Gluconeogenesis in Detail

Question 1

Define the key steps involved in the conversion of 3-carbon intermediates to 6-carbon intermediates in gluconeogenesis

Answer 1

pyruvate (PC)–> oxaloacetate (PEPCK)–> PEP
PEP –> intermediate –> G3P (DHAP)–> F16BP (F16BPase)-> F6P –> G6P (G6Pase) –> glucose

Question 2

PC

Answer 2

pyruvate carboxylase
converts pyruvate to oxaloacetate (this is a anaplerotic reaction = can produce an intermediate from krebs)

pyruvate + bicarbonate (PC)–> oxaloacetate
pyruvate is 3C and adds a CO2 to form oxaloacetate which is 4C, in turn produces ATP (ADP–>ATP

Question 3

PEPCK

Answer 3

PEPcarboxykinase
oxaloacetate loses CO2 (PEPCK) –> PEP
this reaction costs a GTP/ATP

Question 4

*

PEP

Answer 4

Phosphoenolpyruvate (PEP)

Question 5

DHAP

Answer 5

dihydroxyacetone phosphate (DHAP)
converts G3P to F16BP in gluconeogenesis

Question 6

G3P

Answer 6

glyceraldehyde 3-phosphate
DHAP converts G3P –> F16BP in gluconeogenesis
and G3P –> intermediates down in glycolysis

Question 7

F16BPase

Answer 7

Fructose-1,6-bisphosphatase
converts F16BP –> F6P in gluconeogenesis
like G6Pase, only found in liver

Question 8

G6Pase

Answer 8

glucose-6-phosphotase
converts from G6P–> glucose
like F16BPase, only found in liver

Question 9

describe the release of glucose from cytosolic glucose 6-phosphate

Answer 9

glycogen –> G6P in the liver
* transported by G6P transporter into ER lumen
(G6Pase)–> converted into glucose
* glucose exits out through GLUT-2 transporter into blood

Question 10

The effects of the absence of the 2-OH group in glucose

Answer 10

2’OH is replaced by 18F (fluorine-18 isotope)
forms FdG (Fluorodeoxyglucose)
FdG can get trapped (phosphorylated by hexokinase) but can’t be further metabolised
* no longer can convert G6P –> F6P in glycolysis = glycolysis inhibited

Question 11

use of 2-deoxy derivatives in clinical/cancer diagnostics

Answer 11

Use of FdG in cancer diagnosis
–> fluroescent but can’t be used up in glycolysis
fluorescent areas = high glucose oxidation occured/ using lots of glucose
cancer cells : wahlberg effect (glucose –> lactate)
using a lot more glucose than healthy cells
–> can be used to identify cancerous cells

Question 12

Predict the flow of glycolysis and gluconeogenesis based on allosteric Regulators

Answer 12

ATP: inhibits glycolysis
ADP : activates glycolysis
AMP : activates glycolysis AND inhibits gluconeogenesis
citrate : inhibits glycolysis

F26BP overrides all and activates glycolysis AND inhibits gluconeogenesis

Question 13

FBPase-2

Answer 13

converts F26BP –> F6P
activated by glucagon
and activates protein kinase (phosphorylation of PFK-2 deactivates it, converting it into FBPase 2)

PFK is inhibited and F16BPase activity increases

Decrease in [F26BP]
=> glycolysis inhibited
=> gluconeogenesis promoted

Question 14

PFK-2

Answer 14

Phosphofructokinase-2
converts F6P –> F26BP
costs ATP (ATP –> ADP)

activated by insulin
–> activate phosphoproteinphosphotase
F26BP inhibits F16BPase as well as stimulating PFK
– So when F26BP is high, glycolysis is favoured
=> gluconeogenesis inhibited/ glycolysis activated

Question 15

F26BP

Answer 15

Fructose 2,6-bisphosphate
key regulator to glycolysis
activates PFK-1 (F6P –> F16BP) / inhibits FBPase [reverse]
pfk

Question 16

conversion of pyruvate to phosphoenolpyruvate

Answer 16

pyruvate (PC)–> oxaloacetate
oxaloacetate (PEPCK)–> PEP

pyruvate + bicarbonate (PC)–> oxaloacetate
pyruvate is 3C and adds a CO2 to form oxaloacetate which is 4C, in turn consumes ATP

oxaloacetate then loses CO2, costs a GTP/ATP ==> PEP

Question 17

Predict the effect of fatty acid oxidation on glucose fluxes as a consequence of its effects on pyruvate carboxylase

Answer 17

if conc of acetyl CoA in krebs cycle is high, it inhibits PDH (pyruvate –> acetyl CoA)
==> prevents wasteful oxidation of glucose

excess acetyl CoA is used to activate PC (pyruvate–>oxaloacetate) to increase oxaloacetate
High [acetyl CoA] and high [oxaloacetate] = greater capacity of krebs cycle

Question 18

analpelorsis

Answer 18

replenishing intermediates (such as oxaloacetates) from krebs cycle to build glucose for glucoeneogenesis

pyruvate (PC)–> oxaloacetate