Photosynthesis Handout PDF

TOPIC: Photosynthesis A. Light Dependent Reaction Most Essential Learning Competency Describe the patterns of electron flow through light reaction event. (STEM_BIO11/12-IIa-j-4) Light dependent Reaction The energy from sunlight is absorbed by chlorophyll and that energy is converted in...

TOPIC: Photosynthesis A. Light Dependent Reaction Most Essential Learning Competency Describe the patterns of electron flow through light reaction event. (STEM_BIO11/12-IIa-j-4) Light dependent Reaction The energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. It uses light energy to make two molecules needed for the next stage of photosynthesis: the energy storage molecule ATP and the reduced electron carrier NADPH. Photosystem A photosystem is an aggregate of pigments and proteins in the thylakoid membrane responsible for the absorption of photons and the transfer of energy and electrons. o Light-harvesting complex o Reaction-center complex LIGHT-HARVESTING COMPLEX Consist of several different pigments (chlorophyll a, chlorophyll b, and carotenoids) bounded with proteins. When a pigment molecule absorbs a photon, energy is passed on from one pigment molecule to another pigment molecule until the energy reaches the reaction center. REACTION-CENTER COMPLEX Composed of a pair of chlorophyll a and a primary electron acceptor. – The primary electron acceptor is a specialized molecule that is able to accept electrons from the pair of chlorophyll a. – The pair of chlorophyll a in the reaction-center is also specialized because they are capable of transferring an electron to the primary electron acceptor and not just boosting the electron to a higher energy level. Comparison of Photosystem II and I Basis Photosystem I Photosystem II Basis Photosystem I Photosystem II What are they? These use light These are protein Pigment richly Chlorophyll a is Chlorophyll b is energy to convert complexes supplied with more compared to more compared to NADP+ to NADPH absorbing light chlorophyll b chlorophyll a energy. They function in the dissociation of water molecules. Location Outer surface of Inner surface of Photolysis of Water No Yes the grana thylakoid the grana thylakoid membrane membrane Reaction center P700 P680 Type of Cyclic and non-cyclic Non-cyclic photophosphorylati photophosphorylati photophosphorylati on on on Wavelength Approx. 700nm Approx. 680nm Function ATP synthesis Hydrolysis of water pigments NADPH synthesis and ATP synthesis absorbs. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. Photosystem II and ETC 1. Energy absorbed from sunlight Chlorophyll and other light-absorbing molecules in the thylakoid membrane absorb energy from sunlight. The energy is transferred to electrons (e–). High-energy electrons leave the chlorophyll and enter an electron transport chain, which is a series of proteins in the membrane of the thylakoid. 2. Water molecules split Enzymes break down water molecules. Oxygen, hydrogen ions (H+), and electrons are separated from each other. The oxygen is released as waste. The electrons from water replace those electrons that left chlorophyll when energy from sunlight was absorbed. 3. Hydrogen ions transported Electrons move from protein to protein in the electron transport chain. Their energy is used to pump H+ ions from outside to inside the thylakoid against a concentration gradient. The H+ ions build up inside the thylakoid. Electrons move on to photosystem I Photosystem I and Energy-Carrying Molecules 1. Energy absorbed from sunlight As in photosystem II, chlorophyll and other light-absorbing molecules inside the thylakoid membrane absorb energy from sunlight. Electrons are energized and leave the molecules. 2. NADPH produced. Photosystem I and Energy-Carrying Molecules The energized electrons are added to a molecule called NADP+, which functions like ADP. A molecule called NADPH is made. In photosynthesis, NADPH functions like ATP. The molecules of NADPH go to the light-independent reactions ATP Production 1. Hydrogen ion diffusion Hydrogen ions flow through a protein channel in the thylakoid membrane. Recall that the concentration of H+ ions is higher inside the thylakoid than it is outside. This difference in H+ ion concentration is called a chemiosmotic gradient, which stores potential energy. Therefore, the ions flow through the channel by diffusion. 2. ATP Production As the ions flow through the protein channel, ATP synthase makes ATP by adding phosphate groups to ADP. References https://opened.cuny.edu/courseware/lesson/644/student/?section=4 https://byjus.com/neet/difference-between-photosystem-1-and-photosystem-2/ https://ib.bioninja.com.au/higher-level/topic-8-metabolism-cell/untitled-2/light-dependent-reactions.html https://www.studocu.com/en-us/document/spelman-college/cell-biology/biology-worksheet/43808569 General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. B. Light Independent Reaction Most Essential Learning Competency The learners describe the significant events of the Calvin Cycle (STEM_BIO11/12-IIa-j-5) Calvin Cycle Also referred to as light-independent reactions Takes place in the stroma of the chloroplast Although the Calvin Cycle is not directly dependent on light, it is indirectly dependent on light since the necessary energy carriers (ATP and NADPH) are products of light-dependent reactions. Second stage of photosynthesis that is involved in the formation of sugar from CO2 using chemical energy stored in ATP and NADPH, the products of light reactions The cycle was discovered in 1950 by Melvin Calvin, James Bassham, and Andrew Benson at the University of California, Berkeley by using the radioactive isotope carbon-14. Stages of Calvin Cycle https://www.geeksforgeeks.org/calvin-cycle/ 1. CARBON FIXATION Carbon fixation is a process of incorporating an inorganic carbon molecule, CO2, into an organic material. In this phase, the CO2 molecule is attached to a five-carbon sugar molecule named ribulose biphosphate (RuBP) aided by an enzyme named rubisco or RuBP carboxylase. Rubisco is believed to be the most abundant protein in the chloroplast and maybe on Earth. The resulting product, a six-carbon sugar, is extremely unstable and immediately splits in half. The split forms two molecules of a 3-phosphoglycerate (3-carbon). 2. REDUCTION A phosphate group (from ATP) is then attached to each 3-phosphoglycerate by an enzyme, forming 1,3- phosphoglycerate. NADPH swoops in and reduces 1,3-biphosphogycerate to G3P. For every six G3Ps produced by the Calvin Cycle, five are recycled to regenerate three molecules of RuBP. Only one G3P leaves the cycle to be packaged for use by the cell. It will take two molecules of G3P to make one molecule of glucose. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students.  The ADP and NADP+ that is formed during the Calvin Cycle will be transported back to the thylakoid membrane and will enter the light reactions. Here, they will be ‘recharged’ with energy and become ATP and NADPH. 3. REGENERATION OF RuBP Five molecules of G3P undergo a series of complex enzymatic reactions to form three molecules of RuBP. This costs the cell another three molecules of AT, but also provides another set of RuBP to continue the cycle. The remaining glyceraldehyde-3-phosphate is then used to make glucose, fatty acids or glycerol. It takes two molecules of glyceraldehyde-3-phosphate to make one molecule of glucose phosphate. These molecules can remove their phosphate and add fructose to form sucrose, the molecule plants use to transport carbohydrates throughout their system. Glucose phosphate is also the starting molecule for the synthesis of starch and cellulose. To remove the phosphate group from the G3P, a process of glucogenesis will occur. References https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_%28Boundless%29/05%3A_Microbial_Metab olism/5.12%3A_Biosynthesis/5.12C%3A_The_Calvin_Cycle https://www.geeksforgeeks.org/calvin-cycle/ General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students.