Light independent and dependent reactions Flashcards
What powers an electron in both cyclic and non-cyclic photosynthesis?
Photons/light
What happens as a result of a photon energizing an electron in a photosystem?
- The electron is ejected from the photosystem reaction center
In cyclic photophosphorylation, what happens to the electron once it is energized and ejected from the photosystem reaction center?
- It passes to ferredoxin (an electron carrier), then into the enzyme B6F,
- The electron then returns to the photosystem after contributing to a proton gradient
How is ATP produced in cyclic photophosphorylation?
- The energy released while the electron is being transported creates a proton gradient from the movement of H+ ions from the stroma to the lumen,
- This is used to produce ATP from ADP
What is the main difference between cyclic and noncyclic photophosphorylation?
In Cyclic photophosphorylation, the electron returns back to the same reaction center, while in noncyclic, the electron goes from photosystem II to photosystem I
What is cyclic photophosphorylation?
When an electron is energized by light and released from the photosystem, it returns to the same photosystem after creating a proton gradient for ATP synthesis
What cells use noncyclic photophosphorylation?
- Cyanobacteria (photosynthetic bacteria)
- Plant cells
What is the process of noncyclic photophosphorylation?
- A photon energizes and releases an electron from photosystem II
- The electron from photosystem II comes from the splitting of water in the thylakoid lumen (also produces O2)
- The electron from photosystem II then goes through to the B6F and creates a change in conformation in the enzyme, releasing an H+ from the stroma into the lumen
- This proton gradient is used to produce ATP using ATP synthase as the H+ moves back into the stroma
- The electron then moves from the B6F to photosystem I
- When photosystem I absorb a photon, the electron is energized and released, binding to NADP+ at the NADP+ reductase to form NADPH in the stroma,
- NADPH is known as reducing power
- The cycle restarts with the breakdown of water in photosystem II
What is an absorption spectrum?
The range of wavelengths of electromagnetic radiation absorbed by a given substance
What is an antenna protein?
A pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules
What is a carotenoid?
A photosynthetic pigment that functions to dispose of excess energy
What is chlorophyll a?
- Absorbs violet-blue and red light
- Bluish-green colour
- Only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain
What is chlorophyll b?
- An accessory pigment
- Absorbs blue and red-orange light
- Yellowish-green colour
What is a chloroplast?
Organelle for photosynthesis
What is granum?
A stack of thylakoids located inside the chloroplast
What is a light-dependent reaction?
- The first stage of photosynthesis,
- Visible light wavelengths are absorbed to form 2 energy-carrying molecules:
- ATP
- NADPH
What is P680?
The reaction center of photosystem II
What is P700?
The reaction center of Photosystem I
What is a photon?
A distinct quantity or packet of light energy
- A ray of light
What is the function of Photosystem I?
An integral pigment/protein complex in thylakoid membrane that uses light energy to transport electrons from plastocyanin to NADP+
- NADP+ + e- -> NADPH (reduction)
What is the function of Photosystem II?
An integral pigment/protein complex in thylakoid membranes that transports electrons from water to the electron transport chain
- O2 is a product of Photosystem II (PSII)
What is a pigment?
A molecule capable of absorbing certain wavelengths of light and reflecting others,
- This make sit coloured
What is thylakoid?
A disk shaped, membrane-bound structure in chloroplast
- Site for light-dependent reactions of photosynthesis
What is wavelength?
the length of one full wave
- Inversely proportional to the energy of the radiation
What is a light-independent reaction?
The Calvin cycle
What is the purpose of the Calvin cycle?
To produce glucose from CO2, while expending ATP and NADPH
What are the three sections of the Calvin cycle?
- Carbon fixation
- Reduction and sugar production
- Regeneration of RuBP
What is the process of the Calvin cycle?
- CO2 enters the Calvin cycle and combines with a 5C molecule called RuBP,
- The new 6C molecule is then split in half into two sets of 3C molecules (End of Carbon Fixation)
- ATP and NADPH are used to reduce the 3C molecules into sugars
- 6 repetitions of the Calvin cycle produce the sugars necessary to make glucose (End of Reduction and Sugar Production)
- After the sugars are made, the remaining molecules are used to regenerate the RuBP molecule at the cost of ATP to be resued in the cycle (End of Regeneration of RuBP)
How many repetitions of the Calvin cycle are needed to produce a glucose molecule?
6
What is the 5C molecule in the Calvin cycle combined with CO2 during the carbon fixation stage?
RuBP
What molecule is RuBP similar to in the Krebs cycle?
Oxaloacetate (4C)
In photophosphorylation, in what direction do the H+ ions move to create a proton gradient?
From the stroma to Thylakoid lumen
In Photophosphorylation, where is the water broken down to O2 + H+ + e-?
At photosystem II in the thylakoid Lumen
Where is NADP+ reduced to NADPH?
At the NADP+ reductase in the stroma of the chloroplast
Where is ATP synthesized in phosphorylation?
At the ATP synthase in the stroma of the chloroplast
