Gluconeogenesis (3)_١٠٤٣٥٣.ppt of glucousesynthisis

Synthisis glucouse from fat and broten

1. Gluconeogenesis
T. baset
Biochemistry
Benghazi University

2. •Intoduction
•In normal circumstances, glucose is the only fuel for the brain .
•Glucose is also used by muscle during the initial stages of
exercise.
•To ensure the continuous provision of glucose to the brain and
other tissues.
•Carbohydrates are stored as glycogen . but, the amount of
available glycogen stored is not large.
•Liver glycogen can supply glucose for no longer than 16-18h.
•To provide glucose over longer periods, the body transforms
non-carbohydrate compounds into glucose through
gluconeogenesis.

3. Gluconeogensis
Def.: It is the formation of glucose from non CHO sources.
Functions:Its main function is to supply blood glucose in cases of
carbohydrate deficiency (fasting, starvation, and low carbohydrate
diet) and to supply erythrocytes, skeletal muscles, nervous system,
and mammary glands with their need of glucose.
Sites: Cytoplasm and mitochondria of liver(80%) and kidney (20%) due
to presence of glucose-6-phophatase and fructose-1, 6-biphosphatase.
Pathway :reverse to glycolytic pathway (except for three irreversible
kinases).
Q: which steps occurs in cytoplasm & mitochondria

4. Sources of gluconeogenesis
1. Glucogenic amino acids.
2. lactate.
3. Glycerol .
4. Propionic acid ( from odd number fatty acid oxidation)

5. gluco neo genesis
sugar (re)new make/
create
glycolysis
glucose
pyruvate
lactate
gluconeogenesis

7. Energy barrier obstruct reversal of glycolysis at the
following sites:
1.Conversion of pyruvate to phosphoenol pyruvate:This can be
overcomed by dicarboxylic acid shuttle.
2.Conversion of fructose 1:6 biphosphate to F-6-P: -This occurs by
fructose 1:6 biphosphatase, which present in liver and kidneys.
3.Conversion of Glucose-6-P to glucose:This is catalysed by another
enzyme, which is G-6-Phosphatase that is present in liver, intestine,
and kidney.

8. 1. Reversal of PEP → Pyruvate
•Part One
–Enzyme: Pyruvate Carboxylase
•Found only in the Liver and Kidney
•Pyruvate carboxylase contains biotin
–Location: Mitochondria
–Requires ATP & co2
•This reaction occurs in the mitochondria of liver and kidney cells, and
has two purposes (depending on the synthetic needs of the cell):
–to provide OAA for gluconeogenesis,
–to provide OAA that can replenish TCA cycle intermediates that
may become depleted,.
•Muscle cells also contain pyruvate carboxylase, but use the OAA
produced only for the latter purpose only, they do not synthesize
glucose

9. Malate Shuttle
•OAA produced in mitochondria
•mitochondrial membrane
impermeable to OAA
•malate transporter in mito.
Membrane
•malate dehydrogenase in both mito
and cyto
•NADH produced in cytoplasm also
used in gluconeogenesis.

10. •Part Two
–Enzyme: PEP Carboxykinase
–Location: Cytosol
–Requires: GTP

11. Cytosol
Mitochondria

12. Precursers for gluconeogenesis
1. Lactic acid (cori cycle):
•In vigorous skeletal muscle activity and RBCs, large amount of
lactic acid produced → passes to the liver through blood
stream → converted in liver into pyruvic acid by lactate
dehydrogenase and lastly to glucose → reach muscle once
again through blood.

13. 2. Glucose-alanine cycle:
•During starvation, there is muscle protein catabolism →in
presence of NH
3and pyruvic acid (produced from glycosis),
alanine is formed →reach liver and converted into pyruvic acid,
which give glucose through glucogenesis and NH
3 which
converted into urea →excreted in urine.

14. 3. Glucogenic amino acids;
•Amino acids derived from hydrolysis of tissue proteins are
the major sources of glucose during fasting.
•αketo acids such as oxaloacetate and α-ketoglutarate, are
derived from the metabolism of glucogenic amino acids
•These substances can enter the citric acid cycle and form
oxaloacetate : a direct precursor of phosphoenolpyruvate.

