BIO Lect Week 6.1 Metabolism Glyc. PDF

Metabolic Pathways: what they are and the two major types The processes of making and breaking down sugar molecules illustrate two types of metabolic pathways. A metabolic pathway is a series of interconnected biochemical reactions that convert a substrate molecule or molecules, step-by-step, throu...

Metabolic Pathways: what they are and the two major types The processes of making and breaking down sugar molecules illustrate two types of metabolic pathways. A metabolic pathway is a series of interconnected biochemical reactions that convert a substrate molecule or molecules, step-by-step, through a series of metabolic intermediates, eventually yielding a final product or products. In the case of sugar metabolism, the first metabolic pathway synthesized sugar from smaller molecules, and the other pathway broke sugar down into smaller molecules. These two opposite processes—the first requiring energy and the second producing energy—are called anabolic (building) and catabolic (breaking down) pathways, respectively. Consequently, building What ever you choose to eat….eat it! We need food!! This does’nt work Practitioners of breatharianism do not believe in eating food or drinking water; they believe that they can survive on “prana” (the Hindu concept of energy or lifeblood) provided from solar rays, the air, and the energy around them. Digestion: catabolic pathways https://www.youtube.com/watch?v=X3TAR OotFfM GLUCOSE Glucose absobtion is mediate by the Na+ ion gradient (facilitated diffusion) Cotransport of the glucose, and Na+ is driven by a Na+ concentration gradient that is established by the sodium-potassium pump. Diffusion of Na+ down its concentration gradient provides the energy to trans-port glucose across the cell membrane  LIPIDS Lipase, secreted by the pancreas, digests lipid molecules. The primary products of this digestive process are fatty acids and monoglycerides. The first step in lipid digestion is emulsification, by which large lipid droplets are transformed into much smaller droplets. Emulsification is In the intestine, bile salts aggregate around small droplets of digested lipids accomplished by bile to form micelles (small morsels). The hydrophobic (water-fearing) ends of salts secreted by the the bile salts are directed toward the lipid particles, and the hydrophilic liver. The enzymes (water-loving) ends are directed outward, toward the water environment. that digest lipids When a micelle meets the epithelial cells of the small intestine, the lipids, are soluble in water fatty acids, and monoglyceride molecules pass, by simple diffusion, from and can digest the the micelles through the cell membranes of the epithelial cells.  … LIPIDS Once inside the intestinal epithelial cells, the fatty acids and monoglycerides are recombined to form triglycerides. These, and other lipids, are packaged inside a protein coat. The packaged lipid- protein complexes, or lipoproteins, are called chylomicrons. The lymphatic system carries the chyle to the liver, where the Chylomicrons leave the lipids are stored, converted into other molecules, or used as epithelial cells and enter energy. They are also transported to adipose tissue, where they are the lacteals, lymphatic stored until an energy source is needed elsewhere in the body. capillaries within the intestinal villi. Lymph containing large amounts of absorbed PROTEIN S Pepsin is an enzyme secreted by the stomach that breaks down proteins, producing shorter amino acid chains called polypeptides. Only about 10–20% of the total ingested protein is digested by pepsin. After the remaining proteins and polypeptide chains leave the stomach and enter the small intestine, the enzymes trypsin, chymotrypsin, and carbo xypeptidase, produced Absorption of tripeptides, dipeptides, or individual amino acids occurs through the by the pancreas in their intestinal epithelial cells by various cotransport mechanisms. Brush border and inactive forms and basolateral membranes are crossed by amino acids and di-tripeptides by activated in the passive (facilitated or simple diffusion) or active (Na+ or H+ co- intestine, continue the transporters) pathways. Within the intestinal epithelial cells, tripeptides and digestive process. These dipeptides are broken down into amino acids. The amino acids then enter blood enzymes produce small capillaries in the villi and are carried by the hepatic portal vein to the liver. The peptides, which are further amino acids may be modified in the liver, or they may be released into the broken down into tripeptides bloodstream and distributed throughout the body. (three amino acids), The non-absorbed peptides are digested and fermented by colonic bacteria resulting short-chain fatty acids, dicarboxylic acids, phenolic Amino acids are actively transported into the various compounds and ammonia. cells of the body. This transport is stimulated by growth hormone and insulin. Most amino acids are Short-chain fatty acid provides used as building blocks to form new proteins, but energy for colonocytes, and bacteria some may be metabolized, with a portion of the and the ammonia not fixed by released energy used to produce ATP. bacteria returns to the liver for ureagenesis. The body cannot store excess amino acids. Instead, they are partially broken down and used to synthesize glycogen or lipids, which can be stored. The body can store only small amounts of glycogen, so most of the excess amino acids are converted to lipids. Consider endergonic reactions (anabolism), which require much energy input, because their products have more free energy than their reactants. Within the cell, from where does energy to power such reactions come? The answer lies with an energy-supplying molecule scientists call adenosine triphosphate, or ATP. This is a small, relatively simple molecule, but within some of its bonds, it contains the potential for a quick burst of energy that can be harnessed to perform cellular work. ATP powers most energy-requiring cellular reactions. Adenosine is a nucleoside consisting of the nitrogenous base