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Questions and Answers
In the C4 cycle as proposed by Hatch and Slack, which compound is labeled first during the pulse-chase study?
In the C4 cycle as proposed by Hatch and Slack, which compound is labeled first during the pulse-chase study?
- Hexose phosphates
- Malate (correct)
- C3 acids
- 3-PGA
What does the novel carboxylation reaction in the C4 cycle initially combine with CO2?
What does the novel carboxylation reaction in the C4 cycle initially combine with CO2?
- 3-PGA
- Hexose phosphates
- Malate
- C3 compounds (correct)
What is produced after the decarboxylation step in the C4 cycle before it undergoes carboxylation again?
What is produced after the decarboxylation step in the C4 cycle before it undergoes carboxylation again?
- 3-PGA (correct)
- Ribulose bisphosphate
- Oxaloacetate
- Glucose
What role does Rubisco play in the C4 pathway as indicated in the process?
What role does Rubisco play in the C4 pathway as indicated in the process?
Which of the following is NOT an intermediate in the C4 pathway proposed by Hatch and Slack?
Which of the following is NOT an intermediate in the C4 pathway proposed by Hatch and Slack?
What is the primary function of Rubisco in cyanobacterial carbon fixation?
What is the primary function of Rubisco in cyanobacterial carbon fixation?
In what structure are pyrenoids primarily located within chloroplasts?
In what structure are pyrenoids primarily located within chloroplasts?
Which method was employed to reveal the native architecture of the Chlamydomonas chloroplast?
Which method was employed to reveal the native architecture of the Chlamydomonas chloroplast?
What structural feature intersperses the Rubisco found in pyrenoids?
What structural feature intersperses the Rubisco found in pyrenoids?
Which of the following components is not part of the chloroplast structure mentioned in the context?
Which of the following components is not part of the chloroplast structure mentioned in the context?
What is the main role of carboxysomes in cyanobacteria?
What is the main role of carboxysomes in cyanobacteria?
Which enzyme is primarily associated with the carboxylation reaction in C4 plants?
Which enzyme is primarily associated with the carboxylation reaction in C4 plants?
In which structures do many algae concentrate CO2 for photosynthesis?
In which structures do many algae concentrate CO2 for photosynthesis?
Which process is related to the endosymbiotic origin of chloroplasts?
Which process is related to the endosymbiotic origin of chloroplasts?
What is the function of carbonic anhydrase (CA) in photosynthetic organisms?
What is the function of carbonic anhydrase (CA) in photosynthetic organisms?
Which type of plants primarily use the C4 pathway for photosynthesis?
Which type of plants primarily use the C4 pathway for photosynthesis?
Which component is involved in the downstream fixation of CO2 in C4 plants?
Which component is involved in the downstream fixation of CO2 in C4 plants?
What evolutionary development is indicated to have occurred long after plastid endosymbiosis?
What evolutionary development is indicated to have occurred long after plastid endosymbiosis?
What structural feature is labeled with GFP in the study of cyanobacterial carboxysomes?
What structural feature is labeled with GFP in the study of cyanobacterial carboxysomes?
What advantage do C4 plants have in photosynthesis over C3 plants?
What advantage do C4 plants have in photosynthesis over C3 plants?
What does the process of bicarbonate transport refer to in the context of cyanobacterial photosynthesis?
What does the process of bicarbonate transport refer to in the context of cyanobacterial photosynthesis?
What role does carbonic anhydrase (CA) play in the chloroplasts?
What role does carbonic anhydrase (CA) play in the chloroplasts?
Which statement best describes the function of transporters in the context of CO2 and HCO3- in chloroplasts?
Which statement best describes the function of transporters in the context of CO2 and HCO3- in chloroplasts?
What characteristic of the pyrenoid's starch layer affects CO2 back-diffusion?
What characteristic of the pyrenoid's starch layer affects CO2 back-diffusion?
How does HCO3- permeability compare between chloroplast membranes and pyrenoids?
