Glycolysis Steps Flashcards
What are the sources of glucose?
Dietary glycogen/starch breakdown OR gluconeogenesis
Where are the glycolytic enzymes found?
Cytosol.
Glycolysis
Conversion of glucose to two C3 pyruvate units, where free energy released is harrvested to synthesise ATP from ADP and Pi.
What is the first stage of glycolysis?
Energy investment stage, where hexose glucose is phosphorylated and cleaved, yielding two glyceraldehyde-3phosphate, consuming 2 ATP.
What is the second stage of glycolysis?
Energy Recovery, where the two GAH3P are converted to pyruvate with generation of 4 ATP, a net profit of 2 ATP per glucose.
What is the importance of the energy investment stage?
Pi transfer from ATP to hexose does not immediately result in high energy compounds, these result from the proceeding enzymatic reactions, converting low energy compounds to high phospohate group transfer potential capable of ADP phosphorylation.
Glycolytic Reaction Pathway
Glucose + 2 NAD+ + 2 ADP + Pi —> 2 Pyruvate + 2 NADH + 2 ATP + 2 H20 + 4H+
What requirements does glycolysis have due to its NAD dependence?
The 2 NADH formed from glycolysis must be reoxidesed, to keep pathway supplied with NAD+
1) Hexokinase
Transfers ATP phosphate group from ATP to glucose forming G6P.
What is the structure of Glucose?
Cyclical hexagon sturcture with hydroxyl groups + H at all but C5, with an O between C1 and C5, with C6 having two hydrogen.
What is a characteristic of hexokinase, in terms of its ability to phosphorylate?
It is ubiquitous, catalysing phosphorylation of mannose, fructose AND glucose(not galactose)
1) What is Hexokinase dependent on?
Magnesium
1) Why is hexokinase dependent on magnesium?
Shielding of - charge of ATP phosphates O atoms, so the phosphorous atom is more accessible for nucleophilic attack.
1) What part of glucose attacks ATP?
C6 hydoxyl group.
2) Phosphoglucose Isomerase
Converts G6P to F6P in isomerisation.
2) What forms do G6P and F6P exist in and why is this significant?
Cyclical forms, thus reaciton requires opening of rings for isomerisation.
2) Structural change of F6P
C1-C5 oxygen bond changes to C2-C5
2) What are the 5 steps of Phosphoglucose Isomerase?
Substrate binds
Enzymatic acid catalyses ring opening
Enzymatic base abstrats proton from C2, forming the cis-enediolate intermediate
Proton is replaced on C1
Ring close, forming product.
3) Phosphofructokinase
This phosphorylates F6P into F-1,6 Biphosphate.
What makes something a biphosphate opposed to a diphosphate?
The phosphates are not directly attached to one another.
3) Reactive steps of phosphofructokinase
Nucleophilic attack by the C1 hydroxyl of F6P on the electrophilic phosphorous atom of the Mg-ATP, with transfer of the phosphate group to C1.
4) Aldolase
Aldolase cleaves F-1,6 BP into GA3P and DHAP.
4) What are the structural changes of F-1,6 BP to GA3P and DHAP?
C1, C2 and C3 becoming DHAP whilst C4, C5 and C6 becoming GAH3P.