Animal Biochemistry Definition
Basically, biochemical is the type of chemicals that can be found in living organisms. So, biochemistry can be defined as the branch of chemistry that study about chemicals that are found in living organisms from plants, animals, even to human. Biochemistry is the science that studies about molecules and chemical reactions that are catalyzed by enzymes that occur in all living organisms. So, biochemistry is the type of chemistry that studies about chemicals and processes that occur in the body of living organisms as the way to understand the process of life from perspective of chemistry.
As science, animal biochemistry is a branch of science that studies about structure and function cellular components such as protein, carbohydrate, lipid, nucleic acids, and other biomolecules in animals. These days biochemistry is more focused specifically in chemical reactions that involve enzymes and the characteristics of protein. Biochemistry of cell metabolism is also studied commonly these days as well. Other disciplines in biochemistry are the study of genetic codes (DNA and RNA), protein synthesis, cell membrane transportation, and signal transduction.
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1. Biomolecules in Biochemistry
One of the most essential aspects in biochemistry is biomolecules. According to the definition of biochemistry, there are four main classes of molecules that are studied in biochemistry. These molecule classes are lipid, protein, carbohydrate, and nucleic acid.
There are many biological molecules that are considered as polymer. In this case, monomer is micromolecules that are relatively small that merge together and form macromolecules that are known later as polymer. When several monomers merge together to synthesize a biological polymer, these monomers go into a process that is known as dehydration synthesize.
Carbohydrate is a polymer that is formed by monomer that is known as monosaccharides. There are several examples of monosaccharides such as glucose (C6H12O6), fructose (C6H12O6), and deoxyribose (C5H10O4). When two monosaccharides go through dehydration synthesize process, water will be formed because two hydrogen atoms and an oxygen atom are released from two groups of hydroxyl monosaccharide.
The function of carbohydrate is as the source of energy and cell constructor. Sugar is categorized as carbohydrate. However, not all carbohydrates are sugar. The amount of carbohydrate in the universe is more than the amount of any biomolecules.
Lipid is usually formed from a glycerol molecule that bond with other molecules. In triglyceride, there is a glycerol molecule and three fatty acid molecules. Fatty acid is a monomer. Lipid, especially phospholipids, is also used in several products of drug such as solvent material (like in parenteral infusion) or as component of drug carrier (like in liposome or transfersome).
Protein is a very large molecule or also known as macrobiopolymer that is formed by a group of carboxyl, a group of amino acid, and side chain (known as “R” group). This “R” group is the one that will make each amino acid different and the characteristics of this side chain will affect the overall characteristics of a protein. When amino acids are merged, they will form special bond that is called peptide bond through dehydration synthesize process and became polypeptide or protein.
Nucleic acid is the molecule that forms DNA. DNA is a substance that is very important that is used by all cellular organisms to store the genetic information. The types of nucleic acid that are most common are deoxyribose nucleic acid and ribonucleic acid. The monomer of nucleic acid is called nucleotide. The most common nucleotides are adenine, cytosine, guanine, thymine, and uracil. Adenine pairs with thymine and uracil. Thymine only pairs with adenine. Cytosine and guanine only pair with one another.
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2. Animal Biochemistry Synthesis
Here are the sub-branches of animal biochemistry synthesis:
- Lipid Synthesis
Lipid can be synthesized from carbohydrate and protein since in metabolism these three compounds meet in Krebs cycle. Most of these encounters occur through the main gate of Krebs cycle which is co-enzyme A Acetyl. As the result, these three compounds can fill each other as the material that forms all of those substances. Lipid can be formed by protein and carbohydrate while carbohydrate also can be formed by lipid and protein and so on.
Lipid can be synthesized from carbohydrate. Glucose can be broken into pyruvic and this process will create glycerol. Glucose also can be transformed into phosphate sugar which will be turned into acetyl co-A which will be turned again into lipid acid. Glycerol and lipid acid will form lipid. Lipid also can be synthesized from protein as well. Protein will be broken into protease amino acid.
- Protein Synthesis
Protein synthesis that occurs in the cell involves DNA, RNA, and ribosome. The merger of amino acid molecules in large amount will form polypeptide molecule. Basically, protein is a polypeptide. Each cell in organisms can synthesize certain types of protein based on their needs. Protein synthesis in cell can occur since on the nucleus there are substances that play major role as “protein synthesis regulator”. These substances are DNA and RNA.
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3. Carbohydrate Metabolism
Glucose is considered as the most essential types of carbohydrate. Carbohydrate from foods will be absorbed to the blood stream in the form of glucose. Carbohydrate is also conversed in liver in the form of glucose as well. Other form of carbohydrate can be formed inside the body from glucose. Glucose is the main source of energy for metabolism in mammals’ tissue (except for ruminants) and the universal source of energy for fetus. Glucose can be modified into other types of carbohydrate with very specific function.
