Chapter 8 Cellular Energy

1. Chapter 8 Cellular Energy Biology

2. Section 8.1 How Organisms Obtain Energy • Main idea – All living organisms use energy to carry out all biological processes • Objectives • Summarize the two laws of thermodynamics • Compare and contrast autotrophs and heterotrophs • Describe how ATP works in a cell

3. Transformation of Energy • All cellular activities require energy; the ability to do work • Thermodynamics is the study of the flow and transformation of energy in the universe

4. Laws of Thermodynamics • The 1st Law – “Law of conservation of energy” – Energy can be converted from one form to another, but it cannot be created nor destroyed • The 2nd Law – Energy that is “lost” is generally converted to thermal energy – “entropy increases” • Entropy – measure of disorder or unusable energy, in a system.

5. Autotrophs & Heterotrophs • Autotrophs – organisms that make their own food • Chemoautotrophs – uses chemicals as a source of energy • Photoautotrophs – convert light energy from the Sun into chemical energy • Heterotrophs – organisms that need to ingest food to obtain energy

6. Metabolism • All of the chemical reactions in a cell are referred to as the cell’s metabolism • Metabolic pathway is a series of chemical reactions in which the product of one reaction is the substrate for the next reaction • Catabolic pathways – releases energy by breaking down larger molecules into smaller ones • Anabolic pathways –uses the energy released by catabolic pathways to build larger molecules from smaller molecules • The continual flow of energy within an organism is the result of the relationship of anabolic and catabolic pathways

7. Photosynthesis • Photosynthesis is the anabolic pathway in which light energy from the Sun is converted to chemical energy for use by the cell • 6CO2 + 6H2O  C6H12O6 + 6O2

8. Cellular Respiration • Cellular Respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cells • C6H12O6 + 6O2 6CO2 + 6H2O + ATP

9. Photosynthesis & Cellular Respiration Form a Cycle

10. ATP: The Unit of Cellular Energy • Adenosine Triphosphate (ATP) is the most important biological molecule that provides chemical energy • ATP is made of an adenine base, a ribose sugar, and three phosphate groups • ATP releases energy when the bond between the second and third phosphate groups are broken, forming adenosine diphosphate (ADP) and a free phosphate group • Energy is stored in the phosphate bond formed when ADP receives a phosphate group and becomes ATP

12. Section 8.2 Photosynthesis • Main idea – Light energy is trapped and converted into chemical energy during photosynthesis • Objectives • Summarize the two phases of photosynthesis • Explain the function of a chloroplast during the light reactions • Describe and diagram electron transport

13. Overview of Photosynthesis • Photosynthesis is a process in which light energy is converted into chemical energy • 6CO2 + 6H2O  C6H12O6 + 6O2 • Photosynthesis occurs in two phases • Phase 1-Light-dependent reactions-light energy is absorbed and then converted into chemical energy in the form of ATP and NADPH • Phase 2-Light-independent reactions-the ATP and NADPH formed in phase 1 is used to make glucose

14. Chloroplasts

15. Phase 1: Light Reactions • Chloroplasts – capture light energy in photosynthetic organisms; disc-shaped organelles that contain two main compartments • Thylakoids are flattened saclike membranes that are arranged in stacks (grana) and are the location of light-dependent reactions • Stroma are the fluid spaces outside the grana and are the location of light-independent reactions

16. Pigments • Pigments are light-absorbing molecules found in the thylakoid membranes of chloroplasts • Chlorophylls are the major light-absorbing pigments in plants; reflecting green light • Accessory pigments allow plants to trap additional light energy • Carotenoids – reflect yellow, orange and red light

17. Electron Transport • See Figure 8.8 on page 225 • Activated electrons are passed from one molecule to another along the thylakoid membrane in a chloroplast. The energy from electrons is used to for a proton gradient. As protons move down the gradient, a phosphate is added to ADP, forming ATP

18. Electron Transport (cont.) • Light energy absorbed by photosystem II is used to split a molecule of water. When water splits, oxygen is released from the cell, protons (H+; hydrogen ions) stay in the thylakoid space and an activated electron enters the electron transport chain • As electrons move through the membrane, protons are pumped into the thylakoid space • At photosystem I, electrons are re-energized and NADPH is formed

19. Electron Transport (cont.) • Chemiosmosis: Protons accumulate in the thylakoid space, creating a concentration gradient • When protons move across the thylakoid membrane through ATP synthase, ADP is converted to ATP (photophosphorylation) http://highered.mheducation.com/olc/dl/120072/bio13.swf

20. Phase 2: Calvin Cycle Light-independent Reactions • Calvin Cycle – the second phase of photosynthesis in which energy is stored in organic molecules such as glucose • See Figure 8.9 on p. 226 • First step – carbon fixation - 6CO2 + 6 RuBP (ribulose 1,5-biphosphate a 5-carbon compound) to form 12 3-PGA (3-phosphoglycerate, a 3-carbon molecule) • Second step – the chemical energy stored in 12 ATP and 12 NADPH is transferred to the 12 3-PGA to form 12 G3P (glyceraldehyde 3-phosphate, high energy molecules)

