Metabolism refers to the way the body generates energy and otherspecific synthetic material and how these materials are furtherbroken down to generate energy. From the above definition,metabolism is classified into two areas: anabolism and catabolism.Anabolism refers to the process of energy generation during thesynthetic process where various biomolecules including protein,carbohydrates, nucleotides and fats are made. Catabolism refers tothe process of energy breakdown where the above biomolecules aredegraded to produce energy that is subsequently utilized running mostcellular process (Dashty, 2013). Energy generated in the body isalways in the form of ATP. Metabolism is largely important since itensures that cells within the body have the required amounts ofenergy to carry out various activities.In cases, where the cells maybe starved metabolic processes redirect some process to energygeneration while in cases where energy production is high metabolicprocesses are redirected to storage of associated biomolecules to beused in the future. This balance between anabolism and catabolismcellular life processes.
Metabolism is primarily classified depending on the type of reactionthat is taking place. Catabolic reactions involve the breakdown ofcomplex molecules into smaller molecules and the subsequent releaseof the molecules present in chemical bonds. The total amount ofenergy that is released is less compared to the energy presentlystored in the molecule. About 40% of the energy released through thevarious catabolic processes is transferred into ATP, the cellcurrency converter which is utilized in supporting most of thecellular processes within the body. Some of these processes includerepairing damaged tissue, building new tissue and maintaining the newcellular processes within the body. The residual 60 % of the energyis dissipated as heat. ATP consists of three molecules including aribose sugar, three phosphate bases, and adenine. A high energy bondexists between the second and third phosphate groups and remains thegreatest source of energy in any cell. When this bond is broken, theresulting molecules include ADP (adenosine diphosphate), andorthophosphate (Pi ) (van Eunen, Kiewiet, Westerhoff, &Bakker, 2012). Of all the existing biomolecules that are inexistent,carbohydrates remain the major source of energy in the body withglucose being the main sugar used to generate energy. Carbohydratesare largely classified as either monosaccharides, disaccharides orpolysaccharides (van Eunen et al., 2012). Sugar catabolism involvesthe breakdown of polysaccharides to monosaccharides with the majorsingle sugar unit being glucose. In lipids, triglycerides are theprimary source of fuel. Lipids are broken down through a processreferred to as beta oxidation. Excess fats are stored in adipocytesunder the skin. Proteins are made up of polymers with the monomersbeing individual amino acids. Some amino acids have been used in theenergy generation process though they are commonly utilized duringthe period of chronic starvation (Müller et al., 2012). Nucleicacids break to their constituent elements though these molecules arenot utilized to generate energy.
Anabolic reaction involves joining of the individual building blocksinto larger molecules. For carbohydrates, monosaccharides areconverted into polysaccharides amino acids are converted intoproteins while fats are converted into triglycerides. The generationof the larger molecules requires the use of energy that was generatedby catabolic processes. The body strives to ensure that there is abalance between anabolic and catabolic processes.
Metabolic reactions can be classified into three majorcategories based on the type of biomolecule under investigation.These categories include carbohydrate metabolism, lipid metabolism,and protein metabolism. The major anabolic process associated withcarbohydrate metabolism is glycogen synthesis while the maincatabolic processes include glycolysis and Kreb Cycle in whichglucose the most common sugar in the body is used to produce energy.Glycogenesis involves the conversion of glucose molecules intoglycogen and their subsequent storage in the liver and kidney(Müller et al., 2012). This process is controlled by several keyenzymes though the main enzyme is glycogen synthase that initiatesthe process immediately there is excess sugar. Several molecules ofATP are consumed during the conversion process. Catabolic reactionssuch as glycolysis occur when the levels of sugar molecules in thebody increase especially after a meal. Glycolysis breaks down glucosemolecules into pyruvate in the process releasing two net molecules ofATP. The Kreb Cycle and the Electron Transport Chain further breakdown the sugar molecule to produce about 32 molecules of ATP at theend of the reaction (Dashty, 2013). Glycolysis and glycogenesis aretwo processes that are driven by enzymes .
Protein catabolic processes involved deamination of amino acids toproduce components of the TCA cycle. For example, glutamate isconverted to glutarate and utilized in the generation of ATPmolecules. Glucogenic and Ketogenic amino acids are used in thecreation of intermediates which enter the TCA cycle. Some of theproducts of this cycle made from amino acids include pyruvate,acetoacetyl-CoA, acetyl-CoA, α-ketoglutarate, and oxaloacetate(Dashty, 2013). The energy generated by the above process is usedto drive polymerization of amino acids to proteins.
Lipid catabolism involves the breakdown of triglycerides and otherfatty acids to produce energy. The process known as beta oxidationbreaks down all fatty acids after carbohydrates have been depleted asthe major source of energy. Acetyl CoA is the major end product ofthis process and enters the TCA cycle to facilitate the generation ofenergy (van Eunen et al., 2012). Lipid anabolism involves the useof the energy generated to create fatty acids that are later storedas adipose tissue. Lipogenesis occurs when the amounts of glucosewithin the body are high.
Cellular Processes and Tissue Interactions
Metabolic processes take place within all cells of the body thoughthey do not occur at the same time within cells because cells requireenergy at different times. Nonetheless, all metabolic processes areintegrated as one. When cells require energy, glycolysis occurs inthe body resulting in the production of energy in the form of ATP.This process stops all other processes that preserve or consumeenergy. For example, lipogenesis is stopped immediately the processof glycolysis is initiated in the body. Another process that isstopped is glycogenesis or glycogen synthesis that seeks to convertsugar molecules into glycogen (Müller et al., 2012). When the bodyhas excess energy, the latter activities occur, and the rate ofglycolysis is reduced within the cell. These processes ensure thatcells have the requisite energy tp carry out its normal processessuch as cell repair and tissue development without any form ofinterruption caused by the lack of energy.
