WK3 LEC9: Photosynthesis I (Light Dependent) 낱말 카드

• Differentiate between anabolism and catabolism, and oxidation and

reduction

Anabolism:

- Synthesising Complex molecules from simple ones

- Net process is endergonic (ΔG > 0)

i.e Photosynthesis, Protein Synthesis

Catabolism:

- Synthesising simple molecules from complex ones

- Net process is exergonic (ΔG < 0)

i.e Respiration

Mechanism of energy release: Oxidation/Reduction (electron transfer)

- REDOX: OIL (oxidation is loss of electrons) RIG (reduction is gain of electrons)

- Redox Potential = Electron Energy

- Electrons flow from High Energy -> Low Spontaneously,

Oxidation:

- Number of C-O bonds increases, electrons are lost from oxidised species due to oxidising agent.

- Free electrons are available on products side

Reduction:

- Number of C-O bonds decreases, electrons are gained for reduced species due to reducing agent.

- Free electrons are consumed on reactants side

Complex Molecule catabolised (Oxidised) -> Simple Molecule + Energy (Corresponding Free electrons)

Simple Molecule anabolised (Reduced) + Energy -> Complex Molecule (Less free electrons)

• Explain how ATP can power cellular processes

Energy Currency: ATP

- Phosphoester bond contains a high amount of energy which can be released when it's broken.

Cycle:

1. ATP (charged — 3 phosphates)

2. Energy release (cellular work, synthesis — phosphate is transferred)

3. ADP (uncharged — 2 phosphates)

4. Energy Recharge (condensation rxn, Phosphate added to ADP to form ATP)

• Describe, in overview, the conversion of radiant energy into chemical

energy

Light Dependent Photosynthesis:

- Non-cyclic Photophosphorylation (Thylakoids)

- ATP + NADPH produced to power Calvin Cycle

Incident photons excite electrons in antenna (chlorophyll) complex - excitation (resonance energy is transferred) before reaching RXN centre (chlorophyll pair) where e- transfer occurs.

e- transfer between rxn centres via electron transport chain produces ATP, with NADPH produced after photosystem I.

• Explain the overall organisation of the light reactions in photosystems I

and II

Photosystem II:

- Shorter wavelength PHOTON excites RXN centre

- e- travels down transport chain, progressively releasing energy being transferred through membrane proteins.

- Energy released is used to pump [H+] into lumen from stroma from against gradient

- As [H+] passes back out ATP synthetase binds P to ADP to form ATP.

- (e-) transferred to Photosystem I

Photosystem I:

- Longer wavelength PHOTON excites (e-)

- (e-) is transferred to electron carrier NADPH

• Describe ATP synthesis and NADP+ reduction during photosynthesis

Metabolism: Electron Carriers

Metabolic Pathways will involve electron carriers at many intermediary steps — they cancel in the final equation.

Electron transfer (Redox RXN) is the main method of energy transfer in cells. Electron transport chain releases energy in discrete steps, this energy is used to pump H+ across membranes against gradient. H+ attempts to move back down concentration gradient through ATP synthase to store energy as currency in ATP.

Autotrophy vs Heterotrophy

Autotrophy: Self Feeding

- inorganic molecules + energy -> carbohydrate synthesis

- respiration -> ATP + byproducts

(glycolysis, krebbs cycle, oxidative phosphorylation)

- release energy

Heterotrophy: Feed on Organisms

- eat food (organic macronutrients)

- respiration -> ATP + byproducts

(glycolysis, krebbs cycle, oxidative phosphorylation)

- release energy