PHOTOSYNTHESIS Flashcards
Anatomy of chloroplast, photosystems (antenna complex, + reaction centre) Light dependent reactions (process, purpose, location, reactants and products, cyclic vs non-cyclic electron flow) Light-independent reactions (mains steps, purpose, location, reactants and products) Why is RUBISCO so inefficient? Light & photosynthesis (purpose and results of Engelmann's experiment, absorption vs action spectrum)
ANTENNA COMPLEX
Composed of a cluster of chlorophyll molecules and accessory pigments
Embedded in the thylakoid membrane
Absorbs a photon and transfers the energy from pigment to pigment until it reaches the reaction center
REACTION CENTER
Protein complex
Contains a chlorophyll-A molecule
Electrons of chlorophyll absorbs energy and begin photosynthesis
Light dependent reactions PROCESS
Photoexcitation
Absorption of a photon by an electron of chlorophyll
Electron Transport
Transfer of excited electrons through a series of membrane-bound electron carriers, resulting in the pumping of a proton through the photosynthetic membrane, which creates a H+ reservoir and eventually reduces an electron acceptor
Chemiosmosis
The movement of protons through ATPase complexes to drive the phosphorylation of ADP to ATP
Photo excitation
Photon strikes PS2 and excites an e- of chlorophyll P680. This electron is captured by a primary electron acceptor
Whenever photon strikes
Electron Transport
- Electron is transferred to the first electron mobile carrier (PQ). This process occurs twice, causing 2 electrons to pass through the ETC
- A “Z” protein (enzyme) associated with PS2 facing the lumen splits water into O2, Protons and Electrons
- The 2 electrons replace the missing electrons in chlorophyll 680
- O2 leaves as by-product
- The protons remain in the thylakoid space (lumen). Helps create the H+ gradient that will power chemiosmosis
- The electrons that leave photosystem 2 pass through PQ, which transports protons from the stroma into the thylakoid lumen
- Helps create H+ gradient for chemiosmosis
- 4 protons are translocated from the stroma into the lumen for every pair of electrons
-The electrons move to b6-f complex, then to Pc, then to PS1 (by this time, the energy of the electrons has dissipated
- A photon of light strikes PS1 and excites the electrons of chlorophyll P700
Electrons then pass through another ETC containing an iron-containing protein called Fd - They then move to the enzyme NADP reductase that uses the 2 electrons and H+ ions from the stromA to reduce NADP+ to NADPH
Chemiosmosis
Protons that accumulate in the thylakoid lumen contribute to an electrochemical gradient that drives the phosphorylation of ADP to ATP
Light reactions purpose
using light energy and water to make ATP and NADPH for calvin cycle
Light reactions LOCATION
in between the thylakoid lumen and the stroma (aka the thylakoid membrane)
Light reactions REACTANTS:
NADP+, ADP + P, H2O, light energy
Light reactions PRODUCTS:
NADPH, ATP, O2, H+,
Light-independent reactions Carbon Fixation
3 CO2 molecules are added to RuBP and is catalyzed by the enzyme Rubisco
Produces 3 BPG (6 carbon with 1 phosphate group at each end)
Unstable so it splits
Light-independent reactions Reduction reactions
6 ATP → 6 ADP + 6 P
6 NADPH → 6 NADP+ + 6 H+
6 three carbon-phosphate G3P are made
One G3P leaves the cycle (acts as a raw material in the production of other carbohydrates that the cells use for various structural and functional processes (ex. Glucose, starch, cellulose)
Light-independent reactions RuBP regeneration
5 G3P molecules rearranges and becomes RuBP
3 ATP → 3 ADP + 3 Pi
Light-independent reactions PURPOSE
the reactions that convert CO2 into carbs molecules
Light-independent reactions Location
stroma of chloroplast
Light-independent reactions reactants
3 CO2, 3 RuBP, 9 ATP, 6 NADPH
Light-independent reactions products
9 ADP + 8 P, 6 NADP+, 6 H+, 1 G3P, 3 RuBP
Why is RUBISCO so inefficient?
It is a large enzyme and works VERY slowly
It processes 3 substances/sec
Lacks specificity
Binds to CO2 as easily as it binds to O2
O2 is an inhibitor; it takes CO2 into another pathway that does not produce ATP or sugar
Plants need to use energy to reverse this
ENGELMANN’S EXPERIMENT
PURPOSE:
to determine which wavelengths of light optimize photosynthesis
To determine whether all colours of the visible spectrum carried out photosynthesis equally well
ENGELMANN’S EXPERIMENT RESULTS
Bacteria accumulated in areas where the filament was exposed to red and blue-violet light, with very few bacteria gathering in green light
Absorption spectrum
How much wavelength of light is being absorbed by a specific pigment
A graph illustrating the wavelength of light absorbed by a pigment
Chlorophyll a Reflects blue-green Absorbs more red than chlorophyll b Chlorophyll b reflects yellow-green Absorbs more blue than chlorophyll a
Action spectrum
The amount of photosynthesis that occurs by a specific wavelength
A graph of the rate of a physiological activity (such as photosynthesis) plotted against wavelength of light.
Green light
Chlorophyll a and b absorbs almost no green light however looking at the action spectrum, green light does contribute to photosynthesis
Therefore, since chlorophyll a and b does not meet the requirements of absorbing green, there are different pigments that contribute to absorption of green light and so green light is still able to be utilized by plants to create food via
WHY ARE THE LEAVES OF PLANTS NOT GREEN IN THE FALL
Cold temp. result in the plants stopping production of chlorophyll molecules and disassembling the existing chlorophyll a and b pigments
The only pigments the human eye can see is the accessory pigments
Yellow and yellow-orange are located in the thylakoid membrane
Red, violet and blue are located in the vacuoles (not chloroplast) of the cell
The accessory pigment that reflect violet is less abundant
Accessory Pigment
Accessory pigments bounce/transferring energy until it reaches chlorophyll
Chlorophyll are more abundant and more dominant in the case that they can actually being in redox reaction