Specific metabolic process occurs in specific cells, and thereforethere is a need for all tissues to be integrated to ensure that allthe correct pathways are regulated during anabolic and catabolicreactions. For example, glycogen synthesis occurs in the liver whileglycolysis occurs in nearly all the other cells of the body. The twoprocess do not occur concurrently, and one has to inhibit the otherprocess to ensure that energy is utilized for the correct process.Enzymes and other signals are used to block antagonistic processesfrom running concurrently. All tissue interactions are integrated,and the activation of one pathway that results in the use of energywill automatically block all pathways that generate energy to preventa net loss of energy.
Hormonal Control and Feedback Loops
Carbohydrate metabolism is largely under the influence of severalhormones with insulin and glucagon being the major hormonescontrolling both anabolic and catabolic reactions. Insulin results inthe conversion of glucose into glycogen increased rate of glycolysisand conversion of excess sugar into fats while glucagon results inthe breakdown of glycogen to produce glucose and stimulation ofgluconeogenesis (van Eunen et al., 2012). The presence of insulinin the blood stream serves as an indicator that the body should startconserving energy while the presence of glucagon is an indicator thatthe body need to produce more energy. Protein and fat metabolism israrely under the influence of hormones.
Carbohydrate, protein and fat metabolic pathways involve a series ofpathways that are catalyzed by specific enzymes within the cell. Insome cases, enzymatic reactions regulate metabolic processes throughthe use of feedback loops. The formation of certain enzymes andproducts serve to inhibit or activate some specific pathways. Mostenzymes limiting the activity of other enzymes are considered tocatalyze the main reaction that results in the production of specificsubstrates that later produce energy. This method is referred to asnegative feedback. For example, the presence of glucose -6-phosphatase inhibits the activity hexokinase the rate limitingreaction in glycolysis (Stincone et al., 2015). Feedback loops alsogovern the action of insulin and glucagon. Positive loops ensure thestimulation of metabolic steps that take place in the latter stages.For example, hexokinase formation stimulates other enzymes thatpromote glycolysis. Neural control governs the activity of specifichormones such as epinephrine that ensure that metabolic processesrequired during flight and flight are active.
Homeostasis is defined as the process in which all the bodyfunctions act within the normal conditions or standards. Themetabolic process within the body ensures that there is sufficientenergy in the body to carry out all activities of the body. It alsoensures that all activities that generate and utilize energy arecontrolled through the use of feedback loops, enzymes, and hormone(Stincone et al., 2015). This allows for the normal body conditionsto exist within an individual. Metabolism achieves homeostasis thatensures proper functioning of all body organs.
One such modification will be an attempt to increase themuscle cell capacity. Muscle cells store glycogen which is commonlybroken down to produce glucose when an individual is engaged in anyform of physical activity. The glucose provided undergoes glycolysisto increase the amount of ATP that is required in conducting theexercise. By increasing the cell capacity, an individual will be ableto run or engage in any other physical activity for longer periodswithout necessarily getting tired. The second modification will beincreasing the number of adipose tissue cells within the body so thatan individual can preserve more fat that will be utilized in futureto generate energy. This will be essential in areas where peoplelargely die of hunger or where food is scarce. This means when thereis adequate food, more energy will be stored in the form of fats andutilized in the latter periods where food is scarce. Fats are thesecond energy sources that are utilized by the body immediately allthe carbohydrates sources have been depleted. Fat people tend tosurvive longer compared to people with lean body masses since theirfats are broken down during periods of starvation to support cellularfunction. This modification will change the anatomy of an individualand as a result are more likely to change physiology.
Such modifications have impacted negatively on homeostasis. All themetabolic processes present within an individual are supposed to beintegrated so that they are wholly controlled. The body as specificenzymes and hormones that already control some of this processes andthe body is conditioned in maintaining this activity through the useof its system.These modifications target specific areas of the bodythat are key in the metabolic processes and may alter the cellularactivity and more so the regulation of the various metabolic process.The presence of such modification would localize the action ofvarious hormones and enzymes in specific parts of the body only, andas a result, homeostasis will not be achieved. Atrophy is morelikely to occur in individuals where the specific modifications havebeen made. In addition, it is more likely for such modified areas tobecome the prime areas for disease progression.
Dashty, M. (2013). A quick look at biochemistry: Carbohydratemetabolism. Clinical Biochemistry.http://doi.org/10.1016/j.clinbiochem.2013.04.027
Müller, M., Mentel, M., van Hellemond, J. J., Henze, K., Woehle, C.,Gould, S. B., … Martin, W. F. (2012). Biochemistry and evolution ofanaerobic energy metabolism in eukaryotes. Microbiology andMolecular Biology Reviews : MMBR, 76(2), 444–95.http://doi.org/10.1128/MMBR.05024-11
Stincone, A., Prigione, A., Cramer, T., Wamelink, M. M. C., Campbell,K., Cheung, E., … Ralser, M. (2015). The return of metabolism:Biochemistry and physiology of the pentose phosphate pathway.Biological Reviews, 90(3), 927–963.http://doi.org/10.1111/brv.12140
van Eunen, K., Kiewiet, J. A. L., Westerhoff, H. V., & Bakker, B.M. (2012). Testing biochemistry revisited: How in vivo metabolism canbe understood from in vitro enzyme kinetics. PLoS ComputationalBiology, 8(4). http://doi.org/10.1371/journal.pcbi.1002483
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