Photosynthesis 2 Flashcards
(22 cards)
What are the 3 stages of the light independent reaction ?
- Carboxylation
- Reduction
- Regeneration
What is carboxylation stage of the light independent cycle ?
Ribulose 1,5-bis phosphate (RuBP) is converted into Phosphoglyceric Acid (PGA) using the enzyme RUBISCO
5 carbon to 3 carbon
What is the structure of RuBISCO ?
8 large subunits- catalytic activity
8 small subunits- for structure
How are the RuBISCO small subunits synthesised ? And imported ?
In the cytoplasm from a nuclear gene.
It is then imported from the cytoplasm via TRANSLOCONs “TOC” and “TIC”
What is a transit peptide ?
It is found at the start of the protein sequence in the small subunit which targets it to the stroma of the chloroplast.
It is cut off by an enzyme after import.
Where is the large subunit of RuBISCO synthesised ?
In the chloroplast from the plastid genome
How is RuBISCO activated ?
Light activates Thioredoxin which activates RuBISCO activase which activates RuBISCO
What is the reduction phase of the light independent cycle ?
- PGA is converted into BPG using the enzyme Phophoglycerate kinase
- BPG is then reduced to Glyceraldehyde 3-phosphate (GAP) using the enzyme GAP Dehydrogenase
GAP can exist in two forms. What is the other form?
Dihydroxyacetone phosphate (DHAP)
What enzyme switches between GAP and DHAP ?
Triose phosphate isomerase
What is the generic term for GAP and DHAP ?
Triose phosphate
The fate of Triose phosphate. What happens if there is insufficient carbohydrate for metabolic needs ?
Sucrose is synthesised outside of the chloroplast, in the cytoplasm
The fate of Triose phosphate. What happens if there is sufficient carbohydrate for metabolic needs ?
Starch is synthesised inside of the chloroplast
What is the role of the Triose phosphate antiporter ?
It exchanges Triose phosphate with inorganic phosphate
What are the 6 molecules of Triose phosphate used for ?
1 is used to make carbohydrate
The other 5 are used to regenerate RuBP
What is the glyoxylate cycle ?
A process the regenerate RuBP from Phosphoglycolate
Which RuBISCO function is favoured at higher temps ?
Oxygenation- photorespiration
What is photorespiration ?
A process where RuBISCO uses oxygen instead of carbon dioxide, leading to the wasteful loss of fixed carbon and energy.
It mainly occurs in plants in hot, dry weather
What is CAM photosynthesis?
It aims to reduce water loss by keeping stomata closed during the day.
No gas exchange occurs during daylight
How does CAM photosynthesis work ?
CO2 is combined with PEP using the enzyme PEP Carboxylase.
This produces Oxaloacetate.
What is C4 photosynthesis?
It minimises photorespiration.
CO2 is combined with PEP in mesophyll cells using the enzyme PEP carboxylase, forming Oxaloacetate.
Oxaloacetate is then converted into malate, which is transported to bundle sheath cell chloroplasts.
Malate is stripped of CO2
What is LCHII ?
Light-harvesting complex II is part of PSII.
It has high conc of chlorophyll and carotenoid pigments
It increases light absorption and helps to transfer the energy to the reaction centre in PSII.
It can move between PSII and PSI during state transitions.
