Metabolism and Energetics

1. Metabolism and Energetics CHAPTER 25

2. Introduction • Cell will break down excess carbs first, then lipids while conserving amino acids. • Breaking down is catabolism. Only about 40% of energy released through catabolism is captured as ATP, the rest is released as heat. • Cell synthesize new compounds-anabolism 1)to perform structural maintenance or repairs2)to support growth3)to produce secretions.

3. What is cellular respiration ? • The main energy-releasing metabolic pathway that leads to ATP formation. • Also called Aerobic Respiration. • Final acceptor of electrons is oxygen molecule.

4. Overall reaction C6H12O6 +6O2 ---> 6CO2 + 6H2O glucose oxygen carbondioxide water

5. Where does it occur in the cell? • The first step called GLYCOLYSIS occurs in the cytoplasm. • The second and third steps-KREB’S CYCLE AND OXIDATIVE PHOSPHORYLATION occur in the mitochondrion.

6. GLYCOLYSIS occurs in the Cytoplasm Pyruvate forms from glucose generates 2 ATP molecules KREB’S CYCLE Matrix of mitochondrion pruvate to carbondioxide. Liberated electrons and hydrogen are delvered to traansport system by coenzymes. CELLULAR RESPIRATIONC6H12O6+6O2------> 6CO2+6H2O+36 ATP

7. ELECTRON TRANSPORT PHOSPHORYLATION • Occurs in the “cristae” of the mitochondrion. • ATP production is in high gear. • As electrons are transferred ATP production by the process called “CHEMIOSMOSIS” • Final acceptor of electrons is oxygen.

8. ANAEROBIC ROUTES • Lack of oxygen • FERMENTATION • in animal cells produces lactate • in yeast cells produces ethyl alcohol • Anaerobic electron transport • an inorganic substance serves as final electron acceptor.

9. Gluconeogenesis & Glycogenesis • This is the synthesis of glucose from noncarbohydrate precursors such as lactic acid, glycerol or amino acids. • This occurs in the liver and enables the liver to synthesize glucose when carbohydrate reserves are depleted. • Glycogenesis is the process of glycogen formation.

10. Lipid Metabolism • Triglycerides are the most abundant lipids in the body. These are made of glycerol and fatty acids. • Glycerol enters the glycolytic pathway. • The fatty acids undergo beta-oxidation which is used in the TCA cycle. • In lipogenesis there is synthesis of lipids. • Essential fatty acids must be provided in the diet.

11. Lipid transport and distribution • Lipids travel as FFA(water-soluble lipids that can easily diffuse through the membrane) or lipoproteins (lipid-protein complexes that contain triglycerides and cholesterol. • The largest lipoproteins, the chylomicrons carry absorbed lipids from the intestines to the circulation. • Capillary walls of adipose tissue, skeletal muscle , cardiac muscle and liver contain an enzyme called lipoprotein lipase that breaks down complex lipids, releasing a mixture of fatty acids and monoglycerides.

12. Protein metabolism • If other energy sources are inadequate, mitochondria can break down amino acids in the TCA cycle to generate ATP. • In the mitochondria may remove the amino group by transamination or deamination, and the carbon skeleton is converted to one of the compounds involved in glycolysis or oxidative phosphorylation. • Half the amino acids required to build proteins can be synthesized. The other 10 are the essential amino acids which must be provided in the diet. • Amination is the attachment of an amino group to a carbon framework.

13. Nucleic Acid Metabolism • DNA in the nucleus is never catabolized for energy. • RNA molecules are broken down and replaced regularly. They are generally recycled as new nucleic acids. The nucleotides can be catabolized into simple sugars. • Most cells synthesize RNA, but DNA synthesis is restricted during mitosis and meiosis.

14. Metabolic interactions • No one cell can perform all the anabolic and catabolic activities. Homeostasis can be preserved only when metabolic activities of different tissues are coordinated. • The body has five metabolic components:liver, adipose tissue, skeletal tissue, neural tissue and other peripheral tissues. • Liver is the focal point for metabolic regulation and control. • Adipose tissue stores lipids in the form of triglycerides. • Skeletal muscle contains glycogen reserves. • Neural tissue entirely depends on aerobic metabolism. • Peripheral tissues metabolize substances-endocrine sys.

15. The absorptive state • For about four hours after a meal, the nutrients enter the blood stream. • The liver regulates the amount of glucose and the circulating levels of amino acids. • Lipemia marks the absorptive state. • Adipocytes synthesize new triglycerides for later use. • Glucose molecules are catabolized and amino acids are used to build proteins. • Skeletal muscles may also catabolize circ.FA. And inc.glycogen reserves.

16. Postabsorptive State • This extends from the end of the absorptive state to the next meal. • As blood glucose falls, the liver starts to break down glycogen reserves and release glucose. • As duration of fast increases-gluconeogenesis. • Fatty acids undergo beta-oxidation. For ketone bodies. • .

17. continued • Glucogenic amino acids-glucose • ketogenic amino acids-ketone bodies • lipolysis increases. Skeletal muscles metabolize ketone bodies and fatty acids. Glycogen reserves are broken • After a prolonged fast, cathepsins break down contractile proteins. • Neural tissue is supplied with glucose.

18. Bioenergetics • Energy content of food expressed as calories or kilocalories. • Lipids-9.46C/g. • total of all processes=metabolic rate • BMR-rate of energy utilization at rest.

19. Thermoregulation • Homeostatic regulation of body temperature. • Heat exchange with the environment by four processes-radiation, conduction, convection and evaporation. • Preoptic area of hypothalamus-thermostat • mechanisms for heat loss are both physiological-vasodilation, inc. perspiration and respiration- and behavioral

20. Thermoregulation • Shivering and nonshivering thermogenesis • acclimatization • pyrexia.