Lecture 31 Flashcards
Pigments and electron acceptors or carriers are embedded in
Thylakoid membrane
As electrons move down the electron transport chain, protons move from the stroma to the
Thylakoid lumen
A concentration gradient of protons is created between the thylakoid lumen and the stroma reaching an approx. 1000 fold difference in proton concentration
As the protons diffuse through an ATP synthase complex, this ____ process of diffusion down a concentration gradient couples the _____ Endergonic process of phosphorylation of ADP to form ADP
Exergonic
Endergonic
ATP is released into the ______
In Chemiosmosis
Stroma
Chemiosmosis
The pigments and electron acceptors or
carriers are embedded in the thylakoid
membrane.
▪ As electrons move down the electron
transport chain, protons move from the
stroma to the thylakoid lumen
▪ A concentration gradient of protons is
created between the thylakoid lumen
and the stroma, reaching an approx.
1000-fold difference in proton
concentration.
▪ As the protons diffuse through an ATP
synthase complex, this exergonic
process of diffusion down a
concentration gradient couples the
endergonic process of phosphorylation of
ADP to form ATP.
▪ ATP is released into stroma
Chemiosmosis can be divided into 2 classes
Non cyclic electron flow
Cyclic electron flow
Non cyclic electron flow
Involves both photosystems 1 and 2 and produces ATP and NADPH
Cyclic electron flow
Uses only photosystem 1 and produces only ATP
no H2O splitting occurs
No NADPH is produced
No O2 generated
ATP is formed by Chemiosmosis
Generates surplus ATP
PROCESS used by ancient bacteria to produce ATP from light energy
To satisfy the higher demand in the Calvin cycle
To drive other energy requiring processes within the chloroplast
Comparison of Chemiosmosis in photosynthesis vs aerobic cellular respiration
Protein in the electron transport chain are homologous in chloroplasts and mitochondria
P= photosynthesis CR= cellular respiration
P: proteins anchored in thylakoid membrane
CR: proteins anchored in mitochondrial (inner) membrane
P: electron donor is H2O
CR: electron donor is NADH/FADH2
P: final electron receptor is NADP+
CR: final electron receptor is O2
P: products are ATP, NADPH, O2
CR: final products are ATP, H2O
Carbon fixation def
Incorporation of atmospheric CO2 into organic compounds
Energy of ATP and NADPH produced during the light rxn is used to create organic molecules from CO2
This happens in the carbon cycle (Calvin benson cycle)
Carbon fixation C3 plants
CO2 is fixed into a theee- carbon sugar (3-phosphoglycerate) as it enters the Calvin cycle
Carbon fixation
C4 plants and CAM (crassulacean acid metabolism) plants
Carbon fixed into a four-carbon sugar (oxaloacetate)
Calvin cycle formula
6CO2 + 12 NADPH + 18 ATP -> C6H12O6 + 12 NADP+ + 18 ADP + 18Pi + 6H2O
Calvin cycle définition
Cyclic series of chemical reactions that occur in the stroma of a chloroplast, using the carbon in CO2 and the ATP and NADPH produced by the light reactions to make energy rich sugar molecules glyceraldehyde 3-phosphate (G3P)
Step 1 of Calvin cycle
Carbon fixation
Carbon fixation step by step
CO2 fixed to the energy rich 5-carbon compound ribulose 1,5-hi phosphate (RuBP)
This is catalyzed by rubisco (ribulose 1,5- biphosphate carboxylase/oxygenase), the most abundant protein in the chloroplast
The product is 2 molecules of the 3 carbon compound 3-phosphoglycerate (PG)
The product of the initial carbon fixation reaction is a three-carbon compound. Thus the Calvin cycle is also called C3 pathway
Rubisco is the most _____ protein _____
Abundant
on earth
Rubisco (RuBP)
Makes up 50% of total protein content in plant leaves
Catalyzes at a very slow rate, hence need for high concentration
This slow rate is bc it fixes carbon
CO2 (acting as carboxylase) but also uses oxygen to remove a carbon releasing CO2 (acting as oxygenase)
Thus O2 actually inhibits carboxylation and causes photo respiration
Requires coordinated expresses of a gene in the chloroplast genome and a gene in the nucleus
Calvin cycle step 2
Reduction
Réduction Calvin cycle
2 molecules of ATP and 2 molecules of NADPH are consumed for each CO2 molecule fixation during this step
The energy and reducing power from ATP and NADPH are used
The PG molecule is phosphorylated by ATP and reduced by NADPH, resulting formation of glyceraldehyde 3-phosphate (G3P)
At this step an energy rich sugar molecule G3P might be removed from the cycle and 2 molecules of G3P can lead to the formation of glucose or fructose in an Exergonic rxn
Step 3 Calvin cycle
RuBP regeneration
RuBP regeneration
Involves a series of 10 reactions
Intermediate ribulose-5-phosphate becomes phosphorylated, consuming ATP, to regenerate RuBP
after this phase RuBP can accept another CO2
C4 and CAM cycles
Allow carbon fixation at high temperatures or low CO2
C4 cycle
Concentrates the CO2 allowing for more efficient Calvin cycle but comes at the cost of ATP
a way for plants to prevent the loss of water by keeping stomata closed as much as possible
Products of C4 cycle are then transported from mesophyll cells to interior bundle sheath cells that conduct the more efficient Calvin cycle
CAM cycle
Crassulacean acid metabolism
Stomata only open during the night to preserve moisture
