Ch 9 reading quiz

1. "Everyone has the ability of making someone happy, some by entering the room, others by leaving it." ---Unknown

3. Ch 9 reading quiz • What is your muscle cell’s alternative to cellular respiration? • If you GAIN an electron, you have just been _______. • What is the first step in cellular respiration? 4. Which step of cellular respiration receives all of the reduced coenzymes? 5. What does it mean to be “phosphorylated”?

4. 1.Diagram energy flow through the biosphere. • Energy flows into most ecosystems as sunlight • Photosynthetic organisms trap some and transform it into chemical bond energy of organic molecules. O2 released. • Cells use the chemical bond energy in organic molecules to make ATP – the energy source for cellular work • Energy leaves living organisms as it dissipates as heat 

6. 2. Write the overall summary equation for cellular respiration. Food + Oxygen  carbon dioxide + water +energy C6H12O6 + 6 O2  6CO2 + 6H2O + Energy (glucose) (oxygen) (carbon dioxide) (water) (heat &ATP) 

7. 3. Briefly describe how cells recycle the ATP they use for work. • Cells tap stored energy in ATP by transferring the terminal phosphate groups to other compounds - energy is released & the new compound is more reactive - loses phosphate as cellular work is performed - cells need to replenish ATP supply to continue work  cell respiration provides the energy to regenerate ATP 

10. 4. Distinguish between oxidation and reduction, and describe why they are referred to as “redox” reactions. Oxidation – partial or complete LOSS of electrons Reduction – partial or complete GAIN of electrons “LEO GER” “Redox” refers to ‘reduction-oxidation’ reactions where compounds trade electrons 

11. 5. Explain how redox reactions are involved in energy exchanges. • Involve a partial or complete transfer of electrons • Release of energy when electrons move closer to electronegative atoms (ex: O) Xe- + Y  X + Ye-

13. 6. Define coenzyme and list those involved in respiration. Coenzyme  small nonprotein organic molecule that is required for certain enzymes to function NAD+(nicotinamide adenine dinucleotide)  found in all cells that assists electron transfer NADH  reduced coenzyme FADH2  reduced coenzyme FAD(flavin adenine dinucleotide)  without electrons 

15. 7. Describe the role of NAD+ during respiration. • NAD+ acts as an electron ‘carrier’, a coenzyme • Enzymes called ‘dehydrogenases’ remove a pair of hydrogen atoms (electrons) from the substrate • The enzyme delivers these electrons to NAD+, and then NADH is neutral, and carrying electrons to the electron transport chain where they then make their ‘fall’ towards O2, creating ATP

16. 8. Describe the role of ATP in coupled reactions.

17. 9. List the three steps of cellular respiration. • Glycolysis (sugar-splitting) • Krebs Cycle (makes coenzymes & ATP) • Electron Transport Chain (makes ATP) 

18. 10. Distinguish between substrate-level phosphorylation and oxidative phosphorylation. Phosphorylation • A compound receiving the phosphate group from ATP is said to be ‘phosphorylated’ and becomes more reactive Substrate-Level • ATP production by direct enzymatic transfer of a phosphate from an intermediate substrate in catabolism to ADP Oxidative • ATP production that is coupled to the exergonic transfer of electrons from food to oxygen 

20. 11. Describe how the carbon skeleton of glucose changes as it proceeds through glycolysis, and what it looks like after glycolysis. • Starts as a 6 carbon sugar, carbon 6 is phosphorylated • It rearranges from glucose-6-phosphate to fructose-6-phosphate • Carbon 1 becomes phosphorylated • The 6-carbon molecule is cleaved into 2 isomeric 3 carbon sugars • The phosphate on carbon 3 is transferred to carbon 2 • Glucose has now been oxidized into two ‘pyruvates’. 

21. 12. Identify where in glycolysis that sugar oxidation, substrate-level phosphorylation and reduction of coenzymes occur. Sugar oxidation  step 5 energy yielding phase occurs after glucose is split into 2 3carbon sugars and ATP and NADH are produced Substrate-level phosphorylation  last step – this is how ATP is produced; it is a highly exergonic process Reduction of coenzymes  step 6 – where glyceraldehyde phosphate is oxidized and NAD+ is reduced to NADH+ and H+ 

22. 13. Write a summary equation for glycolysis and describe where it occurs in the cell. • Glycolysis occurs in the cytosol of the cell

