Chapter 25 summary Metabolic reactions Catabolism is the breakdown of complex molecules they are exergonic Anabolism is the build up of complex molecules and they are endergonic ATP couples energy releasing catabolic reactions to energy requiring anabolic reactions ATP consists of an adenine molecule a ribose molecule and three phosphate groups bonded to one another About 40 of energy released in catabolism is used for cellular functions The rest is converted to heat Energy Transfer Oxidation reduction reactions and mechanisms of ATP generation are important aspects of energy transfer Oxidation is the removal of electrons decrease in potential energy of molecule They lose a hydrogen atom An example of this is the conversion of lactic acid into pyruvic acid Reduction is the addition of electrons increase in potential energy of molecule This is the conversion of pyruvic acid into lactic acid The oxidized substance sends its liberated hydrogen atoms to be transferred immediately by coenzymes to another compound 2 common enzymes are nicotinamide adenine dinucleotide NAD and Flavin adenine dinucleotide FAD They go through reactions that make them into the final products NADH and FAD2 The addition of a phosphate group to a molecule is called phosphorylation Substrate level phosphorylation is the main mechanism and occurs in the cytosol Oxidative phosphorylation happens in the electron transport chain Carbohydrate Metabolism Glucose can be used in 4 different ways 1 ATP production glucose is oxidized to produce ATP 2 Amino acid synthesis amino acids can be synthesized into proteins 3 Glycogen synthesis done in hepatocytes to form glycogen for storage 4 Triglyceride synthesis done in hepatocytes too when glycogen storage areas are filled up Glucose can be transformed into glycerol and fatty acids that can be used for lipogenesis fat build up or the synthesis of triglycerides Glucose absorption in the GI tract is done by secondary active transport Glucose entry into other body cells happens via facilitated diffusion Summary of cell respiration Glycolysis one glucose molecule broken down into two pyruvates Can produce 2 NET ATP Also produces 2 NADH Does not require oxygen Phosphofructokinase catalyzes Red blood cells can only produce energy via this mechanism Krebs cycle produces 4 CO2 2 ATP 6 NADH 2 FADH2 Occurs in the matrix of the mitochondria Electron Transport Chain oxidize the two coenzymes and transfer their electrons through a series of electron carries usually along the mitochondrial membrane Needs oxygen Within the membrane carries of this process are clustered into three complexes each of which acts as a proton pump that expels H from the matrix and helps create an electrochemical gradiant of H The proton pumps transport electrons and pumps H The pumping of H produces a gradient which makes one side of the inner membrane positively charged compared with the other side This gradient is called the proton motive force ATP synthase will eventually allow H back into the cell This entire process is called chemiosmosis This process is responsible for most of the ATP produced during cell respiration This generates around 32 or 34 ATP Glucose storage If glucose is not needed immediately for ATP production it combines with other molecules of glucose to form glycogen Insulin stimulates hepatocytes and skeletal muscles to carry out glycogenesis the synthesis of glycogen Glucose is phosphorylated into glucose 6 phosphate then converted to glucose 1 phosphate then to uridine diphosphate glucose then finally to glycogen Glucose release When body activities require ATP glycogen stored in hepatocytes is broken down into glucose and released into the blood to be transported to cells where it will be broken down by the process of cellular respiration This is called glycogenolysis Phosphorylase catalyzes this reaction and is activated by glucagon and epinephrine Other methods of glycogen release gluconeogenesis Sometimes your liver runs low on glycogen If you don t eat your body can start to break down triglycerides and protiens Glycerol lactic acid and certain amino acids can be converted in the liver to glucose Lactic acid and amino acids such as alanine cysteine glycine serine and threonine are converted to pyruvic acid which then may be synthesized into glucose or enter the Krebs cycle Glycerol may be converted into glyceraldehyde 3 phosphate which may form pyruvic acid or be used to synthesize glucose This process is stimulated by cortisol and glucagon Thyroid hormones also mobilize proteins and may mobilize triglycerides from adipose tissue Lipid Metabolism Lipids are non polar and cannot dissolve into blood plasma so they need the help of lipoproteins Chylomicrons transport dietary lipids to adipose tissue for storage They enter lacteals of intestinal villi and are carried by lymph into venous blood then into systemic circulation Very low density lipoproteins form in hepatocytes transport triglycerides synthesized in liver to adipocytes for storage Low density lipoproteins carry about 75 of cholesterol in blood and deliver it to cells throughout the body for use in repair of cell membranes and synthesis of steroid hormones and bile salts With these in excess they can deposit fatty plaques in the vessels This is bad cholesterol High density lipoproteins remove excess cholesterol from body cells and blood and transport it to the liver for elimination This is the good cholesterol Cholesterol is consumed with food but it is mostly synthesized by hepatocytes High intake of dietary fats stimulates reabsorption of cholesterol containing bile back into the blood so less cholesterol is lost in the feces When saturated fats are broken down in the body hepatocytes use some of the breakdown products to make cholesterol Lipids can be oxidized to produce ATP If the body has no immediate need to use lipids in this way like if all you do is sit around they are stored in adipose tissue Lipids get used in a couple different ways lipoproteins phospholipids thromboplastin for blood clotting and myelin sheaths for nerve impulses Triglycerides must first be split into glycerol and fatty acids in order for muscle liver and adipose tissue to oxidize fatty acids This is called lipolysis and is carried out by enzymes called lipases found in saliva the stomach and pancreas Epinephrine and norepinephrine enhance triglyceride breakdown into fatty acids and glycerol which makes sense because these constitute adrenaline