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01. MCM Test 1 > 5. Carbohydrate Metabolism > Flashcards

5. Carbohydrate Metabolism Flashcards

1
Q

What is the rate limiting step of Glycolysis?

A

PFK-1 (Phosphofructokinase-1)

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2
Q

Why is glucose extra important to red blood cells?

A

It’s the only fuel RBC’s can use, since they don’t have mitochondria! :(

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3
Q

When might the brain use non-glucose forms of energy?

A

Starvation

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4
Q

Why is glucose extra important to the brain?

A

It’s the only fuel it will use in non starvation conditions.

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5
Q

Where is GLUT 1 found, and where is it especially in high concentrations?

A

GLUT 1 is ubiquitous (found everywhere), but it is especially high in RBC and the brain.

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6
Q

Where is GLUT 2 found,

What kind of transport does it use,

and

Does it have High or Low affinity, and high or low capacity?

A
  • Found in:
  1. Basolateral (blood facing) side of the intestine
  2. Liver cells
  3. Beta cells of the pancreas
  • Uses Facilitated Transport
  • Has Low affinity, High capacity
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7
Q

Where is GLUT 3 found, and does it have High or Low affinity for glucose?

A

GLUT 3 is the major transporter in Neurons, and has High affinity for glucose.

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8
Q

Where is GLUT 4 found, and what is so special about it?

A

GLUT 4 is found in skeletal muscle and fat tissue,

and is INSULIN DEPENDENT (hides in vesicles until insulin causes them to fuse with the plasma membrane)

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9
Q

Where is Hexokinase used, and where is Glucokinase used?

A

Hexokinase is in all cells (including the following)

Glucokinase is in liver and the beta cells of the pancreas

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10
Q

What enzyme catalyzes the glycolysis reaction that produces NADH?

A

Glyceraldehyde 3-Phosphate Dehydrogenase (G3P {in step 3} –> 1,3 biphosphosphoglycerate)

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11
Q

What is the main reactant and product for Phosphoglycerate Kinase?

A

2x 1,3 BPG (1,3 Biphosphoglycerate) –> 2x 3 Phosphoglycerate

AND

2 ATP is also produced / required (depending on the direction)

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12
Q

What are the three enzymes responsible for the three irreversible“checkpoints” for glycolysis?

A
  1. Hexokinase / Glucokinase
  2. Phosphofructokinase 1 (PFK-1)
  3. Pyruvate Kinase
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13
Q

Hexokinase has a high affinity for Glucose. What does that mean in practice?

A

It’s functional at low glucose concentrations.

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14
Q

What inhibits Hexokinase?

A

Glucose 6 Phosphate (G6P)

(its product)

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15
Q

What happens to Glucokinase when blood glucose is low?

A

It is sequestered in the Nucleus like an unwanted child by GK-Regulatory protien.

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16
Q

What induces synthesis of GK?

What inhibits synthesis of GK?

A

Insulin induces synthesis. (We want more sugar in the liver for glycogen)

Glucagon inhibits synthesis. (We want the remaining blood glucose to not go to the liver)

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17
Q

What two molecules activate PFK-1?

A

AMP (AMP is all out of P, and demands more ATP!)

Fructose 2,6 Biphosphate (not F1,6BP [product of PFK1 in the first part of glycolysis], but F2,6BP [product of the regulatory enzyme PFK2])

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18
Q

What four steps does glucagon go through to slow down PFK1?

A

Elevates cAMP

which activates Protien Kinase A

which phosphorylates PFK2

which stops production of F2,6BP (which would otherwise activate PFK1)

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19
Q

What three steps does insulin go through to speed up PFK1?

A

Insulin actvates protein phosphatases

which de-phosphorylate PFK2

which produces F2,6BP (which speeds up PFK1)

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20
Q

Insulin activates protien phosphatases. What does this do to regulate Pyruvate Kinase (PK)?

A

Protien phosphatase dephosphorylates PK, activating it, and driving glycolysis forward.

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21
Q

Glucagon causes elevated cAMP. What does this do to Pyruvate Kinase (PK)?

A

cAMP activates Protien Kinase A, which Phosphorylates PK, Inactivating it. :(

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22
Q

What does Alanine do to PK?

A

Inhibits it. :(

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23
Q

Other than glycolysis, what terrible pathways are G6P involved in?

A

Pentose Phosphate Pathway & Glycogenesis

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24
Q

Once glycolysis is done and you have Pyruvate, what three nifty things can pyruvate do?

A
  1. Get reduced by lactate dehydrogenase into lactate, and restore NAD+ for more glycolysis. (Anaerobic conditions)
  2. Get oxidized by pyruvate dehydrogenase complex (and NADH) to Acetyl CoA for aerobic energy
  3. Get converted by alanine aminotransferase into Alanine to make protiens and whatnot.
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25
Q

What is the most common disease type related to disorders of glycolysis?

A

Hemolytic anemias

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26
Q

What enzyme is affected in 95% of hemolytic anemias?

A

Pyruvate Kinase (PK)

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27
Q

Other than glucose, what molecules can the brain use for fuel?

