Chapter 9 Energy in a Cell

1. http://www.uic.edu/classes/bios/bios100/mike/spring2003/atp.jpghttp://www.uic.edu/classes/bios/bios100/mike/spring2003/atp.jpg ATP Chapter 9 Energy in a Cell http://courses.washington.edu/bangblue/atp.jpg

2. 9.1 – The Need for Energy (p. 221-224) • Active Transport • Cell Division • Transport • Synthesis (proteins) • others http://static.howstuffworks.com/gif/ice-fishing-4a.jpg Energy is essential to life. Organisms are endergonic systems. What do we need “E” for? www.cheetah.bigcats.in/http://hi5.bigoo.wshttp://www.dailymail.co.uk

3. ATP is the universal currency of energy exchange in biological systems. • No matter what form of energy a cell uses as its primary source, the energy is ultimately transformed and conserved as ATP. • adenosine monophosphate (AMP) nucleotide • two phosphate groups • pyrophosphate bonds (~P). • These two bonds are energy rich in the sense that their hydrolysis (breakage which releases water) yields a great deal more energy than a covalent bond of another molecule.

4. The ATP reaction is commonly written as: ADP + Pi + energy ATP • The forming of ADP into ATP • requires energy (endothermic) – 8 kcal/mole • is pH dependent. Note: Forming ADP is like making a bank deposit or coiling a spring for each phosphate bond. (see figure 9.2 on p. 223)

5. The Calorie • Kcal – kilocalorie • equivalent to 1000 calories. • When we say that a cup of milk has 120 calories we really mean 300 kilocalories or 300 000 calories. • Even though we use the word calorie it is, by definition, kilocalorie.

6. ABOUT THE MOLE: Analogous to a dozen, it is a ”count” of molecules used in chemistry and biochemistry. 1 mol = 6.022 x 1023 molecules 0.5 mol = 3.011 x 10 23 molecules 2.0 mol – 12.044 x 10 23 molecules or 1.2044 x 10 24 molecules The Mole

7. 9.2 Photosynthesis: Trapping the Sun’s Energy p. 225-230 • We’ve seen in our past learning that the cell uses energy during ACTIVE TRANSPORT. Where does this energy come from?

8. RECALL FROM EARLIER GRADESAll animals are heterotrophs - require food sources of energy.i.e. trophic levels in a food chain

9. We do not make our own food for energy like plants, algae and some bacteria (autotrophs). This is summarized by the carbon-oxygen cycle below:

10. Photosynthesis: The Energy Maker • Autotrophs under go PHOTOSYNTHESIS to produce sugars (starches made up of glucose molecules)—we say the sun’s energy is stored in a chemicalbond. • Recall: UV energy + CO2 + 6H2O  C6H12O6 + 6 O2

11. In actuality, this reaction is elegant, but is not simple. • MANY reactions occur inside the chloroplast’s grana membrane. • The chlorophyll in chloroplasts is one pigment (a green one, there are others) that absorbs sun energy (all colours except green) which excite electrons and cause a phosphate to attach to ADP molecules.

12. LIGHT DEPENDENT-REACTIONS • Energized electrons provide energy that: • Forms ATP. • Releases oxygen molecules (from the splitting of H2O) See Fig. 9.5 p. 227 Fig. 9.6 p. 228

13. Light Independent Reactions/Dark Reactions • At the same time (and more so at night when there is no sun) the Calvin cycle takes place in the stroma of the chloroplast. • Powered by ATP from photosynthesis

14. Carbon dioxide gas (CO2) is taken in and used to form sugars (CH2O is short hand to represent many different types of sugarmolecules, most importantly glucose). • These are stored as starch granules in chloroplasts. • They are also transported to other cells and accumulate in roots. • See Fig. 9.7 p. 229

15. The new summary of photosynthesis: • Light dependent reactions: 12H2O + 12NADP + 18ADP → 6O2 + 12NADPH + 18ATP • Light Independent reactions (*Calvin cycle) 6CO2 + 12NADPH + 18ATP→C6H12O6+12NADP+18ADP+6H2O • Can you see how we get the overall Ps equation? • The whole point of these reactions is to make a safe, energy rich molecule, glucose.

16. 9.3 Getting Energy to Make ATP Cellular Respiration • When we consume the sugars from plants, (producers) or animals that have eaten plants (primary consumers), energy from the sugar bonds is released. • The release of this energy is called respiration. Recall: C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP)

17. Again, the reaction is elegant but far from simple! • When animals and plants consume energy molecules like starch and glucose, many reactions occur. • Glycolysis (anaerobic) • Citric Acid Cycle (aerobic) • Electron Transport Chain -also aerobic • The last two occur inside the mitochondrion.

18. Glycolysis • Glycolysis is the only metabolic pathway shared by ALL organisms. • Occurs in the cytoplasm. • i.e. not in an organelle

19. Glycolysis (cont’d) • A process whereby glucose molecules are split in half (makes a 3-C compound called pyruvate) in a series of steps. • Glycolysis releases a 2 – ATP molecules per glucose molecule that are used to drive other reactions AND • This process does not require O2 • Anerobic See Fig. 9.8 p. 232

20. Aerobic vs. Anaerobic http://www.dynamicfondue.com/wp-content/uploads/2008/08/aerobic-exercise.jpghttp://images.google.ca/imgres?imgurl=http://graphics8.nytimes.com/images/2007/ • From here, pathways diverge in different organisms and in different situations—oxygen poor (anaerobic) and oxygen rich (aerobic). • More about that later.