21. Calvin Cycle (cont.) • Third step – 2 G3P leave the cycle to form glucose and other organic compounds • Final step – An enzyme called rubisco converts the remaining 10 G3P into RuBP. • Plants use the sugars formed during the Calvin Cycle both as source of energy and as building blocks for complex carbohydrates, including cellulose, which provides structural support for the plant

22. Alternative Pathways • Many plants in extreme climates have alternative photosynthesis pathways to maximize energy conversion • C4 plants minimize water loss by closing stoma in hot days as they fix carbon dioxide into 4-carbon compounds instead of the 3-carbon molecules during the Calvin Cycle • CAM plants (crassulacean acid metabolism) occurs in water-conserving plants as CO2 enters leaves at night fixing it into organic molecules. During the day, CO2 is released and enters the Calvin Cycle

23. 8.3 Cellular Respiration • Main idea – Living organisms obtain energy by breaking down organic molecules during cellular respiration • Objectives • Summarize the stages of cellular respiration • Identify the role of electron carriers in each stage of cellular respiration • Compare alcoholic fermentation and lactic acid fermentation

24. Overview of Cellular Respiration • Organisms obtain energy in a process called cellular respiration • The function of cellular respiration is to harvest electrons from carbon compounds, such as glucose, and use that energy to make ATP • C6H12O6 + 6O2 6CO2 + 6H2O + ATP

25. Cellular Respiration (cont.) • Two main parts • Glycolysis • Anaerobic process – do not require oxygen • Aerobic Respiration • Krebs cycle & electron transport • Aerobic process – requires oxygen

26. Glycolysis • Glucose is broken down in the cytoplasm through the process of glycolysis, refer to Figure 8.12 on p. 229 • First, 2 phosphate groups are joined to glucose • Second, the 6-carbon molecule is broken down into 2 G3P • Next, two phosphates are added and electrons and hydrogen ions combine to produce 4 ATP and 2 NADH, respectfully • Last, the 2 G3P are converted into 2 pyruvate molecules • Glycolysis has a net yield of 2 ATP molecules

27. Krebs Cycle • The series of reactions in which pyruvate is broken down into carbon dioxide is called the Krebs cycle or tricarboxylic acid (TCA) cycle. • This cycle is known as the citric acid cycle, too • The Krebs cycle occurs inside the mitochondria of cells, refer to Figure 8.13 on page 230

28. Krebs Cycle (cont.) • Prior to the Krebs cycle, pyruvate reacts with coenzyme A (CoA) to form acetyl CoA • At the same time CO2 is released and NAD+ is converted into NADH • The reaction results in the production of 2 CO2 molecules and two NADH • The cycle begins with acetyl CoA combining with a 4-carbon compound to form citric acid, a 6 carbon compound

29. Krebs Cycle (cont.) • Then, citric acid is broken down in the next series of steps, releasing 2 molecules of CO2 and generating one ATP, three NADH, and one FADH2. FAD is another electron carrier similar to NAD+ and NADP+ • Finally, acetyl CoA and citric acid are generated and the cycle continues • The net yield from the Krebs cycle is 6 CO2 molecules, 2 ATP, 8 NADH, and 2 FADH2. • NADH and FADH move on to play a significant role in the next stage of aerobic respiration

30. Electron Transport • Refer to Figure 8.14 on p. 231 • Electrons move along the mitochondrial membrane from one protein to another • Electrons are transported to oxygen to form water • Electron transport produces 24 ATP • Each NADH molecule produces 3 ATP • Each group of 3 FADH2 produces 2 ATP • In eukaryotes, one molecule of glucose yields 36 ATP • In prokaryotes, one molecule of glucose produces 38 ATP

31. Anaerobic Respiration • The anaerobic pathway that follows glycolysis is anaerobic respiration, or fermentation • Fermentation occurs in the cytoplasm and regenerates the cell’s supply of NAD+ while producing a small amount of ATP • Two types • Lactic acid fermentation • Alcohol fermentation

32. Lactic acid fermentation & Alcohol fermentation • Lactic acid fermentation • Enzymes convert the pyruvate made during glycolysis to lactic acid • When oxygen is absent or in limited supply, fermentation can occur • Skeletal muscles during strenuous exercise • Microorganisms to produce cheese, yogurt & sour cream • Alcohol fermentation • Occurs in yeast and some bacteria when pyruvate is converted to ethyl alcohol and CO2

33. Photosynthesis & Cellular Respiration • Processes cells use to obtain energy • Metabolic pathways that produce and break down simple carbohydrates • The products of Photosynthesis are oxygen and glucose – the reactants needed for cellular respiration • The products of cellular respiration – carbon dioxide and water – are the reactants for photosynthesis