Cellular Energy 8.1 How Organisms Obtain Energy All living organisms use energy to carry out all biological processes. Transformation of Energy Macromolecules are assembled and broken down. Substances are transported across cell membranes. Genetic instructions are transmitted.

Cellular Energy All cellular activities require energy. Energy is the ability to do work.

Cellular Energy Thermodynamics is the study of the flow and transformation of energy in the universe. Laws of thermodynamics: 1. Law of conservation of energy – energy cannot be created or destroyed. 2. Energy cannot be converted without the loss of usable energy

Cellular Energy Examples of Laws of Thermodynamics: 1. stored energy in food is converted to chemical energy when you eat and to mechanical energy when you run or kick a ball. 2. Food chains – a food chain amount of usable energy that is available to the next trophic level decreases.

Cellular Energy Entropy – the measure of disorder, or unusable energy, in a system. Autotrophs – organisms that make their own food for energy through photosynthesis Heterotrophs – organisms that need to injest food to obtain energy

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 product of one chemical reaction is the substrate for the next reaction is called a metabolic pathway. Metabolic pathways come in two types: Catabolic and anabolic

Metabolism Catabolic pathways release energy by breaking down a larger molecule into smaller molecules. Anabolic pathways use the energy released by catabolic pathways to build larger molecules from smaller particles.

Metabolism The relationship of anabolic and catabolic pathways results in the continual flow of energy within an organism. Photosynthesis is the anabolic pathway in which light energy from the Sun is converted to chemical energy for use by the cell. In photosynthesis, autotrophs use light energy, carbon dioxide, and water to form glucose and oxygen. This can then be consumed by other organisms for food.

Metabolism Cellular respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cell. Oxygen is used to break down organic molecules resulting in the production of carbon dioxide and water. * Note the cyclic nature of these processes – the products of one reaction are the reactants for the other reaction.

ATP: The Unit of Cellular Energy Energy exists in many forms: *light energy *mechanical energy *thermal energy *chemical energy

ATP In biological molecules, chemical energy is stored and can be converted to other forms of energy when needed. Example: chemical energy is converted to mechanical energy when muscles contract. ATP – adenosine triphosphate : the most important biological molecule that provides chemical energy

ATP Structure ATP is a multipurpose storehouse of chemical energy that can be used by cells in a variety of reactions. ATP is the most abundant energy-carrier molecule in cells and is found in all types of organisms. ATP is a nucleotide made of an adenine base, a ribose sugar, and three phosphate groups.

ATP Function ATP releases energy when the bond between the second and third phosphate groups is broken, forming a molecule called ADP (adenosine diphosphate) and a free phosphate group. Energy is stored in the phosphate bond formed when ADP receives a phosphate group and becomes ATP.

ATP Function ATP and ADP can be interchanged by the addition or removal of a phosphate group. Sometimes ADP becomes AMP (adenosine monophosphate) by losing an additional phosphate group. There is less energy released in this reaction. Most of the energy reactions in the cell involve ATP and ADP.

Energy Cycles Sunlight  Photosynthesis (autotrophs)  O2 + Glucose Cellular respiration (heterotrophs)  C02 + H2O Sunlight ATP energy + phosphate +ADP ATP

8.2 Photosynthesis Light energy is trapped and converted into chemical energy during photosynthesis. Most autotrophs – including plants – make organic compounds, such as sugars by a process in which light energy is converted into chemical energy.

Photosynthesis Chemical equation for photosynthesis: 6CO2 + 6H2O — light C6H12O6 + 6O2

Photosynthesis Occurs in two phases: *Light Reactions *The Calvin Cycle Phase One – light-dependent reactions - light energy is absorbed - light energy converted into chemical energy - forms ATP and NADPH

Photosynthesis Phase Two: light-independent reactions - makes glucose using ATP and NADPH. - Once glucose is produced, it can be joined to other simple sugars to form larger molecules – complex carbohydrates (starch)

Light Reactions First step: Absorbption of light Plants have special organelles to capture light energy – chloroplasts. Once energy is captured, two energy storage molecules are produced: NADPH ATP

Chloroplasts Large organelles Capture light energy Found mainly in the cells of leaves Disc-shaped organelles Contain two main compartments: *thylakoid – flattened saclike membranes arranged in stacks called grana. *stroma – fluid-filled space outside the grana

Chloroplasts Light-dependent reactions take place in the thylakoids. Light-independent reactions take place in the stroma. Light-absorbing colored molecules called pigments are found in the thylakoid membranes.

