so can not be used immediately.

Fatty acid transportation is slow and requires 15% more oxygen to break down than glycogen.

ATP-PC system relative contribution during exercise

Produces energy quickest.

Peaks at 5 secs and is exhausted after 12-15 secs.

Lactic acid system relative contribution during exercise

Peaks around 15 secs

Opportunity to oxidise metabolic by-products allowing additional energy in bursts.

Aerobic system relative contribution during exercise

Dominant from around 55 secs

Steady energy demands met until event ends or maximal oxygen consumption is reached.