Medical Biology: Cellular Metabolism (PDF)

Medical Biology Cellular metabolism Dr. Mohammed AL-Obaidi Cellular metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. Cellular metabolism involves complex sequences of controlled b...

Medical Biology Cellular metabolism Dr. Mohammed AL-Obaidi Cellular metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. Cellular metabolism involves complex sequences of controlled biochemical reactions. These processes allow organisms to grow and reproduce, maintain their structures, and respond to environmental changes. Metabolic pathway is divided to: Catabolism: chemical reaction that break down a large compound into smaller unite. Anabolism: chemical reaction in which build more complex molecules from smaller ones. Organisms can be classified according to how they obtain their energy: Autotrophs: are self-feeders, and they get their energy from non-living sources such as the sun and carbon dioxide. Autotrophs are called producers because they provide energy and food sources for all heterotrophic organisms. Autotroph can be classified to: 1- Photoautotroph 2- Chemoautotroph. Heterotrophs – Feeding on others: Heterotrophs obtain energy by oxidation of organic compounds (carbohydrates, lipids, or protein). Ultimately Heterotrophs depend on autotrophs for these organic compounds. Oxygen Living organisms can obtain oxygen from the atmosphere or from water, according to this, organisms can be classified to: Aerobes: live in the presence of oxygen. They use oxygen to oxidize organic nutrients. Anaerobes: Live in the absence of oxygen. Catabolize nutrients without molecular oxygen. Obligate anaerobes: are poisoned by oxygen, like bacteria (Clostridium) and fungus (Piromonas).  Facultative: Some organisms can live in either aerobic or anaerobic conditions. They are called facultative. For examples: yeast and E. coli. Meaning of some abbreviation ATP consists of adenosine (adenine + ribose) and a triphosphate group. GTP: Guanosine tri phosphate, high energy compound, similar to ATP, but with three phosphate groups linked to guanosine.  ATP consists of adenosine (adenine + ribose) and a  triphosphate group. ◦ The bonds between the phosphate groups are high energy bonds. ◦ A - P~P~P  NAD Nicotinamide adenine dinucleotide NADP+ (Nicotinamide adenine dinucleotide phosphate), NADH: the reduce form of (NAD+), this Coenzyme derived from B vitamin niacin, acts as an electron carrier in cell and undergo reversible oxidation and reduction. NADPH is the reduced form of NADP+. CoA: Cofactor derived from Vit B pantothenic. Acetyl Co A: reaction remove one carbon from three Carbone pyruvate adds CoA. FAD: flavin adenine dinucileotide FADH2: the reduce form of (FAD), this Coenzyme derived from B vitamin riboflavin, acts as an electron carrier in cell and undergo reversible oxidation and reduction.  Extracting Energy from Glucose For obtaining energy from carbohydrate, four major metabolic pathways must be occurring: Glycolysis, conversion pyruvic acid to Acetyl CoA, citric acid cycle and the electron transport chain. Glycolysis It first stage in cellular respiration. A series of enzyme catalyzed reactions. Glucose converted to pyruvic acid. 2 ATPs made per one glucose molecule plus 2 NADH molecules which carry high energy electron to the electron transport chain for production ATP  It is possible in the absence of oxygen. All living organisms use glycolysis. Glycolysis take place in the cytosol. Conversion pyruvic acid to Acetyl Co A It occurring in the mitochondria 1- When oxygen is available (Aerobic pathway) Each pyruvate molecules formed from glucose yield one molecule of Acetyl Co A, one CO2 and one NADH (which use in ATP production). 2- When oxygen is not available (Anaerobic pathway) Pyruvate is formed lactate. Lactate is alternative fuel that muscle cells can use or the liver can convert it to glucose. When oxygen is become available, lactate is converted back to pyruvate, then, to Acetyl Co A.  Aerobic Anaerobic 1 - Oxygen present 1 - Oxygen not present 2 - Release more energy 2 - Release less energy 3 - Produce CO 2 , water and 3 - Produce lactic acid and energy energy ( muscle cell) or ethanol, CO 2 and energy (yeast ). 4 -Glucose completely broken 4 -Glucose not completely broken down down 5 - Occurs in mitochondria 5 - Occurs in cytoplasm 6 - It relatively slow. 6 - It relatively speeds. Citric acid cycle (Krebs cycle) Citric acid cycle or tricarboxylic acid (TCA) cycle or the Krebs cycle is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA. It occurring in mitochondria. Electron transport chain (or oxidation phosphorylation): It needs to Co enzyme and cytochromes which located in inner membrane of mitochondria. NADH molecules deliver pair of high electron energy electrons to beginning the chain, FADH2 also enter this pathway but it produces fewer ATP than electron pairs carried by NADH.  The final production is oxygen which react with hydrogen to form water and ADP (joins it P1) to form ATP, hence it called oxidation phosphorylation. Most ATP is produced here. Scientists had estimated that electron pair from NADH produce 3ATP and those from FADH2 produce 2ATP. The finally energy yielded from aerobic respiration about 36-38 ATP per glucose molecule. Fat metabolism Whereas carbohydrates provide a readily available source of energy, lipids function primarily as an energy reserve. Lipids yield 9 kcal of energy per gram while carbohydrates and proteins yield only 4 kcal of energy per gram. Lipid metabolism are involved with fatty acid oxidation to produce energy or the synthesis of lipids which is called Lipogenesis. Protein metabolism It is the breakdown of proteins into amino acids and simple derivative compounds. The primary reason for protein catabolism is so organisms can convert proteins into a form of energy that they can use or store. The first step of protein catabolism is breaking the protein down into amino acids by cleaving their peptide bonds, also known as proteolysis, to convert it to other compounds via the Krebs cycle.