adenine and a five-carbon sugar, ribose. The three phosphate groups, in order of closest to furthest from the ribose sugar, are alpha, beta, and gamma. However, not all bonds within this molecule exist in a particularly high-energy state. Both bonds that link the phosphates are equally high-energy bonds that, when broken, release sufficient energy to power a variety of cellular reactions and processes. These high-energy bonds are the bonds between the second and third (or beta and gamma) phosphate groups and between the first How ATP hydrolysis energy release When ATP hydrolyzes, its gamma performs work inside the cell? This phosphate does not simply float depends on a strategy called energy away, but it transfers onto the coupling. Cells couple the ATP working protein. This process of a hydrolysis' exergonic reaction allowing phosphate group binding to a them to proceed. molecule is called phosphorylation. As with most ATP hydrolysis cases, a phosphate from ATP transfers onto another molecule. In a phosphorylated state, the working protein has more free energy and is triggered to undergo a conformational change. This change allows it to work. Essentially, the energy released from the ATP hydrolysis couples with the energy required to power Electron Carriers In living systems, a small class of compounds functions as electron shuttles: they bind and carry high-energy electrons between compounds in biochemical pathways. The principal electron carriers we will consider are derived from the B vitamin group and are derivatives of nucleotides. These compounds can be easily reduced (that is, they accept electrons) or oxidized (they lose electrons). Nicotinamide adenine dinucleotide (NAD) is derived from vitamin B3, niacin. NAD+ is the oxidized form of the molecule; NADH is the reduced form of the molecule after it has accepted two electrons and a proton (which together are the equivalent of a hydrogen atom with an extra electron). Note that if a compound has an “H” on it, it is generally reduced (e.g., NADH is the reduced form of NAD). When electrons are added to a compound, it is reduced, that means full of Chemical Potential Energy When electrons are removed from a compound, it is oxidized, that means with no more Nearly all the energy used by living cells comes to them in the bonds of the sugar glucose. Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. In fact, nearly all living organisms carry out glycolysis as part of their metabolism. The process does not use oxygen directly and https://youtu.be/hDq1rhUk therefore is V-g termed anaerobic. Glycolysis During cellular metabolic reactions, such as nutrient synthesis and breakdown, certain molecules must alter slightly in their conformation to become substrates for the next step in the reaction series. One example is during the very first steps of cellular respiration, when a sugar glucose molecule breaks down in the process of glycolysis: in the first step, ATP is required to phosphorylate glucose, creating a high-energy but unstable intermediate. This phosphorylation reaction powers a conformational change that allows the phosphorylated glucose molecule to convert to the phosphorylated sugar fructose. Fructose is a necessary intermediate for glycolysis to move forward. Here, ATP hydrolysis' exergonic reaction couples with the endergonic reaction of converting glucose into a phosphorylated intermediate in the pathway. Once again, the energy released by breaking a phosphate https://youtu.be/hDq1rhUkV- Glycolysis https://pmc.ncbi.nlm.nih.gov/articles/PMC9313126/#:~:text=Type%201%20g alactosemia%20is%20due,the%20Caucasian%20population%20%5B19%5D https://rarediseases.org/rare-diseases/galact osemia/ https://www.researchgate.net/figure/The-astrocyte-neuron-lactate -shuttle-hypothesis-The-activation-of-nerve-cells-leads-to_fig1_25 8391116 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8 586693/ https://pmc.ncbi.nlm.nih.gov/articles/PMC5315230/#:~:text=The%20neuron s%20then%20convert%20lactate,channels%20in%20response%20to%20pot assium Homeostatic Neuroenergetics Shifting Neuroenergetics Paradigms The classical view of neuroenergetics is that the blood supplies oxygen and glucose to the brain. Glucose is the primary source of energy utilized by both neurons and astrocytes. It undergoes complete oxidation via glycolysis, the Krebs cycle and oxidative phosphorylation, which ultimately produces adenosine triphosphate (ATP) for energy- dependent reactions. Thus, glucose is used in the same way by all cell types. Since neurons consume the greatest quantity of energy of all brain elements, metabolic intermediates (e.g., in the Krebs cycle) are diverted toward neurons. Some of Glu, glutamate; Gln, glutamine; GluR, glutamatergic the pyruvate produced by glycolysis is converted to receptor; EAATs, excitatory amino acid transporters; lactate and released into the extracellular space. In GLUT, glucose transporter; MCTs, monocarboxylate this classical view, lactate is considered a by-product transporters; LDH, lactate dehydrogenase; GS, glutaminase; GLS, glutamine synthetase. with deleterious effects when in excess The astrocyte–neuron lactate shuttle operates under normal physiological conditions with Astrocytes have long been thought to play a passive astrocytes responding to glutamatergic activation role in supporting neuronal function, with the neuron by increasing their rate of glucose utilization and being the star of the show. However, the dynamic release of lactate in the extracellular space, involvement of astrocytes in the forefront of making the lactate available for neurons to sustain neuroenergetics is now being recognized, their energy demands. https://www.frontiersin.org/articles/10.3389/fnins.2017 The Cori cycle refers to the process of transporting lactate from cells that are undergoing anaerobic metabolism to the liver where it is used to provide glucose back to the cells. It is an example of one of the critical roles of the liver in assuring an adequate supply of glucose in the body. It is named after Carl Ferdinand Cori and Gerty Cori who received the 1947