Unit 4: Chapter 17, Gluconeogenesis Flashcards
Gluconeogenesis
Synthesis of glucose from pyruvate and related 3 and 4 carbon compounds (lactate, amino acids, and glycerol)
Major sites of gluconeogenesis
Liver and kidney
Reactions of glucogenesis of enzymes occur
cytoplasm, mitochondria, ER by enzymes
During fasting or starvation ____ is important and why
gluconeogenesis since glucose is primary fuel for brain and only fuel for red blood cells
gluconeogenesis converts ____ into each glucose
2 pyruvates
Pruvate is formed from
lacid acid fermentation: muscle derived lactate in the liver by lactate dehydrogenase
Carbon skeletons of some _____ can be converted into gluconeogenesis intermediates
amino acids
___ is derived fom hydrolysis of triaglycerols which cna be converted into dihydroxyacetorne phosphate to be processed by glucogenesis or glycolysis
Glycerol
What molecules can go through gluconeogenesis
LActate, amino acids, and glycerol
Why is gluconeogenesis is not complete reversal of glycolysis?
Due to the 3 irreversible steps in glycolysis
Step 1: hexokinase
Step 3: phosphofructokinase (PFK)
Step 10: Pyruvate kinase
To reverse irreversible steps of glycolysis, reactions must turn
endergonic
Why is gluconeogensis expensive process?
Have to spend ATP and GTP since reaction is anabolic and endergonic
Hexokinase will be reversed by and where is location
G6Phosphatase (G6Pase) and occurs in ER
Phosphofructokinase will be reversed by and where is location
F 1,6 biphosphatase (F1, 6BPase) and occurs in cytosol
Pyruvate kinase will be reversed by
Pyruvate Carboxylase which occurs in mitochondria and PEP Carboxykinase which occurs in cytoplasm
Formation of _____ requires 2 enzymes of pyruvate carboxylase and PEP carboxykinase
phosphoneol (PEP) pyruvate
Step 10
Conversion of step 10 begins with formation of ______
oxaloacetate
What is reaction equation of formation oxaloacetate?
pyruvate + CO2 + ATP + H20 –> oxaloacetate + ADP + Pi + 2H+
Formation of oxaloacetate occurs in
mitochondria
Formation of oxaloaetate occurs in 3 stages by
pruvate carboxylase
Pyruvate carboxylase requires what
Vitamin biotin as cofactor
The molecule of ATP invested to form oxaloacetate to bypass step 10 is used to power
addition of CO2 to pyruvate
(carboxylation)
Oxaloactetate is reduced to ______
maltate
Why is oxaloacetate reduced to maltate?
- Maltate can be transported into the cytoplasm where it is reoxidized to oxaloacetate with generation of cytoplasmic NADH
- Oxaloacetate cannot simply just cross the mitcondria and go to cytoplasm since mitochondrial membrane does not have a transporter for oxaloacetate
Oxaloacetate create phosphoneol (PEP) pyruvate in cytosol by
Phosphoenolpyruvate (PEP) carboxykinase
When oxaloacetate becomes Phosphoneol pyruvate what occurs?
- CO2 that was added to pyruvate by pyruvate carboxylase comes off in this step (Decarboxylation)
- Decarboxylation makes reaction exergonic
What enzyme is involved in electron carriers such as NAD+/NADH and FADH/FADH2?
Dehydrogenase (substrate + dehydrogenase)
What is reaction equation for formation of PEP pyruvate from oxaloacetate
Oxaloacetate + GTP –> PEP pyruvate + GDP + CO2
Sume of reactions in step 10 of gluconeogenesis
pyruvate + ATP + GTP + H20 –> Phosphoenol (PEP) pyruvate + ADP + GDP + Pi + 2 H+
Phosphatase
catalyzes reactions which removes phosphates
Reactions of step 3 of gluconeogenesis
Fructose 1,6 biphosphate + H20 –> Fructose 6 Phosphate + Pi
Which step of gluconeogenesis if generation of free glucose?
Step 1
Why is the generation of free gluocse important?
Important control point
What ocurs in final step of gluconeogenesis?
- Occurs only in liver
- Glucose 6 phosphate is transported into the lumen of ER
- catalyzed by glucose 6 phosphatase
How many high transfer potential phosphoryl groups are spent in gluconeogenesis?
6
Overall reaction for gluconeogenesis
2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ and 6 H20 –> glucose + 4ADP + 2 GDP + 6Pi + 2NAD+
Is gluconeogensis exergonic or endergonic?
Exergonic
Gluconeogensis and glycolysis are ____ reaction
Futile
Futile reaction
occurs when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than to burn ATP/GTP and heat produced
