Metabolism 2 (Gluconeogenesis) Flashcards
Which steps aren’t in equilibrium in glycolysis?
1 = glucose into G-6-P
3 = F-6-P into Fructose 1,6-bisphosphate
10 = phosphoenolpyruvate into pyruvate
What happens when there is no glucose around
(starvation/fasting)?
Gluconeogenesis
What is gluconeogenesis?
A process via which glucose is synthesised from non-carbohydrate precursors:
>lactate
>alanine
>glycerol
What are the non-carbohydrate precursors converted into?
Lactate –> pyruvate
Alanine –> pyruvate
Glycerol –> dihydroxyacetone phosphate (DHAP)
Where does gluconeogenesis take placE?
Major extent = liver
Lesser extent = kidney
Why isn’t gluconeogenesis the complete reversal of glycolysis?
The equilibrium of glycolysis lies far on the side of pyruvate formation
(favours conversion of glucose into pyruvate)
What is the equation for converting glucose into G-6-P?
Glucose + ATP
—(via Hexokinase)–>
G-6-P + ADP
What is the equation for converting F-6-P into Fructose-1,6-bisphosphate?
F-6-P + ATP
-(Phosphofructokinase)–>
Fructose-1,6-bisphosphate + ADP
What is the equation for converting phosphoenolpyruvate into pyruvate?
Phosphoenolpyruvate + ADP
—(pyruvate kinase)–>
Pyruvate + ATP
Describe the 1st of the 2 steps involved in converting pyruvate into phosphoenolpyruvate (PEP).
- Pyruvate —> oxaolacetate
Catalysed by pyruvate carboxylase
- requires biotin + Mg2+
Uses ATP + CO2
Describe the 2nd of the 2 steps involved in converting pyruvate into phosphoenolpyruvate(PEP).
- Oxaloacetate —>
PEP
Catalysed by PEP carboxykinase (PEPCK)
- uses GTP or ITP
(simultaneous decarboxylation & phosphorylation)
What does GTP stand for?
What about ITP?
Guanosine triphosphate
Inosine triphosphate
What are the 3 glycolysis enzymes replaced with in gluconeogenesis?
- hexokinase replaced by G-6-Pase
- Phosphofructokinase replaced by Fructose-1,6-bisphosphatase
- Pyruvate kinase replaced by:
>pyruvate carboxylase
> phosphoenolpyruvate carboxykinase
What is the equation for the conversion of Fructose-1,6-bisphosphate into F-6-P?
Fructose-1,6-bisphosphate
–(H2O + fructose-1,6-bisphosphatase)–>
F-6-P + Pi
What is the equation for converting G-6-P into glucose?
G-6-P
–(G-6-Pase)–>
Glucose
(Carbon 6 removed)
Which gluconeogenic enzymes aren’t found in the cytosol?
Where are they found?
Pyruvate carboxylase
= mitochondria
G-6-Pase
= endoplasmic reticulum
Why must oxaloacetate be converted into another substance to be transported out the mitochondria?
What is this substance?
Neither liver nor kidney cells possess a protein for transporting oxaloacetate out mitochondria
Malate
via malate dehydrogenase
Which transporter proteins enable movement of G-6-P?
What about glucose?
What about Pi?
What about malate?
T1
T3
T2
Malate-aspartate shuttle
