Gluconeogenesis

Question 1

where does gluconeogenesis occur primarily?

Answer 1

in the liver

Question 2

what is the first step of gluconeogenesis, starting with pyruvate?

Answer 2

pyruvate carboxylase uses 2 ATP to add CO2 to pyruvate, producing oxaloacetate

Question 3

what enzyme is used in the second step to decarboxylate and phosphorylate oxaloacetate? what products form?

Answer 3

phosphoenolpyruvate carboxykinase (PEPCK)
oxaloacetate turns into phosphoenolpyruvate and CO2.

Question 4

phosphoenol pyruvate undergoes several steps to become fructose_________

Answer 4

fructose-1,6-bisphosphate
(the intermediate steps inc. both 2,2 and 2,3 phosphoglycerate, and glyceraldehyde 3-phosphate and dihydroxyacetone phosphate)

Question 5

what does F-1,6-bP get turned into?

Answer 5

Fructose-6-Phosphate (F6P)

Question 6

What does F6P get turned into?

Answer 6

Glucose-6-Phosphate (G6P)

Question 7

What does G6P get turned into?

Answer 7

glucose

Question 8

what enzyme turns F-1,6-bP into F6P?

Answer 8

fructose-1,6-bisphosphatase

Question 9

what enzyme turns G6P into glucose?

Answer 9

glucose-6-phosphatase

Question 10

what are the 4 major enzymes in gluconeogenesis?

Answer 10

pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), f-1,6-bisphosphatase, g-6-phosphatase

Question 11

which step uses 2 GTP molecules?

Answer 11

second step where phosphoenolpyruvate carboxykinase (PEPCK) turns oxaloacetate into phosphoenolpyruvate

Question 12

How many ATP, GTP, and NADH are used during one round of gluconeogenesis?

Answer 12

4 ATP, 2 GTP, and 2 NADH

Question 13

Fructose-1,6-bisphosphatase catalyzes the removal of a ______ group from F-1,6-bP to form F6P

Answer 13

phosphate

Question 14

F6P is _____ to become G6P

Answer 14

isomerized

Question 15

G6P is _____ to become glucose

Answer 15

dephosphorylated

Question 16

Why must G6P be dephosphorylated in the liver before released from the liver?

Answer 16

because G6P is charged and cannot cross the cell membrane. Only glucose can cross the cell membrane and be delivered into the bloodstream

Question 17

Since glycolysis is such a thermodynamically favorable process, how is the reverse process of gluconeogenesis made thermodynamically favorable?

Answer 17

there are 3 major steps in gluconeogenesis that have a deltaG > 0, which are made thermodynamically favorable by coupling the reactions to the hydrolysis of high energy phosphate bonds of GTP and ATP

Question 18

Why can free fatty acids no be converted into glucose during starvation?

Answer 18

because acetyl-CoA cannot be used in gluconeogenesis (which helps explain why the glycerol backbone of a triglyceride can)

Question 19

what is futile cycling?

Answer 19

refers to running 2 processes with opposite functions/roles at the same time

Question 20

what is reciprocal control?

Answer 20

refers to the same molecule regulating 2 enzymes, each one from an opposing pathway, in opposite ways. i.e. AMP activate PFK (glycolysis) and inhibits F-1,6-bPase (gluconeogenesis).

Question 21

How does fructose-2,6-bisphosphate (F-2,6-BP) exert reciprocal control on glycolysis and gluconeogenesis?

Answer 21

Presence of F26BP stimulates glycolysis while simultanesouly inhibiting gluconeogenesis. The absence of F26BP has the opposite affect.

F26BP is a large protein whose intracellular concentration is controlled by both insulin and glucagon. Insulin stimulates production of F26BP, which then stimulates PFK (glycolysis) and inhibits F16bPase (gluconeogenesis). Glucagon stimulates breakdown of F26BP, so the low amount of F26BP stimulates F16bPase and inhibits PFK.

Question 22

In a pathway, those enzymes which catalyze irreversible (i.e. exergonic) rxns are frequently sites of _____

Answer 22

regulation

Question 23

increased concentrations of intermediates in a pathway generally serve to _____ the activity of that pathway

Answer 23

decrease

i.e. increase citrate decreases the activity of of PFK in glycolysis

Question 24

Each pathway responds to the energy state of the cell. Cellular respirations is stimulated by energy ___1____ and inhibited by energy __2___

Answer 24

1. deficits (i.e. high ADP to ATP ratio or high NAD+ to NADH ratio)
2. surpulses (i.e. high ATP to ADP ratio or high NADH to NAD+ ratio)

Question 25

What is the major regulatory step in gluconeogenesis? Name 1 positive regulator and 2 negative regulators of it.

Answer 25

F16bPase
positive regulator = ATP
negative regulators = F26BP and AMP

Question 26

Gluconeogenesis generates new glucose molecules from precursors such as pyruvate, _____, ___ ___, and ____.

Answer 26

oxaloacetate, amino acids, and glycerol

Question 27

What prevents futile cycles in a cell?

Answer 27

reciprocal regulation

Question 28

When glycogen is depleted, gluconeogenesis can generate glucose from precursors pyruvate, _____, and ___ ____ intermediates

Answer 28

lactate, and Kreb cycle intermediates