2. Energy in a Cell

3. All Cells Need Energy Cells need energy to do a variety of work: Making new molecules. Building membranes and organelles. Moving molecules in and out of the cell. Movement.

4. Where Does A Cell Get Energy? Food is broken down to a form the cell can use. Extra energy is stored in an ATP molecule, a nucleotide.

5. ATP: The energy molecule ATP – this is the energy currency of the cell. It can be directly used to provide energy for any type of cell function. Adenine Ribose

6. How Does ATP Work? Energy is stored in the bond between the second and third phosphate group. When the bond is broken, energy is released and ADP is formed. Adenine Ribose Energy

7. Reaction: ATP ATP  ADP + Energy

8. Where is the energy located? For living organisms: energy is stored in the chemical bonds of biological molecules - FOOD To release that energy, the bonds are broken (breaking down food) This energy is then stored in an ATP molecule

9. Chemical reactions In your body, the food source for cells is glucose (a type of sugar – CARBOHYDRATE) Glucose + Oxygen  Carbon Dioxide + Water + ENERGY C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy Reactions, in your body, need help to happen These reactions need the help of an ENZYME

10. Speeding up the reaction Catalyst: a chemical substance that speeds up a chemical reaction by lowering the activation energy Enzyme: a biological catalyst (enzymes are specialized protein molecules... use a lock and key model) Substrate Active site Diagram on board

11. Making Energy Cells make energy in two ways: Photosynthesis – takes place in the chloroplasts of plants. Respiration – takes place in the mitochondria. We will discuss each in turn

12. Photosynthesis Autotrophs (plants) make their own food by trapping light energy and converting it to chemical energy (carbohydrates). Occurs in a chlorplast

13. Photosynthesis Using light from the sun, plants combine water and carbon dioxide to make sugar. Carbon dioxide + water + sun  glucose and oxygen 6CO 2 + 6H 2 O + energy  C 6 H 12 O 6 + 6O 2 Reactants Products

14. Photosynthesis 2 Reactions Light Reactions Calvin Cycle (Dark Reaction)

15. Photosynthesis – Part I Light Reactions (photolysis) – Light energy is converted to chemical energy Made of 2 photosystems (1 and 2) They both make energy molecules Energy from the sun is required ATP and oxygen are produced Oxygen comes from water NADPH is also produced Another high energy molecule

16. Light absorption Chloroplasts (in plant cells) contain pigments that only absorb certain “colors” of light Chlorophyll a: absorbs mostly “red” light Chlorophyll does not really absorb much “green” light so this light is reflected (why many plants appear green) Carotenoids: absorb mostly “yellow”, “orange” and “brown” light In the fall, many leaves lose their carotenoids and that is why they take on the fall colors because that light is reflected.

17. Purpose of the light reaction The purpose of the light reaction is to capture light energy and then convert it to usable chemical energy Many enzymes are used to convert the light energy into ATP molecules and NADPH molecules As a result of the light reaction, O 2 is released The ATP and NADPH are used in the next part of photosynthesis

18. Photosynthesis – Part II Calvin Cycle – ATP and NADPH from the light reactions are used along with CO 2 to form a simple organic compound (glucose or sugar) Takes place in the stroma (liquid part) of the chloroplasts. Byproducts are glucose and: ADP, and NADP + (return to the light reactions to be remade into ATP and NADPH).

19. Calvin cycle (aka C 3 Pathway) Calvin cycle (also known as the DARK REACTION) is the process by which atmospheric CO 2 is taken in by the plant and utilized to make the high energy molecule, GLUCOSE In order to produce glucose, CO 2 must be incorporated into an organic compound, this is called carbon fixation The carbon dioxide enters the plant through openings in the leaves called STOMATA The carbon dioxide then goes through a series of “cycles” to create glucose

20. Carbon fixation – cont. The carbon dioxide uses the energy from the light reaction (in the form of ATP and NADPH) to combine the carbons in CO 2 to form the glucose molecule, C 6 H 12 O 6 Summary: Now the CO 2 is fixed into an organic compound that can be used by the cell to make either energy or structural molecules

