Chemistry of life
Describe the key differences between prokaryotic and eukaryotic cells, focusing on their internal organization and the presence (or absence) of membrane-bound organelles.
Prokaryotic cells lack a nucleus and other membrane-bound organelles. Their DNA is typically located in a nucleoid region. In contrast, eukaryotic cells possess a true nucleus enclosed by a nuclear envelope, as well as various membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and (in plant cells) chloroplasts. This internal compartmentalization allows for specialized functions within the eukaryotic cell.
Imagine a newly discovered prokaryotic organism that can thrive in extremely cold environments. Its plasma membrane is found to have a significantly higher proportion of unsaturated fatty acids compared to prokaryotes living in warmer temperatures. Explain the biological advantage of this membrane composition in the cold environment.
The higher proportion of unsaturated fatty acids in the plasma membrane of this cold-adapted prokaryote provides increased fluidity. Unsaturated fatty acids have double bonds that introduce kinks in the hydrocarbon tails, preventing them from packing tightly together. In cold temperatures, membrane lipids tend to become less fluid and can even solidify. By maintaining fluidity, the membrane ensures proper functioning of embedded proteins involved in transport, signaling, and other essential cellular processes, allowing the organism to survive and function effectively in the frigid conditions.
In a eukaryotic cell, if the inner mitochondrial membrane were freely permeable to protons (H+), what immediate and most significant consequence would this have on ATP production? Explain your reasoning.
The most significant immediate consequence would be a drastic reduction or complete cessation of ATP production via oxidative phosphorylation. The electron transport chain (ETC) pumps protons from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient (proton-motive force). This gradient, with a higher concentration of H+ in the intermembrane space and a more positive charge, drives protons back into the matrix through ATP synthase, powering ATP synthesis. If the inner mitochondrial membrane were freely permeable to protons, this gradient would dissipate as H+ ions freely flow back into the matrix without passing through ATP synthase. Consequently, the energy stored in the proton-motive force would be lost as heat rather than being harnessed to phosphorylate ADP to ATP.
Describe the general process of signal transduction in a cell, including the three main stages.
Signal transduction is the process by which a cell converts one kind of signal or stimulus into another. It typically involves three main stages:
Describe the role of the enzyme rubisco in the Calvin cycle. What would be the immediate consequence if a plant's rubisco enzyme suddenly became non-functional?
Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the first major step of carbon fixation in the Calvin cycle. It adds a molecule of CO2 to ribulose-1,5-bisphosphate (RuBP), forming an unstable six-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).
If rubisco suddenly became non-functional, the plant would be unable to fix atmospheric carbon dioxide. This would immediately halt the production of 3-PGA, and consequently, the entire Calvin cycle would cease. The plant would no longer be able to synthesize glucose and other organic molecules, leading to a rapid depletion of energy reserves and ultimately death.
Explain how the unique properties of water, such as its polarity and ability to form hydrogen bonds, contribute to its role as a vital solvent for biological systems and its influence on cellular processes.
Water's polarity, arising from the electronegativity difference between oxygen and hydrogen, allows it to form hydrogen bonds with other polar molecules and ions, making it an excellent solvent for hydrophilic substances within cells and organisms. This solvent property facilitates crucial biochemical reactions and the transport of molecules. Furthermore, hydrogen bonding contributes to water's high specific heat, allowing it to buffer temperature fluctuations within cells, and its cohesive and adhesive properties, which are important for water transport in plants and maintaining cell turgor.
A researcher introduces a specific inhibitor that completely blocks the function of a protein channel in a eukaryotic cell membrane. Subsequent measurements show a dramatic decrease in the rate of facilitated diffusion of a particular polar molecule across the membrane. However, simple diffusion of small, nonpolar molecules remains unaffected. Explain why the inhibitor specifically impacts facilitated diffusion and not simple diffusion.
Facilitated diffusion relies on the assistance of specific transmembrane proteins, such as channel proteins or carrier proteins, to transport molecules across the membrane down their concentration gradient. The inhibitor directly targets and blocks the function of these protein channels. Simple diffusion, on the other hand, does not require the involvement of membrane proteins. It occurs directly across the lipid bilayer and is primarily driven by the concentration gradient and the hydrophobic nature of the diffusing molecule. Therefore, an inhibitor that specifically targets protein channels will disrupt facilitated diffusion but have no effect on the movement of small, nonpolar molecules via simple diffusion.
