Guconeogenesis

Question 1

What hormone stimulates gluconeogenesis?

Answer 1

glucagon (think Glucose is Gone)

Question 2

What is used to make glucose when starving, low/no carbs and when you exercise?

Answer 2

Starvation: primarily amino acids
Low/no carbohydrates = primarily amino acids
Exercise = lactic acid alanine

Question 3

What are the main non-carbohydrate precursors for gluconeogenesis?

Answer 3

Lactic acid
alpha keto acid
glycerol

Question 4

What are the main entry points in gluconeogenesis?

Answer 4

Pyruvate
oxaloacetate
DHAP

Question 5

What requires glucose in the body?

Answer 5

Brain
Red blood cells
Testes
Medulla of the kidney
Cornea of the eye
Muscle (during high intensity exercise)

Question 6

What is the energy requirement of the brain for glucose?

Answer 6

100 grams per day (400 kcal)

Question 7

What is the Red blood cells need for glucose?

Answer 7

20 grams per day (the brain needs 5x time at 100g/day)

Question 8

Where does gluconeogenesis occur?

Answer 8

Liver (90% of GNG)
Renal cortex
Small intestine

Question 9

How is GNG made energetically favorable?

Answer 9

by alternative enzymes in the cytosol and mitochondria
coupled reactions
ATP

Question 10

What reactions are irreversible in glycolysis?

Answer 10

Hexokinase (glucokinase)
Phosphofructokinase
Pyruvate kinase
(because these 3 reactions are irreversible in glycolysis we need to find another way around them for GNG)

Question 11

What is the first obstacle in GNG?

Answer 11

Turning pyruvate into phosphoenolpyruvate (this reaction is the opposite of the last irreversible reaction in glycolysis)

Question 12

What are the 2 enzymes used to get turn pyruvate into phosphoenolpyruvate? (get past the first obstacle for GNG)

Answer 12

Pyruvate crboxylase

PEP carboxykinase

Question 13

What coenzyme does pyruvate carboxylase use?

Answer 13

Biotin

Question 14

When does gluconeogenesis occur?

Answer 14

when blood glucose is low from:
starvation
not eating carbohydrates
exercise

Question 15

Where can you find pyruvate carboxylase?

Answer 15

in the mitochondria of liver and kidney

also present in muscle but does not synthesize glucose

Question 16

What does pyruvate carboxylase do in muscle?

Answer 16

Uses OAA produced as intermediate in Kreb’s (in liver/kidney it makes OAA)

Question 17

What is the function of pyruvate carboxylase?

Answer 17

Turn Pyruvate into Oxaloacetate

Question 18

What is the precursor for pyruvate? (the substrate that it works on)

Answer 18

pyruvate or alanine (remember that alanine can be turned into pyruvate by transamination)

Question 19

After pyruvate carboxylase turns pyruvate into oxaloacetate, how is OAA moved into the cytosol.

Answer 19

Through the malate shuttle

malate dehydrogenase is used inside the mitochondria and the cytosol in the malate shuttle

Question 20

What is the function of malate dehydrogenase in the malate shuttle?

Answer 20

In mitochondria: turn OAA into Malate

In cytosol: turn malate into OAA

Question 21

In the cytosol what enzyme turns Oxaloacetate into phosphoenolpyruvate?

Answer 21

PEP carboxylase

Question 22

During what steps is energy used in GNG for the first obstacle?

Answer 22

Pyruvate carboxylase uses ATP (1st step)

PEP carboxykinase uses GTP (2nd step)

Question 23

Which part of the 1st obstacle of GNG does not use energy?

Answer 23

malate shuttle (adds or subtracts hydrogen through NADH)

Question 24

What stimulates Pyruvate carboxylase?

Answer 24

Acetyl CoA (this is produced during FA oxidation or OHOT)

Question 25

In what location will an elevated amount of Acetyl CoA stimulate Pyruvate Carboxylase?

Answer 25

Mitochondria

Question 26

the enzyme PEP carboxykinase is dependent upon what mineral?

Answer 26

Mg2+

Question 27

When is the only time that PEP will act in the mitochondria during GNG?

Answer 27

if lactate is the precursor (lactate will be turned into pyruvate first then transported into the mitochondria. Then phosphoenolpyruvate will be transported to the cytosol)

Question 28

When will Lactate be present in the mitochondria?

Answer 28

after Anaerobic glycolysis or Erythrocyte glycolysis

Question 29

What does the conversion of Lactate to pyruvate in the cytosol yield?

Answer 29

NADH

Question 30

What is the second obstacle in GNG?

Answer 30

Fructose-1,6-bisphosphate

we use PFK for this reaction in glycolysis

Question 31

What enzyme is used to overcome the 2nd obstacle in GNG?

Answer 31

Fructose-1,6-bispohsphatase

it is also Mg2+ dependent

Question 32

What mineral doe Fructose-1,6-bisphosphatase require?

Answer 32

Mg2+

Question 33

What is the third obstacle in GNG?

Answer 33

glucokinase (this turns glucose into glucose-6-phosphate)

Question 34

What enzyme is used to overcome the 3rd obstacle?

Answer 34

Glucose 6-phosphatase (also Mg2+ dependent)

Question 35

What enzymes are Mg dependent in GNG?

Answer 35

1. PEP carboxykinase
   2.Fructose-1, 6-bisphosphatase
2. Glucose-6-phosphatase
   (each obstacle has an Mg2+ dependent enzyme)

Question 36

Why can the l9ver release glucose?

Answer 36

it contains glucose-6-phosphatase (this turns G6P into free glucose which muscle does not have)

Question 37

Why can’t muscle release glucose?

Answer 37

it does not have glucose-6-phosphatase (this enzyme turns G6P into free glucose)

Question 38

Is GNG energy expensive?

Answer 38

yes, it uses 6 high-energy phosphate groups (4ATP and 2 GTP) and 2 NADH. (2 pyruvate are used to make glucose)