23. 14. Describe where pyruvate is oxidized to acetyl CoA, what molecules are produced and how it links glycolysis to the Krebs cycle. • Pyruvate is oxidized in the mitochondria • The Krebs cycle completes glucose oxidation by breaking down a pyruvate derivative (acetyl CoA) into CO2 • Junction between glycolysis and the Kreb’s cycle is the oxidation of pyruvate to acetyl coA • Molecules produced: CO2, NADH, FADH2, and ATP 

25. 15. Describe the location, molecules in and molecules out for the Krebs cycle. • Kreb’s occurs in the mitochondria • For every turn of the Kreb’s cycle: • 2 carbons enter in the acetyl fragment of acetyl coA • 2 different carbons are oxidized and leave as CO2 • Coenzymes are reduced; 3 NADH and 1 FADH2 are produced • 1 ATP molecule is produced by substrate-level phosphorylation • Oxaloacetate is regenerated 

27. 16. Explain at what point during cellular respiration glucose is completely oxidized. • In the Krebs cycle, pyruvate’s fate depends on the presence of O2. • If O2 is present, pyruvate enters the mitochondrion where it is completely oxidized by a series of enzyme-controlled reactions (moved by a carrier protein in the mitochondrial membrane) • Oxidizing of the remaining acetyl fragments of acetyl coA to CO2. Energy is released and used for ATP and reducing coenzymes 

29. 17. Explain how the exergonic “slide” of electrons down the electron transport chain is coupled to the endergonic production of ATP by chemiosmosis. • It is the mechanism that couples the electron flow (exergonic) to oxidative phosphorylation (endergonic) 

31. It is the coupling of exergonic electron flow down an electron transport chain to endergonic ATP production by the creation of a proton gradient across a membrane. The proton gradient drives ATP synthesis as protons diffuse back across the membrane  18. Describe the process of chemiosmosis.

32. 19. Explain how membrane structure is related to membrane function in chemiosmosis. • The existing proton gradient across the inner mitochondrial membrane helps to power ATP synthesis • Cristae, or infoldings of the inner mitochondrial membrane, increase the surface area available for chemiosmosis to occur • Proton gradients across membranes are maintained because the phospholipid bilayer is impermeable to H+ ions and prevents diffusion it is this potential energy that is used to make ATPs 

34. 20. Summarize the net ATP yield from the oxidation of a glucose molecule by constructing an ATP ledger (chart) which includes coenzyme production during the different stages of glycolysis and cellular respiration.

36. 21. Describe the fate of pyruvate in the absence of oxygen. • Pyruvate is reduced, and NAD+ regenerated • Fermentation converts pyruvate to ethanol in 2 steps: • Pyruvate loses CO2 and is converted to the 2C compound acetyldehyde • NADH is oxidized to NAD+ and acetylaldehyde is reduced to ethanol • Oxidizing agent is not O2 but NAD+

37. 22. Explain why fermentation is necessary. • When O2 is scarce, ATP can still be produced • Example: human muscle cells switch from aerobic to anaerobic respiration (lactic acid fermentation) 

38. 23. Distinguish between aerobic and anaerobic metabolism. Aerobic  existing in the presence of oxygen - cell respiration – yields 18x more ATP Anaerobic  existing in the absence of free oxygen - fermentation 

39. 24. Describe how food molecules other than glucose can be oxidized to make ATP. Glycolysis  can accept a wide range of carbs for catabolism • Starch is hydrolyzed to glucose in the digestive tract • Liver hydrolyzes glycogen to glucose • Enzymes in the small intestine break down disaccharides into glucose • Proteins are hydrolyzed to amino acids enzymatically – converted to intermediates (pyruvate, acetyl CoA) • Fat is digested into glycerol or fatty acids, then to the intermediates of glycolysis 

41. 25. Describe evidence that the first prokaryotes produced ATP by glycolysis. • Glycolysis does not require oxygen, and the oldest known bacteria fossils date back to 3.5 billion years • It is the most widespread metabolic pathway, so it probably evolved early on • Glycolysis occurs in the cytosol and does not require membrane-bound organelles (mitochondria). Eukaryotic cells with organelles probably evolved about 2 billion after prokaryotic cells

42. 26. Explain how ATP production is controlled by the cell and what role the allosteric enzyme, phosphofructokinase, plays in this process. • Cells respond to changing metabolic needs by controlling the reaction rates • Most common method is feedback inhibition • Glycolysis/Krebs, catabolic pathways, are controlled by regulating enzyme activity at strategic points • Phosphofructokinase catalyzes the 3rd step of glycolysis - it is sensitive to changes in the ratios of ADP & ATP - helps to control reaction rates 