Consider a plant cell actively engaged in photosynthesis. Under conditions of very low atmospheric CO2 concentration, describe the likely state of the Calvin cycle intermediates (RuBP, PGA, G3P) and explain why this specific distribution would be observed.
Under very low atmospheric CO2 concentrations, the concentration of RuBP (ribulose-1,5-bisphosphate) would likely be high, while the concentrations of PGA (3-phosphoglycerate) and G3P (glyceraldehyde-3-phosphate) would be low. This is because the initial step of the Calvin cycle, carbon fixation, involves the enzyme RuBisCO catalyzing the reaction between CO2 and RuBP to form an unstable six-carbon intermediate that quickly splits into two molecules of PGA. With very little CO2 available, RuBisCO would have fewer substrate molecules to react with. Consequently, the existing RuBP would not be efficiently converted into PGA, leading to its accumulation. The subsequent steps of the Calvin cycle, which reduce PGA to G3P, would also be limited by the low availability of PGA, resulting in lower levels of G3P
A mutation in a gene encoding a receptor tyrosine kinase results in a receptor that is constitutively active, even in the absence of its ligand. What potential downstream effects might this mutation have on a cell, and why could this be detrimental to an organism?
A constitutively active receptor tyrosine kinase could lead to the continuous activation of downstream signaling pathways normally triggered by ligand binding. This could result in:
This uncontrolled signaling can be detrimental to an organism because it disrupts normal cellular functions, leading to developmental abnormalities, tissue dysfunction, and an increased risk of diseases like cancer.
Compare and contrast linear electron flow and cyclic electron flow in the light-dependent reactions of photosynthesis. Under what conditions might a plant favor cyclic electron flow over linear electron flow?
Both linear and cyclic electron flow involve photosystems in the thylakoid membrane and the transfer of energy via electrons.
Linear electron flow involves both photosystem II (PSII) and photosystem I (PSI). Water is split to replace electrons lost by P680 in PSII, producing oxygen as a byproduct. Electrons are passed down the electron transport chain, generating a proton gradient that drives ATP synthesis (photophosphorylation). Ultimately, electrons are transferred to NADP+, reducing it to NADPH. This process produces both ATP and NADPH.
Cyclic electron flow involves only PSI. Electrons excited by light are passed from P700 to ferredoxin (Fd), then back to the cytochrome complex (part of the electron transport chain between PSII and PSI), and finally back to P700. This cycle generates ATP through photophosphorylation but does not produce NADPH or evolve oxygen.
A plant might favor cyclic electron flow when the ratio of NADPH to NADP+ is high, and the plant has a greater need for ATP than for NADPH. This often occurs when the Calvin cycle is proceeding slowly due to factors like low CO2 concentrations, as the cycle consumes more ATP than NADPH. Cyclic electron flow helps to generate the necessary ATP to balance the metabolic demands of the cell.
A scientist introduces a protein into a eukaryotic cell that disrupts the function of the rough endoplasmic reticulum (RER). Predict two specific cellular processes that would be directly affected by this disruption.
Synthesis and modification of secreted proteins and Synthesis of integral membrane proteins:
Consider a plant cell placed in a hypertonic solution. Describe the sequence of events that would occur at the cellular level, focusing on the movement of water and the resulting changes in the cell's structure. Explain why the plasma membrane pulls away from the cell wall in this scenario, but the cell does not burst.
When a plant cell is placed in a hypertonic solution (higher solute concentration outside the cell), water will move out of the cell via osmosis, following the concentration gradient. This loss of water leads to the shrinkage of the cytoplasm and the plasma membrane. As the plasma membrane shrinks, it pulls away from the rigid cell wall, a phenomenon known as plasmolysis. The strong and relatively inelastic cell wall provides structural support and prevents the cell from bursting due to the outward movement of water. While the cell loses turgor pressure and becomes flaccid, the cell wall maintains the overall shape and integrity of the plant cell.
A researcher introduces a specific inhibitor that completely blocks the activity of pyruvate dehydrogenase in a mammalian cell. How would this inhibitor directly impact the citric acid cycle and what would be the downstream effects on oxidative phosphorylation if glycolysis were still functioning normally?
