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Kaplan: Biochemistry Part I > Chapter 14: Glycogen, Gluconeogenesis, and the Hexose Monophosphate Shunt (continued) > Flashcards

Chapter 14: Glycogen, Gluconeogenesis, and the Hexose Monophosphate Shunt (continued) Flashcards

1
Q

What is the normal function of lysosomal α1,4 glucosidase?

A

enzyme normally resides in the lysosome and is responsible for digesting glycogen-like material accumulating in endosomes

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2
Q

Why is Pompe’s disease similar to Tay Sachs or I cell disease?

A

indigestible substrates accumulate in inclusion bodies

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3
Q

What is another name for lysosomal α1,4 glucosidase?

A

acid maltase

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4
Q

What is another name for McArdle’s disease?

A

myophosphorylase deficiency

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5
Q

Why is there amelioration of symptoms for McArdles when one drinks sucrose containing drinks.

A

dietrary glucose increases glucose in body

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6
Q

What is another name for Hers disease?

A

hepatic glycogen phosphorylase deficiency

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7
Q

Why is Hers disease usually a mild disease?

A

because gluconeogenesis compensates for the lack of glycogenolysis

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8
Q

What are important substrates for gluconeogenesis?

A
  1. glycerol 3-phosphate
  2. lactate (from anaerobic glycolysis)
  3. gluconeogenic amino acids (protein from muscle)
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9
Q

What are the ketogenic amino acids?

A

leucine and lysine

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10
Q

List the ketogenic and glucogenic amino acids.

A

phenylalanine
tyrosine
tryptophan
isoleucine
threonine

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11
Q

List the glucogenic amino acids.

A

AS A Goat Vendor 2 Goats ARe PResent At My Home Come See THem

asparagine, alanine, glycine, valine, glutamine, glutamate, arginine, proline, aspartate, methionine, histidine, cysteine, serine, threonine

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12
Q

Can dietary fructose and galactose be converted to glucose?

A

yes; they can be converted to glucose in the liver

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13
Q

Is it possible to convert acetyl CoA to glucose?

A

no; exceptions are odd number carbon fatty acids which yield a small amount of propionyl CoA that is gluconeogenic

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14
Q

Draw out the steps in gluconeogenesis.

A
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15
Q

Alanine is converted to pyruvate by what enzyme?

A

alanine aminotransferase ALT or GPT (serum glutamic-pyruvic transaminase)

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16
Q

Glycerol 3 phophate is oxidized to DHAP via what enzyme?

A

glycerol 3 phosphate dehydrogenase

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17
Q

What are the 4 important enzymes that are req’d to catalyze reactions in gluconeogenesis?

A
  1. pyruvate carboxylase
  2. PEPCK phosphoenolpyruvate carboxykinase
  3. fructose 1,6 bisophosphatase
  4. glucose 6-phosphatase
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18
Q

How can OAA leave the citric acid cycle?

A

It can’t leave the mitochondria but is reduced to malate that can leave via the malate shuttle in the cytoplasm, then

malate re-oxidized to OAA

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19
Q

What vitamin does pyruvate carboxylase require?

A

biotin B7

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20
Q

Pyruvate carboxylase is activated by what? What is the obligate activator?

A

acetyl CoA (from β-oxidation) is the obligate activator

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21
Q

What is PEPCK induced by?

A

glucagon and cortisol

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22
Q

Where is PEPCK found in the cell?

A

cytoplasm

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23
Q

What is the key control point enzyme of gluconeogenesis?

A

fructose 1,6 bisophosphatase

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24
Q

Phosphatases oppose what types of enzymes?

A

kinases

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25
Q

Fructose 2,6 bisphosphate is produced by what enzyme?

A

PFK-2

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26
Q

PFK2 is activated by what enzyme? Inhibited by what enzyme?

A

PFK-2 activated by insulin
PFK-2 inhibited by glucagon

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27
Q

Where is glucose-6-phosphatase found in the cell?

A

in the lumen of the ER

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28
Q

How does glucose-6-phosphate leave the cell?

A

G6P is transported into the ER and free glucose is transported back into the cytoplasm from which it leaves the cell

29
Q

What is the only organ glucose-6-phosphatase is found in?

A

the liver

30
Q

What is the major gluconeogenic amino acid?

A

alanine

31
Q

What are 2 major causes of biotin deficiency?

A

raw egg whites (avidin) or long term home TPN

32
Q

Symptoms of biotin deficiency?

A

alopecia
scaly dermatitis
waxy pallor
acidosis (mild)

33
Q

Acetyl CoA from FA cannot be converted to glucose but can be converted to what energy source as an alternative fuel for cells, including the brain?

A

ketone bodies

34
Q

What are the 2 mitochondrial enzymes that use pyruvate?

A

pyruvate carboxylase
pyruvate dehydrogenase

35
Q

What is the Cori cycle?

