Gluconeogenesis And The Control Of Blood Glucose

Question 1

Prevent a Simple Reversal of Glycolysis

Answer 1

Thermodynamic Barriers

Question 2

GLUCONEOGENESIS INVOLVES

Answer 2

GLYCOLYSIS

THE CITRIC ACID CYCLE,
PLUS SOME SPECIAL REACTIONS

Question 3

Induction & Repression of Key Enzymes Requires

Answer 3

Several hours

Question 4

is of quantitative importance only in ruminants.

Answer 4

Propionate

Question 5

______Modification by Reversible Phosphorylation Is Rapid

Answer 5

Covalent

Question 6

This Modification Is Instantaneous

Answer 6

allosteric

Question 7

Plays a Unique Role in the Regulation of Glycolysis & Gluconeogenesis in Liver

Answer 7

Fructose 2,6-Bisphosphate

Question 8

kidney may contribute up to

Answer 8

40%

Question 9

key gluconeogenic enzymes are expressed in

Answer 9

small intestine, but it is unclear whether or not there is significant glucose production by the intestine in the fasting state.

Question 10

Glucose is also important in maintaining adequate concentrations of intermediates of the

Answer 10

citric acid cycle

Question 11

clears lactate produced by muscle and erythrocytes, and glycerol produced by adipose tissue.

Answer 11

gluconeogenesis

Question 12

Hyperglycemia leads to changes in

Answer 12

osmolality of body fluids,
impaired blood flow,
intracellular acidosis and
increased superoxide radical production (see Chapter 45),

resulting in deranged endothelial and immune system function and impaired blood coagulation

Question 13

impaired downregulation in response to insulin.

Answer 13

gluconeogenesis is also a contributory factor to hyperglycemia in type 2 diabetes

Question 14

nonequilibrium reactions in glycolysis (see Chapter 17), catalyzed by ______3)prevent simple reversal of glycolysis for glucose synthesis

Answer 14

hexokinase, phosphofructokinase and pyruvate kinase

Question 15

Three nonequilibrium reactions in glycolysi

Answer 15

Pyruvate & Phosphoenolpyruvate

Question 16

catalyzes the carboxylation of pyruvate to oxaloacetate, an ATP-requiring reaction in which the vitamin biotin is the coenzyme.

Answer 16

Mitochondrial pyruvate carboxylase

Question 17

presence determines whether a tissue is capable of synthesizing glucose (or glycogen) not only from pyruvate, but also from triose phosphates

Answer 17

fructose 1,6-bisphosphatase

present in liver, kidney, and skeletal muscle, but is probably absent from heart and smooth muscle.

Question 18

present in liver and kidney, but absent from muscle, which, therefore, cannot export glucose into the bloodstream.

Answer 18

glucose-6-phosphatase

Question 19

involves a different pathway via uridine diphosphate glucose and glycogen synthase

Answer 19

Glycogen synthesis

Question 20

After transamination or deamination, glucogenic amino acids yield either pyruvate or intermediates of the citric acid cycle

Answer 20

True

Question 21

arises from the β-oxidation of odd-chain fatty acids that occur in ruminant lipids (see Chapter 22), as well as the oxidation of isoleucine and the side chain of cholesterol

Answer 21

In nonruminants, including human beings, propionate

Question 22

a vitamin B12dependent enzyme, and in deficiency methylmalonic acid is excreted in the urine

Answer 22

Methylmalonyl-CoA mutase

Question 23

Three mechanisms are responsible for regulating the activity of enzymes concerned in carbohydrate metabolism

Answer 23

1) changes in the rate of enzyme synthesis, (2) covalent modification by reversible phosphorylation, and (3) allosteric effects.

Question 24

The enzymes involved in the utilization of glucose (ie, those of glycolysis and lipogenesis) become more active when

Answer 24

there is a superfluity of glucose, and under these conditions the enzymes of gluconeogenesis have low activity.

Question 25

antagonizes the effect of the glucocorticoids and glucagon-stimulated cAMP

Answer 25

Insulin, secreted in response to increased blood glucose,

Question 26

activates cAMP-dependent protein kinase, leading to the phosphorylation and inactivation of pyruvate kinase.

Answer 26

Glucagon and epinephrine, hormones that are responsive to a decrease in blood gluco

Question 27

In gluconeogenesis, pyruvate carboxylase, which catalyzes the synthesis of oxaloacetate from pyruvate, requires acetyl-CoA as an

Answer 27

allosteric activator.

Question 28

The addition of acetyl-CoA results in a change in the

Answer 28

the tertiary structure of the protein, lower-ing the Km for bicarbonate

Question 29

as acetyl-CoA is formed from pyruvate, it automatically ensures the provision of oxaloacetate and, therefore, its further oxidation in the cit-ric acid cycle, by activating

Answer 29

pyruvate carboxylase

Question 30

explain the action of fatty acid oxida-tion in sparing the oxidation of pyruvate (and hence glucose) and in stimulating gluconeogenesis.

Answer 30

The acti-vation of pyruvate carboxylase and the reciprocal inhibition of pyruvate dehydrogenase by acetyl-CoA derived from the oxidation of fatty acids

Question 31

A major role of fatty acid oxidation in promoting gluconeogenesis is

Answer 31

supply the ATP that is required.

Question 32

inhibited by citrate and by normal intracellular concentrations of ATP and is activated by 5′ AMP.

Answer 32

Phosphofructokinase

Question 33

acts as an indicator of the energy status of the cell.

Answer 33

5′ AMP

Question 34

allows rapid equilibration of the reaction

Answer 34

adenylyl kinase in liver and many other tissue

Question 35

activity of phosphofructokinase-1 is thus regulated in response to the energy status of the cell to control the quantity of carbohydrate undergoing glycolysis prior to its entry into the citric acid cycle.

True or False

Answer 35

True

Question 36

accumulation of glucose-6-phosphate, which in turn inhibits further uptake of glucose in extrahepatic tissues by inhibition of hexokinase.

Answer 36

consequence of the inhibition of phosphofructokinase-1 by ATP

Question 37

most potent positive allosteric activator of phosphofructokinase-1 and inhibitor of fructose 1,6-bisphosphatase in liver is

Answer 37

fructose 2,6-bisphosphate

Question 38

relieves inhibition of phosphofructokinase-1 by ATP and increases the affinity for fructose-6-phosphate

inhibits fructose 1,6-bisphosphatase by increasing the Km for fructose 1,6-bisphosphate

Answer 38

fructose 2,6-bisphosphate

Question 39

also responsible for its breakdown, since it has fructose 2,6-bisphosphatase activity.

Answer 39

phosphofructokinase-2.