How does HCO3- permeability compare between chloroplast membranes and pyrenoids?
Which of the following statements about CO2 concentration in pyrenoids is true?
Which of the following statements about CO2 concentration in pyrenoids is true?
What is the primary function of the bicarbonate transporter in chloroplasts?
What is the primary function of the bicarbonate transporter in chloroplasts?
Why is the incorporation of CO2 into pyrenoids important for photosynthesis?
Why is the incorporation of CO2 into pyrenoids important for photosynthesis?
What limits the movement of CO2 from thylakoids to the stroma?
What limits the movement of CO2 from thylakoids to the stroma?
Which of the following correctly describes the carbon fixation process by Rubisco?
Which of the following correctly describes the carbon fixation process by Rubisco?
What is the significance of using bicarbonate as a carbon source instead of CO2?
What is the significance of using bicarbonate as a carbon source instead of CO2?
What is the primary advantage of C4 plants in relation to environmental conditions?
What is the primary advantage of C4 plants in relation to environmental conditions?
What is the role of glycine decarboxylase (GDC) in C3 photosynthesis?
What is the role of glycine decarboxylase (GDC) in C3 photosynthesis?
Which of the following strategies is proposed to engineer more efficient C3 plants?
Which of the following strategies is proposed to engineer more efficient C3 plants?
What is the function of the centripetal microanatomy within bundle sheath cells?
What is the function of the centripetal microanatomy within bundle sheath cells?
What limitation is associated with the glycine decarboxylase (GDC) enzyme in the mesophyll?
What limitation is associated with the glycine decarboxylase (GDC) enzyme in the mesophyll?
Which environmental factor primarily benefits C4 plants over C3 plants?
Which environmental factor primarily benefits C4 plants over C3 plants?
What is one proposed method to increase Rubisco selectivity?
What is one proposed method to increase Rubisco selectivity?
What is the expected outcome of raising the concentration of CO2 at Rubisco?
What is the expected outcome of raising the concentration of CO2 at Rubisco?
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Study Notes
Pyrenoids
- Rubisco is highly concentrated in a structure called a pyrenoid
- Pyrenoids are interspersed with thylakoid membranes
- Pyrenoids are located within the chloroplast
- Starch granules surround the pyrenoid
Carbon Dioxide Concentration
- Carbon dioxide (CO2) is concentrated in pyrenoids in order to improve the efficiency of photosynthesis
- Carbonic anhydrase (CA) within the chloroplast converts bicarbonate (HCO3-) to CO2
- CO2 diffusion is slowed by the pyrenoid’s starch layer, which prevents back-diffusion
Evolution of Pyrenoids and Carboxysomes
- Pyrenoids and carboxysomes evolved long after plastid endosymbiosis
Carbon Concentrating Mechanisms
- Cyanobacteria concentrate CO2 in protein structures called carboxysomes
- Many algae concentrate CO2 in pyrenoids
- C4 plants concentrate and store CO2 using phosphoenolpyruvate carboxylase (PEPC) upstream of Rubisco
- C4 plants have an advantage at higher temperatures and in full sunlight
- C3 plants are more efficient in cool, temperate climates
- C3-C4 intermediates rely on metabolite transfer to specialized bundle sheath cells
- Bundle sheath cells contain an inactive version of glycine decarboxylase (GDC) which is unable to process glycine
- Glycine is transferred from mesophyll cells to bundle sheath cells and decarboxylated by GDC in mitochondria
- Bundle sheath chloroplasts overlay mitochondria, facilitating reassimilation of CO2
Engineering C3 Plants
- Increasing CO2 concentration at Rubisco could be achieved by introducing:
- Bicarbonate transporters
- Pyrenoids
- Carboxysomes
- Other strategies for improving C3 photosynthesis include:
- Increasing Rubisco selectivity
- Engineering new carbon fixation pathways
- Engineering more efficient photorespiration pathways
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