Photosynthesis: Calvin-Benson Cycle Flashcards
my strong, independent reaction
Predominant pathway of autotrophic CO2 fixation
calvin-benson cycle
Number of steps/biochemical reactions in the Calvin-Benson Cycle
thirteen
Three major steps in Calvin-Benson Cycle
- carboxylation of RuBP → 2 molecules of 3-PGA
- reduction of 3-PGA → G3P
- regeneration of RuBP from G3P
or each co2 molecule that reacts with one RuBP, two molecules of 3-PGA f
An enzyme that catalyzes carboxylation and oxygenation of RuBP.
RubiSCO
Plants that form 3-PGA as the 1st stable compound.
C3 plants
Types of RubiSCO
I, II, III, IV
- Type/s of RubiSCO having catalytic function.
- Type/s of RubiSCO with lost RubisCO activity.
- Type of RubiSCO that harbors small subunits, consisting of eight large and eight small subunits; found in most autotrophic organisms; most abundant protein
types I, II, III
type IV
type I
Reduction is a two-step reaction that converts the 6 molecules of ___ from the carboxylation stage into 6 molecules of ___.
3‐PGA to G3P
What is regenerated in the “regeneration” phase of Calvin-Benson Cycle?
RuBP
What modulates the levels of stromal enzymes encoded in nuclear and chloroplast genomes?
light
Light‐linked ___ regulates the Calvin–Benson Cycle.
posttranslational modifications of enzymes
- Accumulation of stromal enzymes = ↓ catalytic effect
- Posttranslational modifications of enzymes = rapid catalytic effect
true
Two mechanisms that alter the protein structure of enzymes for their catalytic rates.
- rubiSCO activase
- ferredoxin–thioredoxin system (FTS)
An ATP-dependent enzyme that modulates RubiSCO activity.
rubiSCO activase
Rubisco activity has a fast capacity for CO2 fixation.
false; 1–12 CO2 fixations per second
RubiSCO is an “automatic” catalyst. True or False?
false; it must first be activated.
An inhibitor, together with other sugar phosphates, that is removed by RubiSCO activase to kickstart RubiSCO catalytic activity.
CAP1
A mechanism that regulates enzymes by redox transitions.
ferredoxin–thioredoxin system
Ferredoxin–thioredoxin system uses ___ to regulate Fructose 1,6-bisphosphatase, etc.
ferredoxin
The oxygenase activity of rubisco causes partial loss of the carbon fixed by the Calvin–Benson cycle and yields ____, an inhibitor of two chloroplast enzymes: triose phosphate isomerase & phosphofructokinase.
2-phosphoglycolate
2-phosphoglycolate is metabolized through the process of ___.
photorespiration
Where does photorespiration occur?
mitochondria, peroxisome, chloroplast
Why do C3 plants close their stomata during dry and hot climate?
open stomata lead to water loss and dehydration; however, it also increases oxygen production and inhibits gas exchange.
When the concentration of O2 is relatively high compared to the CO2
concentration, photorespiration becomes a serious problem.
true
Photorespiration is also known as ___.
C2 pathway
How many molecule/s of O2 is needed to produce 1 molecule of CO2?
two
For every 2 molecules of glycine that enters the mitochondrion, 1 molecule each of serine, CO2, and ammonia are produced, and 1NAD+ is reduced to NADH. True or False?
true
C2 pathway interacts with:
1. Nitrogen metabolism at multiple levels
2. Cell redox homeostasis
3. C1 metabolism
4. Expression of transcription factors
true
Two types of carbon-concentrating mechanisms that land plants use for
increasing the concentration of CO2
at the RubiSCO carboxylation site.
C4 pathway
Crassulacean Acid Metabolism
C4 cycle separates ____; while
CAM separates ____.
spatially
temporally
C3 plants produce ____; while
CAM plants produce ____.
3-PGA
OAA (oxaloacetic acid)
Two concentric cylinders of cells in C4 plants’ leaves.
mesophyll cells: outer cylinder
bundle-sheath cells: inner cylinder
Anatomy unique to plants that use C4 pathway which provides spatial separation of carbon fixations in two types of cells and photosynthetic reactions.
kranz anatomy
C4 pathway requires more energy. True or False?
true; C3 pathway consumes 3 ATP : 2
NADPH : 1 CO2 vs. C4 pathway, 5 ATP : 2 NADPH : 1 CO2
CAM also utilizes PEP carboxylase. True or False?
true
Difference of CAM with C4 pathway:
▪ Stomata are closed during the day, open during night.
▪ Carry out light reaction & CO2
fixation at different TIME of the day ~ temporal separation.
true
