MODULE 5: Energy for Biological Processes !! Flashcards
Equation for photosynthesis:
C₆H₁₂O₆ + 6O₂ –> 6CO₂ + 6H₂O
- reverse is respiration
Photosynthesis and respiration:
Interrelated reactions, as the reactants for one equation are the products of another
Structure of chloroplast: (7)
Inner and outer membrane, lamellae, grana, thylakoid, stoma and DNA
Thylakoid:
Flattened discs that have a small internal volume to maximise hydrogen gradient upon proton accumulation. Location of light dependent phase, membrane contains photosystems I and II, as well as ATP synthase
Stroma:
Central cavity that contains appropriate enzymes and pH for the Calvin cycle to occur. Contains starch, lipids, ribosomes and chloroplast DNA
Grana:
Stacks of thylakoids to increase SA:V of thylakoid membrane
Lamellae:
Connects and separates grana to maximise photosynthetic efficiency
Purpose of pigments in photosynthesis:
Absorb different wavelengths of light to transfer energy to the reaction centre
Primary pigment:
Chlorophyll A
Accessory pigments:
Chlorophyll B, xanophylls, carotenoids
Why do chloroplasts have several pigments?
Create a light harvesting system, as certain pigments absorb some wavelengths of light and reflect others (causing their colour.) This maximises absorption of light
Photosystem:
Light harvesting system and reaction center
Thin layer chromatography in photosynthetic pigments:
- Mobile phase = solution containing mixture of pigments
- Stationary phase = thin layer of silica gel (on glass)
- Different solubilities of pigments = different distances moved, hence different Rf values
Rf equation:
Distance travelled by component / distance travelled by solvent
Two phases of photosynthesis:
Light dependent phase and light independent phase (Calvin cycle)
Light dependent phase brief summary:
Energy from sunlight is used to form ATP, and photolysis of water allows NADP to be reduced into NADPH
Light independent phase brief summary:
Products from light dependent phase are used to produce glucose, lipids and amino acids; ATP supplies the energy, whilst NADPH and CO₂ are converted into organic molecules
Non cyclic vs cyclic photophosphorylation:
Non cyclic = uses photosystems I and II
Cyclic = uses photosystem I only
Photophosphorylation:
Transducing light energy into chemical energy, so ADP can be phosphorylated into ATP
Chemiosmosis:
Diffusion of protons from a region of high concentration to an area of low concentration
Two methods of exciting electrons:
- breaking of chemical bonds (electrons present in respiratory substrates)
- absorbing light from the sun (electrons present in pigments)
Electron transport chain: (ETC)
- series of electrons carriers
- progressively less energy (less excited due to loss of energy moving between carriers)
- released energy is used to pump protons across the membrane
- creates a gradient, which is maintains as the membrane is impermeable to protons
- protons can only re enter the thylakoid via hydrophilic protein channels, which is linked to the enzyme ATP synthase
- flow of proteins through the channel allows the enzyme to catalyse the formation of ATP from ADP and inorganic phosphate
ATP formation from chemiosmosis and ETC:
- protons move out of thylakoid due to energy released from ETC
- creates a proton gradient
- protons move back into the thylakoid by chemiosmosis via the hydrophilic channel protein that is linked to ATP synthase
- movement of protons through the channel allows the enzyme (ATP synthase) to catalyse the formation of ATP from ADP and inorganic phosphate
Photolysis:
H₂O –> 2H⁺ + 0.5O₂ + 2e⁻
- energy from the sun splits water into hydrogen ions, oxygen and electrons.
- electrons released from this process replace the lost electrons from reaction center of PSII.
- catalysed by oxygen-evolving complex enzyme in PSII
