Biochemistry of photosynthesis 1 Flashcards
2 stages of photosynthesis
light dependent and light independent
what stage occurs first
light dependent reactions occur first and light independent reactions occur after
function of light dependent reactions
produce materials that are used in light independent reactions
when does whole process take place
during the hours of daylight but the light independent reactions can also continue when dark
where does the light dependent stage take place
on the thylakoid membranes of the chloroplast
2 main functions of light dependent stage
-split water molecules in photochemical reaction
-produce ATP which is needed to supply energy to produce carbs
function of photochemical reaction
-splitting of water molecules
-provides hydrogen ions to reduce carbon dioxide and produce carbs in the light independent stage
structure of light
form of electromagnetic radiation and smallest unit of light is a photon
what happens when a photon of light hits a chlorophyll molecule
the energy is transferred to the electrons of that molecule
what happens to electrons when they gain energy
they are excited and raised to higher energy levels
-if electron raised high enough they will leave chlorophyll molecule completely
what happens to excited electron leaving chlorophyll molecule
can be picked up by electron acceptor and result in synthesis of ATP
2 ways electron can be picked up by electron acceptor and synthesise ATP
cyclic and non cyclic photophosphorylation
similarities of cyclic and non cyclic photophosphorylation
-both take place at same time and in both cases ATP is formed as excited electron is passed along electron transport chain
whats different about non cyclic photophosphorylation
reduced NADP is also produced
evidence for photosynthesis being a 2 stage process 1
-photochemical reactions get energy from light so temp should not affect rate of photosynthesis but when investigated shows temp had clear effect
-light dependent reactions limiting overall rate of reaction so temp has no effect
-however once light available process limited by different temp sensitive reactions
-suggests 2 phases one light dependent and other controlled by temp sensitive enzymes
evidence for photosynthesis being 2 stage process 2
plant given different amounts of light produced more carbs than plant in one light
-explanation is light dependent and independent reaction
-in continuous light product builds up as light independent stage cant keep up
-as conc rises inhibits enzymes controlling light independent reactions from making carbs
-period of darkness ensures all of light stage products converted without conc getting to high
what does cyclic photophosrylation involve
involves only photosystem 1 and drives the production of ATP
what happens when a photon hits a chlorophyll molecule in PS1
-a light excited electron leaves the molecule
-its take up by electron acceptor and passed directly along electron transport chain to produce ATP
electron that returns to chlorophyll in PS1
it can be excited in same way
what happens during non cyclic photophosphorylation
water molecules are split providing hydrogen to reduce to NADP
-ATP is also produced
-involves PS1 AND PS2
photon activity under light conditions in non cyclic
constantly hit chlorophyll molecules in PS1 AND PS2 exciting electrons to high enough level for them to be lost and picked up by electron acceptor
another electron acceptor in PS2
non cyclic
-another excited electron from PS2 picked up by another electron acceptor and passes along electron transport chain to PS1
-produced one molecule of ATP
what does PS1 receive after letting second electron go to acceptor
gets an electron to replace one that was lost to light dependent reactions
state of chlorophyll molecule in PS2 after losing electron
short of electron and unstable
-original electron cannot be returned to chlorophyll because it has continued on to PS1
-electron comes from splitting of water to restore chlorophyll to original state
photolysis
splitting of water that produces electron
-light dependent
how does photolysis provide another electron for chlorophyll in PS2
-water randomly dissociates into hydrogen and hydroxide ions resulting in plenty of ions being present in cell including chloroplasts and replacing lost electrons
what happens once PS2 has its electrons restored
-it is restored to its original state ready to be excited again when hit by another photon of light
function of electrons in PS1
also excited by light and lost an electron acceptor
-electrons are carried down an electron transport chain and taken up by an electron acceptor NADP
role of NADP non cyclic photophosphorylation
-NADP takes up hydrogen ion from dissociated water at same time to form reduced NADP
function of NADP and ATP during non cyclic photophosphorylation
go on to be used as source of reducing power and energy in light dependent reactions of photosynthesis to make glucose
equation for 4 chlorophylls regaining electrons in production of 1 molecule of oxygen
4OH- + 4e-(lost to chlorophyll) = O2 + 2H2O
explanation for 1 oxygen molecule and 2 water molecules being produced at end of light dependent stage
-lots of photosynthesis occurs in millions of chloroplasts
-many hydrogen ions removed by NADP and many hydroxide ions left behind
-hydroxide ions react to form water and oxygen
-as a result electrons freed and taken up by chlorophyll
-4 chlorophyll molecules regain electrons in production of 1 molecule of oxygen
what happens at light independent stage of photosynthesis
uses the reducing power NADP and ATP produced by light stage to build carbs
calvin cycle
series of reactions that take place as result of the light independent stages
where does the light independent stage take place
in the stroma of the chloroplast
result of the calvin cycle
-results in the reduction of carbon dioxide from the air to bring about the synthesis of carbs
-each stage controlled by enzymes
