Energy Transformation: ATP-ADP Cycle & Photosynthesis PDF

## Energy Transformation: ATP - ADP Cycle and Photosynthesis **Learning Objectives** The learners should be able to: 1. Explain coupled reaction processes and describe the role of ATP in energy coupling and transfer. 2. Describe the major features and chemical events in photosynthesis. 3. Explain...

## Energy Transformation: ATP - ADP Cycle and Photosynthesis **Learning Objectives** The learners should be able to: 1. Explain coupled reaction processes and describe the role of ATP in energy coupling and transfer. 2. Describe the major features and chemical events in photosynthesis. 3. Explain the importance of chlorophyll and other pigments. 4. Describe the patterns of electron flow through light reaction events. 5. Describe the significant events of the Calvin Cycle. **Activity** Match the fruit to its leaves. **Those plants starts from a tiny seed.** - How does it happen? - Where does the mass of a tree come from? - Where do they get their energy? **ATP-ADP Cycle** **The Flow of Energy** - All life on earth depends on the flow of energy through ecosystems. - All energy on the earth ultimately comes from the sun. **Organisms are classified according to their energy source** - Autotrophs - Heterotrophs **Autotrophs** - Organisms capable of making their own food. - Plants are photoautotrophs. - Photoautotrophs use light energy from the sun to produce glucose. **Heterotrophs** - Organisms not capable of making their own food. - Heterotrophs are consumers of the biosphere. - Heterotrophs must eat plants, or other animals who eat plants to acquire the energy indirectly from the sun. **Pyramid of Energy** The pyramid of energy shows the flow of energy through an ecosystem from producers to consumers to decomposers. It is based on the idea that only about 10% of the energy from one level is transferred to the next level. | Level | Energy (kcal) | | --------------- | -------------- | | Producers | 1,000 | | Primary Consumer | 100 | | Secondary Consumer | 10 | | Tertiary Consumer | 1 | **What is the energy currency of the cells of autotrophs and heterotrophs?** **Adenosine Triphosphate** Adenosine Triphosphate (ATP) is the common energy currency of the cells. - ATP is a molecule with one big molecule that is made of 5 smaller molecules bonded together. These include Adenosine, and three phosphate groups. **How energy is released from ATP?** ATP is constantly being broken down and rebuilt. - When a phosphate group is removed from ATP, energy is released. This process is called **hydrolysis**. - When a phosphate group is added to ADP, energy is needed. This process is called **phosphorylation**. **Key concepts of ATP/ADP Cycle** 1. ATP contains more energy that ADP because it has more bonds. 2. When a phosphate is removed, energy is released. 3. When a phosphate is added, energy is needed. **ATP-ADP Cycle: Carbohydrates** - Energy: Up to 36 ATP molecules (1 glucose). - Details: - Carbohydrates are most commonly broken down to make ATP. - Carbohydrates are not stored in large amount. **ATP-ADP Cycle: Fats/Lipids** - Energy: About 146 ATP molecules (triglyceride). - Details: - Lipids store the most energy. - Lipids make up 80% of the energy in our body. **ATP-ADP Cycle: Proteins** - Energy: About 36 ATP molecules. - Details: - Proteins are least likely to be broken down to make ATP. - Amino acids are not usually needed for energy. **Energy Content of Biomolecules** | Molecule | Energy | | --------------- | ------------------------------ | | Carbohydrates | 4 calories per mg | | Lipid | 9 calories per mg | | Protein | 4 calories per mg | **PHOTOSYNTHESIS** Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy that can be used to fuel the organism's activities - Photosynthesis converts light energy into the chemical energy of food. **PHOTOSYNTHESIS** - Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes (cyanobacteria and purple sulfur bacteria). **What are the requirements for photosynthesis to take place?** 1. Inorganic molecules (carbon dioxide and water). 2. Light energy. 3. Chlorophyll inside the chloroplast. **Carbon Dioxide and Water** - Carbon dioxide from the atmosphere enters the leaves of plants through stomata. - Water from the soil enters the roots of plants through the root hairs. **Sun Light** - When the white light from the sun passes through a prism, it produces the rainbow colors. - Two colors are used for photosynthesis: blue and red. These colors are trapped by chlorophyll a (P680 and P700) and b. - Most of the colors are reflected to the environment. **Chloroplasts: The Sites of Photosynthesis** Chloroplasts are organelles found in plant cells that are responsible for photosynthesis: - Chloroplasts reflect light, which includes the colors we see. - Chloroplasts have a double membrane with an inner membrane folded into stacks called grana, which are connected by stroma lamellae. The stroma lamellae connect the grana, creating an interconnected network of thylakoids throughout the chloroplast. **Chloroplasts: The Sites of Photosynthesis in Plants** - The leaves of plants are the major sites of photosynthesis. **Chloroplast** Chloroplasts are composed of: 1. Outer membrane 2. Inner membrane 3. Stroma that contains small circular DNA and ribosomes; its the area for dark reaction. 