Original video: https://youtu.be/e3pR9WMA8yU
This video explores how plants have evolved ingenious "Carbon Concentrating Mechanisms" (CCMs) to overcome the limitations of the enzyme Rubisco. We'll dive into why Rubisco's tendency to bind oxygen leads to wasteful photorespiration and how CCMs help plants minimise this problem by concentrating CO2.
Video Transcript:
Two lessons, you're going to see that the concept of carbon concentration mechanism. The idea is simple, this is all to deal with the inefficiency of Rubisco. Rubisco, it's an ancient enzyme, called dual affinity. It can catalyze two reactions, oxygenation and carboxylation. If it does carboxylate, then that's good, you got your sugar precursor. But if it does oxygenation, then you come with this wasteful, metabolically wasteful photorespiration.
So, there are two more carbon metabolisms that employ this carbon concentrating mechanism that you're going to see today, C4 and also CAM. This is actually a pre-test. Not to worry, we're not going to do it now, we do it in the afternoon. So, let's dive in. What's the story about?
Are you familiar with evolution? Did you learn evolution in any of the classes before? Have you learned evolution before? Did you take your soil science? Did you learn the Bowen reaction series? You got your lava, it solidifies. The first thing you get, the glassy rock, the obsidian, the pumice, and so on. Did you learn that?
In Soil Science, you learn there is a section about rock genesis, okay? You learn about metamorphic rock, igneous rock, sedimentary rock. These things all take a very long time to happen, especially the sedimentary rock and also the metamorphic, right? Igneous rock is quite straightforward, from the lava, it cools down, then you get your rock. Igneous, Latin, it means fire.
The concept here is similar, like evolution, with the progression of times, things change, just the effect of time to it, because time makes a lot of other events happening on the subject. In the case of metamorphosis, what factors change the original igneous rock? You start with igneous rock, and then after 200 million years, it changes into a metamorphic rock. So, what are the factors affecting this? Pressure, temperature, cementation, so many things. Then you got your metamorphic rock. From the slate, you get your marble, from sheets, you got quartz, and so on.
Evolution, kind of like that. The terminology of evolution is not only restricted in the case of, from rat, you get human, you get orangutan, okay? Is the concept of the change of, developmental, physical of something, right? The baby, the embryo, the zygote in the fetus, evolve to form a full-grown baby. It started with just two cells, right? So, it will evolve.
The concept also applies here. Most of the plants, actually, C3 plants started, that's the ground of it. However, due to the decline of CO2, the increase of oxygen, it's causing the function of Rubisco, which started very long, long time ago, not any more suitable for the current environment. Meaning that, Rubisco, it's actually quite happy with whatever environment it was from 200 million years ago. But now, what has changed now in terms of oxygen, carbon dioxide concentration?
In the past, do we have more CO2 or less CO2? Why? Because, at first, the photosynthesis is still not around, you still get all these individual bacteria and microbes that still do not do this endosymbiotic-like activity. So, they are pretty much producing CO2. Because there's no photosynthesis. But with the advent of photosynthesis, there is a booming of oxygen, which is good, because other lives started to appear, and this is why you get all the dinosaurs, and birds, and so on, including your sinful ancestor. The problem is, Rubisco is not equipped with this. It's kind of happy in the high CO2, but not in high oxygen. However, it still needs to do the job, but it doesn't really evolve until now. So, some plants, they had to go through with this, and on top of it, certain plants, especially in the hot, arid climate, think of Brazil, think of Peru, think of Mexico, think of, uh, you know, certain dry area in Thailand, they got the distinct dry period.
So, the plants in this region, they have actually undergone very difficult situation. In addition to the inefficient Rubisco, they have to deal with the Rubisco's stubbornness to do photorespiration, and then they need to reproduce. So, over the time, the plants actually have started to evolve their self-characteristics. Two important things, they change the biophysical appearance of it, meaning that they change the leaf structure, they evolve, and also they change the biochemical pathway inside the leaf.
It is still a plant, okay? It's not like, suddenly, it evolved to become some kind of alien, no. If you go out, and you compare between the corn and other grass plant, it still looks like a plant. So, suddenly the crown, uh, the sorry, the corn is wearing a skirt. It looks similar on the outside, but anatomically it's different. Biochemically it's different. So, what's the different? So, that different is very crucial to deal with photorespiration. Remember, the whole idea is to prevent photorespiration from happening.
Keywords: Carbon fixation, photosynthesis evolution, plant physiology, biochemistry, Rubisco, photorespiration, carbon concentrating mechanisms, C3 photosynthesis, C4 pathway, CAM photosynthesis
Reference book: Plant Physiology and Development 7th Edition
by Lincoln Taiz, Ian Max Møller, Angus Murphy, Eduardo Zeiger
Watch full video: https://youtu.be/0rBZkk8AYRg
Attribution 4.0 International — CC BY 4.0 - Creative Commons
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