gluconeogenesis and ketogenesis

Question 1

role of the liver as an energy provider

Answer 1

• maintains blood glucose levels through glycogen breakdown and gluconeogenesis
  -produces ketone bodies through ketogenesis

Question 2

the liver produces glucose through gluconeogensis through

Answer 2

carbon sources: lactate, amino acids, glycerol, fructose
energy source: ATP from fatty acid oxidation

Question 3

many enzymes for glycolysis are also used for gluconeogenesis except for _______

Answer 3

irreversible steps

Question 4

______ is a TCA intermediate; the TCA pool is used to make glucose

Answer 4

oxaloacetate

Question 5

the step catalyzed by _________ is the rate-limiting step for gluconeogenesis

Answer 5

phophoenolypyruvate (PEP) carboxykinase

Question 6

the transport of oxaloacetate from mitochondria occurs through ____ or ______

Answer 6

aspartate or malate shuttle

Question 7

3 irreversible steps

Answer 7

-gluconeogenesis needs different enzymes at the steps corresponding to the 3 irreversible steps of glycolysis
-the pairs of glycolytic and gluconeogenic enzymes make futile cycles; require tight regulation
-glucose 6 phosphate is expressed only in the liver
-6 phosphofructo 1 kinase and pyruvate kinase are regulated allosterically

Question 8

comparison of glycolysis and gluconeogenesis

Answer 8

-conversion of glucose to pyruvate yields 7 ATP equivalent
-synthesis of glucose from pyruvate requires 11 ATP equivalent

Question 9

glucokinase

Answer 9

-liver cells have glucokinase instead of hexokinase for glycolysis
-glucokinase utilizes glucose only when the concentration is high
-futile cycle formed by glucokinase and glucose 6 phoshayase keeps the cellular glucose concentration high

Question 10

activation of gluconeogenesis is largely accomplished in large part by

Answer 10

-inhibition of glycolysis
-ATP inhibits 6 phosphofructo 1 kinase and pyruvate kinase

Question 11

_____ occurs hand in hand with gluconeogenesis, promoting glucose synthesis

Answer 11

-fatty acid oxidation
-supplying ATP –> used in gluconeogenesis
-increases acteyl CoA –> inactivation of pyruvate dehyrogenase and activation of pyruvate carboxylase

Question 12

increase in oxaloactate and acetyl CoA results in increase in ____

Answer 12

-citrate, which is a negative allosteric regulator of 6 phosphate 1 kinase

Question 13

alcohol and gluconeogenesis

Answer 13

-oxidation of ethanol by the liver depletes NAD+ in the cytosol
-excess NADH converts pyruvate to lactate
-gluconeogenesis by the liver is suppressed
-may cause hypoglycemia and alcohol induced lactic acidosis
-problem is more severe when glycogen storage in the liver is depleted under malnutrition or strenuous exercise

Question 14

pentose phosphate pathway

Answer 14

-produces NADPH, the major reducing equivalent for biosynthesis
-produces ribose 5 phosphate, which is used for DNA and RNA synthesis
-first step is the rate-limiting step and the commitment step for pentose phosphate pathway

Question 15

glucose 6 phosphate has many fates in the cells

Answer 15

-glycolysis
-glycogen synthesis
-pentose phosphate pathway
-glucose production (only in liver)

Question 16

NADH

Answer 16

source: glycolysis, TCA cycle, fatty acid oxidation
uses: generation of ATP by oxidative phosphorylation

Question 17

NADPH

Answer 17

source: pentose phosphate pathway
uses: reducing cofactor in anabolic reactions

Question 18

ketone bodies

Answer 18

-water soluble products from lipid oxidation (acetyl CoA)
-produced mostly by the liver during prolonged fasting or ketogenic diet
-concentration can be > 3mM in blood
-ketogenesis reduces the need for gluconeogenesis (reducing protein waste)
-utilized by many tissues as a fuel

Question 19

synthesis of ketone bodies

Answer 19

-occurs in the mitochondria
-HMG CoA synthase is expressed at high level in the mitochondria during prolonged fasting

Question 20

ratio of acetoacetic acid to B-hydroxybutyric acid is dependent on the ratio of ___________ in liver mitochondia

Answer 20

NAD+/NADH

Question 21

the spontaneous production of ____ from acetoacetic acid is significant only when the concentration of ketone bodies is high

Answer 21

acetone

Question 22

utilization of ketone bodies

Answer 22

-converted to acetyl CoA in the mitochondria of nonhepatic tissues
-reducing equivalent in B-hydroxybutyric acid is harvested as NADH
-Acetyl CoA is used as fuel in the TCA cycle

Question 23

______ is more versatile energy source than fatty acids

Answer 23

glucose

Question 24

glucose can be used to generate ATP through ______ in case of insufficient O2 supply

Answer 24

anaerobic fermentation

Question 25

when O2 is sufficient

Answer 25

fatty acids and ketone bodies are preferred to glucose

Question 25

active fatty acid oxidation increases citrate which ______ glycolysis

Answer 25

suppresses

Question 25

the regulation mechanism is analogous to the switching between ____ and _____ in the liver

Answer 25

glycolysis and gluconeogenesis

Question 26

ketoacidosis

Answer 26

-occurs mostly in type 1 diabetic patients
-low insulin levels promote lipolysis in the adipose tissues
-the production of an excess amount of ketone bodies drops the pH level of the blood
-medical emergency