Photosynthesis Flashcards
1
Q
What is the overall reaction that takes place in photosynthesis
A
6CO2 + 6H2O —> C6H12O6 + 6O2
2
Q
What is the main difference between NAD and NADP
A
- NAD in animal cells and NADP in plant cells
- have mostly the same properties, but are made by separate pathways and are independently regulated
- NADP used exclusively for anabolic (biosynthetic) pathways excess of NADPH (high [NADPH]/[NADH] ratio) to drive biosynthetic reductions
- NAD used exclusively for catabolic pathways, excess of NAD (low [NADH]/[NAD] ratio) to accelerat oxidation of sugars and generation of NADH
3
Q
Describe the process of capturing light energy
A
- photosynthesis utilizes light waves in the visible light spectrum because they have just enough energy to excite an electron
- wavelengths too short = damage to the cell
- wavelengths too long = on converted to vibrational energy of the molecules and heat is released
4
Q
What happens when an electron is excited
A
3 possible outcomes:
- decay by giving off light and heat
- decay by resonance energy transfer to neighboring chlorophyll molecule
- decay by successive electron transfer (one donor chlorophyll is oxidized and an electron acceptor is reduced)
5
Q
Where does photosynthesis occur? How is light energy captured?
A
- occurs in the chloroplasts
- pigments known as chlorophyll absorb photons of light and are located in the thylakoids (stacks of thylakoids are found in the chloroplast)
6
Q
What is the light harvesting complex and why is important?
A
- the antenna complex is a light harvesting complex which has over 100 chlorophyll and carotenoid molecules
- it is required because individual chlorophyll molecules are excited too rarely
7
Q
What is the reaction center?
A
- where all of the excited electrons accumulate
8
Q
When does the transfer of light energy occur?
A
- transfer of light energy nto chemical energy occurs when the reaction center chlorophyll gives up its excited electron to reduce pheophytin
9
Q
Describe the non-cyclic electron transport or Z-scheme
A
- chlorophyll and carotenoids in photosystem II absorb photons (water is also reduced and waste products H2 and O2 are formed) and excites electrons
- electrons are transferred to the reaction center (one chlorophyll known as P680)
- electrons are transferred to pheophytin which is then transferred to plastoquinon (PQ)
- PQ goes to cytochrome complex which carries an H+ from the stroma to the thylakoid lumen (generates proton motive force and ATP is produced via ETC)
- electrons are then transferred to plastocyanin (PC) where it carries the electrons to photosystem I (new reaction center is a chlorophyll known as P700)
- here photons are absorbed again because a lot of energy has been lost
- electrons are then transferred to ferredoxin where it reduces 2NADP+ to 2NADPH
10
Q
Describe the cyclic electron transport
A
- when electrons are transferred from PQ to the cytochrome complex, PC, PSI, then finally to ferredoxin, instead of reducing NADP+, it instead carries the electrons back to PQ
- this cycle only produces ATP
11
Q
What are the 3 steps in the Calvin Cycle?
A
- Fixation of carbon dioxide
- Reduction of 3-phosphoglycerate to G3P
- Regeneration of RuBP from G3P
12
Q
Describe fixation of carbon dioxide
A
- three RuBP molecules have three CO2 molecules fixated onto them and are split into a total of six 3-phosphoglycerate
- this is done by an enzyme named RUBISCO
13
Q
Describe the reduction of 3-phosphoglycerate to G3P
A
- after using energy from 6 ATP molecules (converting them to ADP +P) and oxidizing 6 NADPH molecules,the six 3-phosphoglycerate are converted to six G3P molecules
- one of the G3P molecules go through a series of reactions to be converted to glucose or fructose
14
Q
Describe the regeneration of RuBP
A
- the remaining five G3P undergoes a series of reactions that utilizes the energy from three ATP molecules to regenerate them back into 3 RuBP molecules, where the Calvin Cycle can begin again
