Metabolism II Lipids and Proteins Transport of Lipids by Lipoproteins o Most lipids are nonpolar and must be combined with protein to be transported in blood o Lipoproteins are spheres containing hundreds of molecules o Lipoproteins are categorized by function and density o 4 major classes of lipoproteins chylomicrons very low density low density and high density Classes of lipoproteins lipoproteins o Chylomicrons 2 protein 85 TG Form in intestinal epithelial cells to transport dietary fats to adipose cells o VLDLs 10 protein 50 TG Form in hepatocytes to transport triglycerides to adipose cells o LDLs 25 protein 50 cholesterol bad cholesterol Carry blood cholesterol to body cells o HDLs 40 protein 20 cholesterol good cholesterol Carry cholesterol from cells to liver for elimination Fate of lipids o Oxidized to produce ATP o Excess stored in adipose tissue or liver o Synthesize structural or other important molecules Phospholipids of plasma membranes Lipoproteins that transport cholesterol Thromboplastin for blood clotting Myelin sheaths to speed up nerve conduction Cholesterol used to synthesize bile salts and steroid hormones Overview of Lipidmetabolism o 1 Lipolysis Lipolysis triglycerides are broken down into glycerol and fatty acids within liver or adipose cells in the presence of epinephrine norepinephrine cortisol Fatty acids undergo beta oxidation in mitochondria to produce Acetyl CoA and lots of ATP Ketogenesis occurs in liver cells ketone bodies are used by heart muscle and kidney cortex for ATP production o 2 Lipogenesis triglycerides are synthesized from amino acids or glucose within liver or adipose cells in the presence of insulin o Proteins are broken down into amino acids which are transported to the Fate of Proteins liver o Amino acids may be Deaminated to enter the Krebs Cycle Donate amino group to form new amino acids transamination Used to synthesize new proteins throughout the body o Excess amino acids may be converted into glucose or triglycerides no o Absorption of AA into body cells is stimulated by insulin like grouth factors IGFs and insulin Metabolism during absorptive state storage to be stored o Represents the time after a meal when nutrients enter the blood and need o Hepatic portal system for glucose and amino acids go to liver first o Lacteals for dietary fats Absorptive state summary o Storage of excess fuels occurs in hepatocytes adipocytes skeletal muscle o Most glucose entering liver cells is converted to glycogen 10 or o Dietary lipids are stored in adipose tissue o Amino acids are deaminated to enter krebs cycle or are converted to o Amino acids are not taken up by hepatocytes are used by other cells for Metabolism during postabsorptive state o 4 hours after a meal when absorption of all nutrients is complete similar triglycerides 40 glucose or fatty acids synthesis of proteins to starvation maintaining normal blood glucose level 70 to 110 mg dl of blood is major challenge goal is to put glucose back into the blood or use alternative fuel sources Postabsorptive state summary o Glucose enters blood from the liver Glycogenolysis Glucogenesis Glycerol from adipose tissue Amino acids and lactic acid from muscle Alternative fuel sources are Fatty acids from adipose fed into krebs as acetyl CoA for most cells except brain which still prefers glucose Oxidation of ketone bodies by heart and kidney