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BCHM 270 > Module 04 - Gluconeogenesis and Glycogen Metabolism (Section 04) > Flashcards

Module 04 - Gluconeogenesis and Glycogen Metabolism (Section 04) Flashcards

1
Q

Which 3 main sources is blood glucose obtained from?

A
  1. Diet
  2. Gluconeogenesis
  3. Glycogen Breakdown
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2
Q

What is Glucose Metabolism?

A

the net production of glucose (gluconeogenesis) and breakdown of glucose (glycolysis)

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3
Q

What is Gluconeogenesis?

A

an anabolic pathway that converts pyruvate (or lactate) to glucose

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4
Q

Where does Gluconeogenesis occur?

A

partially in the mitochondria and partically in the cytoplasm of liver and kidney cells

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5
Q

What are the 3 most important substrates for Gluconeogenesis?

A
  1. Glycerol from the breakdown of lipids
  2. Lactate released into the blood from red blood cells and exercising muscles
  3. Amino acids released from breakdown of proteins and converted into a-keto acids during amino acid metabolism
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6
Q

What is the Cori Cycle?

A

the metabolic pathway where lactate produced by anaerobic glycolysis in exercisng muscle cells is transported to the liver to be converted back to glucose

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7
Q

What happens in step 1 of the cori cycle?

A

glucose from blood is taken up by intensely exercising skeletal muscle

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8
Q

What happens in step 2 of the cori cycle?

A

anaerobic glycolysis converts glucose to lactate

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9
Q

What happens in step 3 of the cori cycle?

A

lactate diffuses into the blood and is taken up by the liver

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10
Q

What happens in step 4 of the cori cycle?

A

liver synthesizes glucose from lactate via gluconeogenesis

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11
Q

What happens in step 5 of the cori cycle?

A

glucose is released back into the blood

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12
Q

How many reactions is Gluconeogenesis comprised of?

A

11 reactions, including:
- 7 reversible reactions of glycolysis
- 4 reactions unique to gluconeogenesis

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13
Q

What are the 4 unique reactions to gluconeogenesis?

A
  1. conversion of pyruvate to oxaloacetate
  2. formation of phosphoenolpyruvate
  3. dephosphorylation of fructose 1,6-bisphosphate
  4. dephosphorylation of glucose 6-phosphate
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14
Q

What is pyruvate carboxylated by? Where does this take place?

A

pyruvate carboxylase in the mitochondria of liver and kidney cells

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15
Q

What does pyruvate carboxylase use as a coenzyme?

A

biotin

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16
Q

What occurs in step 1 of carboxylation of pyruvate?

A

hydrolysis of ATP to ADP powers the formation of an enzyme-biotin-CO2 intermediate

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17
Q

What occurs in step 2 of carboxylation of pyruvate?

A

CO2 is transferred to pyruvate generating oxaloacetate and release the enzyme-biotin complex

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18
Q

What is pyruvate carboxylase activated by?

A

acetyl-CoA

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19
Q

What is pyruvate carboxylase inhibited by?

A

ADP

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20
Q

What is oxaloacetate in the mitochondria reduced to to cross the mitochondrial membrane?

A
  • maltate
  • NADH is oxidized to NAD+
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21
Q

What happens after maltate crosses into the cytosol?

A

it is oxidized back to oxaloacetate, with NADH regenerated from NAD+

22
Q

What happens to oxaloacetate once in the cytosol?

A

it is decarboxylated and phosphorylated by PEP-carboxykinase to form phosphoenolpyruvate (PEP)

23
Q

What happens to PEP in the cytosol?

A

it undergoes reversible reactions that are part of glycolysis until it is converted to fructose 1,6-bisphosphate

24
Q

What occurs during the dephosphorylation of fructose 1,6-bisphosphate?

A

phosphate is removed from fructose 1,6-bisphosphate by fructose 1,6-bisphosphatase

25
Q

What is fructose 1,6-bisphosphatase inhibited by?

A

high levels of AMP and fructose 2,6-bisphosphate

26
Q

What is fructose 1,6-bisphosphatase activated by?

A

citrate and ATP

27
Q

What is the product of PFK-2?

