Allocation and Translocation Review

Define Carbon Allocation

Deovtion of sugars to starch and sucrose synthesis

Define Translocation

Transport of photoassimilates over long distances

Define Partitioning

Distribution of photosynthates between sinks

What are starches?

Insoluble storage form synthesized in stroma

What is sucrose?

Soluble transport form synthesized in cytoplasm

What are hexose phosphate pools and why are they important?

Produced by build-up of triose phosphates from Calvin Cycle. Synthesis of starch and sucrose starts here

What is required to start starch synthesis?

Requires ADP-glucose

What are the two principle forms of starch produced?

Amylose and Amylopectin

Describe Amylose

linear glucose polymer with a-(1,4) linkages

Describe Amylopectin

Branches glucose polymer with a-(1,6) linkages

Starch Degradation

Starch phosphorylation forms maltose for exportation into the cytoplasm. Requires maltose-glucose translators so that they can exit into the cytosol

What is dihydroxyacetone phosphate and why is it important for sucrose synthesis?

DHAP comines with G3P to form fructose-1,6-bisphosphate, and then fructose 6-phosphate to enter the cytosolic hexose phosphate pool, where sucrose is synthesized

What form of energy is required to begin sucrose synthesis and what is produced?

Requires glucose. Activated by UTP, which requires ATP and UDP-glucose pyrophosporylase. Produces UDP-glucose and pyrophosphate

What is FBPase?

Fructose 6 phosphate 2-kinase/fructose 2,6-bisphosphate phosphatase

How does FBPase regulate sucrose and starch synthesis? What inhibits it and how does it work?

Determines balance between sucrose and starch synthesis.

Fructose 6 phosphate 2-kinase activity is inhibited by triose phosphates, which allows fructose 2,6 bisphosphate phosphatase activity and suppresses fructose 2,6 bisphosphate formation.

Phosphates stimulate fructose 6 phosphate 2-kinase activity, which inhibits fructose 2,6 bisphosphate phosphatase and promotes fructose 2,6-bisphosphate formation