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Metabolism Overview: Lipids, Carbs & Proteins · Acedra
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Metabolism Overview: Lipids, Carbs & Proteins
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Hello! In today's video, we shall learn in detail about Metabolism. By the end of this video, you'll have a clear understanding about lipids metabolism, beta oxidation of fatty acids, carbohydrate metabolism, protein metabolism, breakdown of amino acids, followed by steps to increase metabolism in our body. Let us begin with the introduction to metabolism. Metabolism is a sum total of all the reactions occurring within the cells of living organisms to sustain
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life. It is a biochemical pathway through which the cells obtain energy. Two types of metabolic pathways are Anabolic Pathways and Catabolic Pathways. Anabolic Pathways build up complex macromolecules from simpler substances by utilizing energy. Anabolic pathways are sequences of enzyme catalyzed reactions. Examples are formation of glucose from carbon dioxide and synthesis of proteins from amino acids. Catabolic Pathways involve the breakdown or degradation of
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complex organic molecules into simpler ones with the release of energy. Examples- Proteins are converted into different amino acids, lipids or fats are broken down into fatty acids and glycerol and carbohydrates are degraded to simple sugars. Both the pathways are associated with each other through reactions of phosphate transfer involving Adenosine monophosphate (AMP), Adenosine diphosphate (ADP), Adenosine triphosphate (ATP) and also through electron transfer. Now,
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let us first understand lipid metabolism. It is the synthesis and degradation of lipids in cells and storage of fats for energy requirement. Lipids are synthesized in the liver. Fatty acids and triglycerides are the two important components in lipid metabolism. Lipids are metabolized mainly in the liver and in adipocytes. By the way, if you're getting some value out of this video, please like and share this video, so that all of us can learn, unlearn and relearn together. Also,
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please consider subscribing the channel and press the Bell icon to get instant notification of all the upcoming videos. Now, let us continue with lipid metabolism. Metabolic processes include lipid digestion, lipid absorption, lipid transportation, lipid storage, catabolism and biosynthesis. Pancreatic lipase help in the hydrolysis of triglycerides into fatty acids and glycerol units. Majority of the lipid digestion and absorption occurs
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when the fats reach the small intestine. Fatty acids and glycerol along with cholesterol aggregate to form a structure called Micelle. Fatty acids and monoglycerides separate out from the micelle, move across the intestinal mucosa and are again resynthesized and transported to liver or adipose tissue. Triglycerides and cholesterol form Chylomicrons which are amphipathic structures and help in transporting digested lipids. Triglycerides and cholesterol
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enter the lymphatic system and are transported to circulatory system. They may enter the liver or may be stored in adipocytes or fat cells. Very low density lipoproteins (VLDL) transport the triglycerides synthesized by our body and low density lipoproteins (LDL) transport cholesterol to the peripheral tissues. Lipoprotein lipase enzyme helps to hydrolyze very low density lipoproteins (VLDL) which are rich in triglycerides. VLDL particle size decreases and
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is converted into LDL particles which transport cholesterol to the peripheral tissues. HDL is the smallest and densest lipoprotein which returns excess cholesterol to the liver. Triglycerides get stored in white adipose tissue. Chylomicrons or other lipoproteins release triglycerides in the presence of enzyme lipoprotein lipase. Triglycerides further break down into fatty acids and glycerol before entering the cells. Cholesterol travels through blood and reaches
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the liver. The enzymes of lipid biosynthesis are distributed between the cytosol and inner membrane. The major class of membrane lipids are the glycerophospholipids. Synthesis of glycerophospholipids begins in the endoplasmic reticulum. A series of reduction and acylation reactions takes place which leads to the formation of phosphatidic acid. From phosphatidic acid, glycerophospholipids are formed by the addition of a polar head group.
