Describe the three sources of energy to produce ATP for muscles and distinguish between aerobic and anaerobic processes.

Answer 1

ATP is the "currency" of energy used in cells such as muscle fibers. The molecules that comprise the body's "fuel" are too big to be used by cells so they must be converted into ATP in order to power the body. Let's say you wanted to get some gumballs from the gumball machine. Having $10 could get you a lot of gumballs, but not if you had a $10 bill. You can only get the gumballs if you broke the $10 bill into quarters. This is basically the reason why your body needs to break large fuel molecules into ATP.

In muscles, ATP activates a protein called myosin which is responsible for converting chemical energy into movement (in the form of muscle contraction). Specifically the breakdown of ATP into ADP and a phosphate group provides this energy. The T in ATP stands for tri and the D in ADP stands for di so these molecules have 3 and 2 phopsphate groups respectively. Think of it this way - when you snap a dry twig or a pencil, energy is released in the form of sound. Snapping an ATP molecule also provides energy that powers activity in a cell.

In muscles, snapping one of the P's off of an ATP molecule provides energy which is stored in myosin. Think of the energized myosin like being a stretched rubber band or a compressed spring - if you let it go, some movement will happen. In this analogy, ATP is responsible for stretching the rubber band. Myosin energized by ATP is bound to other proteins that form that structure of the muscle. When myosin releases its energy to act (i.e. letting the rubber band or spring go) it pulls on the proteins to which it's bound. This is how a muscle contracts.

But where does the ATP come from? ATP is formed by adding a phopshate group to ADP (i.e. phosphorylation). This can be accomplished in 3 different ways:

1) Phosphorylation of ADP by creatine phosphate (also called the phospagen system)

2) Phosphorylation of ADP by glycolysis

3) Oxidative phosphorylation of ADP in mitochondria

Aerobic means that the process involves the use of oxygen. A brief inspection of this list indicates that #3 is an aerobic process. In oxidative phosphorylation, hydrogen combines with oxygen to form water; energy is released in the process and this energy is transferred to ATP. Most ATP in the body is produced this way. But oxygen isn't always readily available and your cells still need ATP so other, anaerobic mechanisms exist.

Glycolysis is a complex process by which glucose and ADP react to form a molecule called pyruvate and ATP. Oxygen isn't involved in this process, but note that oxidative phosphorylation can occur after glycolysis if oxygen is present. But glycolysis itself does not require oxygen. As oxygen is used up (such as during exercise), this becomes the predominant form of ATP production.

In the creatine pathway, a phosphate group is transferred from creatine phosphate to ADP to form ATP. This form of ATP formation is most common at the beginning of big bursts of activity like sprinting and weightlifting.