F. OXYDATIVE PHOSPHORYLATION; CHEMIOSMOTIC COUPLING

Production of ATP from ADP and P is powered by a proton gradient. This mechanism is known as chemiosmotic coupling. Chemiosmotic refers to the fact that the production of ATP molecules is a chemical process and a transport process across a semipermeable membrane.

Two events take place in chemiosmotic coupling:

1) The proton gradient is established across the inner mitochondiral membrane

2) Potential energy stored in the gradient is released and captured to form ATP from ADP and Phosphate.

The proton gradient is established as electrons as electrons move down the ETC. At three different times in the ETC, there is a significant drop in potential energy held by electrons. These are the three reactions: Fe-S->Q CytC1-> Cytc ,and Cyt a3-> O2. As a result relatively large amount of energy is released. This energy powers the pumping of H+ from the mitochondrial matrix through the inner membrane to the space that separates the inner and outer membrane. One in that space, the protons are free to leave the mitochondrion.

The electron carriers in the chain are positioned so that the electrons travel in a zig zag manner– from the inner to the outer surface of the inner membrane. Each time the electrons travel to the inside surface, the electrons pick up two H+. When the electrons travel to the outer surface, they release two H+. The actual number of protons moved is not known. It is known, however, that at least six protons are moved.

The difference in the proton gradient on the outside of the inner membrane represents the potential energy. The potential energy results from a difference in pH and electric charge. H+ flow through the channels, ATP is formed from ADP and phosphate. It is not known how many flowing H+ it takes to form an ATP molecule (3 ATPs from 1 NADH and 2 ATPs from FADH2).

Oxygen acts as the final electron acceptor. Once the oxygen accepts the electrons, it is converted into water. That is why you need to breathe oxygen. If oxygen were not there to accept the electrons, the electron transport system would get backed up, no energy would be produced, and without energy there would be no life. Cyanide is a powerful poison because it blocks the transfer of electrons from cyt a3 to oxygen.

The elctron transport syustem produces 17 to 32 molecules of ATP. Add this to the previous total of four ATP molecules produce in Glycolysis and the Krebs Cycle, and we now have a total of 21 to 36 molecules of ATP from each molecule of glucose oxidized.

Oxygen is used as the final electron acceptor. Carbon dioxide is produced during the Krebs Cycle and most of the energy is produced from the ETC and H+ concentration / gradient.

G. OTHER CATABOLIC PATHWAYS

Starch is broken down into monosaccharides. The monosaccharides are phosphorylated to glucose-6-P and enter glycolysis.

Fats are split into glycerol and fatty acids. The fatty acids are cut up into two carbon fragments and slipped into the Krebs Cycle as Acetyl CoA. Glycerol slips in as Glyceraldehyde-3-P.

Proteins are broken Down into Amino Acids. Amino acids have the amino group removed. The carbon skeleton is either converted into acetyl group or a larger compound that can enter glycolysis. If the amino group is not used, it is excreted as urea.

H. HOW ELSE CAN THIS AFFECT YOU?

In the muscle tissue, there are a lot of mitochondria. During heavy exertion a great deal of ATPs can be used. Muscle systems usually work aerobically; but, in larger animals, it is impossible for the circulatory system to bring enough oxygen tot eh tissues during heavy exertion. Therefore, we have two back up systems.

1) Creatine Phosphate

This transfers a phosphate to ADP in order to form ATP. Creatine Phosphate + ADP —-> Creatine + ATP. As the Creatine phosphate is used up, there is another quick source of energy.

2) Anaerobic Glycolysis

NADH combines with pyruvate to form lactic acid (lactate0. Lactic acid accumulates quickly during intensive use of muscles. This is the burn that is felt when excercising. Animals can remove lactic acid in two ways.

a. Lactic acid combines with oxygen to form the circulatory system. The oxygen reverses the lactic acid to pyruvate which proceeds in the aerobic pathway.

b. lactic acid can be washed away by the circulatory system and carried to the liver. In the liver, the lactic acid can be metabolized back into glucose with oxygen.

After periods of heavy exertion, the muscle tissue will be depleted of creatine phosphate and the liver and muscles will be loaded with lactate. This causes pain. When the activity stops, it takes a long time, and lots of oxygen and ATP, for the lactic acid to be metabolized and for the creatine to regenerate into creatine phosphate.

During this time, a person will breathe hard and try to take in as much oxygen as possible. This is called oxygen debt. How long it takes to recuperate depends on physical condition. The better condition people are, the more oxygen they can take in and the heart can pump more blood with the oxygen to their tissues.

Runners enlarge their lung capacity, increasing their capillary beds. The heart becomes stronger and can pump more blood with each stroke, which increasing the ability for runners to utilize oxygen.

Remember that starch and glycogen are polymers of glucose. These polymers are broken down into single glucose molecules during a process called phosphorolysis. During this process the bond is split by an enzyme that places a phosphate on the #1 carbon of the glucose molecule. This makes Glucose-1-P which changed to Glucose-6-P

Runners in the marathon who have hit ‘the wall’ have used up all of the glucose in their bodies. All that is left are fat and proteins which will be broken down for energy. This is very dangerous since the heart is a muscle that is made up of protein. This is why runners try to load up with carbohydrates before a big race.