Metabolism Lecture Notes PDF

Metabolism Dr Greg Davis Martini Chapter 25 Copyright notice  Objectives 1. Define energetics and metabolism and explain why cells must synthesise new organic components 2. Describe the basic steps in cellular respiration (glycolysis, citric acid cycle,...

Metabolism Dr Greg Davis Martini Chapter 25 Copyright notice  Objectives 1. Define energetics and metabolism and explain why cells must synthesise new organic components 2. Describe the basic steps in cellular respiration (glycolysis, citric acid cycle, electron transport system) 3. Describe the basic pathways involved in lipid metabolism 4. Describe the main processes of protein metabolism  Energy Cells break down molecules to obtain energy: – used to generate ATP Most production takes place in mitochondria  Metabolism Refers to all chemical reactions in an organism – Anabolic is building up – Catabolic is breaking down – Both processes happen in cells Even at rest cells must spend ATP to: – perform routine maintenance – remove and replace structures and components Cells spend additional energy for vital functions: – growth – secretion – contraction  Materials Transport Cardiovascular system: – carries materials through body Materials diffuse: – from bloodstream into cells  Organic Compounds Glycogen: – most abundant storage carbohydrate – a branched chain of glucose molecules Triglycerides: – most abundant storage lipids – primarily of fatty acids Proteins: – most abundant organic components in body – perform many vital cellular functions Nutrient usage  Carbohydrate metabolism Generates ATP and other high-energy compounds by breaking down carbohydrates: glucose + oxygen ® carbon dioxide + water C6H12O6 + 6O2 ® 6CO2 + 6H2O Several parts: – Glycolysis – Citric acid cycle – Oxidative phosphorylation  Glucose Breakdown Occurs in small steps: – which release energy to convert ADP to ATP 1 molecule of glucose nets 36 molecules of ATP For 1 glucose molecule processed, cell gains 36 molecules of ATP: – 2 from glycolysis – 4 from NADH generated in glycolysis – 2 from Citric acid cycle (through GTP) – 28 from Oxidative Phosphorylation Glycolysis Citric acid cycle Oxidative Phosphorylation  Anabolism Reversing direction not directly possible Enzymatic processes prevent this Gluconeogenesis (new process) – Synthesis of glucose from non-carbohydrate precursors: lactic acid glycerol amino acids – Stores glucose as glycogen in liver and skeletal muscle  Glycogenesis Second stage of replenishing glycogen supplies – Is the formation of glycogen from glucose – Occurs slowly  Glycogenolysis Is the breakdown of glycogen – Occurs quickly – Involves a single enzymatic step – Allows access to energy by muscle when needed  Lipid Metabolism Lipid molecules contain carbon, hydrogen, oxygen: – in different proportions than carbohydrates Triglycerides are the most abundant lipid in the body  Lipid Catabolism Also called lipolysis Breaks lipids down into pieces Hydrolysis splits triglyceride into component parts: – 1 molecule of glycerol – 3 fatty acid molecules Is important as energy reserves Can provide large amounts of ATP, but slowly Saves space, but hard for water-soluble enzymes to reach  Beta-Oxidation Cell can gain – 144 ATP molecules from one 18-carbon fatty acid molecule Fatty acid breakdown – yields about 1.5 times the energy of glucose breakdown Energy benefits!  Lipid Usage Lipid synthesis – Also called lipogenesis – Can use almost any organic substrate: Lipid storage – Important energy reserves – Provides large amounts of ATP, but slowly – Saves space, – hard for water-soluble enzymes to reach  Lipid Transport Cells require lipids: – to maintain cell membranes Steroid hormones must reach target cells in many different tissues Most lipids are not soluble in water: – special transport mechanisms carry lipid Most lipids circulate through bloodstream as lipoproteins Free fatty acids fraction of total circulating lipids  Lipoproteins Are lipid–protein complexes Contain large insoluble glycerides and cholesterol 5 classes – Chylomicrons – Very low-density lipoproteins (VLDLs) – Intermediate-density lipoproteins (IDLs) – Low-density lipoproteins (LDLs) – High-density lipoproteins (HDLs)  Role of LDL HDL LDLs deliver cholesterol to cells – Sometimes called ‘bad’ lipids HDLs remove excess cholesterol & returns it to the liver – Sometimes called ‘good’ lipids  Proteins The body synthesises 100,000 to 140,000 proteins: – each with different form, function, and structure All proteins are built from the 20 amino acids 10 essential amino acids – 8 not synthesized: isoleucine, leucine, lysine, threonine, tryptophan, phenylalanine, valine, and methionine – 2 insufficiently synthesized: arginine and histidine  Protein Synthesis The body synthesizes half of the amino acids needed to build proteins Nonessential amino acids: – amino acids made by the body on demand  Catabolism Cellular proteins are recycled in cytosol: – peptide bonds are broken – free amino acids are used in new proteins If other energy sources are inadequate: – mitochondria generate ATP by breaking down amino acids in TCA cycle  Summary 1. Define energetics and metabolism and explain why cells must synthesise new organic components 2. Describe the basic steps in cellular respiration (glycolysis, citric acid cycle, electron transport system) 3. Describe the basic pathways involved in lipid metabolism 4. Describe the main processes of protein metabolism