Calvin Cycle - Video Tutorials & Practice Problems
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1
concept
Calvin Cycle
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3m
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in this video, we're going to begin our introduction to the Calvin Cycle. And so we know already that the Calvin Cycle is the second stage of photosynthesis following the light reactions. And so the Calvin Cycle as the second stage of photosynthesis. It's actually going to use the N A, D. P H and the A T P that was generated from the light reactions the first stage of photosynthesis. And so, ultimately, the n a. T. PH and the 80 p made from the light reactions is going to be used to power the Calvin cycle. And ultimately, this energy from the light reaction is gonna be utilized by the Calvin cycle to make organic molecules, for example, glucose, a sugar that is widely widely prevalent and abundant. Now the Calvin cycle specifically occurs in the strom A of the chloroplast. And so this is contrary to the light reactions which occurs in the Fila coid of the of the chloroplast. And so the light reactions occur in the Fila coid of the chloroplast. But the Calvin cycle does not occur in the Fila coid. It occurs in the strom a of the chloroplast and again Strom, a is not to be confused with Stow Mata. Still, Mata are the openings that can open and close within leaves themselves. But Strom A is referring to the fluid filled space within the chloroplast. And so it's going to occur in the Strom A. And it's also going to consume carbon dioxide, gas or CO two gas from the atmosphere. And ultimately, the co two gas from the Atmosphere is gonna be utilized to build glucose. And so let's take a look at our image down below, which notice the light reactions Region over here is all great out, and it's much smaller and de emphasize because we already covered the light reactions over here in our previous lesson videos. And so we already know from our previous lesson videos that the light reactions occurs in the Thilo Coid size, specifically these green pancake structures that air within the chloroplast. And of course, this great out structure in the background represents the chloroplast itself. And so we know from our previous lesson. Videos with light reactions uses photons of light from our sun and water molecules, and ultimately it converts these, uh, these react INTs into the products of oxygen gas and 80 p and N a. D pH and ultimately the deep and Enoch pH coming from the light reaction is gonna be utilized to power the Calvin cycle, which is really the main focus of this video. And the Calvin cycle occurs again in the strom A of the chloroplast, which is this fluid filled space that we see here within the chloroplast itself. And the Calvin cycle is gonna be powered by the 80 p and any DPH provided by the light reactions. And it's also going to take in carbon dioxide gas from the atmosphere and ultimately used the 80 p and N 80 ph and carbon dioxide gas to generate organic molecules such as glucose, which we can see down here. And so we're going to talk more about the Calvin Cycle as we move forward in our course. So this year is just the introduction, and I'll see you all in our next video when we'll talk more about the Calvin cycle.
2
Problem
Problem
Where in a plant cell does the Calvin cycle take place?
A
Stroma
B
Thylakoid space
C
Thylakoid membrane
D
Chloroplast inner membrane
3
concept
3 Phases of the Calvin Cycle (C3 Pathway)
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10m
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In this video, we're going to introduce the three phases of the Calvin cycle, which we know the Calvin cycle is the second stage of photosynthesis following the light reactions. And we're gonna talk about the three phases of the Calvin cycle. And what's known as the C three pathway, which we'll get to define what that means here very shortly. Now notice that the three phases of the Calvin cycle, we have number down below as number one, number two and number three. And notice that we have each of these phases color coordinate so that they color coordinate to the image that we have down below for each of these three phases of the Calvin cycle. And so that's important to keep in mind. Now, the first phase of the Calvin cycle is what's known as carbon fixation. And the fixation part here actually has nothing to do with fixing something that's broken. Instead, this term fixation is derived from the term to a fix something. And the term a fix is really just a term that means to fasten something to something else, to attach something to something else. And really, that's what's happening here in carbon fixation. And so, carbon fixation is going to utilize the enzyme that's known as R bisco. And Rub Bisco is a very important enzyme because RBIs has this amazing ability to a fix or to add carbon dioxide gas from the atmosphere to a five carbon sugar molecule called rullo bisphosphate or rubp. And so Rubis go is the enzyme that takes carbon dioxide and adds it to RUBP. And so uh because uh this is adding carbon dioxide, uh it's called carbon and because it's being affixed to rubp, it's called carbon fixation. Now, it turns out that the very first stable molecule that's produced in this carbon fixation phase is a three carbon molecule. And because the very first stable molecule that's produced is a three carbon molecule or ac three molecule. Uh this pathway is called the C three pathway. Now, later in our course, when we're talking about different types of photosynthesis, we'll talk about other pathways that do not form a stable three carbon molecule. Instead, they end up forming a four carbon molecule. But we'll talk about those other types of photosynthesis including C four and C AM pathways. Later in our course for now, this pathway, the C three pathway is the standard pathway and it forms a stable three carbon molecule and that stable three carbon molecule is called phosphoglyceraldehyde. And so phosphoglyceraldehyde is also known as PGA. Now, uh if we take a look at our image down below, at the first phase of the Calvin cycle. Just focusing on this left hand side. Notice that the first phase of the Calvin cycle is right here in green called carbon fixation. And what it does is it uses this enzyme RBIs and the enzyme RBIs has this amazing ability to take carbon dioxide, which we are showing you up here and it can take the carbon dioxide and affix it to the RUBP molecule that we're showing you here. And ultimately through a series of reactions, the very first stable molecule that's produced is a three carbon