21. BUT more ATP is made inside the mitochondrion in two separate pathways: • The Citric Acid Cycle, CAC (KREBS CYCLE, KC) • ELECTRON TRANSPORT CHAIN (ETC) • CAC releases 1 ATP molecule • ETC releases 30 ATP molecules! • These reactions drive far more chemical reactions in our tissues because of it.

22. Citric Acid Cycle (CAC) • The CAC occurs inside the mitochondrial matrix. • It is called a cycle, because one of its end-products is recycled in the cycle. • Named because it forms citric acid • an important intermediate molecule.

23. Citric Acid Cycle (cont’d) • The main outcome is the generation of a variety of energy intermediate molecules, not just ATP. • GTP • NADH • FADH2. • This cycle also releases 3 CO2 molecules per pyruvate (3-C). • See Fig. 9.10 p. 233

24. A diagram shows the numbers of energy molecules generated: animation

25. The Electron Transport Chain (ETC) • From the Krebs cycle (Citric Acid cycle) inside the mitochondrion, the ETC occurs inside the mitochondrial membrane. • It causes a cascade of energy release by using the other energy molecules of NADH, FADH2 to cash in and make more ATP. • See Fig. 9.11 p. 234

26. The specialized molecules that do this are called CYTOCHROMES and they pass excited electrons from one cytochrome to another stepwise—this releases even more ATP—30 more ATP!—in a controlled manner. • This is where oxygen is consumed, and water formed. • TOTAL ATP from 1 glucose molecule: - 2 gly - 2 (Act T)+ 2 CAC + 30 ETC = 32 ATP

27. The schematic below shows how electrons transferred from the NADH in Krebs are transferred in a cascade of reactions in the ETC—note the need for flavin M (part of the group of riboflavins, or B vitamins—B2) and the role of iron ions (Fe). • This releases a LOT of ATP molecules.

28. Cellular Respiration Schematic

29. In summary www.goldiesroom.org

30. In summary: • SO, back to our original reaction—the important component is the ENERGY: C6H12O6 + 6O2  6CO2 + 6H2O + 32ATP • We now know • where oxygen is consumed, • how CO2 is generated, • where the H2O comes from • and how many energy molecules are made.

31. Anaerobic Respiration • If no oxygen continues to be present or, in some organisms like yeast, where it is not used, fermentation occurs. • This is also known as anaerobic respiration. • uses the 3-C molecules (pyruvate) and makes lactic acid in our muscles or in yogurt) or ethanol (as in brewing).

32. Anaerobic Respiration (cont’d) Only another 2 ATP molecules are made This occurs with some fungi, and with Lactobacillus acidophilus in yogurt, and in yeasts. This is the basis of cheese, yogurt, buttermilk, root beer (real root beer), breads, wines, spirits.

33. Anaerobic Exercise • In vigorous exercise, lactic acid builds up in our muscles when we’ve exhausted the oxygen supply in our haemoglobin • i.e. We produce more lactic acid than our cells can remove and they begin to seize up creating pain. • Athletes can increase their tolerance for lactic acid.

34. Aerobic Respiration • AEROBIC RESPIRATION occurs in our mitochondria • these pathways occur when oxygen is required (as in us) and is present in sufficient amounts. • Longer duration of exercise • For these cycles to occur, active transport of pyruvate from glycolysis is needed – this uses up the 2 ATP that were made.

35. Metabolism • METABOLISM refers to two contrasting cellular activities: • the total biochemical reactions required for energy making reactions called CATABOLISM (includes breaking down foods to store energy – ATP - in our tissues) and • the use of energy to synthesize cell material from small molecules in the environment, called ANABOLISM (energy consuming, using ATP to release energy).

36. Catabolic Reactions • Produce energy in the chemical bonds of a molecule called ATP (adenosine triphosphate). • glycolysis • CAC • ETC • lead to end products, which are "waste products" like water and CO2 • most important—they generate ATP which is later used in anabolic reactions to build cell material from nutrients in the environment, like muscle tissue.

37. Anabolic Pathways • Lead to release of the energy to drive other reactions. • These reactions make important molecules like proteins for our muscles, hair, nails, lipids for our fatty tissues, and so on. • When energy is required during anabolism, it may be spent as the breaking of a high energy bond of ATP which has a value of about 8 kcal/mol of ATP molecules. This is like a withdrawal from your account.

38. Role of Water

39. Breaking the ATP to make ADP releases 8 kcal/mol. The ATP reaction is commonly written as: ATP  ADP + Pi + 8 kcal/mol

40. The diagram showing the relationships between catabolism and anabolism is not to be memorized, but to help you understand the connections:

41. IMP: During catabolism, energy is changed from one form to another, but such energy transformations are never completely efficient, i.e., some energy is lost in the form of heat. This forms part of our body heat. • In both catabolism and anabolism, energy is formed stepwise and broken down stepwise in a number of cycles. • This controls the amount of energy stored or released.

42. The energy is passed along in two energy processes: Exergonic reactions and Endergonic reactions.