A

When, in the fasting state, lactate from RBCs (and possibly exercising sk. muscle) is converted in the liver to glucose that can be returned to the RBC or muscle

36
Q

What is the alanine cycle?

A

slightly different version of the cori cycle in which muscle releases alanine, delivering both a gluconeogenic substrate (pyruvate) and an amino group for urea synthesis

37
Q

What are reasons that patients who abuse alcohol are susceptible to hypoglycemia?

A

in addition to poor nutrition and the fact that alcohol is metabolized to acetate (acetyl-CoA) high amounts of cytoplasmic NADH formed by alcohol dehydrogenase and acetaldehyde dehydrogenase interfere with gluconeogenesis

38
Q

What are metabolic products that high amounts of NADH favor?

A

Formation of:
1. lactate from pyruvate
2. malate from OAA in the cytoplasm
3. glycerol 3-phosphate from DHAP

39
Q

Draw the pathway of alcohol metabolism.

A

Refer to diagram on page 215

40
Q

What is hepatic steatosis?

A

fatty degeneration of liver tissue

41
Q

Accumulation of what products in the liver may contribute to lipid accumulation?

A

cytoplasmic NADH and glycerol 3-P

42
Q

Pathology of hepatic steatosis?

A
  1. Free fatty acids released from adipose in part enter the liver where B-oxidation is very slow (high NADH)
  2. In presence of high glycerol 3-P, fatty acids are inappropriately stored in liver as triglyceride
43
Q

Why can alcohol consumption after extreme exercise lead to light headedness, and muscle cramping?

A
  1. Because NAD is req’d by LDH to oxidize lactate to pyruvate; however much of available NAD is being used for ethanol metabolism and is unavailable for lactate oxidation.
  2. Result is metabolic acidosis and hypoglycemia
44
Q

What does HMP shunt stand for?

A

hexose monophosphate pathway

45
Q

Another name for the HMP shunt pathway?

A

PPP pathway or pentose phosphate pathway

46
Q

Where does the HMP Shunt take place in the cell??

A

in the cytoplasm of all cells

47
Q

What is the purpose of the HMP shunt? (What are its 2 major functions?

A
  1. NADPH production
  2. source of ribose 5-phosphate for nucleotide synthesis
48
Q

Is the change of G6P to ribulose 5-P in the HMP shunt reversible or irreversible?

A

irreversible

49
Q

What is the rate limiting enzyme in the first part of the pathway of the HMP shunt?

A

G6PDH glucose 6-P dehydrogenase

50
Q

What hormone is G6PDH induced by?

A

insulin

51
Q

What is G6PDH inhibited by?

A

NADPH

52
Q

What is G6PDH activated by?

A

NADP

53
Q

Draw out an abbreviated diagram of the HMP shunt.

A

Refer to diagram page 216

54
Q

What is a major function of ribose 5-P?

A

for nucleotide synthesis

55
Q

Transketolase requires what B vitamin?

A

thiamine (B1)

56
Q

What are the enzymes in metabolism that require thiamine?

A

PDH
transketolase
α-ketoglutarate

57
Q

What are major functions of NADPH?

A
  1. biosynthesis (fatty acids, cholesterol, nucleotides)
  2. maintenance of a supply of reduced glutathione to protect against reactive oxygen species (ROS)
  3. bactericidal activity in polymorphonuclear leukocytes (PMN)
58
Q

Create a diagram on the main function of the HMP shunt and resultant NADPH function in the liver.

A
59
Q

Create a diagram on the main functions of the HMP shunt in the neutrophil.

A
59
Q

Create a diagram on the main function of the HMP shunt on the erythrocyte.

A
59
Q

Where are diets of fava beans common? What countries?

A

Mediterranean countries (Greece, Italy, Spain, Portugal, Turkey)

59
Q

What is favism?

A

Severe hemolysis caused by exacerbation of symptoms associated with G6PDH deficiency

60
Q

What are some symptoms of favism?

A

pallor, hemoglobinuria, jaundice, and severe anemia 24 - 48 hours after ingestion

61
Q

What is the major cause of CGD?

A

genetic deficiency of NADPH oxidase in the PMN

62
Q

Which infections are patients with CGD susceptible to?

A

infections by catalase-positive organisms:

S. aureus,
Klebsiella,
E coli,
Candida,
Aspergillus

63
Q

What test helps to confirm CGD?

A

a negative nitroblue tetrazolium test

64
Q

Why are those with G6PDH less susceptible to infection by certain parasites like plasmodium?

A

because many of these parasite are deficient in antioxidant mechanism making them susceptible to O2 radicals

In G6PDH deficiency, the ability of erythrocytes to detoxify O2 radicals is impaired

In turn, the accumulation of these radicals in erythrocytes in G6PDH def gives protection against malaria

65
Q

What is the inheritance pattern of those with G6PDH deficiency?

A

X-linked recessive

Kaplan: Biochemistry Part I (27 decks)

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