Pyruvate dehydrogenase is the enzyme complex that converts pyruvate (the end product of glycolysis) into acetyl-CoA, which is the primary substrate that enters the citric acid cycle. If pyruvate dehydrogenase is completely blocked, the citric acid cycle would essentially halt because there would be no acetyl-CoA to feed into it. Consequently, the production of the high-energy electron carriers NADH and FADH2 within the mitochondrial matrix via the citric acid cycle would cease. While glycolysis would continue to produce a small amount of ATP and NADH in the cytoplasm, the lack of NADH and FADH2 entering the electron transport chain would severely limit or abolish oxidative phosphorylation. The proton gradient across the inner mitochondrial membrane would not be established or maintained, leading to minimal ATP production despite the presence of oxygen and a functioning ETC
Explain how a single signaling molecule can elicit different responses in different target cells. Provide specific examples of mechanisms that contribute to this phenomenon.
A single signaling molecule can elicit different responses in different target cells due to variations in:
Explain the evolutionary significance of the different photosynthetic pigments (e.g., chlorophyll a, chlorophyll b, carotenoids) found in plants. How does the absorption spectrum of these pigments relate to the efficiency of photosynthesis?
The presence of multiple photosynthetic pigments reflects an evolutionary adaptation to maximize the range of light wavelengths that can be harvested for photosynthesis.
Chlorophyll a is the primary photosynthetic pigment and absorbs light most effectively in the blue-violet and red regions of the spectrum.
Chlorophyll b is an accessory pigment that absorbs light most strongly in the blue and orange-red regions. It broadens the range of light that can be used by indirectly transferring the absorbed energy to chlorophyll a.
Carotenoids (including carotenes and xanthophylls) absorb light in the blue-green region of the spectrum. They also play a photoprotective role by dissipating excess light energy that could damage chlorophyll or react with oxygen to form harmful molecules
Consider a mutation in a gene that codes for a protein involved in maintaining the structure of the cytoskeleton in an animal cell. Describe two potential consequences of this mutation on cell function or behavior, and explain how the cytoskeleton's normal structure contributes to preventing these issues.
Impaired cell motility and shape: The cytoskeleton, composed of networks of protein fibers like microtubules, microfilaments (actin), and intermediate filaments, provides structural support and facilitates cell movement. A mutated cytoskeletal protein could lead to a weakened or disorganized cytoskeleton, hindering the cell's ability to change shape (essential for processes like phagocytosis or embryonic development) or to move (e.g., migration of immune cells). Normally, the dynamic yet stable network of the cytoskeleton allows for controlled changes in cell morphology and provides the machinery for movement through the polymerization and depolymerization of its components. and Disrupted intracellular transport: The cytoskeleton, particularly microtubules, serves as tracks for motor proteins (kinesins and dyneins) that transport vesicles and organelles within the cell. A mutation affecting cytoskeletal integrity could disrupt these tracks, leading to inefficient or misdirected intracellular transport. This would impact the delivery of essential molecules to different cellular compartments, potentially disrupting various cellular processes that rely on this organized movement, such as protein trafficking, waste removal, and organelle distribution.
A certain genetic mutation in a eukaryotic cell results in the production of a non-functional signal recognition particle (SRP). Predict the likely consequences of this mutation on the synthesis and localization of proteins destined for the endoplasmic reticulum (ER) and subsequent secretion out of the cell. Explain your reasoning.
The signal recognition particle (SRP) plays a crucial role in protein targeting to the ER. It binds to the signal peptide of a growing polypeptide chain destined for the secretory pathway and halts translation. The SRP then escorts the ribosome-mRNA complex to the ER membrane, where it binds to an SRP receptor, and translation resumes with the polypeptide entering the ER lumen through a protein translocator. If the SRP is non-functional, it will not be able to bind to the signal peptide and halt translation or guide the ribosome to the ER. Consequently, proteins destined for the ER, Golgi apparatus, lysosomes, plasma membrane, or secretion will likely be synthesized in the cytoplasm instead of being translocated into the ER. This mislocalization will prevent these proteins from undergoing proper folding, modification (like glycosylation), and transport through the secretory pathway, ultimately disrupting their function and potentially leading to cellular dysfunction.
