Introduction to Metabolism

1. Introduction to Metabolism Artika Nath Biochemistry School of Health Sciences

2. Objectives We are now going to look at two major questions in Biochemistry • How do cells extract energy from their environment • How do cells synthesize the building blocks of their macromolecules • This leads to the study of …………………………

3. Metabolism • Is the sum total of all chemical reactions involved in maintaining the living state of the cells, and thus the organism. Divided into two categories • Catabolism – break down of molecules to obtain energy • Anabolism- the synthesis of all molecules needed by cells e.g. DNA, protein etc.

4. Thermodynamics of Metabolism • Metabolic reactions are catalyzed by enzymes and obey the laws of thermodynamics   • (1) First Law of Thermodynamics (conservation of energy): energy can be transformed from one form to another but cannot be created nor destroyed. Energy in the universe is constant. • 2) Second Law of Thermodynamics: energy transformations are never 100% efficient (some energy is lost as heat)

5. Major purpose living things require energy for: • 2. Active transport of molecules and ions • 1. mechanical work in muscle contraction and other cellular movement • 3. Synthesis of bio-molecules and simple precursors : proteins, glycogen, fat

6. What carries energy???? The energy currency in combustion engines is heat: heat is produced and used to expand the volume of a gas • The energy currency or coin of the cell • Energy rich molecule • Triphosphate contains 2 phosphoanhydride bonds The 2 phosphate bonds (phosphoanhydride) bond) is here the energy is stored in ATP

7. A large amount of energy is liberated when 1. ATP → ADP + Pi (orthophosphate) 2. ATP → AMP + PPi (pyrophospahte) The free energy liberated with the hydrolysis of ATP is used to drive reactions that require input f free energy

8. ATP is continuously formed and consumed • It’s the principal immediate donor and not long term storage of energy • Rate of turnover of ATP is high. A molecule of ATP is consumed within a minute it is formed • Resting person consumes ~ 40kg of ATP/ 24 hr. Motion, Active transport, Biosynthesis, Signal amplification ATP ADP Photosynthesis or oxidation of fuel molecules Basic model of energy exchange in biological systems

9. How do cells make ATP • ByPHOSPHORYLATION...    adding a phosphate to ADP ADP   +   P    ------>    ATP 3 mechanisms of phosphorylation: • substrate level phosphorylation- where a substrate molecule ( X-p ) donates its high energy P to ADP making ATP • Oxidative phosphorylation • e- transferred from organic molecules and passed through a series of acceptors to O2 • 3. Photophosphorylation • Occurs during photosynthesis –light energy used to make ATP    

10. Electron carriers • When food molecule oxidized – electrons are removes • These electrons are carried to oxygen • e- O2 • ANS: Electron carriers NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) • Reduced form (with electrons bound) is • NADH and FADH2 • NADH and FADH2 transfer e- to O2 in the mitochondria by means of ETC > ATP generated in this process How does the e- get to oxygen???????

12. Stage 1 Large molecules broken int o smaller units Stage 2 The numerous small units are degraded to a few simple units that play a central role in metabolism. Most re converted to the acetyl unit of acetyl CoA. Some ATP generated Stage 3 Kreb cycle and oxidative phosphorylation Most energy generated here

13. Carbohydrates • 2-3% of your total body weight • Monosaccharides – the building block • e.g. glucose (the main energy supplying molecule of the body • Fructose- found in fruits; Galactose – present in milk; Deoxyribose – in DNA; Ribose- RNA • Glycogen – main storage (liver and skeletal muscle) form of carbohydrate. • Starch – main carbohydrate in food • Cellulose- no digested by humans

14. 18-25% of body weight in lean adults • Hydrophobic • Usually combine with proteins (lipoproteins) and move in the blood • Hydrophobic , so cannot exert osmotic pressure on cell walls – therefore stored easily. • Triglycerides most plentiful lipid in your body. Each gram can produce twice as much as energy compared to carbohydrates and proteins • Triglycerides stored unlimited in adipose tissues

15. Proteins • 12-18% body weight • Many functions: • catalyst, transport and storage, movement, structural, immune system and regulatory role • Amino acids building blocks • Cannot store proteins

16. What is a polysaccharide? A disaccharide? A monosaccharide? Give some examples of monosaccharides. Which monosaccharide does the body use for energy production? • How is carbohydrate stored in the body? • What is a polypeptide? A dipeptide? An amino acid? What distinguishes an amino acid from a carbohydrate? • What does the body use proteins for? • What is a triglyceride? A fatty acid? Glycerol? Name some uses of lipids in the body. How are excess fatty acids stored in the body? • Define metabolism. • Distinguish between anabolism and catabolism. • ATP is the cell's storehouse of energy. Where, within the ATP molecule, is this energy stored? Where does that energy come from? • Which of the three nutrients produces more energy, gram for gram, when oxidized? • What is the difference between glycogenesis and glycogenolysis?