gluconeogenesis

Question 1

major substrates for gluconeogenesis during fasting

Answer 1

alanine- from pyruvate/branched chain aa in mm

glycerol- from FA

Question 2

what is the most “direct” substrate for gluconeogenesis?

Answer 2

pyruvate

Question 3

what 2 substances can be converted to pyruvate? enzymes?

Answer 3

• lactate with lactate dehydrogenase

- alanine with alanine aminotransferase

Question 4

what is the cori cycle?

Answer 4

interactions that occurs between RBCs and skeletal mm during strenuous exercise in which lactate is exported to the liver and liver uses it to re-generate glucose via gluconeogenesis, net ATP = -4

Question 5

what are the 4 enzymes in gluconeogenesis that replace the regulated steps in gluconeogenesis?

Answer 5

• pyruvate carboxylase
• PEP carboxykinase
• fructose-1,6-bisphosphatase
• glucose-6-phosphatase

Question 6

what run in catalyzed by pyruvate carboxylase? inputs?

Answer 6

pyruvate is converted to oxaloacetate, cofactor is biotin and inputs are ATP and CO2

Question 7

what reaction is catalyzed by PEP carboxykinase? inputs?

Answer 7

oxaloacetate is converted to PEP, inputs - GTP and CO2 is expelled

Question 8

what is “released” by fructose-1,6-bisphosphatase and glucose-6-phosphatase?

Answer 8

Pi, ATP is not generated in gluconeogenesis

Question 9

what is von Gierke’s disease?

Answer 9

glycogen storage dz characterized by deficiency of glucose-6-phosphatase

Question 10

how is oxaloacetate exported from the mitochondria?

Answer 10

it is converted to malate by malate dehydrogenase in the mitochondria, then it travels to the cytosol where malate dehydrogenase converts it back.

Question 11

how does glycerol contribute to gluconeogenesis?

Answer 11

glycerol kinase converts glycerol to glycerol-3-P; glycerol-3-P dehydrogenase then converts it to DHAP, DHAP enters gluconeogenesis

Question 12

discuss use of alanine in gluconeogenesis

Answer 12

in muscle during a fast, branched chain aa are broken down to yield NH4+, NH4+ will combine with pyruvate to make alanine by alanine aminotransferase, alanine travels to the liver, where alanine aminotransferase removes NH4+ to make pyruvate that can enter gluconeogenesis and NH4+ enters urea cycle

Question 13

what is the substrate for gluconeogenesis in the kidney?

Answer 13

glutamine

Question 14

why is gluoneogenesis most important in the kidney?

Answer 14

renal medulla depends on glycolysis

Question 15

how does glutamine enter gluconeogenesis?

Answer 15

glutamine is converted to glutamate by glutaminase; glutamate is converted to a-ketoglutarate by glutamate dehydrgoenase, a-ketoglutarate is then converted to oxaloacetate that enters gluconeogenesis

Question 16

what is unique about gluconeogenesis that starts from glutamine?

Answer 16

yields ATP (because of it’s partial use of TCA cycle to generate oxaloacetate- NADH and FADH2 generated)

Question 17

gluconeogenesis is inhibited by?

Answer 17

low energy states= want to break down glucose, not build it

Question 18

3 energy inputs of gluconeogenesis

Answer 18

-ATP for pyruvate carboxylase
-GTP for PEP carboxykinase
- ATP for phosphoglycerate kinase
=3 x 2 pyruvate/glucose = 6 ATP

Question 19

what is the source of ATP for gluconeogenesis in the liver?

Answer 19

from the partial oxidation of fatty acids to acetly-CoA

Question 20

what is the role of PEPcarboxykinase in adipocytes?

Answer 20

not gluconeogenesis but for synthesis of glycerol-3-P