Original video: https://youtu.be/n8siyvawuiE
Delivered on: 27 NOVEMBER 2023
Photorespiration is a complex process that occurs in plants when the enzyme rubisco, responsible for carbon fixation in photosynthesis, binds with oxygen instead of carbon dioxide. This creates a toxic byproduct that the plant must recycle through a series of reactions involving three organelles: the chloroplast, peroxisome, and mitochondrion. This process, while metabolically expensive, is essential for plants to recover carbon, maintain metabolic stability, and protect themselves from damage.
Video Transcript:
Now, what happens to glycine here? So, this glycine, it will proceed to the, the third organelle. What is that? Mitochondria or mitochondrion. Glycine. So, in the mitochondrion, this glycine can be converted to serine, another amino acid. And in the process, it releases a number of things. It releases NADH. It releases CO2. It releases ammonium ion, NH4⁺. You see, you start to get back your CO2 here. This is the first step you start to get back CO2. Just now, you have lost your CO2 in the form of two-carbon phosphoglycolate. Plants want to release back this. I want CO2, stop making unnecessary compounds. So, this is the first step, CO2 is retrieved back.
And based on this table, that would be reaction number six, is that right? Yep, number six. It might look a bit complicated in there because glycine to serine is not a straight process, okay? What happens is, I know it looks a bit complicated there. Let's, let's put it this way, glycine needs to react with NAD⁺, okay? Then it reacts with GDC. This is actually an enzyme, glycine decarboxylase complex. When you see it in this form, meaning that this thing is not activated yet, okay? It's not activated yet.
When this thing is activated, when this thing happens, you will get, I'm talking about reaction number six, okay? You will get your GDC-THF-CH2 plus NADH plus CO2 plus NH4⁺. Do you see any serine yet? No, there is no serine because this is the key molecule here. How do you pronounce this such a long, MTH thing? Activated methylene tetrahydrofolate, okay? Originally, it's in this form, just GDC here. Now, once it becomes activated, it becomes this form.
And guess what, this thing now, we move to reaction number seven, okay? I think number seven should be number seven. So, this GDC-THF-CH2 reacts again with glycine. You see, just now it would react with glycine to activate itself. Now, it reacts again with glycine to get what? Serine, number seven here. Oh, there's a water here. So, you will get serine.
How does this happen? Remember, whenever there is water involved, the name of the enzyme is not going to be just simply decarboxylase synthetase. It will be a weird name something like this. So, this is serine, so it should be, the enzyme involved for this reaction is called serine hydroxymethyl transferase. Oh, how I know, you want to create serine, there is a water involved, and then this thing got a methyl, you see, CH2 is methyl. You want to transfer this methyl group to glycine. When methyl is transferred to glycine and then gets hydrated, you will get serine, right?
You get serine, and guess what? The moment it has donated methyl to glycine, it becomes what? It becomes deactivated again. It becomes back the GDC, then this thing can be used again here. Okay, okay, right.
Keywords: Photorespiration, C2 cycle, Calvin cycle, Plant metabolism, Carbon fixation, Oxygenation, Mitochondrion
Watch full video: https://youtu.be/X3c81GRbN2M
Watch the Introduction and the Brief Operation Mechanism photorespiration: https://youtu.be/UkPosfJ8IwA
Watch the Chloroplast Reactions - Rubisco's Oxygenase Activity & Phosphoglycolate Production: https://youtu.be/ISE3Ln_5aHY
Watch the reactions in the Peroxisome - Glycolate Oxidation & Glycine Formation: https://youtu.be/pkqkajc-2Tw
Watch the reactions in Peroxisome & Chloroplast - The Final Path from Serine to Phosphoglycerate: https://youtu.be/43m8xoweG48
Reference book: Plant Physiology and Development 7th Edition
by Lincoln Taiz, Ian Max Møller, Angus Murphy, Eduardo Zeiger
Attribution 4.0 International — CC BY 4.0 - Creative Commons
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