For example, glycogen is used as reserved energy, ribose in the form of nucleic acid, galactose in milk lactose, in certain lipid complex compounds, and in combined form with protein such as glycoprotein and proteoglycan. The event that is experienced by foods’ substances after they are digested and absorbed is known as intermediate metabolism.
So, the study of intermediate metabolism covers a very wide discipline that tries to understand not only about metabolism pathways that are experienced by each molecule but also the interrelation and mechanism that control the metabolism flow that pass on those metabolism pathways. Metabolism pathways can be categorized into three categories:
- Anabolic pathway (the merger/forming). This is the pathway that is used in synthesis of compounds that from structures and body organs. One of examples of this category is protein synthesis.
- Catabolic pathway (the breakage). This pathway consists of various oxidation processes that release free energy, usually in the form of high energy phosphate or equivalent reductor substances such as respiration chain and oxidative phosphorylation.
- Amphibolic pathway (the intersection). This pathway has more than one function and can be found in metabolism intersection so that it works as the connector between anabolic pathway and catabolic pathway. The example of this category is citric acid cycle.
Carbohydrate Metabolism Pathways
There are several carbohydrate metabolic pathways, whether it’s categorized as catabolism or anabolism. These pathways are glycolysis, pyruvic oxidation, citric acid cycle, glycogenesis, glycogenolysis, and gluconeogenesis. Shortly, the carbohydrate metabolism pathways can be explained as below:
- Glucose as the main source of energy will be broken through glycolysis into two pyruvics if there is oxygen available. In this phase, energy will be released in the form of ATP.
- After that, each pyruvic will be oxidized into Co-A Acetyl. In this phase, energy will be released in the form of ATP.
- Co-A Acetyl will go to the intersection pathway which is citric acid cycle. In this phase, energy will be released in the form of ATP.
- If the amount of glucose is more than the needs of energy, then glucose will not be broken. Instead, it will be assembled into glucose polymer (known as glycogen). Glycogen will be stored in liver and muscles as short term energy reserve. If the capacity of glycogen storing is full, then the carbohydrate will be converted into lipid tissue as long term energy reserve.
- If there is a lack of glucose from diet as the source of energy, then glycogen will be broken into glucose. After that, glucose will go through glycolysis and followed by pyruvic oxidation and citric acid cycle.
- If glucose from diet is not available and the glycogen reserve is also not available, then non-carbohydrate energy source which is lipid must be used. This pathway is known as gluconeogenesis (the forming of new glucose) since lipid and protein must be modified into new glucose that will go through catabolism to acquire energy.
Glycolysis occurs in cytosol of all cells. This catabolism pathway is the process of breaking the glucose into:
- Pyruvic acid in aerobe environment.
- Lactate acid in anaerobe environment.
Glycolysis is the main pathway of glucose metabolism so that pyruvic acid can be formed. After that, the Co-A Acetyl will be available for oxidize in citric acid cycle. Besides that, glycolysis also became the main pathway of fructose and galactose metabolism.
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4. Amino Acid Metabolism
There are about 75% of amino acids that are used for protein synthesis. These amino acids can be acquired from protein that you consume or from the result of protein degradation in body. Protein degradation is a continuous process. This is because the protein in body is replaced continuously (protein turnover). Amino acids also provide nitrogen for:
- Nitrogen alkali structure of DNA and RNA.
- Heme and other similar structures such as myoglobin, hemoglobin, cytochrome, and enzyme.
- Acetylcholine and other neurotransmitter.
- Hormone and phospholipids.
Besides providing nitrogen, these amino acids can also be used as energy source when the nitrogen is released.
Main Metabolic Pathways of Amino Acids
Main metabolic pathways of amino acids consist of four stages. The first stage is amino acids production from the breaking of body protein, protein digestion, and amino acids synthesis in liver. The second stage is the taking of nitrogen from amino acids. The third stage is amino acids catabolism into energy though acid cycle and urea cycle as step of processing the side result of amino acids breaking. The fourth stage is protein synthesis from amino acids.
Amino Acids Catabolism
Amino acids can’t be stored in body. If the amount of amino acids is excessive or if there is a lack of other energy sources (protein and carbohydrate), the body will use amino acids as the source of energy. Unlike lipid and carbohydrate, amino acids require the release of amine group. This amine group then will be discarded since it’s toxic to the body. There are two stages of the release of amine group from amino acids. These stages are:
- This is the process when aminotransferase moves the amine to α-ketoglutarate and produce glutamate or moves the amine to oxaloacetate to produce aspartate.
- Oxidative deamination. This is the process of the release of amine from glutamate to produce ammonium.
