Glycolysis and PPP Flashcards
1
Q
describe the GLUT transporters
A
- GLUT 2 = liver
- GLUT 1 and 3 = neurons and brain
- GLUT 1 = erythrocytes
- GLUT 4 = adipose tissue and muscle in response to insulin
- increases in presence of insulin
2
Q
describe the formation of glucose 6 phosphate
A
-
glucokinase in liver has high Km (more active when the blood glucose is elevated; functions as a glucose sensor)
- also present in B-cells of pancreas (MODY-2 = rare inherited form of DM since the B-cells of pancreas cannot respond to high blood glucose levels)
- other tissues contain hexokinase which has a low Km for glucose
3
Q
describe the major points of PPP
A
- all enzymes are in the cytosol
- glucose 6 phosphate dehydrogenase (key enzyme)
- pentose phosphate pathway forms NADPH
- PPP forms ribose phosphate which is used for purine and pyrimidine nucleotide synthesis
- transketolase requires thiamine pyrophosphate (TPP aka vit. B1)
4
Q
describe the energy investment phase of glycolysis
A
- 2 phosphorylation rxns that requires 2 ATP
- PFK-1 is the 2nd irreversible rxn of glycolysis and also the most important regulated step (allosteric regulated enzyme)
5
Q
describe the cleavage of 6C sugar into 3C intermediates (stage 2)
A
- aldolase A is present in muscle and aldolase B is in liver
- the isomerase converst the dihydroxyacetone phosphate to glyceraldehyde 3-phosphate to enable it to be further metabolized by glycolysis
- glucose is cleaved to 2 molecules of glyceraldehyde 3-phosphate
6
Q
describe the energy generation phase of glycolysis (stage 3)
A
- glyceraldehyde 3-phosphate dehydrogenase results in the formation of an NADH
- phosphoglycerate kinase results in the formation of the first ATP (substrate level phosphorylation, SLP)
- 1,3-BPG is a high energy intermediate that results in the formation of ATP without involving the mitochondrial ETC
- SLP important during hypoxia
7
Q
describe the second part of the energy generation phase (2-phosphoglycerate to pyruvate)
A
- phosphoenolpyruvate is a high energy compound that results in the formation of ATP without the involvement of the ETC in mt (substrate level phosphorylation)
- SLP important during hypoxia and in RBC
- pyruvate kinase is an irreversible rxn
9
Q
describe the Cori cycle
A
10
Q
describe the anaerobic fate of pyruvate
A
- pyruvate formed in glycolysis is metabolized anaerobically in the absence of mt or poorly vascularized tissues
- the NADH formed by the glyceraldehyde 3-P dehydrogenase rxn is reoxidized to form NAD+; this allows glycolysis to proceed even in the absence of mt
- LDH is a cytosolic enzyme
- the direction of the rxn depends on the NADH/NAD+ ratio
- higher the NADH levels, the rxn is driven towards lactate formation
12
Q
name the 3 irreversible rxns (regulatory steps) in glycolysis
A
- glucokinase/hexokinase
- phosphofructokinase-1
- pyruvate kinase
13
Q
name the 2 SLP rxns in glycolysis
A
- phosphoglycerate kinase (reversible)
- pyruvate kinase (irreversible)
14
Q
name inhibitors of glycolysis
A
- pentavalent arsenate poisoning results in inhibition of glyceraldehyde 3-P dehydrogenase enzyme
- in clinical labs, blood is collected in fluoride containing tubes for the estimation of blood glucose
- if fluoride is not added, there would be reduction in the glucose due to its utilization by RBC and WBC, which leads to erroneously low blood glucose
- fluoride inhibits enolase