molecule called PGA. And again, each of these black circles that you see throughout here represent carbon atoms. And so that's really it for the carbon fixation stage. Uh Rubis O is going to take carbon dioxide and attach it to RUBP and ultimately through a series of reactions is gonna generate uh PGA, a three carbon molecule. Now moving on to the second phase of the Calvin cycle, what we have is G three P synthesis. And in this G three P synthesis phase, what's going to happen is the PGA is going to be used to synthesize glyceraldehyde three phosphate or G three P and G three P is a precursor molecule that's needed to build glucose. And so the cell is going to use specifically two G three P molecules to synthesize a single glucose molecule. And so if we take a look at our image down below at the G three P synthesis phase. Notice that it starts with PGA and it converts this PGA into another three carbon molecule called G three P and G three P is going to be the precursor that's needed to build glucose. And so ultimately, there are going to need to be two G, three P molecules needed to build one glucose. And also in this G three P synthesis phase, it's actually going to require the use of energy. And this energy is gonna come in the form of N AD Ph and A TP. And this N AD Ph and A TP that's needed as energy for G three P synthesis. This N ad Ph and A TP is coming from the light reactions which is the first phase of photosynthesis. And so uh the light reactions produces the energy in the form of N AD Ph and A TP that's needed to power the Calvin cycle, specifically needed to power the second phase of the Calvin cycle NG three P synthesis. And so, ultimately, what we have here are some G three PS and it takes two G three P molecules again to make just one single glucose. But ultimately, there's gonna be some leftover G three P molecules that are not going to be utilized to build glucose. Instead, these leftover G three P molecules are gonna be used in the third and final phase of the Calvin cycle. And so in the third and final phase of the Calvin cycle. What we have is rubp regeneration and recall that rubp is Bulos bisphosphate. It's the very first molecule that was generated uh the fir very first molecule that was uh reacting here in the Calvin cycle. And so in order for rubp, in order for the Calvin cycle to be a cycle, in order for it to start and end in the same place, it needs to have a phase that's dedicated to regeneration, essentially uh getting RUBP uh back to its original state. And so here in the third phase, uh what we have is RUBP regeneration, which is gonna use the remaining leftover G three P that's not utilized to build glucose. And it's gonna rearrange this G three P in a series of enzymatic reactions that's driven by A TP to regenerate Rubp. And then once Rubp has been regenerated, it's ready to go for a second round of the Calvin cycle here. And so, uh when we take a look at RUBP regeneration phase down below, it's over here and notice that it takes the remainder of the G three P and uses it to rebuild to regenerate rubp here. And it's going to take energy in the form of a TP in order for this regeneration to occur. And so ultimately, that is the end of the carbon cycle, those three phases. And at the end of the carbon cycle, again, notice that carbon dioxide is ultimately being used as a reactant. And also N ad PH and A TP are being used as reactants as well. And in terms of the products, what we get is a glucose molecule. And so, in order to remember the reactants and the products of the Calvin cycle over here on the right, what we have is a memory tool to help you guys remember the reactants and the products of the Calvin cycle. And so when you think about the Calvin cycle, you really want to think about Calvin's can of sugar, which is uh really just this soda can right here. And so here we have Calvin and you can see he's got even a little name tag that says, hi, my name is Calvin. And so Calvin has his can of sugar here, this uh soda can here. And so when you're thinking about the Calvin cycle, just think about Calvin's can of sugar. And when you think about that again, that'll help you remember the reactants of the Calvin cycle and the products of the Calvin cycle. And so the reactants of the Calvin cycle are gonna come from this can over here where the C in the can represents the C in CO2 carbon dioxide. The A in the can represents the A in A TP and the N in the can represents the N in N AD Ph. And so CO2 A TP and N ad PH are the reactants needed for the Calvin cycle. And of course, Calvin's can of sugar. The sugar over here is going to represent the product which is glucose. And so by remembering Calvin's can of sugar, once again, you'll be able to remember the reactants and the products of the Calvin cycle. Now, in terms of this image over here and what you're supposed to memorize uh that is going to be up to your professor, your professors uh are going to vary in exactly the amount of detail that they want you to know about the Calvin cycle. But uh one thing that is pretty consistent about what you should know is that it's going to take a total of six carbon dioxide molecules entering the Calvin cycle to create glucose. And one way to help you remember that is that uh within six carbon dioxides, there are six carbon atoms and glucose also has six carbon atoms. And so ultimately, these six carbon atoms of the carbon dioxide end up as the six carbon atoms that are in a glucose molecule. And also you should know that it takes two G three P molecules to make a glucose. So basically the interactive portions here are the portions that you really want to focus on the most. And so this year concludes our introduction to the three phases of the Calvin cycle in the C three pathway. And we'll be able to get some practice applying these concepts as we move forward in our course.
4
Problem
Problem
The enzyme rubisco combines RuBP with a carbon atom from:
A
Glucose
B
ATP
C
Carbon monoxide
D
Organic compounds
E
Carbon dioxide
F
NADPH
5
Problem
Problem
Which of the following processes occurs during the Calvin cycle?
A
Reduction of NADPH
B
Release of oxygen
C
Regeneration of RuBP
D
Production of ATP
6
Problem
Problem
The function of the light reactions is to ___________, while the function of the Calvin Cycle is to __________.
A
Convert light energy into chemical energy; Store chemical energy in the form of organic molecules.
B
Use light energy to produce ATP; Use chemical energy to produce ATP.
C
Store light energy; Use light energy to produce carbon.
D
Transfer heat captured from light to electrons; Use electrons to generate organic molecules.