A

fructose 2,6-bisphosphate

28
Q

What is PFK-2? What is it regulated by?

A

a bifunctional protein that is regulated by the hormones insulin and glucagon

29
Q

What occurs during the dephosphorylation of glucose 6-phosphate?

A
  • glucose 6-phosphate is transported to the lumen of the ER and dephosphorylated by glucose 6-phosphatase
  • once formed, glucose is shuttled back to the cytoplasm
30
Q

What does gluconeogenesis use/produce?

A
  • uses 2 pyruvate, 4 ATP, 2 GTP, and 2 NADH
  • produces 1 glucose molecule
31
Q

How do glucagon levels stimulate gluconeogenesis?

A
  1. decreases fructose 2,6-bisphosphate which activates fructose 1,6-bisphosphatase and inhibits PFK-1
  2. leads to phosphorylation of pyruvate kinase, inactivating it which diverts PEP to glucose synthesis
32
Q

How does substrate abailability regulate gluconeogenesis?

A

in an energy poor state, proteins are broken down and amino acids provide substrates for gluconeogenesis

33
Q

How does allosteric activation of pyrucate carboxylase by acetyl-CoA regulate gluconeogenesis?

A

during starvation, breakdown of lipids results in increased acetyl-CoA

34
Q

Where does glycogen synthesis and degradation occur?

A

in the cytoplasm of cells

35
Q

Where is glycogen stored?

A

in the liver and skeletal muscle

36
Q

What does liver glycogen do?

A

maintains blood glucose levels, primarily during the initial stages of fasting

37
Q

What does muscle glycogen do?

A

functions as a fuel reserve for ATP synthesis during muscle contraction; muscle cells do not share their glycogen with the rest of the body

38
Q

Describe the structure of glycogen.

A
  • branched-chain homopolysaccharide made up of a-D-glucosse held together by glycosidic bonds
39
Q

Describe the formation of glycosidic bonds of glycogen.

A
  • primary bond is an a(1-4) linkage
  • after 8-10 glucose moecules, there is a branch formed by an a(1-6) linkage
40
Q

What is the source of all glucose molecules added to glycogen?

A

a-D-glucose attached to uridine diphosphate (UDP)

41
Q

Which two enzymes catalyze glycogen synthesis

A
  • glycogen synthase: makes a(1-4) linkages
  • branching enzyme: makes a(1-6) linkages
42
Q

What occurs at the beginning of flycogen synthesis (glycogenesis)?

A
  • UDP-glucose is synthesized from glucose 1-phosphate and UTP by UDP-glucose pyrophosphorylase
43
Q

What is UDP-glucose? How does it act in glycogensis?

A
  • an activated, high energy form of glucose
  • acts as another source of energy, like ATP
44
Q

What occurs in the middle of glycogenesis?

A

glycogen synthase requires a primer fragment of glycogen; in the absence of a glycogen fragment, glycogenin can accept glucose molecules on the -OH of a Tyr side chain

45
Q

What occurs at the end of glucogenesis?

A
  • chain elongation proceeds with the transfer of the glucose from UDP-glucose to the non-reducing end of the growing chain
  • chain branching is catalyzed by branching enzyme, which transfers a chain of 6-8 glucose by breaking a(1-4) bonds and forming an a(1-6) link
46
Q

What occurs during glycogen degradation (glycogenolysis)?

A
  • produces glucose 1-phosphate from breaking a(1-4) glycosidic bonds and glucpse from breaking a(1-6) glycosidic bonds
47
Q

Which two enzymes do degradation of glycogen need?

A
  • glycogen phosphorylase
  • debranching enzyme
48
Q

What does glycogen phosphorylase do?

A

cleaves a(1-4) linkages

49
Q

What does debranching enzyme do?

A
  • glycosol (4,4) transferase activity removes the out 3 or 4 glucose molecules from the branch to the straight chain forming a new a(1-4) bond
  • a(1,6) glucosidase removes the remaining glucose
50
Q

What is synthesis of glycogen stimulated by?

A

high levels of glucose and ATP (well-fed state)

51
Q

What is breakdown of glycogen stimulated by?

A

low glucose and energy levels (fasted state)

52
Q
A

BCHM 270 (5 decks)

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