12 Questions
What is the main difference between the accumulation of protons in photosynthesis and respiration?
Protons accumulate in the lumen of thylakoids in photosynthesis, while in respiration, they accumulate in the intermembrane space of mitochondria.
What causes the development of a proton gradient across the membrane during photosynthesis?
Splitting of water molecule on the inner side of the membrane and transportation of protons across the membrane.
Why do protons get transported across the membrane during photosynthesis?
The primary electron acceptor transfers electrons to an H carrier and simultaneously removes protons from the stroma.
Where does the splitting of water molecules occur during photosynthesis?
On the inner side of the thylakoid membrane
What happens when a molecule passes its electron to an electron carrier on the inner side of the membrane during photosynthesis?
A proton is released into the inner side or lumen side of the membrane.
How do protons get transported across the membrane during photosynthesis?
Through transfer by the primary electron acceptor to an H carrier
Where is the NADP reductase enzyme located?
Stroma side of the membrane
What is the main function of the proton gradient across the thylakoid membrane?
Lead to the synthesis of ATP
What is the role of the CF0 portion of the ATP synthase enzyme?
Facilitate diffusion of protons across the membrane
How is energy used in chemiosmosis to create a proton gradient within the thylakoid lumen?
Pumping protons across a membrane
Which component of the ATP synthase enzyme protrudes on the outer surface of the thylakoid membrane?
CF1
What is the fate of the ATP synthesized within the chloroplast?
Immediately used in biosynthetic reactions in the stroma
Study Notes
Chemiosmotic Hypothesis and ATP Synthesis
- In photosynthesis, ATP synthesis is linked to the development of a proton gradient across the thylakoid membrane.
- Proton accumulation occurs towards the inside of the membrane, i.e., in the lumen.
Proton Gradient Development
- Water splitting takes place on the inner side of the membrane, producing protons that accumulate within the lumen of thylakoids.
- As electrons move through photosystems, protons are transported across the membrane.
- The primary acceptor of electrons transfers its electron to an H carrier, removing a proton from the stroma and transporting an electron.
- This molecule releases a proton into the lumen side of the membrane when passing on its electron to the electron carrier.
NADP Reduction and Proton Gradient
- The NADP reductase enzyme is located on the stroma side of the membrane, requiring electrons and protons to reduce NADP+ to NADPH+ H+.
- Protons are removed from the stroma, decreasing their number, while accumulating in the lumen.
- This creates a proton gradient across the thylakoid membrane and a measurable decrease in pH in the lumen.
ATP Synthesis and Chemiosmosis
- The proton gradient breakdown leads to ATP synthesis through the movement of protons across the membrane.
- ATP synthase consists of two parts: CF0 (a transmembrane channel) and CF1 (protrudes on the outer surface of the thylakoid membrane).
- The breakdown of the gradient provides enough energy for a conformational change in CF1, enabling ATP synthesis.
- Chemiosmosis requires a membrane, a proton pump, a proton gradient, and ATP synthase.
- Energy is used to pump protons across a membrane, creating a gradient, and ATP synthase releases energy to catalyze ATP formation.
Learn about the chemiosmotic hypothesis in photosynthesis and respiration, where ATP synthesis is linked to the development of a proton gradient across a membrane. Understand the differences in the accumulation of protons in thylakoid membranes and mitochondria intermembrane space.
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