Chapter 8: Cellular Energy

Transcription

1 Chapter 8: Cellular Energy

2 Section 1: How Organisms Obtain Energy

3 Transformation of Energy All cellular activities require Energy!! ( The ability to do work). The study of flow and the transformation of energy is called Thermodynamics. There are two laws of thermodynamics.

4 Laws of Thermodynamics 1.The law of conservation of energy. Energy can be converted to one form to another, but cannot be created nor destroyed. Ex. Stored energy in food is converted to chemical energy when you eat and into mechanical energy when you run or kick a ball.

5 2. Energy cannot be converted without the loss of usable energy. Energy that is lost is converted without the loss of usable energy. Entropy- Is the measure of disorder, or unusable energy, in a system. Ex. Food chain ( energy decreases with the next trophic level)

6 Organisms that make their own food are called Autotrophs. Some autotrophs (Chemoautotrophs) use inorganic substances such as hydrogen sulfide as a source of energy while others, such as plants, convert light energy from the sun into chemical energy. Autotrophs that convert energy from the sun are called Photoautotrophs.

7 Heterotrophs are organisms that need to ingest food to obtain energy.

8 Metabolism All of the chemical reactions in a cell are referred to as the Cell s Metabolism. A series of chemical reactions in which the products is the substrate (starting products) for the next reaction is called a metabolic pathway.

9 There are two broad categories of metabolic pathways. 1. Catabolic Pathways Release energy by breaking down larger molecules to smaller molecules. 2. Anabolic Pathways Use the energy released from catabolic pathways to build larger molecules from smaller molecules. The relationship between these two pathways results in the continual flow of energy within an organism.

10 Photosynthesis The anabolic pathway in which light energy from the sun is converted to chemical energy for use by the cell. In this reaction autotrophs use light energy, carbon dioxide, and water to form glucose and oxygen. The energy stored in the glucose produced can be transferred to other organisms when those molecules are consumed as food.

11 Cellular Respiration The catabolic pathway in which organic molecules are broken down to release energy for use by a cell. In cellular respiration oxygen is used to break down organic molecules, producing carbon dioxide and water.

12 ATP: The Unit Of Cellular Energy Adenosine triphosphate (ATP) is the most important biological molecule that provides chemical energy. ATP Structure: Nucleotide made of an adenine base, a ribose sugar, and three phosphate groups.

13 ATP Function ATP releases Energy when the bond between the second and third phosphate group is broken. (forming ADP)

14 Section 2: Photosynthesis Phase # 1

15 Photosynthesis Process by which most autotrophs, including plants, make organic compounds such as sugars. Recall that during this process Light energy is converted into chemical energy(glucose and Oxygen). 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

16 Photosynthesis Occurs in Two Phases In Phase 1 (lightdependent reactions) light is absorbed and converted into chemical energy in the form of NADPH and ATP. In Phase 2 ( lightindependent reactions) the ATP and NADPH that were formed in phase one are used to make glucose.

17 Once glucose is produced, it can be joined to other simple sugars to form larger molecules. Their larger molecules are complex carbohydrates(such as starch) and other organic molecules (proteins, lipids and acids).

18 Phase one: Light Reactions The first step in photosynthesis is the absorption of light. Plants have special organelles to capture light energy called chloroplasts. Once the energy is captured, two energy storage molecules, NADPH and ATP, are produced to be used in the light-independent reaction.

19 Chloroplasts Large organelles that are used to capture light energy in photosynthetic organisms. In plants, chloroplasts are found mainly in the cells of their leaves.

20 Disk-shaped organelles that contain two main compartments important for photosynthesis. 1. The Thylakoid Flattened, saclike membranes that are arranged in stacks (Grana). Location where lightdependent reactions take place.

21 2. The stroma Fluid like space that Is outside of the grana. Location where Lightindependent reactions take place in phase 2.

22 Light-absorbing colored molecules called pigments are found within the thylakoid membranes of chloroplasts. The major light-absorbing pigments in plants are called chlorophylls. (most common are chlorophyll A and B.

23 Different pigments absorb different wavelengths of light. Chlorophylls absorb most strongly in the violet-blue region of the visible light spectrum. This is why plants appear Green to the human eyes.

24 Electron Transport The Structure of the thylakoid membrane is the key to efficient transfer during electron transport. Thylakoid membrane has a large surface area, which provides space to hold large numbers of electron transporting molecules and photosystems (electrontransporting molecules.)

25 Photosystem 1 and 2 contain light absorbing pigments and proteins that play major roles in the light reaction phase.

26 How exactly does this work?

27 First, the light energy excites electrons in photosystem 2 and causes water molecules to split, releasing an electron into the electron transport system.

28 hydrogen ion (H + ) are released into the thylakoid space and oxygen (O 2 ) as a waste product. * This break down of water is essential for photosynthesis to occur.

29 The excited electrons move from photosystem 2 to an electron acceptor molecule in the thylakoid membrane.

30 The electronacceptor molecule transfers the electrons along a series of electroncarriers in photosystem 1.

31 In the presence of light, photosystem 1 transfers the electrons to a protein called ferrodoxin. The electrons lost by photosystem 1 are replaced by electrons shuttled from photosystem 2.

32 Finally, ferrodoxin transfers the electrons to the carrier NADP +, forming NADPH.

33 ATP is produced in conjunction with electron transport by the process of chemiosmosis. The H + released during the electron transport acclimated in the interior of the thylakoid (causing a high concentration in the interior and a low in the exterior)

34 H + protons will diffuse down their concentration gradient out of the thylakoid interior into the stroma through a channel spanning the membrane (enzymes called ATP synthases) As H + moves through the ATP synthase, ATP is formed in the stroma.

35 Section 2: Photosynthesis Phase # 2

36 RECAP! The end products for the first phase of photosynthesis were ATP and NADPH.

37 Phase 2: The Calvin Cycle ATP and NADPH are able to provide the cell with a large amount of energy but they are not stable enough to store chemical energy for a long period of time. This is when the second phase of photosynthesis comes into play!

38 The Calvin Cycle! Also referred to as Light-independent reactions. Stores energy in organic molecules, such as glucose.

39 How exactly does this work?

40 The first step is called carbon fixation. Six carbon dioxide molecules (CO 2 ) combine with six 5-carbon compounds to form Twelve 3-Carbon molecules called 3- phosphoglycerate(3- PGA).

41 In the second step, the chemical energy stored in ATP and NADPH is transferred to the 3-PGA molecules to form highenergy molecules called glyceraldehyde 3-phosphate (G3P). ATP provides the phosphate groups, which NADPH supplies the hydrogen ions and electrons.

42 In the third step, two G3P molecules leave the cycle to be used for the production of glucose and other organic molecules.

43 In the final step, an enzyme called rubisco converts the remaining G3P molecules into 5- carbon molecules called Rubisco 1,5- bisphosphate (RuBP).

44 These molecules combine with new carbon dioxide molecules to continue the cycle.