17. 4. Glycerol
Derived from adipocytelipolysis,
In liver: hepatic glycerol kinaseconvert glycerol to Glycerol phosphate
is oxidized by glycerol phosphate dehydrogenase to
dihydroxyacetonephosphate which is an intermediate of glycolysis.
Adipocytescannot phosphorylateglycerol because they lack glycerol
kinase

18. 5. Fatty acids
Derived from adipocyte lipolysis,
Even number fatty acid oxidation not give glucose, as it is
converted to acetyl coA .
ODD number fatty acid oxidation give glucose, as it is
converted to propionyl → suuccinyl CoA → OAA → glucose.

20. Energetics of Gluconeogenesis
•Pyruvate Carboxylase
–2 ATPs
•PEP Carboxykinase
–2 GTPs
•3-P-glycerate kinase
–2 ATPs
•Glyceraldehyde-3-P
dehydrogenase
–2NADH

21. Glycolysis GNG
Hexokinase Undone
by
Glucose-6-Phosphatase
PFK Undone
by
Fru-1,6-BisPhosphatase
Pyruvate Kinase Undone
by
PyruvateCarboxylase
AND
PEP Carboxykinase

22. •Muscle lacks glucose 6-phosphatase and, therefore, muscle
cannot form glucose either from glycogenolysis or
gluconeogenesis.
•So, glucose 6-phosphate derived from muscle glycogen
cannot be dephosphorylated to yield free glucose.
•The only source for muscle glucose is blood glucose.
•Q; Is muscle needed to convert g6p →glucose.

23. Acetyl CoA
•Acetyl CoAand compounds that make Acetyl CoA
(acetoacetateand amino acids such as lysine and leucine=
ketogenic) cannot be made into glucose.
•WHY?
1.This is due to the irreversible nature of the pyruvate
dehydrogenase reaction, which converts pyruvateto acetyl
CoA
2.It is energetically unfavorable, because we make
approximately 24 ATP from 2Acetyl CoAand it costs 6 ATP to
make Glucose.

24. regulation of gluconeogenesis

25. 1. Glucagon
•This pancreatic islet hormone stimulates gluconeogenesis by
three mechanisms
1. Changes in allosteric effectors
2. Covalent modification of enzyme activity
3. Induction of enzyme synthesis

26. 1. Changes in allosteric effectors= role of PFK 2
•Glucagon ↓ fructose 2,6-bisphosphate, resulting in
–activation of fructose 1,6 bisphosphatase and
–inhibition of phosphofructokinase , so inhibit glycolysis.
And stimulate gluconeogenesis.
–Fructose 2,6-bisphosphate inhibits of glycolysis (thus
allowing for reciprocal control of glucose synthesis and
oxidation

27. 2. Covalent modification of enzyme activity
•Glucagon, ↑ cAMP level and cAMP-dependent protein
kinase activity,
•Phosphorylate and so on inactivates pyruvate kinase.
•This decreases the conversion of PEP to pyruvate, which has
the effect of diverting PEP to the synthesis of glucose

28. 3. Induction of enzyme synthesis
•Glucagon increases the transcription of the PEP
carboxykinase gene.
•Insulin causes decreased transcription of the mRNA for this
enzyme.]

29. Allosteric activation by acetyl CoA
•↑ acetyl CoA
–activation of pyruvate carboxylase.
–inhibits pyruvate dehydrogenase.
•Thus, this single compound can divert pyruvate toward
gluconeogenesis and away from the TCA cycle

30. Allosteric inhibition by AMP ( energy level in the cell)
•↑AMP
–inhibites Fructose 1,6 bisphosphatase
–activates phosphofructokinase.
•Elevated AMP thus stimulates pathways that oxidize
nutrients to provide energy for the cell.
•ATP and NADH, produced in large quantities during fasts by
catalytic pathways, such as fatty acid oxidation, are required
for gluconeogenesis

31. Regulation of gluconeogenesis:
Inhibition
–High blood Glucose
–Insulin
–Low Energy Charge=AMP
–Fructose -2,6 –Bis
Phosphate
Stimulation
Low blood Glucose
Glucagon
ATP
Citrate
Acetyl Co A
Pyruvate
Lactate
Alanine
OAA

32. Coordinated Regulation of Gluconeogenesis and
Glycolysis
•Regulation of enzyme quantity
•Fasting:glucagon, cortisol
–induces gluconeogenic enzymes
–represses glycolytic enzymes
–liver making glucose
•Feeding:insulin
–induces glycolytic enzymes
–represses gluconeogenic enzymes
–liver using glucose