Light Dependent Reaction Flashcards
What is the light dependent reaction?
First stage of photosynthesis that requires absorbance of light from chlorophyll
Where does the light dependent reaction occur?
In the thylakoids within the chloroplast of a leaf cell
First step of LDR name
Photoionisation of chlorophyll
Photoionisation of chlorophyll
When chlorophyll in thylakoids membranes absorb light energy from sun
So electrons in chlorophyll are excited to a higher energy level
Then lost from the molecule
Where are the electrons from the Photoionisation of chlorophyll lost to?
The electron transfer chain: chain of proteins in thylakoids membrane to transport the electrons
Electron transfer chain
Chain of proteins that will transport e- across the thylakoid membrane
What happens when electrons in electron transfer chain pass the proton pump protein?
This supplies energy so H+ ions can actively be bumped against their electrochemical gradient from stroma into thylakoid empty space
Proton pump protein
A protein pump that actively pumps H+ ions into thylakoid empty space using energy from electrons passing through from the electron transfer chain
Electrochemical gradient
A gradient of H+ ions that is created by the proton pump protein so it is higher inside the thylakoid empty space than outside in the stroma
H+ ions movement once in the thylakoid empty space
Move out back into the stroma again via facilitated diffusion using the channel protein ATP synthase
Facilitated diffusion of H+ ions allows…
The synthesis of ATP from ADP and Pi as the movement of H+ ions releases energy catalysed by enzyme ATP synthase
ATP synthase and what it does?
A channel protein and enzyme
Facilitates diffusion of H+ ions down electrochemical gradient out the thylakoid
To also catalyse the synthesis of ATP from ADP and Pi using this energy
What do we use synthesised ATP for?
Used for light independent reaction
Chemisomosis
The process of the facilitated diffusion of H+ ions down an electrochemical gradient to provide the energy needed for ATP synthesis, that is aided by the enzyme ATP synthase
What is at the end of the electron transfer chain?
The enzyme dehydrogenase
What does Dehydrogenase enzyme do?
Used electrons from electron transfer chain
And H+ ions from the stroma
To reduce NADP
Reduction of NADP
NADP + e- + H+ ——> NADPH
Reduced NADP
NADPH
How do we replace electrons lost from the chlorophyll?
Using the photolysis of water
Photolysis of water
‘Splitting’ water
H2O ——> H+ + O2 + e-
Products of photolysis of water
O2 is one of the overall products of photosynthesis, so diffuses out of chloroplast, plant cell then stomata
E- replaces electrons lost of the chlorophyll
H+ ions enters thylakoid space contributing to electrochemical gradient and chemiosmosis
What is NADPH used for?
Used for light independent reaction
What triggers photolysis of water?
When electrons are lost from chlorophyll which is caused by chlorophyll absorbing light
NOT directly by absorbing light energy
Does temperature have much of an effect of light dependent reaction?
No light is a bigger factor
AND does not effect rate of enzyme catalysed reaction: dehydrogenase enzyme is bound to thylakoid membrane so increasing its Ek has little effect
