01:694:301 Lecture Notes - Lecture 16: Triosephosphate Isomerase, Glucose-6-Phosphate Isomerase, Dihydroxyacetone Phosphate

35 views4 pages
Chapter 16 – ‘Glycolysis and Gluconeogenesis’ PART I
Glycolysis is the sequence of reactions that metabolizes 1 molecule of glucose to 2
molecules of pyruvate with net production of 2 molecules ATP
o It is an
anaerobic
pathway (very ancient)
o Parts of it are essentially ‘universal’; takes place in cytoplasm
! Glucose is common and important fuel source. Why?
Availability in primitive conditions
Strong tendency to exist in ring formation and little tendency to
modify proteins (ring conformation – equatorial " high stability)
o Takes place in cytoplasm in eukaryotes
o Stage I – the cleavage of the fructose 1,6-bisphosphate into two three-
carbon fragments
!
The strategy of initial steps of glycolysis is trap glucose and form
compound that can be cleaved by phosphorylated 3-C unit
o Stage II – ATP harvested when 3-C fragments are oxidized by pyruvate
**You need to KNOW all intermediated with structures, all enzyme, and all
cofactors as shown in Fig. 16.2 (Refer to handout)
o Note in that figure that 3 steps (all ‘kinase rxn’) are irreversible. KNOW which
ones they are
STAGE I
o Step 1Hexokinase traps glucose in cell and begins glycolysis
! It phosphorylated by ATP "
glucose 6-phosphate
! This step is important for two reasons:
1) Glucose 6-phosphate can’t pass membrane through glu-transporters
2) Addition P-group destabilizes glucose
! Hexokinase – catalyzes transfer of P-group from ATP to hexoses; requires
Mg2+ for activity; substrate induced cleft closing around glucose
o Step 2Glucose 6-phosphate converted to fructose 6-phosphate
! Isomerization converts aldose (glucose) to ketose (fructose)
! Catalyzed by phosphoglucose isomerase; this rxn takes time due to opening
of cyclic forms of sugars
o Step 3 Fructose 6-phosphate is then phosphorylated to fructose-1,6-BP
! Uses ATP
! Catalyzed by phosphofructokinase (PFK), an allosteric enzyme that sets
pace of glycolysis
o Step 4 F-1,6-BP is cleaved into 2 3-C fragments (GAP and DHAP)
! Fructose 1,6-BP is cleaved into
glyceraldehyde 3-phosphate
and
dihydroxyacetone phosphate
! Catalyzed aldolase (reverse rxn is aldol condensation)*
! GAP is on direct pathway while DHAP is not
There needs to be means for converted DHAP to GAP (or else lose
fragment)
o Step 5 DHAP isomerized to GAP
! GAP (aldose) and DHAP (ketose) are isomers that readily interconvert
! Catalyzed by triose phosphate isomerase (TPI); rxn rapid and reversible
TPI catalyzes transfer of H-atom from C-1 to C-2 intramolecular redox
STAGE II (each step occurs 2x)
o Step 6Conversion GAP into 1,3-biphosphoglycerate (1,3-BPG)
Unlock document

This preview shows page 1 of the document.
Unlock all 4 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
Monthly
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.