21. Photosynthesis – Putting it together Breakdown of photosynthesis: 6CO 2 + 6H 2 O + energy  C 6 H 12 O 6 + 6O 2 CO 2 is absorbed from atmosphere for Calvin cycle through stomata H 2 O is absorbed through roots of plant Energy comes from the sun Glucose is the end product of the Calvin cycle O 2 is created from the H 2 O used in the light cycle

22. Sunlight NADP + ADP NADPH CO 2 H2OH2O O2O2 CHLOROPLAST ATP

23. FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS How fast photosynthesis occurs can be affected by the following: Temperature: as the temperature increases, the rate of photosynthesis tends to increase Above 40°C (104°F) the rate of photosynthesis decreases (the enzymes needed begin to break apart) CO 2 : the more CO 2, the faster photosynthesis Chlorophyll: the more chlorophyll, the faster photosynthesis Light: if there is more light, increased rate Trace elements will increase photosynthesis (often present in fertilizers)

24. Alternative ways to fix carbon In very hot climates, the Calvin cycle does not work very well: Stomata (the small pores on leaves) through which carbon dioxide enter the plant and oxygen exits When it is extremely hot, plants can lose a lot of water through these pores As a strategy, many plants partially close these stomata to limit water loss This prevents CO 2 from getting into the plants Also prevents O 2 from leaving (build up of O 2 in the chloroplasts prevents the Calvin cycle from functioning) Therefore, there must be other ways for plants to fix carbon

25. C 4 Pathway – only lose ½ the water Some plants have an enzyme that allows them to fix carbon into a 4 carbon organic compounds (hence the 4 from C 4 ) These enzymes function during times of low CO 2 concentration and high O 2 concentration Again, these conditions are created by the partially closed stomata These 4 carbon compounds are then transported to other parts of the cell where the CO 2 is released and can then begin the Calvin cycle ANALOGY: This system is like a mail system where you piggy back the CO 2 to another molecule and then ship it to where you are doing the Calvin cycle This mostly occurs in tropical plants

26. CAM Pathway CAM Pathway open their stomata at night and close them during the day This is the opposite of what normal plants do The plant can only receive CO 2 during the night (without the hot sun out) This lets them accumulate and store CO 2 during the night During the day, the CO 2 is available to be used by the Calvin cycle This process loses less water than the C 3 or C 4 pathways This mostly occurs in desert plants

27. Chemosynthesis – Where’s the sun? Some autotrophs can convert inorganic substances to energy. Most are adapted to live in conditions where there is no oxygen or little sunlight. Marshes. Lake sediments. Digestive tracts of mammals. Deep in the ocean.

29. Cellular Respiration The process of breaking down food molecules to release energy. Occurs in the cytosol and mitochondria. Two types: Anaerobic – does not require oxygen. Glycolysis Fermentation Aerobic – requires oxygen. Kreb’s cycle Electron transport chain

30. Glycolysis Glycolysis is the first step to create energy Glycolysis takes place in the cytosol of the cell It occurs on the inner side of the plasma membrane For most cells, glucose is the molecule used to create energy in the cell Like in photosynthesis, many of the systems are the same ATP is the energy molecule that is created

31. Glycolysis Two molecules of ATP activate (start) a chemical reaction causing glucose to break into two molecules known as G3P (glyceraldehyde-3-phosphate). These two molecules are then broken into two molecules of pyruvic acid. The breaking of the glucose bonds releases enough energy to make four molecules of ATP. NEED 2 ATP TO START AND MAKE 4 ATP Glycolysis makes a net of 2 ATP REMINDER: This process DOES NOT need oxygen

32. Fermentation – Lactic acid Some cells can take the pyruvic acid that is created in glycolysis and use it to keep the process of glycolysis continuing Lactic acid fermentation The pyruvic acid made in glycolysis is changed into another molecule called lactic acid This allows you to keep producing more ATPs in glycolysis without oxygen

33. Lactic acid fermentation Lactic acid fermentation happens in your body when you perform strenuous activity The oxygen needed to get more energy out of pyruvate is used up so your body must continue to use glycolysis The build up of lactic acid in your muscle cells cause: Muscle cells to reduce their ability to contract Cause muscle fatigue Pain Cramping

