Exam 3: Calvin Cycle Flashcards
What products from the light-dependent reactions are used in the Calvin Cycle?
NADPH and ATP
Where does the Calvin Cycle take place?
Outside of the thylakoid, in the stroma
What are the three steps of the Calvin Cycle?
- CO2 fixation
- Reduction
- Regeneration
Step 1: What happens?
CO2 reacts with RuBP, forms 2 molecules of 3PG
Step 2: What happens?
3PGA is phosphorylated by ATP and reduced by NADPH to form G3P
Step 3: What happens?
G3P from step 2 forms RuBP to keep the cycle going, needs ATP
How many times does the calvin cycle turn in order to make 1 G3P?
3 times
Step 1: What is the ratio of molecules for the 3 turns of the cycle?
3 RuBP + 3 CO2 –> 6 3PGA
Step 2: What is the ratio of molecules for the 3 turns of the cycle?
6 3PGA + 6 ATP + 6 NADPH –> 6 G3P (1 of them is used to make glucose/fructose, the remaining 5 move on to step 3)
Step 3: What is the ratio of molecules for the 3 turns of the cycle?
5 G3P + 3 ATP –> 3 RuBP
Which enzyme fixes CO2?
Rubisco
Which enzyme is the most abundant on Earth?
Rubisco
How many polypeptides does rubisco have?
16
How many active sites does rubisco have?
8
Which two molecules can bind to rubisco?
CO2 and O2
Why is rubisco inefficient?
When oxygen binds, only 1 3PG is produced and 2PG is produced which produces CO2 when broken down.
How many reactions can rubisco facilitate per second?
3
What is the process when O2 binds to rubisco?
Photorespiration
Carbon fixation is favored over photorespiration when CO2 concentration is ___ and O2 concentration is ___
High, low
What prevents the rapid evaporation of water when it is hit by sunlight?
The leaf surface is coated in cuticle, which is a waxy substance that prevents gas exchange
Stomata are normally ___ during the day and ___ during the night
Open, closed
In dry conditions, is photorespiration or carbon fixation more likely?
Photorespiration because of the build-up of O2
What are C3 plants?
90% of plants, these are 3 carbon plants
What are the 2 mechanisms that plants in dry environments use to adapt to conditions?
- C4 pathway
- CAM plants
How does the C4 pathway work?
Spatially separates carbon fixation from the calvin cycle, fixes CO2 into 4-carbon orgnanic acids
Which enzyme facilitates the C4 pathway?
PEP carboxylase
Where does PEP carboxylase fix CO2?
Mesophyll cells
Where do the 4-carbon organic acids travel to?
Bundle sheath cells
What do the 4-carbon organic acid release that initiates the calvin cycle?
a CO2 molecule
How do CAM plants work?
Temporally (time) separates carbon fixation and the Calvin cycle. The stomata is only open during the night. This allows the calvin cycle to occur during the night.
When is CO2 stored in CAM plants?
during the night
During the day, what is released from the organic acids that have CO2 fixed into them?
CO2
In which environments is C4 favored?
Warm and dry, where evaporation is favored
In which environments is C3 favored?
Normal and cooler
What is G3P made into? What is this process called?
Glucose and fructose; gluceogenesis
What are glucose and fructose combined into?
Sucrose (disaccharide)
When photosynthesis is slow, what is glucose stored as?
Sucrose
When photosynthesis is fast/sucrose is high, what is glucose stored as?
Starch
When is starch broken down and what for?
at night, to make more sucrose for transport
