1. Chapter 13 How Cells Obtain Energy from Food

2. From Chapter 3 (Energy) Sun is source of all energy Through photosynthesis/dark reactions, plants convert solar energy  chemical energy + sugars Other organisms consume sugars, convert sugars to chemical energy –Chemical bond energy in food –Catabolism of sugars (glucose) is most direct pathway to chemical energy

3. Sugar  Chemical Energy Use steps to harvest all the energy and not waste it as heat Aerobic metabolism yields the most energy (O 2 needed) Metabolites more oxidized than glucose –Enzymes catalyze reactions Oxidation reactions must be coupled with reduction reactions –The reduced molecules are the carriers (NADH and NADPH)

4. Sugar  Chemical Energy Overall products of sugar catabolism: –CO 2 –H 2 O –Reduced (activated) carriers NADH NADPH –In mitochondria, reduced carriers now oxidized (lose electrons) –Electrons released to electron transport system »Allow ATP synthesis in mitochondria

5. Stage 1 - Digestion In eukaryotes (mammals): Digestion –HCl -- stomach –Enzymes – mouth, stomach, small intestine –Enzymes in the lysosome for internal cellular digestion Absorption through specialized cells in small intestine  bloodstream  body’s cells Metabolism begins in cell cytosol

6. Location of Macromolecules in Cell

7. Stage 2 - Glycolysis Glycolysis starts in the cytoplasm Glucose (6C)  2 pyruvate (3C each) –Other sugars can be used but must convert to intermediates of glycolysis 2 carrier molecules generated per pyruvate –2 molecules ATP (carries energy) –2 reduced NADH (carries electrons) Pyruvate molecules move to the mitochondria

8. Stage 3 – Kreb’s Cycle/ETC In the mitochondria pyruvate broken down to CO 2 and the remaining 2 Cs (acetyl group) are added to Coenzyme A –Also can get Acetyl CoA from fats Each acetyl CoA transfers the 2C’s to citric acid cycle where carrier molecules are generated –GTP carries energy –NADH/FADH 2 carry electrons Electrons  electron transport chain –Release energy used for oxidative phosphorylation –O 2 needed for successful reaction ADP + Pi  ATP –ATP moved to the cytosol for use

9. Glycolysis 10 reactions, each catalyzed by an enzyme Products or intermediates become more oxidized through pathway –Doesn’t react with oxygen atoms; rather lose electrons to carriers 2 NADH generated from catabolism 1 glucose Some steps are not spontaneous (+DG) –Coupled with subsequent spontaneous reactions

10. Glycolysis Uses 2 ATP to catabolize glucose –In coupled reactions – hydrolysis of ATP allows non- spontaneous reactions to proceed –Phosphates from ATP added to intermediates Form high energy phosphate bonds Now intermediates have higher energy In later steps, generates 4 ATP –When phosphates cleaved from intermediates Overall glycolysis yields (net gain) 2 ATP

11. Overall Process

12. Glycolysis

17. Net Result of Glycolysis Glucose + 2 ATP  2 NADH + 4 ATP + 2 pyruvate Net energy outcome 2 NADH and 2 ATP

18. What to Know About Glycolysis 10 enzymes / 5 reaction types –Kinases – add a phosphate group to intermediates, phosphate transfer –Isomerases – rearranges the atoms in the intermediates –Dehydrogenase – causes a redox reaction, electron ends up on FADH 2 or NADH –Dehydrations – removal of H 2 O –Cleavage reaction – split glucose to 2 3-C molecules Net outcome of glycolysis

19. Steps and Reactions Step 1 – kinase, phosphate transfer Step 2 – isomerase, rearrange atoms Step 3 – kinase, phosphate transfer Step 4 – cleavage to 2 3-C molecules Step 5 – isomerase, rearrange atoms Step 6 – dehydrogenase, make NADH Step 7 – kinase, phosphate transfer Step 8 – isomerase, rearrange atoms Step 9 – removal of H 2 O Step 10 – kinase, phosphate transfer

20. Enzymatic Coupling Steps 6 and 7 are coupled to take advantage of the high- energy phosphate intermediate to create ATP Step 6: glyceraldehyde 3-phosphate has a inorganic phosphate group added to create 3-phosphoglycerate, substrate for Step 7 and generates NADH Step 7: 1,3-bisphosphoglycerate releases the energy in the phosphate bond to create 1 ATP for each 1,3- bisphosphoglycerate

22. Overall Results Enzyme-mediated energy storage through coupled reactions to create high energy bonds Intermediate is higher in energy than before –Has second high energy phosphate bond –NADH is generated and will also increase energy when it participates in oxidative phosphorylation

