Hello everyone. Welcome back to my COURSERA class: Biochemical Principles of Energy Metabolism. My name is Seyun Kim from KAIST in Korea. We are beginning week four. Why don't we review previous three weeks. The first week was about the basic concept of metabolic processes. In the second week we reviewed about various metabolic organs and in the very beginning, we started with the, how we feel hunger. The answer is Ghrelin Hormone release an action on your brain hypothalamic region. And carbohydrates it's going to be consumed and then digested and then absorbed. And then, the previous week, week three, we went into the glucose breakdown processes. Three reprocesses glycolysis, citric acid cycle and Oxidative phosphorylation, OXPHOS pathway. And finally, we studied about how ATP can be extracted, generated out of glucose oxidation processes. What about this week, week four? Week four is about photosynthesis. So, for today in the first session, I'm going to give you an overview about energy cycle and the basic principle of photosynthesis, and secondly week light-dependent reaction and Carbon fixation. And finally, I'm going to introduce various plant metabolic strategies to cope against harsh environmental condition to make sure photosynthesis can proceed. Okay. So, let's talk about Energy cycle in life on this planet Earth. So basically, human beings and many Heterotrophs, we are relying on plants and algae and those photosynthetic Autotroph and plants and algae, those photosynthetic bacteria can produce high energy containing organic compound by using the light energy from the sun. And then, the other major product out of these photosynthetic reaction is oxygen. And this oxygen and organic compound, I mean, sugar, glucose can be consumed and utilized for sustaining our life, our means human beings. So, let me begin with the sunlight. So, according to Quantum mechanical theory of radiation, light can be viewed as both waves, as well as particles. So, and then we can calculate, well let's calculate the amount of energy from the sun. So, we have to think of light as a stream of particles, particles so-called photons and those photons from the sun exhibit like wave property. The wavelength is quite diverse, the visible range and invisible range. High energy and low energy spectrum. And the amount of energy from the sun can be expressed as a product of Planck's constant and the frequency of light. So over all, one mole of photons can give us almost 109 kilojoule which means a lot. So, let's talk about plant cells, which are responsible for photosynthetic biochemical reactions. So, compared to animal cells, plant cells have unique thick and rigid cell wall structure and ions and nutrient containing Vacuoles structures. You can see over here in this diagram huge Vacuoles, quite dramatically developed inside the plant cells. And the last, the unique feature of plant cell is the presence of Chloroplast. So, what is Chloroplast? Chloroplast is the organelle, the organelle of photosynthesis for glucose breakdown in ATP generation in both animal and plant cells, can be mediated by the action of the mitochondria. You remember the previous lecture information. So, in this photosynthetic reactions, Chloroplast is the organelle, for photosynthetic reactions. Its main job is to capture light energy from the sun obviously and then utilize it for food generation, that means sugar production as well as the oxygen release. As you can see this diagram, let me briefly show the simple diagram. Chloroplast is also a double membrane organelle. Outer membrane and inner membrane and this space inside of chloroplast, the so-called Stroma. You can see also this diagram Stroma here, the fluid. And the inside the chloroplast there is another membrane structure so-called the Thylakoid membrane and those are sack like. Thylakoid membrane structures are quite clearly and massively developed. So, let me introduce a little bit more about Chloroplast. So, obviously chloroplast is the site for photosynthetic reactions and it's like mitochondria, chloroplast also contain its own, their own genome DNA genetic material, and the minimal molecular machinery like tRNA or Ribosomal RNA for their own genomic information, genetic information processing. And then, as I expressed in the previous slide, there is the third membrane structure which is a Thylakoid membrane structure and this Thylakoid membrane structure is the main site, main compartment for photosynthetic reaction. And in plants, so obviously there is a collection of pigments. Pigments means the specialized chemical organic compound which is very very specialized for absorbing light. You are looking at over here chlorophyll pigments, a and b are those two most abundant pigments available for photosynthetic reactions in plant cells. And photosynthesis is, I mean the chemical formula for photosynthesis can be expressed like this, CO2 molecules and water. This CO2 you know in other word inorganic, that means from the air, atmospheric. Carbon dioxide can be fixed into solid organic compound, glucose. And as a by-product out of this reaction, oxygen can be synthesized, released. And this reaction thermodynamically, the free energy, G value is over 2800 kilojoule per mole. That thing is you have to keep in mind that this is positive, 2870 kilojoule per mole, which means this reaction is Endergonic, that means this reaction is very very difficult to occur. So, to drive this reaction, huge amount of energy from the sun supposed to be supplied. This is the basic simple overview of Photosynthesis. So, what's going on? What's going on inside the chloroplast? This is the more advanced type of review diagram for photosynthesis. So, inside the chloroplast as I said, there is the third membrane structure, Thylakoid membrane structures available. And we can divide this photosynthesis into two. One is Light-dependent reaction, second reaction is scalloping cycle. So light-dependent reaction is as its name implies, this reaction is exclusively dependent upon the light energy and as a product of this light-dependent of reaction ATP and the other product NADPH which means electron carriers can be produced. And these these products are indeed utilized for Calvin cycle. So, Calvin cycle is the cycle for fixing inorganic carbon dioxide into organic compound glucose. So, I'm going to wrap up this session by showing this written summary. There are two stages of photosynthesis: Light-dependent reaction and light independent reaction so-called Calvin cycle. So, Light-dependent reaction is about the generation of ATP which means energy source and the other one is NADPH which means electron donors, electron carriers and oxygen. The Calvin cycle is about production of organic molecules like glucose by consuming ATP and NADPH produced from light-dependent reaction.
