Lecture 5-Chromoplast Flashcards
Steps of Calvin Cycle
Carbon dioxide fixed to cmpnds by actions of enzyme
some of resulting molecule is reduced in size and exported
some of resulting molecule is reduced in size and recylced
RuBisCO
enzyme that fixes CO2 to existing carbon skeletons
takes 5C sugar w/ 2phosphate group (RuBP), adds CO2 as carboxyl group, creates shortlived 6C sugar
3-phosphoglycerate
3-C compound that is made by hydrolysis of 6C sugar
PGAL, phosphoglyceraldehyde
3C compound made by 3-phosphoglycerate and 2 NADPH, 3ATP
some pushed out of chloroplast, some used to regenerate RuBP within chloroplast
3 turns of cycle produces
1 surplus PGAL
6 turns of cylle produces
1 glucose sugar
Prevention of explosion
surplus glucose shipped back to chloroplast, turned into starch
Starch
branched polymer of glucose units
Why don’t grapes explode?
glucose stored in vacuole to regulate water intake
Phosphoglycolate
2C compound produced by RuBisco and O2, releasing CO2 when recylced
Plants are inefficient at higher temp b/c
o2 more soluble than co2
Anatomical Solution to Curse of RuBisCO
RuBisCO restricted to leaf bundle sheath cells
Physiological solution
alternative biosynthetic pathway
substrate: phosphoenolpyruvate (PEP)
Enzyme: PEP carboxylase. no oxygenase function
product: malate
Malate
4C compound, moves down [ ] gradient from mesophyll to bundle sheath. decarboxylated to produce co2 donated to calvin cycle.
3 carbon compound-based dark reaction
etioplast
chlpst reserve, immature chlpsts