34. Fermentation - Alcohol Occurs in yeasts and bacteria In this process, pyruvic acid is converted to ethyl alcohol to allow glycolysis to continue Instead of pyruvic acid being turned into lactic acid, it is converted to ethanol, and carbon dioxide Pyruvic acid  Ethyl alcohol + CO 2 Again, the purpose of fermentation is to allow glycolysis without oxygen

35. Summary Glycolysis and fermentation are anaerobic (no oxygen present) To start glycolysis, you need 2ATP Glycolysis produces a total of 4ATP Therefore, it is a net gain of 2ATP If you want glycolysis to continue without oxygen, you have to resupply the levels of a molecule called NAD This can be done with fermentation Lactic acid fermentation Alcohol fermentation

36. Summary of Glycolysis GLUCOSE  2 ATP 4 ADP in 4 ATP out Pyruvic Acid Lactic Acid Alcohol OR Muscle Cells Yeast & Bacteria

37. Aerobic respiration Reminder: aerobic respiration needs oxygen Aerobic respiration takes place in the mitochondria of eukaryotic cells The mitochondria is a membrane-bound organelle that acts in a similar manner to the chloroplasts dicussed in photosynthesis Aerobic respiration has 2 steps: Kreb’s cycle Electron transport chain

38. Aerobic respiration Aerobic respiration is simply the continuation of anaerobic respiration. All cellular respiration starts with anaerobic glycolysis as shown previously. When oxygen is available the pyruvic acid can be broken down many more times thus releasing far more energy.

39. Aerobic respiration So, instead of making lactic acid or alcohol, the pyruvic acid is further broken down, in a long series of steps, which release energy forming new ATP molecules. The stages pyruvic acid goes through are very complex. A detailed understanding is not necessary at this time. The aerobic portion of respiration is often shown in two sections. Krebs cycle Electron transport chain

40. Aerobic respiration Basically these complex processes break most of the bonds that made the original glucose molecule. As these bonds are broken the energy released is used to make ATP molecules. The ATP molecules are then available as a direct energy source for the cell to do its jobs.

41. Aerobic respiration Energy from breaking bonds is used to turn an ADP into an ATP ADP ATP

42. Kreb’s Cycle Energy from breaking bonds ADP + P + Energy  ATP Every time the Krebs cycle is completed a new ATP molecule is made. This cycle occurs twice for each glucose molecule forming two ATP molecules Aerobic Respiration Think of the electron transport chain as a series of steps in which a small bit of energy is given off as the ball falls down the stairs. Each step releases a little energy. The energy is used to make more ATP molecules Energy Electron Transport Chain In most cells(eukaryotic) 32 ATP molecules are made as the molecules “fall” through the steps.

43. Summary In aerobic respiration many complex reactions result in producing 38 ATP molecules from every glucose molecule consumed. 4 ATP from glycolysis in the cytoplasm 2 ATP from the Krebs cycle 32 ATP from the electron transport chain 38 ATP total produced by cellular respiration Since two ATP’s were needed to get this reaction started the NET ATP production is 36 ATP for every glucose molecule consumed. The balanced chemical formula for aereobic cellular respiration is: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy (ATP)

44. MITOCHONDRION CO 2 H2OH2O O2O2 ATP NADH Heat Electron Transport System ATP NAD + Pyruvate Glucose ATP

45. COMPARE PHOTOSYNTHESIS TO CELLULAR RESPIRATION Question: What biological interaction does this look like?

46. Sunlight Photo- System I Photo- system II NADP + ADP NADPH ATP Calvin CO 2 H2OH2O O2O2 ATP NAD + NADH Electron Transport System Cycle Citric Acid Heat CHLOROPLASTMITOCHONDRION ATP Glycolysis Glucose Pyruvate Cycle

47. Sunlight Photo- System I Photo- system II NADP + ADP NADPH ATP Cycle Calvin CO 2 H2OH2O O2O2 ATP NAD + NADH Electron Transport System Cycle Citric Acid Heat CHLOROPLASTMITOCHONDRION Glucose ATP Pyruvate Glycolysis