A

Ketone Bodies (they can cross the blood brain barrier like glucose can)

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28
Q

In Tarui Disease

What enzyme is deficient?

What class of disease is this?

What are the three mentioned clinical presentations?

A
  • PFK 1 is deficient
  • Glycogen Storage Disease (GSD VII)
  1. Exercise caused muscle cramps / weakness
  2. High billirubin and jaundice
  3. Hemolytic anemia (of course)
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29
Q

How much glucose is readily available from glycogen?

A

about 190g (just over one day’s worth)

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30
Q

In what three organs does gluconeogenesis occur?

A
  1. Liver
  2. Kidney
  3. Small Intestine
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31
Q

What are gluconeogenesis’s positive regulators? (5)

A
  1. Acetyl CoA
  2. Thyroxine
  3. Citrate
  4. Cortisol
  5. Glucagon
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32
Q

What are gluconeogenesis’s negative regulators?

A
  1. ADP
  2. AMP
  3. F2,6BP

(Low energy molecules say we need to burn energy, and F2,6BP is always down for glycolysis)

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33
Q

What gluconeogenesis enzyme bypasses PFK1?

A

Fructose 1,6 biphosphatase (-> Fructose 6 Phosphate)

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34
Q

Pyruvate carboxylase is necessary for the first step of gluconeogenesis, but it itself needs a B vitamin cofactor. What vitamin is it?

A

Biotin. Biotin is in charge of many carboxylation reactions.

35
Q

What important human cell type does not have pyruvate carboxylase?

A

Red blood cells. No mitochondria.

36
Q

What is the point of going from Pyruvate to Oxaloacetate to Malate and then back to Oxaloacetate?

A

Mitochondrial membrane is impermeable to Oxaloacetate (OA).

37
Q

What two enzymes facilitate the reactions that help gluconeogenesis cross the mitochondrial membrane?

A

Mitochondrial Malate Dehydrogenase

(OAA -> Malate)

and

Cytosolic Malate Dehydrogenase

(Malate -> OAA)

38
Q

What is the rate limiting step of gluconeogenesis?

A

F1,6BPase

39
Q

What hormone activates every regulatory step of gluconeogenesis (except malate dehydrogenase)?

A

Cortisol

40
Q

What are the three parts of glucose 6 phosphatase?

A
  1. Catalytic Unit
  2. G6P / Pi antiporter (transports into the ER)
  3. GLUT 7 (Transports glucose back to the cytoplasm)
41
Q

Where is Lactate changed to Pyruvate and run through gluconeogenesis?

A

The liver.

42
Q

Where does Glycerol enter gluconeogenesis?

A

It becomes Glycerol 3-P, and then

DHAP

43
Q

Where does propionate enter glycolysis?

A

becomes Succinyl CoA which then becomes Malate

44
Q

Where does Alanine enter gluconeogenesis?

A

Pyruvate via deamination. (Remember that pyruvate can become alanine if you need it to as well.)

45
Q

Where do all amino acids except Leucine, Lysine and Alanine enter gluconeogenesis?

A

as TCA cycle intermediates, which all are converted to malate

46
Q

If someone consumed Fructose, Sorbitol, or Glycerol and starting showing signs of Lactic acidosis, hypoglycemia, hyperventilation, ketosis, and apnea, what presumptive diagnosis might you consider?

A

Fructose 1,6 Biphosphatase deficiency

47
Q

In Von Gierke Disease

  • What is the deficient enzyme?
  • What does this cause?
A
  • Glucose 6 Phosphatase (specifically the catalytic site)
  • Deficient release in free glucose by the liver
48
Q

How is lactose uptaken by the intestine?

A

It is cleaved in the intestine by lactase into glucose and galactose and then uptaken by SGLT1

49
Q

An inability to take up glucose, frucose, and galactose might be due to what disease?

What transporter is affected?

A

Fanconi-Bickel syndrome

GLUT 2

50
Q

What 4 locations in the body might be most sensitive to sorbitol accumulation, and why?

A
  1. Kidneys
  2. Lens
  3. Retina
  4. Schwann cells

They don’t have sorbitol dehydrogenase

(Sorbitol -> Fructose)

51
Q

Hereditary fructose intolerance is caused by a deficiency in which enzyme?

A

Aldolase B

52
Q

Sorbitol and Glactose buildup is likely to cause what disease?

A

Cataracts

53
Q

What two enzymes can be deficient to cause galactosemia?

A

GALT (Glucose 1P uridyltransferase)

Galactokinase

54
Q

What are the two main purposes of PPP (pentose phosphate pathway?)

A

NADPH for reducing power (biosyntehtic stuff making)

Producing Ribose for Nucleic acid synthesis

(Putting the R in RNA :) )

55
Q

What is a negative regulator of the PPP?

A

NADPH

56
Q

What is the final product of the oxidative phase of PPP?

A

Ribulose 5-P

(NOT RIBOSE! Ribose 5-P is made in the non-oxadative steps)

57
Q

What reaction is the “shunt” towards PPP from glycolysis, and what super important regulatory enzyme performs it?

