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(OMS1) SFM Exam 1 > Lecture 3: Carbohydrate Metabolism > Flashcards

Lecture 3: Carbohydrate Metabolism Flashcards

1
Q

What does GLUT 1 transport? Does it have a low or high affinity?

A 
RBC and Brain
High Affinity (so low Km)
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2
Q

What does GLUT 2 transport? Does it have a low or high affinity?

A 
Liver
Low Affinity (so high Km)
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3
Q

What does GLUT 3 transport? Does it have a low or high affinity?

A 
Neurons
High Affinity (so low Km)
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4
Q

What does GLUT 4 transport? What is it dependent on?

A

Skeletal Muscle, Heart, Adipose Tissue

Insulin dependent

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5
Q

When insulin signals a cell that utilizes GLUT 4, what happens?

A

GLUT 4 transporter sequestered in cell will insert itself into plasma membrane to induce glucose uptake

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6
Q

Where does glycolysis occur?

A

Cytoplasm

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7
Q

What is the net yield of glycolysis with one glucose molecule?

A

2 ATP
2 NADH
2 pyruvate

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8
Q

What is the difference between hexokinase and glucokinase?

What do these enzymes do?

A

Hexokinase: utilized in all cells
-High affinity (low Km)

Glucokinase: pancreas and liver only

  • Low affinity (high Km)
  • Most active with high glucose levels

Both convert glucose to glucose 6-P

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9
Q

What activates and inhibits step 1 of glycolysis?

A

Activators:
Glucose
Insulin
Fructose 1-P

Inhibitors
Glucose 6-P/Fructose 6-P
Glucagon

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10
Q

What is the rate limiting step of glycolysis? What enzyme is involved?

A

Step 3: Fructose 6-P –> Fructose 1,6-BP

via PFK-1 (phosphofructokinase-1)

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11
Q

What activates and inhibits rate limiting step of glycolysis?

A

Activators:
Fructose 2,6-P
AMP

Inhibitors:
Citrate
ATP

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12
Q

Which step yields NADH?

A

Step 6: G3P –> 1,3 BPG

via Glyceraldehyde 3P dehydrogenase (GADPH)

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13
Q

When 1,3BPG –> 3-PG, what enzyme is used and what is a product of this reaction?

A

Phosphoglycerate kinase

ATP

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14
Q

How is pyruvate formed?

A

PEP –> Pyruvate via pyruvate kinase

ATP is produced

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15
Q

How does glucokinase allow glucose to enter liver and pancreatic cells?

A

When there is high glucose, Fructose 6-P will promote the translocation of nucleus.

Most of the time, glucokinase is sequestered by GK-Regulatory Protein. Glucokinase moves to cytoplams.

Insulin induces synthesis.

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16
Q

How does PFK-2 regulate glycolysis?

A

Fructose 6-P produces Fructose 2,6-BP via PFK 2.
PFK 2 promotes PFK 1 (hence promoting glycolysis)

When PFK is dephosphorylated, it is favored by insulin.
When PFK is phosphorylated, it is favored by glucagon.

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17
Q

What happens to glycolysis when insulin levels are high and glucagon levels are low? (fed state)

A

Insulin promotes dephosphorylation of PFK 2.

Fru 2,6 BP is produced –> promote PFK 1

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18
Q

What happens to glycolysis when glucagon levels are high and insulin levels are low? (fasting state)

A

Glucagon induces Protein Kinase A, which phosphorylates PFK-2, reducing PFK-1 activity.

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19
Q

What is Tarui Disease?

A

Deficiency of PFK-1

-Can cause muscle weakness

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20
Q

How is pyruvate kinase regulated?

A

Activators:
Insulin: dephosphorylates PK
Fructose 1,6-BP

Inhibitors:
Glucagon: phosphorylates PK
Alanine
ATP

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21
Q

What pathways can intermediate Glucose 6-P be utilized in?

A

Glucose 6-P:
-Pentose Phosphate Pathway (precursor)

As Glucose 1-P:

  • Galactose metabolism
  • Glycogen Synthesis
  • Uronic Acid Pathway
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22
Q

What are the fates of pyruvate?

A

Acetyl Co A –> TCA Cycle
Alanine –> Protein synthesis, gluconeogenesis, urea cycle
Oxaloacetate –> Gluconeogensis
Lactate –> Cori Cycle

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23
Q

What cells are most affected by glycolysis disorders? What is the biggest clinical finding?

A

Red Blood Cells (no mitochondria)

-hemolytic anemia

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24
Q

When the brain can no longer utilize glucose as a fuel source, what will it use?

A

Ketone Bodies

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25
Q

What are clinical markers for hemolytic anemia?

A

Elevated Lactate Dehydrogenase

Unconjugated bilirubin

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26
Q

What is mutated in Fanconi-Bickel Syndrome?

A

GLUT 2

-liver and pancreas can’t take up glucose

27
Q

Where does gluconeogenesis take place? Why does it take place?

A

Liver, kidney, and small intestine

-Glucose and glycogen stores are depleted

28
Q

What are major precursors of gluconeogenesis?

A

Pyruvate Derivatives

  • lactate
  • amino acids
  • glycerol
29
Q

What are enzymes found in gluconeogenesis and not glycolysis?

