Photosynthesis Flashcards
(32 cards)
List the membranes present in chloroplasts
- outer envelope membrane
- inner envelope membrane
- thylakoid membrane
- lamellae
- grana
List some carotenoids
a-carotene
B-carotene
a-cryptoxanthin
B-cryptoxanthin
lutein
zeaxanthin
List the main types of synthetic pigments
- chlorophyll - plants, most cyanobacteria
- caretenoids - plants, some cyanobacteria and bacteria
- phycobillins - cyanobacteria, photosynthetic bacteria
- anthacyanins - common chemicals in plantas
- Rhodobacter, purple bacteria - other bacterial pigments
List three important features embedded in the thylakoid membrane
D1, D2, manganese cluster
List three ways excited electrons restabilise
- decay by giving off light and heat
- decay by resonance energy transfer
- decay by successive electron transfers
Describe the passage of electrons in photosystem II
P680 –> pheophytin –> (bound) plastoquinone A –> (bound) plastoquinone B –> (lipid soluble) plastoquinone
What replaces the excited electron?
an electron from water
2H2O -> 4e- + O2 + 4H+
takes place in the manganese cluster
How many protons and electrons are passed to plastoquinone?
2 protons and 2 electrons
Describe the linear cycle through the cytochrome b6f complex
- plastoquinol (plastoquinone with 2 electrons and 2 protons) binds to the luminal side
- splits into 2 electrons, 2 protons, plastoquinone
- one electron passes through FeSr to CytF
- one electron passes through Cytb complexes and eventually forms a semi quinone intermediate
- process occurs again and the semi quinone intermediate becomes 2- charged - enough to gain some protons and form plastoquinol
- increase number of protons in lumen by 4, decrease number of protons in stroma by 2 –> potential difference of 6 protons
What is the electron donor for photosystem I (P700)?
plastocyanin
Describe the passage of electrons in P700
plastocyanin –> ferredoxin –> NADP+ reductase –> NADPH
What is the light-harvesting complex?
- a tetramer
- high concentration of chlorophyll and carotenoid pigments
- embedded in the thylakoid membrane
- can move laterally within the thylakoid membrane
- can associate with either PSI or PSII
How does the LHC regulate activity of the photosystems?
- PSII activity high, more QH2 –> activates LHCII kinase
- LHCII dissociates from PSII
- LHCII binds PSI
- PSII activity reduces and PSI activity increases
- PSII activity low, more Q (less QH2) –> activates LHCII phosphatase
- LHCII dissociates from PSI
- LHCII binds PSII
- PSI activity reduces and PSII activity increases
Write the equation for the calvin cycle
3x5C + 3CO2 + 3H2O –> (ATP and NADPH) –> 6x3C + 6H+
What are the products of the ‘light’ reactions?
protons (lumen)
NADPH (stroma)
Describe the process of carboxylation
- fusion of CO2 into carbon precursor using enzyme Rubisco
- 3CO2 input
- temporarily forms 5 x ribulose 1,5-bis phosphate
- split to form 6 x phosphoglyceric acid (3-phosphoglycerate)
What is rubisco?
- contains 8 large subunits (catalytic) and 8 small subunits (structural)
- synthesised in the cytoplasm from a nuclear gene
- imported from the cytoplasm via 2 translocons ‘toc’ and ‘tic’
- the SSU has a transit peptide at the start of the protein sequence which targets it to the stroma of the chloroplast
How is Rubisco indirectly regulated by light?
light –> thioredoxin –> rubisco activase –> rubisco
Describe the reduction reactions that occur during the calvin cycle
6 x 3-phosphoglyceric acid reacts with phosphoglycerate kinase
Forms 6 x 1,3-bis phosphoglyceric acid
BPG needs to be reduced
6 x 1,3-bis phosphoglyceric acid reacts with GAP dehydrogenase to form 6 x glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP)
What is triose phosphate?
- can exist in two forms (GAP and DHAP)
- enzyme triose phosphate isomerase switches between these forms
Describe the fate of triose phosphate
insufficient carbohydrate –> sucrose is synthesised in the cytoplasm
sufficient carbohydrate –> starch is synthesised inside the chloroplast
Describe the conversion of triose phosphotase to sucrose in the cytosol
- triose phosphate
- aldolase
- FBPase
- hexose phosphate isomerase
- phosphoglucomutase
- UDP glucose pyrophosphatase
- sucrose phosphatase
- sucrose phosphate phosphatase
- sucrose
Describe the conversion of triose phosphate to starch in the chloroplast
- triose phosphate
- aldolase
- FBPase
- hexose phosphate isomerase
- phosphoglucomutase
- ADP pyro phosphatase
- starch synthase
- starch
Describe the mechanisms of the triose phosphate antiporter
- production of sucrose creates excess of Pi
- Pi import exchanges for triose phosphate export
- sucrose need decreases
- less conversion to sucrose
- conc. of Pi drops
- no exchange
- triose phosphate stays inside chloroplast
- starch produced
