L26: Calvin Cycle Flashcards
The stroma is like the ___ of the ____
- Matrix, Mitochondria
Where does photosynthesis occur in bacteria?
- Do not have chloroplasts
- Have photosynthetic internal membranes
What are the light dependant reactions?
- Chloroplast needs to make lots of energy (ATP) and high energy intermediates (NADPH)
- Water is oxidized to produce O2 (donates electrons to an ETC)
How do light dependant reactions occur?
- Via an ETC called photophosphorylation
Why do light dependant reactions occur?
- For the next set of reactions in the Calvin cycle
Where do light dependant reactions occur?
- in the thylakoid membranes
What is going on with NADPH?
- Similar to NADH but with an extra phosphate group
- NADH = catabolic reactions, NADPH = anabolic reactions
- Another high energy intermediate that is synthesized in photophos and then used in anabolic reactions
The Calvin Cycle is an __ __
- Anabolic reaction
Photophos in a nutshell
- cell uses the chloroplast to convert light energy into high energy intermediates such as ATP and NADPH
- this is accomplished by photophos - an ETC
- there are 2 photosystems and are often referred to as the Z-scheme
Why is it called a z-scheme?
- photosystems II and I work together in the thylakoid membrane
- hits of light provide energy
- energy is used to pump protons across the membrane
What are the inputs and outputs of photophos?
- Inputs: Photons, water, NADP+, ADP
- Outputs: ATP, NADH, O2
Where is ATP synthesized?
- Stroma
Where is the ETC?
- Thylakoid membranes
Is NADPH a TEA?
- NO! NADP+ is an internal molecule and not from the environment.
What is step 1 of photophos?
Electrons are supplied by H2O
What is step 2 of photophos?
Light energy is required for PS2 to “strip” the electrons from the water
What is step 3 of photophos?
Electrons move along the ETC to provide energy to pump protons (H+) into the lumen
What is step 4 of photophos?
an electrochemical gradient is created in the thylakoid lumen
What is step 5 of photophos?
more light energy input at PSI. this energizes the electrons to drive the reduction of NADP+
What is step 6 of photophos?
NADPH is synthesized in the stroma and will be used in the Calvin cycle
What is step 7 of photophos?
ATP is synthesized in the stroma via chemiosmosis. H+ moves through the ATP synthase
In the light-dependent reactions of photosynthesis, light energy is used to oxidize __ to ___
H2O to O2
The electrons derived from H2O are used to reduce __ to ___ in the dependent reactions
NADP+ to NADPH
Photophos summary
- called the Z scheme
- 2 photosystems work together to synthesize ATP and NADPH
- light energy captured in the photosystems excites electrons to drive them through an ETC
- the ETC creates a proton (H+) gradient for the synthesis of ATP
- a second photosystem and ETC drives electrons to end up on high energy intermediate NADPH
What is oxygenic photophos?
- electrons from water reduce the PSII photosystem and release O2
- oxygen is a product of the reaction and released
Does photophos have a TEA?
- NO!!!
- NADP+, the electron acceptor, is a molecule found inside the cell, and is thus not by definition the TEA!
- it’s just an electron acceptor
Photosynthesis overview
LIGHT DEPENDENT REACTIONS:
- water is oxidized to O2
- NADP is reduced to form NADPH
- ATP is synthesized via proton gradient driven by chemiosmosis
LIGHT INDEPENDENT REACTIONS:
- ATP and NADP are used
- CO2 is reduced to form carbohydrates
Where is the H+ gradient created?
Thylakoid lumen
Chloroplast and mitochondria equivalents.
- thylakoid lumen = intermembrane space
- stroma = matrix
What is the evidence that mitochondria and chloroplasts evolved from ancient prokaryotes?
- both have double membranes
- both have their own circular DNA (genomes)
- both grow and multiply by binary fission - independently of the eukaryotic cell!
- both have their own ribosomes, synthesizes proteins, etc
Where does the Calvin Cycle Occur?
Stroma
Photolithoautotrophs use __ as a carbon source and fix them into ___ ___
CO2, Organic molecules
When something is fixed, it means that…
- it is being converted from a gaseous state to a solid or liquid state
- oxidized form → more reduced form
Oxidized carbon vs reduced carbon
OXIDIZED: CO2
- only C-O bonds
- More strongly bonded
REDUCED: Cellular biomolecules
- i.e. glucose, proteins, etc.
- C-H bonds
- less strongly bonded
What are the 3 steps of the Calvin Cycle?
- Carbon Fixation
- Reduction
- Regeneration
What is the first step of the Calvin Cycle?
CARBON FIXATION:
- each CO2 reacts with RuBP, producing two G3P molecules
- the enzyme that catalyzes this reaction is called rubisco
- the attachment of CO2 to an organic compound is called carbon fixation
What is the second step of the Calvin Cycle?
REDUCTION:
the two 3-phosphoglycerate molecules are phosphorylated by ATP and reduced by NADPH to produce glyceraldehyde 3-phosphate (G3P or called GAP)
What is the third step of the Calvin Cycle?
REGENERATION:
- the remaining G3P/GAP is used in ATP dependent reactions that regenerate RuBP
How is the GAP/G3P (reduced carbon) related to CR?
- notice that after the “glucose splitting” (step 5 of glycolysis) the substrate produced is G3P
- the G3P from the Calvin cycle can enter glycolysis here
What is the fate of GAP/G3P?
leaves the chloroplast and can be used in CR or used to build other macromolecules
what are the inputs and outputs of the Calvin cycle?
- Inputs: RuBP, CO2, NADPH, ATP
- Outputs: GAP, ADP, Pi, NADP+
Calvin Cylce Summary
- CO2 is oxidized
- NADPH donates electrons for reducing C
- GAP/G3P is reduced carbon
- Used to build all other C-containing organic cellular molecules