Some anaerobic organisms utilize electron acceptors other than oxygen in their electron transport chains, such as sulfate (SO42−). Compare and contrast the potential ATP yield of a metabolic pathway that uses sulfate as the final electron acceptor to one that uses oxygen, assuming all other upstream processes (like glycolysis and the citric acid cycle or analogous pathways) proceed at similar rates and efficiencies. Explain the underlying biochemical principles responsible for any differences.
the potential ATP yield of a metabolic pathway using sulfate as the final electron acceptor would be significantly lower than one using oxygen. Oxygen is a highly electronegative molecule, meaning it has a strong affinity for electrons. This large difference in electronegativity between NADH/FADH2 (electron donors) and oxygen (electron acceptor) results in a substantial release of free energy as electrons are passed down the electron transport chain. This large energy drop allows for the pumping of a significant number of protons across the inner membrane, establishing a strong proton-motive force that drives substantial ATP synthesis. Sulfate, on the other hand, is a much less electronegative electron acceptor than oxygen. Consequently, the transfer of electrons from NADH/FADH2 to sulfate releases less free energy. This smaller energy drop would likely result in fewer protons being pumped across the membrane per electron transferred, leading to a weaker proton-motive force and thus lower ATP production via oxidative phosphorylation (or its analogous process in the anaerobic organism).
A single signaling molecule can elicit different responses in different target cells due to variations in:
If the G protein could not hydrolyze GTP back to GDP, it would remain in its active, GTP-bound state. This would lead to the following consequences:
Consider a C4 plant growing in a hot, arid environment. Describe the biochemical adaptations that minimize photorespiration in these plants. Detail the spatial separation of carbon fixation and the Calvin cycle, and explain the advantages of this separation under such environmental conditions.
C4 plants have evolved a spatial separation of carbon fixation and the Calvin cycle to minimize photorespiration, a process where rubisco binds to O2 instead of CO2, reducing photosynthetic efficiency.
Initial Carbon Fixation in Mesophyll Cells: In mesophyll cells, CO2 is initially fixed by the enzyme PEP carboxylase, which has a much higher affinity for CO2 than rubisco and does not bind to O2. PEP carboxylase adds CO2 to phosphoenolpyruvate (PEP) to form a four-carbon compound, oxaloacetate. Oxaloacetate is then converted to malate (or aspartate).
Transport to Bundle-Sheath Cells: Malate (or aspartate) is transported from the mesophyll cells to specialized bundle-sheath cells located deeper within the leaf and surrounding the vascular bundles.
Decarboxylation in Bundle-Sheath Cells: In the bundle-sheath cells, malate is decarboxylated, releasing a high concentration of CO2 in the vicinity of rubisco. This high CO2 concentration effectively outcompetes O2 for binding to rubisco, minimizing photorespiration. Pyruvate is also produced and transported back to the mesophyll cells, where it is converted back to PEP, requiring ATP.
Calvin Cycle in Bundle-Sheath Cells: The Calvin cycle occurs in the bundle-sheath cells, where the high concentration of CO2 fixed by the C4 pathway ensures efficient carbon fixation by rubisco.
Advantages in Hot, Arid Environments: In hot, arid conditions, plants close their stomata to conserve water. This closure limits CO2 entry into the leaf and causes O2 levels to rise inside the leaf due to ongoing photosynthesis. The C4 pathway allows C4 plants to efficiently fix carbon even when stomata are partially closed and CO2 concentrations are low. PEP carboxylase's high affinity for CO2 enables the plant to capture what little CO2 is available. The subsequent delivery of a concentrated supply of CO2 to the bundle-sheath cells minimizes photorespiration, allowing C4 plants to maintain high rates of photosynthesis under conditions that would severely limit C3 plant productivity.
Imagine a scenario where a newly discovered unicellular organism thrives in an environment with extremely high concentrations of nonpolar molecules. Propose two possible adaptations in the structure or function of this organism's plasma membrane that would allow it to maintain cellular integrity and function effectively in this environment. Explain the underlying principles that make these adaptations advantageous.
increased proportion of longer and saturated fatty acid tails in the phospholipid bilayer: In a high concentration of nonpolar molecules, there's an increased risk of these molecules disrupting the hydrophobic core of the standard phospholipid bilayer, potentially increasing membrane fluidity and permeability to unwanted substances. By increasing the proportion of longer fatty acid tails, the hydrophobic core becomes thicker and more tightly packed due to increased van der Waals interactions between the longer chains. Furthermore, increasing the proportion of saturated fatty acid tails reduces the number of double bonds, leading to more linear chains that can pack more closely, further decreasing membrane fluidity and permeability. This adaptation would enhance the membrane's barrier function against the influx of external nonpolar molecules, maintaining cellular integrity.
