Self Analysis / Progress

In the past, I've struggled with cellular respiration. This unit, working on botany and photosynthesis really helped me understand the process of cell respiration.

Cell respiration takes place inside the mitochondria of the cell. It is the process of which an organism takes in organic compounds with the presence of oxygen is turned into ATP. Aerobic respiration is respiration in the presence of oxygen.

There are three steps in cellular respiration: glycolysis, kreb cycle, and the electron transport chain. Glycolysis takes place outside the mitochondria in the cytoplasm of the cell. In glycolysis, glucose (six-carbon molecule), is broken down into two molecules of pyruvate, each containing a three carbon molecule. Two ATP is generated for every glucose molecule in this process. The chemical NADH is also yielded from this process.

Pyruvate then diffuses into the matrix of the mitochondria, yielding a pyruvate dehydrogenase conplex, which is going to convert the three carbon molecule into acetyl CoA (two carbon molecule), which will go into the kreb cycle. In order to go from a three carbon pyruvate into a two carbon molecule, the third carbon molecule is released in the form of carbon dioxide.



The kreb cycle gives off the two carbons from the acetyl CoA in the form of carbon dioxide as well as two ATP. The kreb cycle adds energy to NADH and FADH2. NADH and FADH2 both have high energy electrons, which they are going to carry into the electron transport chain.

NADH and FADH2 then moves through a series of proteins (electron transport chain). The energy from those proteins are used to pump protons (hydrogen ions) to the outside of the inner membrane into the inner membrane space. In the electron transport chain, NADH and FADH2 pass off their electrons through the proteins in the electron transport chain, pumping two or three hydrogen ion out as it passes through each protein. The inner membrane space is then overwhelmed by the positive charge. ATP synthase then brings the hydrogen ion back in, attaching the hydrogen onto ADP (with phosphate), creating ATP in the process. The electrons are then added to other protons and oxygen (we breathe in) to create the by-product, water. The oxygen that is inhaled will be the last electron acceptor in the matrix. The protons will then flow through a protein, ATP synthase, and combine with the electrons and oxygen, yielding water. This process yields anywhere between 32 to 34 ATP.

In the event of a lack of oxygen, gycolysis will shut down due to the absence of NAD+.  In order to counter this, lactic acid fermentation takes place. This takes place in the muscle. Cells will take glucose in glycolysis, creating two pyruvate molecules, then furthur converting it into lactic acid, which allows it to accept electrons from NADH in order to yield NAD+. This process precipitates two ATP each cycle. The problem with this cycle is that lactate, which is toxic, will build up in the muscles. This requires oxygen to be broken down.

Another solution to the lack of oxygen (in bacteria) is alcoholic fermentation. Instead of breaking down pyruvate into lactate like in lactic acid fermentation, the pyruvate is broken down into ethynol. The second difference between alcoholic fermentation and lactic acid fermentation is that in alcoholic fermentation, carbon dioxide is yielded instead of a three carbon molecule.