23. High Energy Bonds

24. Fermentation Can generate ATP in absence of O 2 – anaerobic Anaerobic organisms create ATP through glycolysis –Pyruvate converted to ethanol and CO 2 (yeast) or lactate (muscle) Process called fermentation

25. Stage 3 Pyruvate is moved to the mitochondria In the presence of O 2 it is converted to 1 molecule of CO 2 and the remaining 2 C’s are attached to Coenzyme A, creating Acetyl CoA using pyruvate dehydrogenase complex Also generates a molecule of NADH

26. Fatty Acids as Energy Source Fatty acids can be linked to CoA (fatty acyl CoA) and therefore yield acetyl CoA that can enter the citric acid cycle Generates NADH and FADH 2 for each acetylCoA Amino acids also can be made to acetylCoA and used in the Kreb’s cycle

27. Energy Produced in Mitochondria Fats and sugars are major sources of energy Acetyl CoA is made in the mitochondria No surprise to learn that the energy is also harvested in the mitochondria In bacteria – glycolysis and citric acid cycle in cytosol

28. Citric Acid Cycle 2/3 of oxidation of C compounds in the average cell End product is CO 2 (waste) and NADH high energy molecules (used later) Requires O 2 to regenerate NAD + but not actually used in reactions Link the acetyl group of Acetyl CoA to 4 C molecule, oxaloacetate, to make 6 C citrate By end of cycle, all the C of glucose is released as CO 2, remembering that 1 CO 2 was released in previous stage

29. Citric Acid Cycle (TCA Cycle, Kreb’s Cycle) ***

30. Activated Carriers Two new energy molecules are introduced –FADH 2 (flavin adenine dinucleotide) High energy electrons and H –GTP (ribonucleotide) Similar to ATP and will give up PO 4 to ADP to make ATP

31. Requires O 2 but as H 2 O (red circle) Some of the steps products can leave mitochondria and used in the cytosol to make precursors like amino acids

32. Steps and Reactions Step 1 – add acetyl CoA to oxaloacetate, citrate (6 C) Step 2 – isomerase, rearrange atoms (6 C) Step 3 – dehydrogenase, make NADH, lose CO 2 (5 C) Step 4 – dehydrogenase, make NADH, lose CO 2, add CoA back to molecule (4 C) Step 5 – generate GTP, remove CoA (4 C) Step 6 – dehydrogenase, make FADH 2, rearrange atoms (4 C) Step 7 – add H 2 O (4 C) Step 8 – dehydrogenase, make NADH, regenerates oxaloacetate (4 C), why a cycle

33. Electron-Transport Chain Final step in energy generation – most energy released here e - of NADH and FADH 2 move through the chain, moving to lower energy level Occurs in the inner membrane of the mitochondria Specialized molecules accept and donate e - as they move down chain Create an electrochemical gradient –As e - move down chain, H + move across the membrane, altering the concentration of H + on either side = gradient –Gradient used to generate ATP (Chapter 14)

34. Oxidative Phosphorylation e - eventually end up on O 2 and with the H + form H 2 O – e - is at least energy level Complete oxidation of glucose produces 6 CO 2, H 2 O and ~30 ATP Glycolysis alone produces just 2 ATP In bacteria – plasma membrane In eukaryotes – in the inner mitochondrial membrane

35. Storing and Using Food Need to generate ATP constantly, can because store “food” within our cells Fatty acids in fat cells, globules in cells –Holds more energy gram for gram than sugar Glucose stored as glycogen, a branched polysaccharide in granules in animal cell cytoplasm –Used when not enough glucose in bloodstream –Released as glucose 1-phosphate and can enter glycolysis

36. Sugar Storage in Plants and Mammals

37. Plants Have chloroplasts as well as mitochondria –Mitochondria will generate ATP from the sugars made during photosynthesis Especially in cells without chloroplasts such as roots or when without sunlight Excess sugars can be converted to fats or starch, the equivalent to glycogen in animals, different branching pattern –Stored in the chloroplast

38. Chloroplasts and Mitochondria Chloroplasts make ATP and NADPH that cannot leave ATP and NADPH converted to sugar that can leave and be used in glycolysis and ATP generation in the mitochondria and into other building blocks

39. Biosynthetic Pathways Begin with Glycolysis or TCA Cycle Intermediates can be used by other enzymes as the starting point in making amino acids, nucleotides, lipids and other small organic compounds Black arrows – one enzyme reaction Red arrows – multi step reactions

40. Pathway Interactions Some molecule can be substrate in many different pathways Elaborate network of control mechanisms

41. Bringing It All Together Metabolism High ATP LevelsLow ATP Levels Anabolism Glycogen Fats Proteins Catabolism Glycogen Fats Proteins