A

Glucose 6 Phosphate -> 6-phosphoglucono-delta-lactone

Glucose 6 Phosphate Dehydrogenase (G6PDH)

58
Q

G6PDH is deficient in a significant population of humans. Particularly those of African descent. What does this deficiency cause, and when does that symptom happen?

A

Hemolytic anemia

when NADPH need is greatest, such as during infection or oxidizing meds / using glutathione)

59
Q

Rapidly dividing cells might favor which part of the pentose phosphate pathway (PPP), and why?

A

Ribose 5-Phosphat synthesis, so they can make more nucleotides.

60
Q

What especially important immune cells have high PPP activity?

A

Phagocytes

61
Q

When might adipose cells have high PPP activity?

A

During fatty acid synthesis

62
Q

When NADPH need is high, what portion of PPP is focused on? Why?

A

The non-oxidative side, because non-oxidative products go to gluconeogenesis to come back through the oxidative side once they get to G6P to make even more NADHP.

63
Q

Straight glycogen is chained together with what sort of bond?

A

Alpha-1,4 glycosidic

64
Q

Branched glycogen is held together with what sort of bond?

A

Alpha-1,6 glycosidic

65
Q

What end of the sugar faces away from the anchoring protien in glycogen, and what extra special functional group does it have?

A

The Non-reducing end

A free hydroxyl group

66
Q

What glycogen protien is the reducing end attached to?

A

Glycogenin

67
Q

What is glycogen stored as?

What else is in there? (Excuse the poor wording)

A

Granules

Enzymes needed for glycogen metabolism

68
Q

What reaction is the “shunt” for glycogenesis?

What enzyme (not rate limiting!) catalyzes this reaction?

A

G6P -> G1P

Phosphoglucomutase

69
Q

What reaction primes glucose 1 phosphate for glycogenesis?

What enzyme catalyzes this reaction?

A

UTP + Glucose 1 Phosphate -> PPi + UDP-Glucose (not as important)

UDP-Glucose pyrophosphorylase

70
Q

What is the rate limiting enzyme in Glycogenesis?

A

Glycogen Synthase

71
Q

What does glucosyl 4:6 transferase do?

A

Takes about 7 glucose residues off of a glycogen chain and sticks them on via an alpha 1,4 glycosidic linkage somewhere else.

72
Q

What is the rate limiting step in glycogenolysis?

A

Glycogen phosphorylase (GP)

73
Q

What vitamin is used as a cofactor for glycogen phosphorylase?

A

Pyridoxine (B6)

74
Q

What happens when a glycogen branch gets down to 4 residues in glycogenolysis in order to free them?(2 things)

A
  1. Debranching Enzyme uses its transferase power to take three of the four and sticks them on the non reducing end of the main chain.
  2. Then, Debranching Enzyme uses its alpha 1,6 glucosidase power and cleaves the remaining glucose residue, releasing it as free glucose.
75
Q

Some glycogenolysis happens in the lysosomes. What enzyme accomplishes this, and what disease occurs when this enzyme isn’t functioning properly?

A

Acid maltase

Pompe disease

76
Q

After glycogenolysis, most of those tasty glucose residues are floating around as G6P. What does the liver do next (and what enzyme does it use), and what does the muscle do next (and what enzyme does it use)?

A

Liver: Takes G6P and uses Glucose 6 Phosphatase to make it into free glucose, which is released into blood stream.

Muscle: They undergo glycolysis for energy, the next step from G6P of which is phosphoglucose isomerase to fructose 6 phosphate.

77
Q

Is Glycogen Synthase activated with phosphorylation or without?

A

Without! Glycogen synthase prefers to not be phosphorylated.

78
Q

Is Glycogen Phosphorylase active with phosphorylation or without?

A

With! Glycogen Phosphorylase LOVES phospate. Phospho is even in the name.

79
Q

Other than a low energy state, what can induce glycogenolysis in muscle tissues?

A

High cellular calcium levels. (Lots of contractions)

80
Q

What enzyme is deficient in GSD 0? What occurs?

A

Glycogen Synthase

Muscle cramps, due to lack of glycogen

Have to eat all the time.

81
Q

What enzyme is deficient in Cori Disease? What occurs?

A

alpha 1,6-glucosidase deficiency (debranching enzyme)

Patients have glycogen molecules with too many branches.

(mnemonic ate all the outer glucoses, but left the cores)

82
Q

What enzyme is deficient in Andersen Disease? What occurs?

A

Glucosyl 4:6 transferase (branching enzyme)

Cirrhosis and death due to unbranched glycogen!

(Agent Smith’s don’t branch, and neither does Mr. Andersen)

83
Q

What enzyme is deficient in McArdle Disease? What occurs?

A

Muscle Glycogen Phosphorylase

Patients cannot supply muscles with enough glucose

Exercise intolerance

(McArdle was hungover in PE, and made up this disease to get himself excused)

84
Q

What enzyme is deficient in Hers Disease? What occurs?

A

Liver Glycogen Phosphorylase

Cannot breakdown liver glycogen, and therefore you have low blood glucose levels and hepatomegaly from all the accumulated glycogen.

(Think of the liver like a his and Hers closet)

01. MCM Test 1 (10 decks)

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