PED 291 - Chapter 4 Notes

The body’s ability to take energy from food and transfer it to the skeletal muscles determines it’s capacity to swim, run, bike, etc long distances at high intensity. The transfer occurs through thousands of reactions that require nutrients fueled by oxygen (aerobic).

Anaerobic reactions generate energy rapidly for short durations without oxygen.

Food energy is not released suddenly. Reactions controlled by enzymes with the cell (which is 70% water) extract the energy slowly to reduce energy loss and make for efficient energy transfer.

ATP is the special carrier for free energy that is extracted from every cell by a complex controlled reaction. This slow extraction allows the body to make direct use of chemical energy for biological work.

Adenosine triphosphatase (an enzyme) speeds up this process and forms a new compound ADP.

Anabolic reactions require energy for synthesizing new compounds. Example: amino acids + amino acids = protein. (page 99)

Catabolic reactions release energy and forms the ATP that becomes the carrier of energy to the cells. When the ATP process becomes ADP...7.3 kcals of free energy are released (energy available for work). Page 100 shows the biological work it powers.

The splitting of ATP for energy does not require oxygen and it is immediate. (running for the bus).

The body only stores about 3.5 ounces of ATP for a few seconds of explosive exercise. ATP has to be resynthesized, and some of it comes from the breakdown of phosphocreatine (creatine phosphate). Changing from a walk to an all out sprint accelerates energy transfer rate up to 120 times.

Cells store creatine phosphate in much larger quantities than ATP, and the enzyme that facilitates creatine breakdown is creatine kinase.

The creatine phosphate is split, which releases a large amount of energy. The enzyme kinase is responsible for this breakdown to remake ATP

The energy released can sustain all out activity for 5-8 seconds (during the 100 meter dash, people actually slow down at the end). This is the immediate energy system of high energy phosphates. You can train it by doing 6-10 second intervals of all out activity.

After this time, ATP resynthesis requires an additional energy source. (the food we eat and store).

Food breakdown serves one crucial purpose: to take ADP for reforming ATP. This occurs through energy transfer through chemical bonds of phosphate (phosphorylation). The energy from bond transferring comes from the oxidation (burning) of food.

What becomes oxidized? The energy factor (mitochondria) of the cell. 90% of ATP resynthesis takes place in the respiratory chain by oxidative reactions and chemical bond energy transfer (phosphorylation)

A.    Carbohydrates- generates ATP ANAEROBICALLY (without oxygen). Very important for vigorous exercise that requires rapid energy release. It provides about half of the body's energy during aerobic exercise, and helps process fat (we need carbos to metabolize fat). Page 105

Glucose breakdown occurs in 2 phases:

1. glucose breaks down rapidly into 2 molecules of pyruvate without the use of oxygen (anaerobic).This stage is termed glycolysis, and takes place within the cell. Glycolysis takes place in the watery medium of the cell outside of the mitochondria.

Hydrogen atoms are needed by the cell to form water when they are joined with oxygen, and through the return process they are made continuously available. During exercise if this occurs our bodies are in a steady state (aerobic glycolysis). This occurs because hydrogen oxidizes (burns) at the same rate it becomes available. When this hydrogen is burned, pyruvate is left afterwards, which converts to glucose.

However, during very strenuous exercise: energy demands exceed oxygen supply, thus the hydrogen going back and forth to the cell no longer occurs. Now anaerobic glycolysis occurs, and forms a substance called lactate. Lactate is a form of chemical energy because once oxygen is available,, hydrogen grabs lactate to make ATP, and is also used to remake glucose (cori cycle). It forms into the muscle, and diffuses into the blood for quick removal, to supply more ATP for anaerobic energy. Eventually this process cannot keep pace, fatigue sets in and exercise stops. The non oxidized (not burned) hydrogen forms with pyruvate to create excess lactate, which causes fatigue.

2. Pyruvate converts to acetyl-CoA (acetic acid) and enters into a breakdown process called the Krebs cycle: a long complex process that breaks down glucose during long periods of aerobic activity. Through stage 1 (glycolysis) and stage 2 (krebs cycle), 36 ATP are formed through complete glucose breakdown in skeletal muscle. Anaerobic glycolysis only releases 10% of the energy within the glucose molecule (2 ATP). The Krebs cycle releases 36 ATP.

Difference between types of muscle fibers: page 112.

B.  (food breakdown) Fat-stored fat represents the body's most plentiful source of potential energy. The fuel reserves in an average adult male represent between 60,000 and 100,000 calories of energy from adipocytes (a triglyceride in fat cells).

Lipolysis-a process that splits the triglyceride in fat cells (adipocytes) into glycerol and fatty acids: components that yield about 457 molecules of ATP. This process requires oxygen (aerobic activity). The enzyme needed for this process is lipase.

The glycerol is broken down to pyruvate to form ATP (done by phosphorylation). The pyruvate is oxidized by the Krebs cycle. This glycerol molecule gives out 19 ATP and takes place when GLYCOGEN RESERVES DEPLETE DUE TO HEAVY TRAINING OR CARBOHYDRATE RESTRICTION.

Fatty acids turn to acetyl CoA that enters the Krebs cycle for breakdown. Oxygen must be present for this breakdown to occur (it joins up with hydrogen)

_95% of fat molecules cannot be converted to glucose.

It represents 30-80% of energy for physical activity.

For fats to be broken down there must also be carbohydrate breakdown (excess CHO converts to triglycerides for adipose tissue storage).

Adipocytes (adipose tissue) store these triglycerides, and the free fatty acids from them leave during exercise and are transported to all different kind of tissues for energy with the help of an enzyme called lipoprotein lipase (fatty acids can not be converted to glucose). This enzyme activity level increases with blood flow during continuous exercise.

C.    Protein: amino acids have their nitrogen removed from the molecule. Skeletal muscle contains enzymes that remove nitrogen and passes it to other compounds, so the muscle can use the amino acid by product for energy. The amino acid losing it's nitrogen can now contribute to ATP formation.

Some amino acids are glucogenic. When deaminated (broken down) they yield products for glucose synthesis by gluconeogenesis (pyruvate is one example). Some aminos are ketogenic: they cant be turned into glucose, but can be converted to fat.