ATP Synthesis: $H^+$ Gradient Formation Sites
ATP biosynthesis in both mitochondria and chloroplasts relies on a proton ($H^+$) gradient established across specific membranes. This process is known as chemiosmosis.
Mitochondrial $H^+$ Gradient
In mitochondria, the electron transport chain pumps protons ($H^+$) from the mitochondrial matrix into the intermembrane space. This creates a proton gradient and an electrochemical potential difference across the inner mitochondrial membrane. ATP synthase, located in the inner membrane, uses the flow of protons back into the matrix to synthesize ATP.
Chloroplast $H^+$ Gradient
In chloroplasts, during the light-dependent reactions of photosynthesis, protons ($H^+$) are pumped from the stroma into the thylakoid lumen. This builds up a high concentration of protons within the lumen, establishing a proton gradient across the thylakoid membrane. Protons then flow back into the stroma through ATP synthase, driving ATP production.
Summary of Sites
- Mitochondria: Across the inner mitochondrial membrane (protons move from matrix to intermembrane space).
- Chloroplasts: Across the thylakoid membrane (protons move from stroma to thylakoid lumen).
Therefore, the correct sites for $H^+$ gradient formation utilized in ATP biosynthesis are across the inner membrane of mitochondria and across the thylakoid membrane of chloroplasts.
Important Questions from Photosynthesis Respiration and Electron Transport Chain
- Correctly match the Inhibitor with its respective Function in mitochondrial respiration.
Inhibitor Function P. FCCP 1. Inhibits cytochrome c oxidase Q. Cyanide 2. Makes the membrane permeable to protons R. Oligomycin A 3. Blocks mitochondrial uptake of succinate S. Butyl malonate 4. Inhibits ATP synthase Which of the following are true with regard to anaerobic respiration in bacteria?
P. The final electron acceptor is an inorganic substance other than molecular oxygen
Q. The number of ATP molecules produced per glucose molecule is more than that produced in aerobic respiration
R. The number of ATP molecules produced per glucose molecule is less than that produced in aerobic respiration
S. Only substrate level phosphorylation is used to generate ATP
Match the compounds in Group I with the correct entries in Group II.
Group I Group II P) Cyanide 1) K$^+$ ionophore Q) Antimycin A 2) Electron transfer from cytochrome b to cytochrome c$_1$ R) Valinomycin 3) F$_1$ subunit of ATP synthase S) Aurovertin 4) Cytochrome oxidase 5) Adenine nucleotide translocase - During photorespiration under low $CO_2$ and high $O_2$ levels, $O_2$ reacts with ribulose 1,5- bisphosphate to yield
Match items in Group I with Group II.
Group I Group II
P. Glycolytic pathway 1. Chloroplast
Q. Eukaryotic oxidative metabolism 2. Glyoxysomes
R. Glyoxylate cycle 3. Mitochondria
S. Calvin cycle 4. Cytosol
