Cellular+Respiration


 * Aerobic and anaerobic respiration**

The first step of Cellular Respiration is an anaerobic process (meaning it does NOT require oxygen) known as Glyclolysis. Glycolysis begins in the cytoplasm of a cell. It has a net production of 2 Pyruvate molecules, 2 ATP molecules, 2 Hydrogen ions, and 2 NADH molecules, which are electron carriers.

Glycolysis begins with a 6-carbon glucos molecule undergoing phosphorylation (Important to remember that this is different that oxidative phosphorylation, which occurs later in respiration). In phosphorylation, 2 ATP molecules become 2 ADP molecules and 2 inorganic phosphate molecules. This changes the 6-carbon molecule to a 6 carbon molecule with 2 phosphate groups at the each end of the carbon chain. This molecule is now known as hexose biphosphate.

Lysis then splits the molecule down the middle, resulting in 2 Triose Phosphate molecules, which are 3-carbon chains with a phosphate at the end of one of the chains. These molecules then simultaneously undergo oxidation and ATP formation. In oxidation, 2 NAD+ molecules are reduced to become 2 NADH electron carriers along with 2 Hydrogen ions. Then, 4 (ADP + inorganic phosphates become 4 ATP molecules, for a net production of 2 ATP molecules, as 2 ATP were used previously in Phosphorlyation.

The final result are two 3-carbon molecules known as pyruvates. This process, known as glycolysis, is outlined below. The process of glycloysis can also be defined in an equation. C6H1206 (glucose) ---> 2 C3H403 (2 Pyruvate molecules) + 2 H+ (2 hydrogen ions)

The next step of respiration depends on whether or not oxygen is present. If oxygen is NOT present, then anaerobic respiration continues. In the mitochondria of animal cells (eg Human cells), Anaerobic respiration usually occurs during short bursts of strenuous muscle activity, as ATP can be created very quickly for a short time. The product of doing this in animal cells results in the production of lactate. This explains lactic acid buildup, which accounts for soreness after more intense muscle activity.

In plant and fungi cells (like yeast), pyruvate molecules are not converted into lactate, and instead are converted into ethanol and carbon dioxide, which serves as the basis of fermentation. This can also be described with an equation. C6H1206> 2 C2H5OH + 2 CO2

The discrepancies between the two anaerobic processes can be seen below

However, if oxygen is present, then the products from glycolysis enter the mitochondria and proceed through what are known as the link reaction, the Krebs cycle, and oxidative phosphorylation. This ultimately will produce (theoretically) 36 moles of ATP molecules along with carbon dioxide and water. Carbon dioxide is considered a waste product of cellular respiration, the goal of which is to produce ATP, as ATP provides energy to the body. The entirety of aeorbic respiration, including the anaerobic step of glycolysis, can be described in the equation 2 C6H1206 + 602 ---> 6CO2 + 6H20

But again, it is key to also know that (theoretically) 36 ATP molecules are also formed.

People often confuse cellular respiration with breathing. Yes, cellular respiration requires oxygen, but it is not the same thing as //ventilation//, which occurs in the lungs, and is not a chemical process, but the physical process of breathing that we are familiar with. In order to bridge the gap and bring oxygen to the cells in our body, a process known as gas exchange helps oxygen diffuse into our erythrocytes (red blood cells). When oxygen is diffused into our red blood cells, it binds to a heme group of a complex protein known as haeomoglobin. Haeomogobin is composed of four large polypeptide chains and four iron moleculules surrounded by heme groups, and is responsible for transporting oxygen throughout the blood. A heme group is a prosthetic group essential for the protein to be able to carry out its function as it's where oxygen binds to haemoglobin.
 * Haemoglobin as an oxygen carrier.**

As each oxygen molecule binds, it alters haemoglobin's structure so that it is easier for more oxygen moleucles to bind. Thus, at higher concentrations of oxygen, it is easier for oxygen to bind to haemoglobin. Conversely, as each molecule is released, it makes it easier for other oxygen molecules to be released. This relationship makes sense. In the lungs, where oxygen concentrations are high, it is important to easily bind the oyxgen to the haemoglobin and transport it to areas in the body not so lucrative in oxygen. And where oxygen levels are low, that means this area //needs// oxygen, so it needs to be easy for haemoglobin to release oxygen molecules. This relationship can be seen in an oxyhaemoglobin dissociation curve.


 * The Electron Transport Chain**

Nearing the end of aerobic cellular respiration, we conclude with the electron transport chain. Within the electron transport chain various electron carries such as, NADH+H and FADH2, are formed within the Kreb's cycle and find their way to the phospholipid bilayer of a cell. Here electron carries donate hydrogen ions and electrons to form the final products of aerobic cellular respiration - CO2, H2O, and ATP(energy). However, there are vital metal ions that aid the this process and utilize its products to aid in other functions in the body.

There are vital metal ions that are found in our diet that are crucial in certain biological systems. Many metal ions play a key role in differing biological systems due to their charge density, redox properties, and complex ion formation. Iron is one example of a metal ion that are body often uses, other transition metals include, cobalt and copper. Thus, metal ions such as these are important because they form complex ions and exist in multiple oxidation states that catalyse redox reactions.

Metal ions such as iron and copper play a key role in the electron transport chain. For instance, they are intertwined with the structure of a //Cytochrome//. Cytochrome are proteins that aid in the electron transport chain as it generates ATP, additionally these proteins contain copper and iron and energetic electrons so that they may produce ATP.



Interestingly enough, living organisms use ATP to transfer energy from exothermic reactions, this includes the oxidation of carbohydrates to biosynthetic reactions and even includes other endothermic reactions that occur within the body. The formation of ATP and water is many possible by the addition of ADP to a phosphate ion, this reaction is endothermic reaction. The hydrolysis of ATP to ADP is exothermic, and thus is the reverse reaction to the formation of ATP. This reaction provides the energy for a cell to function.
 * Exothermic and Endothermic Reactions in Cells**


 * Iron and Copper in the Electron Transport Chain**

The iron atoms and copper atoms in a cytochrome undergo one-electron-oxidation-reduction reaction during aerobic cellular respiration. Iron undergoes the reaction with Iron(II) and Iron(III); whereas copper undergoes the reaction with copper(I) and copper(II).

Initially, co-enzymes such as NADH+H or FADH2 (electron carriers), carry hydrogen ions and electrons from metal ions such as copper and iron in a cytochrome. These electrons and hydrogen are then used to form water, CO2, and ATP within the electron transport chain. Secondly, the exothermic reaction pictured below is made possible through a number of steps that involve different enzymes. Here copper also acts as a terminal electron carrier in the electron transport chain and aids in the conversion of oxygen into water. Finally the energy that is produced is used to form ATP.

Next, haemoglobin comes into play within the electron transport chain. As we know, haemoglobin is an oxygen transport protein. It binds to oxygen in the lungs and transports it throughout the blood stream. Additionally, the heme within haemoglobin is a complex of iron that is surrounded by a hydrophobic environment. It is because of this environment that oxygen is able to bind to Fe2+ and does not convert it into Fe3+. Thus, the iron in haemoglobin bonds to oxygen and carries it to cells where it then releases oxygen. Once the oxygen has been released haemoglobin carries CO2, which has been produced from the electron transport chain, to the lungs where it is then released. However, carbon dioxide is often transported in the form of carbonic acid, thus as, hydrogen carbonate and hydrogen ions: