A human body needs energy in order to undertake the daily chores effectively. Without energy, most of body functions will be interfered with and as a result can be causative factors for inappropriate functioning of the body. The energy expenditure in the body will depend on many factors which will determine how much energy the body will require. Activity levels are believed to be one of the factors that influence energy requirements of the body. Since we don’t take food in form of energy, it undergoes a series of reaction for it to be in energy form that can be utilized directly by the body. As mentioned earlier, other factors like the growth level, weather condition, injuries, lifestyle among many others will have a direct bearing on how much energy the body will demand. All activities that we do on daily basis demands for energy without which, we can not be better placed to do them. For this to happen, number of activities and processes play part where by all these are geared to make energy available to the system so that normal functioning of the body can take place. This paper is thus intended to review how different organs in the body get energy they require for normal functioning of the cells and the key body organs that are tasked to supply body with energy needed. The discussion will look at the cellular respiration and the associated organs that execute these tasks.
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Once we ingest food, it undergoes various processes before it can be converted into useful state in the body. Our biological set up allows food to be ingested via the mouth all the way to the stomach. Depending on the group of the food, some will be digested from the mouth whereas others the digestion starts in the stomach. Our bodies require energy and this energy comes from the food we eat. The cells however can not benefit from the food we eat until it has been digested by being processed and converted into usable state. The food remnant that is not digested in the process is expelled from the body as waste products which can be in form of feces. It is very paramount to understand how we manage to do our daily chores, with all the energy demands and at the same time being in a position to tackle them effectively. Why do we usually have people perform different activities at different rates? Through an understanding of how energy is derived for various cells is crucial and it is also important to analyze the various processes in the body that takes place before food we ingest is completely broken down to present it in form that is ready to be used by our bodies.
Cellular respiration is termed as the process by which food molecules like glucose are oxidized to water and carbon dioxide. This energy is normally held in form of ATP to be utilized by all activities of the cell that needs the energy. Cellular respiration is ranked as one of the major ways in which the body cells are able to change energy from cells to ATP. It involves catabolic reactions that lead to oxidation of a molecule while reducing the other. Nutrients that are normally utilized in respiration are fatty acids, glucose and amino acids. On the other hand one of the oxidizing agents is oxygen. Organisms that utilize oxygen to get final products during respiration are termed as aerobic whereas those that do not use oxygen are called anaerobic. Energy released in the process of respiration to synthesize ATP is used to store the energy. The energy stored in ATP is later used in the processes that require or demand for energy and includes energy for movement among other daily duties that require energy both internally and externally. Categorized as ATP (Adenosine Triphosphate) is a multifunctional nucleotide that is endowed with a number of activities in the body. It plays a major role in cell biology. ATP is tasked in transport of energy (chemical energy) within the cells for the purpose of metabolism. This form of energy is normally produced during cellular respiration and is usually utilized by vast cellular processes and many enzymes. ATP is made of ADP (Adenosine diphosphate) or AMP (adenosine monophosphate). ATP is thus recycled on daily basis in the body of organisms (Richard, 2001).
Cellular respiration normally occurs in eukaryotic and prokaryotic cells. The stages involved in cellular respiration are citric acid cycle, glycolysis and electron transport. Cells can either derive energy aerobically (by use of oxygen) or anaerobically (without use of oxygen) glycolysis takes place anaerobically whereas aerobic will require oxygen (Neil, 1999)
Glycolysis process is the one that is responsible for the production of the adenosine Triphosphate (ATP) as a result of degrading glucose. The process of glycolysis does not make use of molecular oxygen, thus does it anaerobically and takes place in cytosol of the cell. The process of glycolysis can occur both in aerobic and anaerobic organisms. In simple terms, glycolysis can be said to be the process that sees the formation of pyruvic acid as a result of breakdown of glucose. There are ten steps that occur in glycolysis.
Step umber one involves phosphorylation of glucose molecules where by ATP creates sugar phosphate. Due to the negative charges, glucose molecules are able to remain inside the cell. The step that follows after this is the relocation of carbonyl oxygen. This process since it is reversible ends up creating a ketose. The hydroxyl group which is now located on the first carbon, is phosphorylated through ATP. The fructose 1which is a 6 carbon sugar, is sliced. The slicing leads to the creation of two 3 carbon molecules. One of 3 carbon molecules (glyceraldehydes) through glycolysis. Proceeds immediately the dihydroxyacetone phosphate is reorganized, to become glyceraldehyde 3-phosphate
Glyceraldehydes are then oxidized to form NADH and a proton. the enzyme phosphoglycerate kinase uses the power of glyceraldehydes oxidation to create an ATP molecule. The phosphate ester linkage is moved to carbon 2. This process leads to formation of a molecule of 2-phosphoglycerate. From which1 molecule of water is extracted, leading to the formation of phosphoenolpyruvate.
Water extraction facilitates the formation of a high-energy phosphate connection. The connection conveys energy to an ADP, forming an ATP. 2 molecules of NADH, 4 molecules of ATP, and 2molecules of 3 carbon sugars becomes the end product of glycolysis.
Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O
Oxidation of pyruvic acid
This step is very important for it acts as the link reaction between glycolysis and Krebs cycle. Oxidation of pyruvic acid leads to production of 1 NADH for each pyruvic that is oxidized as well as 3ATP. Pyruvic I oxidized to form acetyl-CoA and carbon dioxide by a cluster of enzymes that are found in mitochondria.
In aerobic respiration, oxygen is required for the release of energy which is in form of ATP. Here pyruvate is required to enter into mitochondrion for the fully oxidization by the Krebs cycle. The end product of this process is breakdown of glucose which results in release of energy, water and carbon dioxide. There is also phosphorylation, FADH2 and NADH2. Utilization of oxygen is very key in this form of respiration for it make cells be in a position to be provided with nutrients that are most essential as well as important in the provision of energy that all cells need to be able to live and operate effectively.
C6H12O6 (aq) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) ΔG = -2880 kJ per mole of C6H12O6
due to the reducing potential, FADH and NADH are further converted into ATP ( Richard, 2001).
After glycolysis, there is always the formation of pyruvate which undergoes more breakdowns, and in most cases it is through aerobic respiration in most of the living organisms. Under aerobic respiration, there are two distinct processes that takes place; the Krebs cycle and the electron transfer chain, whereby the two processes yields ATP in through chemiosmotic phosphorylation. The process involves break down of glucose by use of oxygen to release energy carbon dioxide and water. This can be summarized as follows (Shiresh, 2008).
C6H12O6 + 6O<2 -> 6CO2 + 6H2O + energy (ATP)
Various processes takes place in Krebs cycle that at the end of it all, number of processes will have taken place. All these processes are geared towards providing energy in the body that can be relied on to help the body carry various activities that demand for the presence of energy.During glycolysis, the pyruvate molecules that are produced usually contain a lot of energy that is between the bonds of their molecules. In order for this energy to be utilized, it is prerequisite for the cell to convert it into ATP.
Tricarboxylic acid cycle or also termed as the Krebs cycle is the step that follows after the glycolysis. In presence of oxygen, acetyl coenzyme A is formed from the pyruvate that happens during the process of glycolysis. With formation of acetyl-CoA, anaerobic or aerobic processes can occur. With the presence of oxygen aerobic respiration will take place in the mitochondria which will culminate into Krebs cycle. When the oxygen molecules are not available, there will be fermentation of the pyruvate molecules. When acetyl CoA enters the Krebs cycle, it gets oxidized to carbon dioxide and at the same time, NAD is reduced to NADH which can be utilized by electron transport chain to form more ATPs. In order to oxidize 1 molecule of glucose, it requires 2 acetyl-CoA in the Krebs cycle. The waste product of this process is water and carbon dioxide which are created during the cycle ( Cellular,2008).
Krebs cycle diagram
Before pyruvate enters into krebs cycle, it is converted into acetyl coenzyme A and this process is achieved when carbon dioxide molecule is removed from pyruvate as well as removal of electron in order to reduce NAD+ into NADH. When coenzyme A (an enzyme) is combined with the lest acetyl making acetyl coenzyme A which then is fed to Krebs cycle ( Cellular,2008).
Steps in citric acid cycle.
There are 8 steps and which involves 8 different enzymes. In the entire process of the Krebs cycle, acetyl-coA changes into citrate, oxaloacetate, isocitrate, succinyl-CoA, fumarate succinate, malate, and finally, α-ketoglutarate
When acetyl coenzyme A is combined with oxaloacetate from previous Krebs cycle, it forms citrate which is then converted to its isomer isocitrate.
This isocitrate is in turn oxidized after which it forms 5-carbon α-ketoglutarate. In this process, 1 molecule of carbon dioxide will be released and NAD+ will be reduced to NADH+.. α-ketoglutarate is oxidized to form succinyl co enzyme A leading to the formation of carbon dioxide and NADH2+. After this process, succinate gets oxidized to fumarate and converts FAD to FADH2. fumarate is hydrolyzed to malate. On the other side, malate gets oxidized to form oxaloacetate and reduces NAD+ to NADH2+. This cycle continues, and as a result of glycolysis, two molecules of pyruvate are produced from one glucose, thus each glucose is processed through the Krebs cycle twice.
Electron transport chain
At the Krebs cycle, FADH2 and NADH2+ are some of the products that are produced in the cycle. Then what happens to them? At this chain, the two products happen to be reduced and receives highly energized electrons from the molecules from the pyruvic acid that happens to have been dismantled from the Krebs cycle. At this point, they represent energy that is in available form to do work. The molecule carriers convey highly energized electrons and hydrogen protons to electron transport chain that is found in inner mitochondrial membrane. Through utilization of enzymes in the mitochondrial membrane NADH2+ gets oxidized to NAD+ and FADH2 gets oxidized to FAD. The highly energized electrons get transferred to ubiquinone (Q) as well as to cytochrome (C) molecules which are the electron carriers in the membrane. From here, electrons gets passed from one molecule to another and in the process, they lose some energy at each step. In the final stages, hydrogen atoms combine with oxygen to form water. These molecules that are involved in transporting these electrons are the ones that are called electron transport chain ( Richard, 2001).
In a nut shell, electrons delivered to the electron transport system provide energy that helps in pumping hydrogen protons to the inner side of the mitochondrial membrane to outer compartment. The highly concentrated hydrogen protons yields free energy that is very potential to use in doing work. There is movement of hydrogen protons down against the concentration gradient from outer to inner compartment. The only path that protons have is through enzymes in the inner membrane. It is thus true to say that protons pass in a channel that is always lined with enzymes. The freed energy from hydrogen protons is the one that is used to form ATP through phosphorylation and bonding of phosphate to ADP. The electrons from Krebs cycle having yielded their energy, combines with oxygen and forms water. When supply of oxygen is cut off, the flow of electrons and protons cease to take place and when this happens, there lacks enough power to synthesis ATP and this is the reason why human beings and other species can not survive for long without the presence of oxygen (cellular, 2008).
Living organisms can use ATP like a power supply. ATP provides energy and the power needed for various reactions simply by losing one of the phosphorous groups to form ADP. Food energy in the mitochondria can also be used in reversing the ADP to ATP necessitating availability of energy needed to perform work and other activities (Ibid)
In conclusion, cellular respiration is very key in the bodies of the living organisms. The whole process necessitates the availability of energy to the body of organism. For life to continue and other biological processes to take place, oxygen availability plays a very crucial role since it activates and enhances the availability of energy by facilitating break down of glucose to release energy and other by-products. Cellular respiration is essential and it is believed to help many organs remain alive as well as active. Through the processes that takes place in the three categories, it becomes possible to supply cells with required energy.
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