Light-dependent & Light-independent Stages Flashcards
Define the term photophosphorylation
-the generation of ATP from ADP and inorganic phosphate, in the presence of light
What are electron carriers
-molecules that can accept one or more electrons and then donates these electrons to another carrier
Example: NADP
What is NADP
-a coenzyme and electron and hydrogen carrier
What stages does the light-dependent stage consist of
1) light harvesting at the photosystems
2) photolysis of water
3) photophosphorylation- production of ATP in the presence of light
4) the formation of reduced NADP
In summary what happens in the light-dependent stage of photosynthesis
-light energy is absorbed by chloroplast pigments and is used to synthesise ATP and reduced NADP (NADPH), this takes place in the thylakoid membranes
-it converts light energy into chemical energy
How is ATP made; what type of reaction is it and what helps its formation
-condensation reaction
- ADP + Pi——> ATP
-ATP synthase
How is ATP broken down; what type of reaction is it and what helps in its break down
-hydrolysis reaction
- ATP——> ADP + Pi
-ATP synthase
What does the term phosphorylation mean
-used to describe the formation of ATP
What are the 3 ways phosphorylation can occur
-photophosphorylation
-substrate level phosphorylation
-oxidative phosphorylation
Describe photophosphorylation
-occurs in the chlorophyll during photosynthesis (requires co-enzyme NADP)
Describe oxidative phosphorylation
- occurs in the mitochondria during the electron transport chain (part of respiration requires co-enzymes NAD or FAD —> both shuttle hydrogen)
Describe substrate level phosphorylation
- occurs in the mitochondria during the electron transport chain (part of respiration requires co-enzymes NAD or FAD —> both shuttle hydrogen)
What does light dependent reactions need to
-light
Where does the light-dependent reaction take place
-thylakoid membrane
What does the light dependent reaction produce
-ATP
-NADPH
-O2
Describe the process of non-cyclic photophosphorylation
1) PSII absorbs light energy. This excites a pair of electrons in chlorophyll
2) the pair of electrons have so much energy that they leave the chlorophyll molecule and are taken up by an electron carrier
3) these electrons are replaced by electrons from photolysis of water, light splits water into protons, electrons and oxygen
(2H2O —> 4H+ + 4e- + O2)
4) the electrons pass down a number of electron carriers in a series of oxidation-reductions reactions in the electron transfer chain, loosing energy at each stage
5) this energy is used to pump protons across the thylakoid membrane into the thylakoid space
6) light energy is absorbed by PSI, which excites electrons to an even higher energy level
7) as protons accumulate in the thylakoid space, a proton gradient forms across the membrane
8) protons diffuse down their concentration gradient through T ATP synthase enzymes which cause ADP and Pi to join forming ATP
9) as the protons pass through the channel they along with electrons combine with the NADP forming NADPH and this reaction is catalysed by the enzyme NADP reductive
Describe the differences between 3 cyclic and non-cyclic photophosphorylation
1) light energy is absorbed by PSI
2) this light energy excites a pair of electrons
3) this pair of electrons leave the chlorophyll and are taken up by electron carriers
4) the electrons undergo a series of redox reactions in the electron transfer chain loosing energy at each stage
5) This energy is used to combine ADP and Pi to form ATP
6) the electrons go back to PSI to be used again when excited by light energy
Describe the process of cyclic photophosphorylation
1) light energy is absorbed by PSI
2) this light energy excites a pair of electrons
3) this pair of electrons leave the chlorophyll and are taken up by electron carriers
4) the electrons undergo a series of redox reactions in the electron transfer chain loosing energy at each stage
5) This energy is used to combine ADP and Pi to form ATP
6) the electrons go back to PSI to be used again when excited by light enegy
When does light-dependent reactions occur
-ONLY during daylight
When does the light independent reaction occur
-in the dark
What is required for the light-independent stage
-CO2
Where does the light-independent stage takes place
-takes place in the stroma
What does the light-independent stage produce
-TP (which is used to make glucose)
-RuBP
What is one thing that the light-independent stage doesn’t require that the light-dependent stage does require
-light
What is the cycle of the light-independent stage known as
-the Calvin cycle
What are the three stages of the light-dependent stage
1) carboxylation (or fixation)
2) reduction
3) regeneration
Describe the first step (carboxylation) in the Calvin cycle
-carbon dioxide fixation with RuBP
Describe the second step (reduction) in the Calvin cycle
-reduction of GP to TP
Describe the third step (regeneration) in the Calvin cycle
-re-formation of the CO2
-acceptor molecules RuBP
Describe the Calvin cycle
CARBOXYLATION
1) CO2 enters the leaf through the stomata and combines with RuBP (5C compound) with the enzyme RuBisCo catalysing the reaction forming an unstable 6C compound
2) the 6C compound quickly splits into two molecules of GP (3C compound)
REDUCTION
3) GP is reduced into TP (a different 3C compound) ATP from the light-dependent reaction provides the energy for this
4) The H+ ions from NADPH from the light dependent reaction are uses to reduce GP and NADP is recycled and goes back to the light-dependent reaction
5) 1/6 of TP is converted into glucose
REGENERATION
6) 5/6 of TP is used to regenerate RuBP, ATP is broken down into ADP + Pi to produce energy for this regeneration
What products does TP make
-glycerol
-glucose
-amino acids
-fatty acids
How many turns of the cycle are required to make one molecule of glucose and why
6
-because one Hexose sugar is made by joining 2 molecules of TP
