Topic 6: Photosynthesis Flashcards
(28 cards)
Define Metabolism.
All of an organisms reactions.
Consisting of CATABOLIC and ANABOLIC pathways
Energy conversion in Photosynthesis vs Cellular Respiration?
Photosynthesis:
- anabolic
- Light Energy -> Chemical Energy
- CO2 + H2O + Light -> C6H12O6 + O2
Cellular Respiration:
-Catabolic
Chemical Energy -> Chemical Energy
C6H12O2 -> CO2 + H2O + ATP
Define Photoautotroph?
Photosynthetic organism:
Producers; self-feeders
Use sunlight energy to create organic molecules that are used as food.
How do the following Molecules store Energy?
- Sugar/Fat
- ATP
- NADH, NADPH, FADH2
- PROTON GRADIENT
- Sugar/Fat: C-C; C-H bonds
- ATP: P-P-P
- NADH, NADPH, FADH2: pair of high energy e-
- Proton Gradient: separation of charges
Define the following terms: Leaves: Stomata: Chloroplast: Chlorophyll:
Leaves: major site of photosynthesis
Stomata: Openings on leaf that allow for Gas exchange
Chloroplast: Cell organelles of photosynthesis
Chlorophyll: Green pigment; light harvesting chemical found in thylakoid Membrane
What is the purpose of photosynthesis? What are the reactants and products of the rx?
Purpose: to convert light energy to chemical energy. Energy Transformation
Light energy + CO2 + H2O -> O2 + C6H12O6
What are the two major processes of photosynthesis?
1: light reactions
2: calvin cycle
Light reactions:
Where?
What happens?
Site: Thylakoid Membrane and Space
What Happens: Sunlight is absorbed by chlorophyll in chloroplasts
- energy is converted into ATP and NADPH
Calvin Cycle:
Where?
What?
Site: Stroma
What: Synthetic Cycle where CO2 is incorporated into more complicated carbon molecules through Carbon Fixation coupling
CO2 -> C6H12O6
Requires energy (endergonic). Uses atp and nadph from light rxn’s
There are two chlorophylls
a vs b
How are chorophylls arranged in cell?
Chlorophyll a:
Main photosynthetic pigment
-light is absorbed by specific atoms within the porphyrin ring of chlorophyll a
-other pigments absorb & transfer energy to Chl ‘a’
Chlorophyll are inserted in the thylakoid membrane (has hydrocarbon tail) and are anchored b/c of hydrophobic sidechain
Where and how is light absorbed?
- Light absorbed by specific atoms in porphyrin ring of chlorophyll a
- excites e- (become less stable (higher energy) e- move to higher orbital
- When e- return to “ground state” absorbed energy is released and trasnferred
There are three options for an excited e- what are they?
- e- returns to ground state by emitting a less energetic photon or releasing energy as heat * lose absorbed energy
- The e- returns to ground state as its energy is transferred to an e- in a neighbouring pigment - funnels to final destination like dominoes
- The high energy e- is transferred to another molecule, an e- acceptor and e- in chlorophyll is replaced
What are photosystems?
Light harvesting unit located in thylakoid membranes - made of chlorophyll and proteins arranged in an antenna complex: allows photosystem to harvest light energy cooperatively - funnels energy to one “special” chlorophyll molecule called the reaction centre chl. molecule
Difference between two types of photosystems?
Photosystem 1 (PS1): Absorbs light at 700nM
Photosystem 2 (PS2) Absorbs light at 680nM
e- go from ps2 to ps1
What is a REDOX Reaction?
Oxidation - reduction reaction
- > Chemical rxn where there is a transfer of e- from one ractant to another
- e- carry energy used by cell
Redox rxn’s are coupled. What does this mean?
e- lost is gained by another molecule.
One is reduced: Addition of e- (-)
One is oxidized: loss of e- (+)
Describe the energy pathway of photosynthesis (light rxn)
Noncyclic Electron Flow (linear)
- light energy absorbed by chlorophyll
- converted into ATP & NADPH
- Uses two photosystems, e- transport chain and chemiosmosis
What are steps one and two of photosynthesis
- Resonance transfer of energy from one chlorophyll molecule to the next
- > energy reaches rxm center chlorophyll molecule in photosystem 2 and excites e- - Rxn center chlorophyll molecule transfers its high energy e- to a primary e- acceptor molecule
-> e- keeps high energy conformation
-> Primary e- acceptor is reduced
Chlorophyll-> oxidized (has a hole)
Step 3: must fix the e- hole in the p680 chlorophyll molecule,
How?
Splitting of water provides e- that fill this hole
- O2 created is released from cell (waste)
- H+ created contributes to proton gradient
Step 4: Photoexcited e- moves via e- transport chain in PS2
- describe this process
- name the complexes
- ETC is series of membrane spanning protein complexes called Plastoquinone, cytochrome, and plastocyanin
- Everytime e- moves from one molecule to the next a small amount of energy is released (cell couldnt deal if all was released at once)
** electronegativity increases along path to determine direction of e-
Step 5: Exergonic fall of e-‘s along ETC
Describe:
What is the result:
Energy is released at every e- transfer (as e- moves from protein complex to protein complex energy is released)
Result:
The released energy is used to make atp through chemiosmosis
Why is water split at beginning of light rxn’s?
What is an ETC?
- Need e- from H2O to replace p680 chlorphyll hole. Releases O2 and contributes to proton gradient
- Electron transport chain:
Series of e- carrier molecules (proteins) that transfer e- from high energy substrates
-releases energy in controlled steps
-chain molecules sequentially reduced and oxidized
Define photophosphorylation
-refers to the use of light energy to provide the energy to convert ADP to ATP
Step 6: now at bottom of p680 e- transport chain in PS2
e- reaches bottom of ETC and is now low energy - fills e- hole of p700 (ps1) rxn center chlorophyll molecule