4. Thylakoids are piled into granum (plural: grana) - The membrane of the thylakoid consist of reaction centers, electron acceptors, and enzymes needed for light reactions. **Chloroplast: Chlorophyll** Chloroplasts are the sites of photosynthesis. Chlorophyll is a green pigment found in chloroplasts that absorbs light energy; - Thylakoid membrane consists of photosystem I (P700) and photosystem II (680) for light reaction; electron acceptors and ATPase. These systems are found in the chlorophyll, responsible for trapping light energy. - Chlorophyll a is the main photosynthetic pigment. - Chlorophyll b is an accessory pigment. **Chloroplast: Chlorophyll** - When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable. **Chloroplast: Chlorophyll** - Chloroplasts split water into Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules. **Chloroplast: Photosynthesis overview** Two phases of photosynthesis: 1. Light reactions: These reactions occur in the thylakoid membranes of chloroplasts. They use light energy to produce ATP and NADPH. 2. Dark reactions: These reactions occur in the stroma of chloroplasts. They use the ATP and NADPH produced in the light reactions, along with carbon dioxide, to produce glucose sugars. **Electrons from chlorophyll travel through the carriers organized in the "Z scheme" ** The Z scheme is a diagram that shows the flow of electrons through the light-dependent reactions of photosynthesis. - The Z scheme starts with photosystem II, where light excites the electron in a chlorophyll molecule. This energy is used to split water and release electrons. - The electrons move through a series of electron carriers. These electron carriers include the plastoquinone pool, the cytochrome b6f complex, and plastocyanin. - The electrons eventually reach photosystem I, which re-energizes them. - The energized electrons from photosystem I are used to reduce NADP+ to NADPH. This NADPH is used in the Calvin cycle. <strong>The transfer of electrons and protons is carried out by four protein complexes</strong> - The transfer of electrons and protons across the thylakoid membrane through four protein complexes generates a proton gradient, which is used by ATP synthase to produce ATP. - The four protein complexes that participate include: - Photosystem II (PSII) - Cytochrome b6f complex - Photosystem I (PSI) - ATP synthase - The protons move through ATP synthase, creating a chemiosmotic potential, which allows for the production of ATP. **How is ATP formed?** - Electron and proton transport form a proton motive force (PMF): PMF occurs as protons are pumped across the thylakoid membrane as electrons move down the electron transport chain - a process known as chemiosmosis. - PMF is used to make ATP. - The protons are produced through: - Splitting of water - Oxidation of plastoquinone - The light-dependent ATP synthesis is called **photophosphorylation.** - **Peter Mitchell (1960)** proposed the **chemiosmotic mechanism** - a theory that explains the coupling of electron transport and ATP synthesis. **ATP synthase (ATPase)** - ATP synthase is an enzyme found in the thylakoid membrane of chloroplasts that uses the proton gradient to produce ATP. **Light and Carbon reactions of Photosynthesis** Photosynthesis can be broadly categorized into two sets of reactions, which are often called light-dependent reactions and light-independent reactions (Calvin cycle). 1. Light Absorption: Electrons are "pulled" from water, and $O_2$ is evolved (Light reaction) 2. Electron Transport: NADPH is formed (Ligth reaction) 3. Generation of ATP: (Light reaction) 4. Conversion of $CO_2$ into Carbohydrates (Carbon reaction) **Overview of the Calvin Cycle - 3 Stages** The Calvin cycle is a series of chemical reactions that take place in chloroplasts during photosynthesis to convert carbon dioxide into sugar. The Calvin cycle is divided into three stages: 1. **Carbon fixation:** $CO_2$ is incorporated into an organic molecule. 2. **Reduction:** The organic molecule is reduced and energy is required from ATP and NADPH. 3. **Regeneration:** The starting molecule is regenerated. **The patterns of translocation of photosynthetic products: source to sink** Photosynthetic products or the metabolites move from the source to the sink. - **Source** = Area of supply - Exporting organs: mature leaves. - Storage organs: seed endosperm, storage root of second growing season beet. - **Sink** = Areas of metabolism (or storage) - Non-photosynthetic organs and organs that do not produce enough photosynthetic products to support their own growth or storage. - Example: roots, tubers, developing fruits/seeds, immature leaves. **Application of Photosynthesis.** - **In-vitro culture of plant tissues** - using fluorescent bulbs. - **Farming** **Thank you. Have a green day**