hill reaction
BIOL2220 Lab 3: Hill Reaction
Introduction
In 1937, Robert Hill discovered that isolated chloroplasts can generate oxygen when they are illuminated in the presence of a suitable electron acceptor, even in the absence of carbon dioxide. This finding was a landmark in the study of photosynthesis because it established that the source of the electrons used in the light reactions is water. It also confirmed that the released oxygen is derived from water instead of carbon dioxide. In chloroplasts, the final electron acceptor is NADP+, which is reduced to NADPH. ATP is generated by photophosphorylation during the light-induced electron transfer reaction. NADPH and ATP produced in the light reactions are utilized for the biosynthetic reactions in the dark reactions for making carbohydrates. Light reactions can be investigated in the laboratory using isolated chloroplasts.
The Hill reaction is defined as the reduction of an electron acceptor (A) by electrons from water, with the evolution of oxygen, when isolated chloroplasts are exposed to light: light
2H2O
+
2A
2AH2
+
O2
chloroplasts
The reagent 2,6-dichlorophenolindophenol (DCPIP) is a useful artificial electron acceptor. The following reaction can be monitored by measuring the loss of the blue color of DCPIP. DCPIP replaces NADP as the final electron acceptor in the light reactions. DCPIP
(blue)
DCPIPH2
(colorless)
Light reactions can be affected by the presence of different compounds. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; known commercially as diuron) inhibits the transport of electrons from PQA to PQB. On the other hand, ammonia eliminates the H+ gradient across the thylakoid membrane, thus functioning as an uncoupler of electron transport and photophosphorylation.
There are three objectives for this laboratory.
(1) To isolate active chloroplasts
from spinach leaves. (2) To measure the rate of the Hill reaction. (3) To examine
the
Introduction
In 1937, Robert Hill discovered that isolated chloroplasts can generate oxygen when they are illuminated in the presence of a suitable electron acceptor, even in the absence of carbon dioxide. This finding was a landmark in the study of photosynthesis because it established that the source of the electrons used in the light reactions is water. It also confirmed that the released oxygen is derived from water instead of carbon dioxide. In chloroplasts, the final electron acceptor is NADP+, which is reduced to NADPH. ATP is generated by photophosphorylation during the light-induced electron transfer reaction. NADPH and ATP produced in the light reactions are utilized for the biosynthetic reactions in the dark reactions for making carbohydrates. Light reactions can be investigated in the laboratory using isolated chloroplasts.
The Hill reaction is defined as the reduction of an electron acceptor (A) by electrons from water, with the evolution of oxygen, when isolated chloroplasts are exposed to light: light
2H2O
+
2A
2AH2
+
O2
chloroplasts
The reagent 2,6-dichlorophenolindophenol (DCPIP) is a useful artificial electron acceptor. The following reaction can be monitored by measuring the loss of the blue color of DCPIP. DCPIP replaces NADP as the final electron acceptor in the light reactions. DCPIP
(blue)
DCPIPH2
(colorless)
Light reactions can be affected by the presence of different compounds. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; known commercially as diuron) inhibits the transport of electrons from PQA to PQB. On the other hand, ammonia eliminates the H+ gradient across the thylakoid membrane, thus functioning as an uncoupler of electron transport and photophosphorylation.
There are three objectives for this laboratory.
(1) To isolate active chloroplasts
from spinach leaves. (2) To measure the rate of the Hill reaction. (3) To examine
the