Chloroplasts Different pigments absorb specific wavelengths of light. The major light-absorbing pigment in plants is chlorophyll. There are several types of chlorophylls, most important two are: *chlorophyll a *chlorophyll b

Chloroplasts Structure can differ from one molecule to another. Enables distinct chlorophyll molecules to absorb light at unique areas of the visible spectrum. Absorb most strongly in violet-blue region of visible light spectrum. Reflect light in the green region of the spectrum.

Chloroplasts This is why plant parts that contain chlorophyll appear green to the human eye!

Chloroplasts In addition to chlorophylls, most photosynthetic organisms contain accessory pigments that allow plants to trap additional light energy from other areas of the visible spectrum. Example: carotenoids (beta-carotene) absorb light mainly in the blue and green regions – reflect light in the yellow, orange and red regions – carrots, sweet potatoes

Chloroplasts What happens to the chlorophyll molecules of trees in the fall?

Electron Transport The structure of the thylakoid membrane is the key to efficient energy transfer during electron transport. Thylakoid membranes have large surface area, providing the space needed to hold large numbers of electron-transporting molecules and two types of protein complexes called photosystems.

Electron Transport Photosystem I and Photosystem II contain light-absorbing pigments and proteins that play an important role in the light reactions. 1. light energy excites electrons in photosystem II causing a water molecule to split, releasing an electron into the electron transport chain A hydrogen ion (H+) goes into the thylakoid space and oxygen (O2) becomes a waste product The breaking down of water is essential for photosynthesis to occur.

Electron Transport 2. The excited electrons move from photosystem II to an electron-acceptor molecule in the thylakoid membrane. 3. The electron-acceptor molecule transfers the electrons along a series of electron-carriers to photosystem I. 4. In the presence of light, photosystem I transfers the electrons to a protein called ferrodoxin. The electrons lost by photosystem I are replaced by electrons shuttled from photosystem II.

Electron Transport Ferrodoxin transfers the electrons to the electron carrier NADP+, forming the energy-storage molecule NADPH.

Chemiosmosis ATP is produced in conjunction with electron transport by the process of chemiosmosis – the mechanism by which ATP is produced as a result of the flow of electrons down a concentration gradient. Essential – the breakdown of water – provides the electrons that initiate the electron transport chain and also provides the protons (H+) necessary to drive ATP synthesis during chemiosmosis.

Chemiosmosis The H+ released during electron transport accumulate in the interior of the thylakoid. High concentration of H+ in the thylakoid interior and low concentration of H+ in the stroma causes H+ to diffuse down their concentration gradient out of the thylakoid interior into the stroma through ion channels. Figure 8.8 pg. 225 These channels are enzymes called ATP synthatases. As H+ moves through ATP synthatase, ATP is formed in the stroma.

The Calvin Cycle

The Calvin Cycle NADPH and ATP provide cells with large amounts of energy – but not stable enough to store chemical energy for long periods Calvin Cycle allows for energy storage in the form of glucose Light-independent

The Calvin Cycle Step 1: Carbon fixation – six CO2 molecules combine with six 5-carbon compounds to form twelve 3-carbon molecules called 3-phosphoglycerate (3-PGA) Step 2: Chemical energy stored in ATP and NADPH is transferred to the 3-PGA molecules to form high-energy molecules called glyceraldehyde 3- phosphates (G3P) ATP supplies the phosphate groups for forming G3P, while NADPH supplies H+ and electrons.

The Calvin Cycle Step 3: Two G3P molecules leave the cycle to be used for the production of glucose and other organic compounds Step 4: Final stage – An enzyme, rubisco, converts the remaining 10 G3P molecules into 5-carbon molecules called ribulose 1 , 5-bisphosphates (RuBP) which combine with new CO2 molecules to continue the cycle

The Calvin Cycle Rubisco – one of the most important biological enzymes Plants use sugars formed during Calvin Cycle both as a source of energy and as building blocks for complex carbohydrates Complex carbohydrates include cellulose providing structural support for plants.

Alternative Pathways If plants do not have sufficient water, CO2, or sunlight, they use adaptive pathways. C4 plants: occurs in plants, such as sugar cane and corn *they fix CO2 into 4-carbon compounds instead of 3-carbon molecules *have significant structural modifications in arrangement of leaves *keep their stomata closed on hot days *carbon compounds are transferred to special cells where CO2 enters the Calvin Cycle *allows for sufficient CO2 uptake, while minimizing water loss

Alternative Pathways CAM plants: crassulacean acid metabolism Occurs in water-conserving plants Allow CO2 to enter leaves only at night Fix CO2 into organic compounds During day CO2 is released from these compounds and enter the Calvin Cycle Allows for sufficient CO2 uptake with minimal water loss.