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Triglycerides can be synthesized by either the glycerol 3-phosphate or monoacylglycerol pathway. Phosphatidic acid in the presence of enzyme phosphatidic phosphatases gets converted into Diacylglyceride which in the presence of enzyme acyltransferase forms triglyceride in the cytosol. Triglyceride synthesis occurs in the liver and in the adipose tissues. Lipogenesis is a process that converts carbohydrates and proteins into fatty acids. When glucose level is high,
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excess acetyl coenzyme A from glycolysis is used to form fatty acids, triglycerides, cholesterol, steroids and bile salts. These fatty acids and fatty acids from dietary fats combine with glycerol and form triglycerides. These triglycerides reach the VLDL particles and are released into the bloodstream for transportation to the peripheral tissues. Lipolysis is the breakdown of triglycerides into glycerol and fatty acids. It takes place in the cytoplasm
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and is regulated by glucagon and adrenaline hormone. The resulting fatty acids are oxidized by beta oxidation into acetyl co-enzyme A. Next, let us learn about beta oxidation of fatty acids. Beta oxidation is a process by which fatty acids are broken down to produce energy. Oxidation of fatty acids is initiated on the outer mitochondrial membrane. A long chain fatty acid gets activated by the addition of co-enzyme A and it enters the
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beta oxidation pathway. This takes place in the presence of acyl coenzyme A synthetase in the presence of enzyme ATP. Fatty acyl coenzyme A thus formed diffuses into the inner mitochondrial membrane. Here it combines with a carrier molecule Carnitine in the presence of Carnitine acyltransferase enzyme. The acyl-carnitine derivative is converted back to fatty acyl coenzyme A when it reaches the mitochondrial matrix. Acyl coenzyme A dehydrogenase oxidizes
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fatty acyl coenzyme A molecule. A trans double bond is formed between Carbon 2 and Carbon 3 to produce Trans delta 2-enoyl co-enzyme A. FAD acts as an electron acceptor and gets reduced to Flavin-adenine dinucleotide (FADH2). Trans delta 2-enoyl coenzyme A is hydrated by Enoyl coenzyme A hydratase to produce L-3-Hydrooxyacyl coenzyme A. L3-Hydroxyacyl coenzyme A in the presence of enzyme 3-hydroxyacyl co-enzyme A dehydrogenase gets dehydrogenated to form beta ketoacyl
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coenzyme A. NAD+ acts as an oxidizing agent or an electron acceptor. Thiolysis occurs between Carbon 2 and Carbon 3 i.e. alpha and beta carbons of beta ketoacyl coenzyme A. Beta-ketothiolase enzyme catalyzes the reaction leading to the cleavage of the bond between alpha and beta carbon. It is a thiolytic reaction producing one molecule of acetyl coenzyme A and a fatty acyl coenzyme A. This process continues until the entire chain is adhered to acetyl coenzyme
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A units. Acetyl co-enzyme A may enter the citric acid cycle NADH and FADH2 which are produced by both beta oxidation and TCA cycle are used in the electron transport chain (ETC) to generate ATP. Acetyl coenzyme A may be used for the formation of ketone bodies or it may serve as the starting material for the synthesis of fatty acids. Next is Carbohydrate Metabolism. Four major Pathways of carbohydrate metabolism are- Glycolysis- breakdown of glucose to
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pyruvate. Gluconeogenesis- synthesis of glucose from non-carbohydrate source. Glycogenesis- synthesis of glycogen. Glycogenolysis- breakdown of glycogen. Glycolysis is the process of breaking a molecule of glucose into two pyruvate molecules and generating two high energy ATP molecules and two electron carrying NADH molecules. Glucose in the presence of ATP, NAD+ and inorganic phosphate,
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breaks down into two pyruvate molecules generating 4 ATP molecules for a net yield of 2 ATP and NADH coenzymes. Glycolysis generates energy for the cell and forms pyruvate molecules that can be used in Krebs cycle or may be used later for synthesis of glucose through gluconeogenesis. We have learnt about glycolysis in detail in one of our previous video. I will leave a link of the video. You can watch the video for complete understanding of Glycolysis. Next,
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Gluconeogenesis- It is a metabolic pathway, that results in the production of glucose from certain non-carbohydrate substrates. It occurs mainly in the liver and kidneys. Gluconeogenic substrates include lactate, glycerol, amino acids etc. Enzymes such as Glucose-6-phosphatase, Fructose-1,6-bisphosphatase, pyruvate carboxylase etc play an active role in the production of glucose. Gluconeogenesis is stimulated by hormones glucagon, epinephrine, growth hormone and
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cortisol. Gluconeogenesis reverses Glycolysis. It maintains blood glucose levels during starvation. Next, let us take up Glycogenesis. It is the process of synthesizing glycogen from glucose. Glucose in the presence of hexokinase enzyme and ATP molecule and Magnesium ions gets converted into Glucose-6-phosphate. Glucose-6-phosphate forms Glucose-1-Phosphate in the presence of magnesium ions and phosphoglucomutase enzyme. Glucose-1-Phosphate gets attached
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to UTP by enzyme Glucose-1-Phosphate transferase or pyrophosphorylase forming UDP-glucose. With the help of alpha-1,4-glycosidic linkage, glycogen synthase adds glucose to the glycogen primer and forms a linear chain of 10 to 12 glucose residues. The branching enzyme Glycosyl transferase attaches few glucose units by alpha-1,6-linkage creating a branching point. Linear chain and branching
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points are repeated and glycogenesis is completed. Glycogenolysis is the process in which degradation of glycogen occurs resulting in the formation of glucose. Glycogenolysis occurs in the liver, muscles and adipose tissue. In the muscle cells, adenyl cyclase and cyclic adenosine monophosphate (cAMP) activate enzyme Phosphokinase. Phosphorylase b gets converted to Phosphorylase a, which catalyzes the breakdown of glycogen. Glycogen Phosphorylase in the presence of
