Light Dependent Reaction (Q2) Flashcards
Flow of electrons through the photosystems and other molecular components built into the thylakoid membrane
Linear Photophosphorylation/linear electron flow
Two stages of photosynthesis
Light-dependent reaction and light-independent reaction
This stage of photosynthesis requires sunlight, occurs in the thylakoid membrane, and involves two photosystems and the electron transport chain.
Light-dependent reaction
What is the goal of light dependent reaction?
To create ATP and NADPH by energizing photosynthesis through sunlight
Large protein complexes of proteins and pigments that harvest light
Photosystems (PSII and PSI)
The photosystem is composed of:
- Reaction-center complex
- Light-harvesting complexes
A reaction-center complex consists of:
- Special chlorophyll A molecules
- Primary electron acceptor
Consists of various pigment molecules that harvest light photons
Light-harvesting complex
Special pair of chlorophyll a molecules in Photosystem II
P680
Special pair of chlorophyll a molecules in Photosystem I
P700
What do the numbers on the photosystem names mean?
Reflects the order of discovery of the photosystem
Four parts of the light-dependent reaction
- Light absorption in PSII
- ATP synthesis
- Light absorption in PSI
- NADPH formation
What explains the concept of how energy is transferred from one pigment molecule to another until it reaches the special pair of chlorophyll a molecules?
Resonance energy transfer
What happens when a chlorophyll molecule absorbs a photon?
It causes a transition of the chlorophyll molecule from its ground state to excited state.
Primary electron acceptor of PSII
Pheophytin
Primary electron acceptor of PSI
A0
Chlorophyll a molecules of PSII
P680, best absorbs light with a wavelength of 680 nm (red part of spectrum)
Chlorophyll a molecules of PSI
P700, best absorbs light with a wavelength of 700 nm (far-red part of spectrum)
Process of breaking water molecules using the energy provided by light
Photolysis
End products of photolysis
2 electrons, 2 hydrogen ions, and 1 oxygen atom
The electrons from photolysis are supplied one by one to the _____.
Special pair of chlorophyll a molecules
The hydrogen ions from photolysis are stored in the _____.
Thylakoid lumen
Strongest biological oxidizing agent that greatly facilitates the transfer of electrons from the split water molecule
P680
Three components of the electron transport chain connecting the electron flow between PSII and PSI
- Plastoquinone (electron carrier)
- Cytochrome complex
- Plastocyanin (protein)
What causes the electron transport chain to release free energy?
Redox reactions
Movement of hydrogen ions down their electrochemical gradient in order to start ATP synthesis
Chemiosmosis
What is the name of the enzyme that hydrogen ions go through during chemiosmosis?
Transmembrane enzyme ATP synthase
Protein that helps in passing electrons down to the electron transport chain after being excited in PSI
Ferredoxin
Electrons from ferredoxin are transferred to _______ and is turned into _______ with the help of the enzyme _______ and through the process of _______. It also requires _______ ions from the stroma.
NADP+, NADPH, NADP+ reductase, reduction, hydrogen
How many electrons are needed to reduce NADP+ into NADPH?
2 electrons
Process wherein electrons loop back to the first part of the electron transport chain, repeatedly cycling through PSI instead of ending
up in NADPH.
Cyclic photophosphorylation
Does cyclic photophosphorylation produce NADPH?
No, only ATP.
Five reasons why cyclic photophosphorylation happens
- Organisms with single photosystems
- Mutations
- Too little NADP available
- High ATP needs
- Photoprotection
Reactants of light dependent reaction
- H2O
- ADP
- NADP+
- Pi (inorganic phosphate)
- Light
To produce one glucose molecule, how many water molecules are needed?
12
To produce one glucose molecule, how many NADP+ are needed?
12
To produce one glucose molecule, how many NADPH are needed?
12
To produce one glucose molecule, how many O2 molecules are needed?
6
To produce one glucose molecule, how many ADP are needed?
18
To produce one glucose molecule, how many ATP are needed?
18
To produce one glucose molecule, how many inorganic phosphate molecules are needed?
18
When excited electrons fall back to the ground state, photons are given off and releases an afterglow called ______.
fluorescence
If illuminated, an isolated solution of chlorophyll will fluoresce, giving off ______ and ______.
light, heat