A

Pyruvate Carboxylase
PEP carboxykinase
Fructose 1,6-bisphosphatase [Rate Limiting]
Glucose 6-phosphatase

30
Q

How much ATP/GTP is used in gluconeogenesis?

A

6 ATP

  • 2 from pyruvate–> oxaloacetate
  • 2 from oxaloacetate –> PEP
  • 2 from 3-PGA –> 1,3 BP
31
Q

Pyruvate Carboxylase is found where? What is an important cofactor?

A

PC is found in mitochondria

Imp cofactor - Biotin

32
Q

What regulates Pyruvate Carboxylase?

A

Activators

  • Acetyl Co-A
  • cortisol

Inhibitors
-ADP

33
Q

How does pyruvate leave the mitochondria?

A

After being carboxylated to oxaloacetate, it is reduced to malate and leaves via the shuttle
-Enzyme: mitochondrial malate dehydrogenase

In the cytosol, it is oxidized back to OAA.
-Enzyme: cytosolic malate dehydrogenase

34
Q

What regulates PEPCK?

OAA –> PEP

A

Activators:

  • Cortisol
  • Glucagon
  • Thyroxine
35
Q

What regulates Fructose 1,6 Bisphosphatase?

[Rate limiting]

A

Activators:

  • Cortisol
  • Citrate

Inhibitors

  • AMP
  • Fructose 2,6 BP
36
Q

What regulates Glucose 6-phosphatase?

A

Activators:

-Cortisol

37
Q

Where is Glucose 6-phosphatase?

A

lumen of ER

  • Glucose 6-P is transported into ER
  • Glucose leaves ER via GLUT 7
38
Q

What are gluconeogenesis precursors?

A

Uses Glucose 6-P

  • Galactose
  • Glycogen

G3P
-Fructose

DHAP
-glycerol

TCA Cycle

  • Propionate
  • amino acids (except leucine, lysine)

Pyruvate

  • lactate
  • alanine
39
Q

What is F1,6 BP Deficiency?

A

Lacking F1,6 Bisphosphatase

-similar to Tauri

40
Q

What is Von Gierke Disease?

A

Deficiency in Glucose-6 phosphatase

41
Q

GLUT 5 transports what? Where does it do this?

A

Transports Fructose

-basal and apical side

42
Q

What does SGLT-1 transport?

A

Glucose, Galactose, Sodium

intestine to enterocyte

43
Q

What does GLUT 2 transport?

A

Glucose, Galactose, Fructose

to bloodstream

44
Q

What is the Cori Cycle?

A

Liver takes up lactate from muscles and converts it back to glucose for muscles to use.

45
Q

What is the Polyol Pathway?

A

Glucose –> Sorbitol –> Fructose

46
Q

What happens if there is an accumulation of Sorbitol?

A

Water influx that causes swelling

  • Retinopathy
  • Cataracts
  • Peripheral Neuropathy
47
Q

What makes fructose metabolism special (compared to glycolysis?)

A

Can skip rate limiting step of glycolysis

Fru –> Fru-P —–> G3P

48
Q

What is the rate limiting step in galactose metabolism?

A

Galactose 1-P –> Glucose 1-P

via GALT

49
Q

What is Galactosemia?

A

Deficiency in GALT enzyme or Galactokinase

Symptoms for Classic Galactosemia

  • Vomiting/Diarrhea after consuming milk
  • Enlargement of liver
  • Cataracts

Symptoms in Deficiency in Galactokinase
-build of galactitol (cataracts)

50
Q

What is the point of pentose phosphate pathway?

A

Produce NADPH and sugar for DNA/RNA?

51
Q

What happens in the oxidative phase of PPP?

A

Glucose 6-P will eventually become Ribose 5-P (3 steps)

-Rate limiting: G6P Dehydrogenase

52
Q

What happens in the non-oxidative phase of PPP?

A

Reversible reactions with end products that can enter glycolytic and gluconeogenic reactions.

53
Q

What regulates Pentose Phosphate Pathway?

A

Activators:

  • Rapidly dividing cells (need ribose)
  • NADPH needed for FA synthesis
54
Q

What is rate limiting step in Glycogensis?

A

Glucose Synthase

UDP-Glucose –> Glycogen

55
Q

What linkage is used to extend chain?

A

alpha 1,4

56
Q

What linkage is used for branches of chains?

A

alpha 1,6 via glucosyl (4:6) transferase

57
Q

What is the difference between how liver and muscle cels utilize Glucsoe 1-P

A

Liver: Glu 1-P –> Glu 6-P –> Glucose

Muscle: Glu 1-P –> Glu 6-P –> Glycolysis and TCA cycle

58
Q

What is GSD 0?

A

Deficiency in glycogen synthase

59
Q

What is GSD 1a?

A

Von Gierke

Deficiency in Glucose 6-phosphatase

60
Q

What is GSD II?

A

Pompe Disease

Deficiency in Acid Maltase

61
Q

What is GSD III?

A

Cori Disease

Deficiency in alpha 1,6 branching enzyme

62
Q

What is GSD IV?

A

Andersen Disease

Deficiency in Glucosyl (4:6)

63
Q

What is GSD V?

A

McArdle Disease

Deficiency in muscle glycogen phosphorylase

64
Q

What is GSD VI?

A

Hers Disease

Deficiency in liver glycogen phosphorylase

(OMS1) SFM Exam 1 (11 decks)

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