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inorganic phosphate brings about the cleavage of alpha-1,4 linkage to form Glucose-1,4-Phosphate. Phosphorylase acts on the non-reducing ends of glycogen branches and releases Glucose-1-Phosphate. 1,4-Glycosyl residues are removed one by one from the non-reducing ends of glycogen chains, until 4 glucose residues remain on either side of an alpha-1,6 branch. Enzyme glucan transferase exposes the alpha-1,6 branch point. Alpha-1,6 glucosidic linkage is
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hydrolyzed by enzyme glucosidase. It results in the formation of Glucose-1-Phosphate and one free glucose molecule. Glycogenolysis is stimulated by hormones glucagon and epinephrine or adrenaline. Glucagon is released from pancreas when the blood sugar level is low in order to maintain adequate blood glucose levels. Epinephrine is excreted during the fight or flight responses. Glycogen breakdown in muscle cells give instant resource of Glucose-6-Phosphate for glycolysis. Next,
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let us try to understand Protein Metabolism. It is a biochemical process which brings about the synthesis of proteins and amino acids by anabolism or is responsible for the breakdown of proteins by catabolism. Central dogma of protein synthesis was forwarded by Crick. It postulates that genetic information flows from nucleic acids to protein. The first step of central dogma is known as Transcription. It is the formation of mRNA on DNA template in the presence of DNA
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dependent RNA polymerase. Genetic information from DNA is copied into RNA. The second step of central dogma is Translation. In this process, ribosomes use mRNA template to synthesize proteins. The sequence of codons on the mRNA strand is decoded and accordingly the amino acids are joined together by peptide bonds to form a polypeptide chain that makes proteins. The different steps in protein synthesis are as follows- In the presence of enzyme Aminoacyl-synthetase, the amino acid
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molecule is activated and each amino acid gets attached to the specific tRNA molecule to form aminoacyl complex. Formation of initiation complex requires mRNA having codons for a polypeptide, sub-units of ribosomes, initial amino acid tRNA complex, ATP and GTP. The mRNA always has first triplet codon as AUG. The amino acid tRNA complex gets attached to the start codon AUG. In protein synthesis, the peptide chain grows in a particular sequence. After initiation, the process
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of elongation starts by the formation of peptide bonds between the successive amino acid molecules. Enzyme Peptidyl transferase, GTP molecules and transfer factors play a crucial role in this process. Each tRNA complex brings a specific amino acid to the decoding site, moves to the condensing site and transfers the amino acid to the carboxyl end of the polypeptide. Finally, it moves to the exit site and the polypeptide chain is released from the ribosome. When the mRNA reaches the
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termination codon (UAA / UGA / UAG), a complete polypeptide chain is released along with a free tRNA molecule. The released polypeptide chain possesses its primary structure, some portion has secondary structure in the form of an alpha helix. The protein chain may form tertiary and quaternary structures. Protein catabolism is the breakdown of proteins into peptides and finally into amino acids. The stomach and the pancreas release endopeptidases which cleaves the polypeptide chain
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between particular amino acid residues. Hydrolysis of protein linkages occurs with the action of gastric juice and active enzyme pepsin. Trypsin, chymotrypsin, carboxypeptidases synthesized by pancreas break the polypeptide into amino acids. Free amino acids are absorbed into the bloodstream and are transported to various cells for further breakdown by facilitated and active transport mechanism. The amino acids can be degraded further to their carbon and nitrogen skeletons.
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The amino acids undergo certain reactions like transamination followed by deamination for the liberation of ammonia. During transamination, transfer of amino acid alpha-amine group to a alpha-keto acid takes place. The amino acid becomes a keto acid and the alpha-keto acid is converted into corresponding amino acid. It takes place in the presence of enzyme transaminase.
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By transamination, amino acid gets densed in glutamate. Glutamate is the only amino acid in mammals that undergo oxidative deamination. Deamination of glutamate forms toxic ammonia which is converted into urea. Urea is the end product of protein metabolism. Urea is synthesized in the liver by using 2 molecules of ammonia and 1 molecule of carbon dioxide. It is then incorporated into urine in the kidney to be excreted from the body. There
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are certain steps to increase metabolism. Make exercise a part of your routine as it burns more calories in less time. Exercise also helps to control blood sugar spikes after meals. Drink enough water as it is necessary for optimal metabolism. Include protein in your diet as it causes rise in thermic effect of food (TEF). Extra calories are required to digest and absorb various nutrients in the body. Sleep well as it plays a vital role in regulating metabolism and
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appetite. Eat regular meals. The caffeine in coffee stimulates the central nervous system. It may increase energy expenditure and may help in reducing the weight of the body. So today, we have learnt in detail about lipid metabolism, carbohydrate metabolism and protein metabolism. I have some practice questions for you. Please share your answers in the comment section below. You can pause the video and write down the questions if you like. Thank
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you so much for your time and participation. If you haven't subscribed to my channel yet, please consider subscribing the channel and press the Bell icon to get instant notification of all the upcoming videos. Also, if you want to discuss any particular topic in Biology, please mention that in the comment section below. I'll see you there. Goodbye! All the Best!
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