Incorporation of a unique type of membrane protein that actively pumps nonpolar molecules out of the cell: To counteract the constant influx of nonpolar molecules from the environment, the organism could evolve specialized transmembrane proteins that function as active transport pumps. These proteins would utilize cellular energy (e.g., ATP hydrolysis or an existing electrochemical gradient) to selectively bind to the nonpolar molecules that have entered the cytoplasm and actively transport them back out of the cell against their concentration gradient. This adaptation would allow the organism to maintain a stable intracellular environment despite the high external concentration of nonpolar substances, ensuring proper cellular function by preventing the accumulation of potentially disruptive molecules within the cytoplasm.
Two artificial vesicles are created. Vesicle A contains a solution with a high concentration of glucose and is surrounded by a membrane permeable only to water. Vesicle B contains the same high concentration of glucose but is surrounded by a membrane permeable to both water and glucose. Both vesicles are placed in a beaker containing pure water. Describe the changes in volume of each vesicle over time and explain the underlying principles driving these changes, including the concept of osmotic pressure and its influence in each scenario.
Vesicle A: Initially, the concentration of solutes (glucose) is higher inside Vesicle A than outside (pure water). This creates a difference in water potential, with a lower water potential inside the vesicle. Consequently, water will move into Vesicle A via osmosis, down its water potential gradient. This influx of water will cause the volume of Vesicle A to increase over time. The osmotic pressure, which is the pressure required to prevent the net movement of water across a semipermeable membrane, is driving this water movement into the vesicle. The volume will continue to increase until the turgor pressure inside the vesicle counteracts the osmotic pressure, reaching an equilibrium where there is no net movement of water, or until the vesicle bursts (if the membrane cannot withstand the pressure).
Vesicle B: Similar to Vesicle A, initially, water will move into Vesicle B due to the higher glucose concentration inside. However, because the membrane of Vesicle B is also permeable to glucose, glucose will simultaneously move out of the vesicle down its concentration gradient into the pure water. Over time, this outward movement of glucose will decrease the solute concentration inside Vesicle B, reducing the osmotic pressure difference across the membrane. Eventually, both water and glucose will reach equilibrium, with the concentration of glucose being the same inside and outside the vesicle. At this point, there will be no net movement of water, and the volume of Vesicle B will likely return to its initial volume or close to it, as the driving force for water influx (the osmotic pressure difference) dissipates due to the glucose efflux.
Imagine a scenario where a mutation in a plant's chloroplast genome leads to a non-functional cytochrome b6f complex. Describe the immediate effects this would have on both the light-dependent and light-independent reactions of photosynthesis. Furthermore, predict how this mutation would ultimately impact the plant's ability to produce glucose.
The cytochrome b6f complex is a crucial component of the light-dependent reactions of photosynthesis. It facilitates the transfer of electrons between photosystem II (PSII) and photosystem I (PSI) and is responsible for pumping protons from the stroma into the thylakoid lumen, establishing the proton gradient that drives ATP synthesis via photophosphorylation.
Light-dependent reactions: A non-functional cytochrome b6f complex would have several immediate effects. Firstly, electron flow between PSII and PSI would be blocked, preventing the linear electron flow necessary for the reduction of NADP+ to NADPH. While PSII could still split water and release oxygen, the electrons would not be efficiently passed along to PSI. Secondly, and critically, the pumping of protons into the thylakoid lumen would be severely impaired or halted. This would drastically reduce or eliminate the proton-motive force across the thylakoid membrane, leading to a significant decrease or complete cessation of ATP production by ATP synthase.
Light-independent reactions (Calvin cycle): The light-independent reactions rely heavily on the products of the light-dependent reactions: ATP and NADPH. With a non-functional cytochrome b6f complex, the supply of both ATP and NADPH to the Calvin cycle would be severely limited. NADPH is required to reduce 1,3-bisphosphoglycerate to G3P, and ATP is needed for the phosphorylation of RuBP and the reduction of 1,3-bisphosphoglycerate.