Amino Acids Synthesis
All tissues have ability to synthesize non essential amino acids, perform remodeling of amino acids, and change the carbon structure of non amino acids into amino acids and other derivatives that contain nitrogen. However, liver is the main place where nitrogen metabolism occurs.
In the condition of diet surplus, potential toxic nitrogen of amino acids is released through transamination, deamination, and urea formation. Carbon structure usually will be modified into carbohydrate through gluconeogenesis pathway or become fatty acids through fatty acids synthesis pathway. Related to this, amino acids are categorized into three categories which are glucogenic amino acids, ketogenic amino acids, and glucogenic and ketogenic amino acids.
Glucogenic amino acids are amino acids that can go to pyruvic production pathway or citric acid intermediate cycle such as oxaloacetate and α-ketoglutarate. All of these amino acids are the precursor for glucose through gluconeogenesis pathway. All amino acids except lysine and leucine contain glucogenic property. Lysine and leucine are amino acids that are ketogenic only that only can go to Co-A Acetyl intermediate or Co-A acetoacetyl.
A little group of amino acids that consists of isoleucine, phenylalanine, threonine, tryptophan, and tyrosine are glucogenic and ketogenic. Finally, we should know that there are three possibilities of the utilization of amino acids. During the hunger, the reducing of carbon structure is used for producing energy with oxidation process of CO2 and H2O.
Meanwhile, from 20 types of amino acids, there are some that can’t be synthesized by body so that you should get them from foods. This type of amino acids is known as essential amino acids. The rest of them are amino acids that can be synthesized from other amino acids. This type of amino acids is known as non essential amino acids.
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5. Animal Biosynthesis
Here are the brief explanation of sub-branches of animal biochemistry:
- Biosynthesis of Glutamate and Aspartate
Glutamate and aspartate are synthesized from α-keto acid with simple transamination reaction. The catalysator of this reaction is glutamate dehydrogenase enzyme and after that by aspartate aminotransferase. Aspartate is also derived from asparagine with help from asparaginase. The important role of glutamate is as main intercellular amino donor for transamination reaction. Aspartate plays a role as ornithine precursor for urea cycle.
- Biosynthesis of Alanine
Alanine is transported to circulation by various tissues but usually by muscles. Alanine is formed by pyruvic. Liver accumulate plasma alanine which is the reverse version of transamination that occurs on muscles and proportionally increase the production of urea.
Alanine is transported from muscles to the liver together with glucose transportation from liver to muscles. This process is called glucose-alanine cycle. Main key of this cycle is that in a molecule of alanine the periphery tissue export pyruvic and ammonia to liver where the carbon structure is recycled and most of nitrogen is eliminated. There are two main pathways to produce muscle alanine which are:
- Directly through protein degradation.
- Through pyruvic transamination with help from alanine transaminase enzyme (which is also known as glutamate-pyruvic transaminase serum)
- Biosynthesis of Tyrosine
Tyrosine is produced in cells with phenylalanine hydroxylation. Half of phenylalanine is needed to produce tyrosine. If the diet is rich of tyrosine it will reduce the needs of phenylalanine up to 50%. Phenylalanine hydroxylase is the combination of oxygenase function. An oxygen atom is combined to water and the other id combined to hydroxyl group from tyrosine. Reductant that is produced is tetrahydrofolate cofactor tetrahydrobiopterin that is maintained in reducted status by NADH-dependent enzyme dihydropteridine reductase.
- Biosynthesis of Ornithine and Proline
Glutamate is the precursor of ornithine and proline. With glutamate, semialdehyde became intermediate branch point to one of two products or others. Ornithine is not one of 20 amino acids that are used for protein synthesis. Ornithine plays major role as carbamoyl phosphate acceptor in urea cycle. Ornithine also has additional role as precursor for polyamine synthesis. The production of ornithine from glutamate is important when arginine diet as other source for ornithine is limited.
The use of glutamate semialdehyde depends on cellular condition. Ornithine production from semialdehyde is through the reaction of glutamate-transamination dependent. When the concentration of arginine is increased, ornithine is acquired from urea cycle and added from glutamate semialdehyde that block the aminotransferase reaction. As the result, semialdehyde accumulation occurs. Semialdehyde is recycled spontaneously into Δ1pyrroline-5-carboxylate that later will be reducted into proline by NADPH-dependent reductase.
- Biosynthesis of Serine
The main pathway for serine begins from intermediate glycolytic 3-phosphogliserate. NADH-linked dehydrogenase changes 3-phosphogliserate into a keto acid which is 3-phosphopyruvic according to subsequent transamination. The activity of aminotransferase with glutamate as donor produces 3-phosphoserin that is modified into serine by phosphoserine phosphatase.
Meanwhile, animal biochemistry is a branch of science in chemistry which is the study about structure and function cellular components in animals. Thus, animal biochemistry
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