BCM 475 Chapter Notes - Chapter 16: Dihydroxyacetone Phosphate, Hexokinase, Ketose
Document Summary
Step 1 phosphorylation | hexokinase traps glucose in the cell glycolysis begins. Phosphorylated by atp to form glucose-6-phosphate: cannot pass through membrane due to the negative charges on the phosphoryl groups, addition of phosphoryl facilitates eventual metabolism of glucose into 3-carbon molecules (high phosphoryl transfer potential) Importance of glucose-induced structural change of hexokinase: environment around glucose becomes more nonpolar. Favors reaction between hydrophilic oh groups of glucose and terminal phosphoryl group of. Atp: enables kinase to discriminate against h2o as a substrate, keeps water out of active site. Step 2 isomerization | glucose-6-phosphate fructose 1,6-biphosphate. Multistep process including ring opening, isomerization, ring closing into 5 membered ring. Step 3 second phosphorylation | fructose-6-phosphate to fructose 1,6-biphosphate. Catalyzed by phosphofructokinase (pfk) prevents re-formation of glucose 6-phosphate (f-1,6 bp) Step 4 cleavage | f-1,6 bp two 3-carbon fragments. F-1,6 bp is cleaved into: glyceraldehyde 3-phosphate (gap) aldose, on direct pathway of glycolysis, dihydroxyacetone phosphate (dhap) ketose, not on direct pathway.