Glucose production: Ultimately, the inability to produce sufficient ATP and NADPH due to the non-functional cytochrome b6f complex would severely impair or completely halt the Calvin cycle. Without the regeneration of RuBP and the reduction of PGA, the plant would be unable to fix carbon dioxide and synthesize glucose. Even if some initial intermediates were present, the cycle would quickly stall due to the lack of energy and reducing power. Therefore, this mutation would have a devastating impact on the plant's ability to produce glucose and sustain itself through photosynthesis.
Imagine a complex cellular environment where two different signaling molecules, Ligand A and Ligand B, bind to their respective cell surface receptors. Ligand A binding activates a pathway that ultimately inhibits the activity of a specific protein, Protein X. Ligand B binding activates a different pathway that ultimately promotes the phosphorylation and activation of Protein X.
Design an experiment to investigate the hierarchical relationship between these two signaling pathways. Specifically, how could you determine if one pathway can override the effect of the other, or if their effects are integrated in a more nuanced way? What potential outcomes could you observe, and what would each outcome suggest about the interaction between the two pathways?
o investigate the hierarchical relationship between these two pathways, we could design an experiment with the following conditions and observations:
Experimental Design:
Potential Outcomes and Interpretations:
Outcome 1: Protein X activity is similar to the "Ligand A Alone" condition (inhibited). This would suggest that the signaling pathway activated by Ligand A is dominant or epistatic to the pathway activated by Ligand B under these conditions. The inhibitory signal overrides the stimulatory signal. This could occur if the Ligand A pathway acts downstream of or blocks a crucial step in the Ligand B pathway.
Outcome 2: Protein X activity is similar to the "Ligand B Alone" condition (activated). This would suggest that the signaling pathway activated by Ligand B is dominant or epistatic to the pathway activated by Ligand A. The stimulatory signal overrides the inhibitory signal. This could happen if the Ligand B pathway directly modifies Protein X in a way that renders it insensitive to the inhibitory effects of the Ligand A pathway.
Outcome 3: Protein X activity is at an intermediate level between the "Ligand A Alone" and "Ligand B Alone" conditions, or even close to the baseline. This would suggest that the two pathways are integrated in a more nuanced way. Their effects might partially counteract each other, leading to a balanced or modulated response. This could involve cross-talk between the pathways at some intermediate point, where the signals are integrated before affecting Protein X. For example, both pathways might influence the concentration of a common second messenger with opposing effects on Protein X.
Outcome 4: Protein X activity shows a non-additive or synergistic effect (significantly higher or lower than expected based on individual ligand effects). This would indicate a complex interaction where the presence of both ligands leads to an unexpected outcome. For example, the activation of one pathway might prime or sensitize the cell to the effects of the other.
By analyzing the activity of Protein X under these different conditions, we can gain insights into the hierarchical relationship and the nature of the interaction between the two signaling pathways. Further experiments could then delve into the specific molecular mechanisms underlying the observed interactions.
Imagine a scenario where a mutation in a plant species alters the thylakoid membrane structure, specifically disrupting the mobility of the plastoquinone (Pq) molecule within the lipid bilayer. Predict the most significant impact of this mutation on the light-dependent reactions of photosynthesis and explain the underlying mechanism. How might this disruption indirectly affect the Calvin cycle?
The most significant impact of disrupted plastoquinone (Pq) mobility would be a severe reduction or complete blockage of electron flow between photosystem II (PSII) and the cytochrome b6f complex.
Underlying Mechanism: Plastoquinone is a mobile electron carrier within the thylakoid membrane's lipid bilayer. It accepts electrons from PSII (specifically from pheophytin and then QA and QB) and carries them to the cytochrome b6f complex. If Pq's mobility is impaired, it cannot effectively shuttle electrons from PSII to the cytochrome b6f complex. This blockage would lead to:
Indirect Effects on the Calvin Cycle: The disruption of Pq mobility and the resulting lack of ATP (and potentially a severe reduction in NADPH) would have profound indirect effects on the Calvin cycle. The Calvin cycle requires both ATP and NADPH to convert CO2 into glucose. Specifically:
In conclusion, a mutation disrupting Pq mobility would cripple the light-dependent reactions by blocking electron flow and ATP production. This, in turn, would severely inhibit or completely shut down the Calvin cycle, leading to a cessation of sugar synthesis and ultimately the death of the plant,