L photosynthesis Flashcards
how does photosynthesis produce triose phosphate?
- During light dependent reaction, light energy is absorbed by chlorophyll pigment -> In cyclic phosphorylation only ATP is yield whereas non-cyclic phosphorylation yields O2, ATP and reduced NADP
- During light independent reaction (Calvin cycle), carbon fixation first occurs by fixing CO2 with RuBP to produce 2 molecules of glycerate-3-phosphate (GP) and In carbon reduction, reduced NADP and ATP from light dependent reaction provide reducing power and energy to convert GP to glyceraldehyde-3-phosphate (GALP)
what are two factors that directly limit the rate of Calvin cycle?
- CO2 conc -> CO2 diffuses into the leaf tissues via stomatal pore and its conc affects the rate of CO2 fixation as CO2 is a substrate of Rubisco enzyme
- temperature -> affects the rate of enzyme reactions such as those catalysed by Rubisco
why is light needed for the Calvin cycle to continue?
light is needed to produce ATP and reduced NADP + in CO2 reduction, reducing power of reduced NADP and energy from the hydrolysis of ATP are used to convert GP to GALP/trios phosphate
Calvin cycle (LIGHT INDEPENDENT involves series of enzyme-catalysed reaction and occurs in the stroma of chloroplast)
- Fixation of CO2 by Rubisco, catalysed by RuBP carboxylase-oxygenase giving an UNSTABLE 6C intermediate which immediately breaks down into 2 molecules of GP
- Reducing power of reduced NADP and energy from the hydrolysis of ATP are used to convert GP to trio phosphate/GALP where about 1/6 of the total amount of GALP is used to synthesise glucose, other carbs and glycerol
- about 5/6 of the total amount of GALP has to be used to regenerate the RuBP, requiring energy from the hydrolysis of ATP
what is the role of NADP in linking the light dependent reactions to the Calvin cycle?
oxidised NADP acts as an electron acceptor, accepting electrons from ferrodoxin and the reduced NADP then proceeds to the Calvin cycle to provide reducing power to convert GP to GALP
explain photoactivation of chlorophyll
light strikes a chlorophyll molecule in the light harvesting complex and this energy is relayed to neighbouring accessory molecules until it accumulates and reaches a special chlorophyll a where its electron gets EXCITED to a higher energy level and emitted
explain photoactivation of chlorophyll
light strikes a chlorophyll molecule in the light harvesting complex and this energy is relayed to neighbouring accessory molecules until it accumulates and reaches a special chlorophyll a where its electron gets EXCITED to a higher energy level and emitted
function of thylakoid membrane
- provide large SA for numerous electron carriers and photosystems to be embedded
- contains stalked particles which have ATP synthase for the synthesis of ATP from ADP and Pi
- Impermeable nature of thylakoid membrane to protons allows electrochemical proton gradient to be set up
non-cyclic vs cyclic phosphorylation
- first electron donor for NC is water vs C is PSI
- final electron acceptor for NC is oxidised NADP vs for C is PSI
- products for NC is ATP, reduced NADP and O2 vs for C only ATP
photophosphorylation vs oxidative phosphorylation
- both involved the transport of HIGH ENERGY ELECTRONS along the ETC from one e carrier to another, each with an energy level lower than the one preceding it
- energy released from electron transport is used to actively pump protons from the mitochondrial matrix into intermembrane space and from the stroma into the thylakoid space to create an electrochemical proton gradient
- light energy to chemical energy (reduced NADP and ATP) vs chemical energy (food) to chemical energy (ATP)
- takes place in thylakoid membrane of chloroplast vs inner mitochondrial membrane
- light energy required for photolysis and photoactivation vs light energy not required
Calvin cycle vs Krebs cycle
- stroma of chloroplast vs mitochondrial matrix
- coenzymes involved: reduced NADP vs oxidised NAD + oxidised FAD
