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UWorld - Biochemistry > Biochem - Metabolism > Flashcards

Biochem - Metabolism Flashcards

1
Q

Which pathway (Glycolysis or Gluconeogenesis) are more active if there is:

a. High levels of Fructose-1,6-Biphosphate

b. Low levels of Fructose-1,6-Biphosphate

A

a. Glycolysis
b. Gluconeogenese

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2
Q

Pyruvate Dehydrogenase Complex Deficiency

  1. How does it present?
  2. Why?
A
    • Lactic Acidosis

- Neurologic defects

- increased serum alanine

  1. Since there is no pyruvate dehydrogenase, pyruvate will not be able to be converted into acetyl-coA and enter the TCA cycle so instead, this buildup of pyruvate will be shunted into the lactic acid and alanine pathways of pyruvate
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3
Q

What is the treatment for Pyruvate Dehydrogenase complex deficiency and why does it work?

A

Increased intake of ketogenic nutrients (lysine and leucine)

Metabolism of ketogenic amino acids (lysine and leucine) can provide energy in the form of acetyl-coA without increasing lactate production

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4
Q

What are the 4 possible fates of pyruvate?

A
  1. Acetyl-CoA (TCA cycle)
  2. Oxaloacetate (Gluconeogenesis)
  3. Alanine
  4. Lactate (anerobic glycolysis)
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5
Q

Pyruvate —-> Alanine

What enzyme is responsible?

What cofactors are required?

A

Alanine Aminotransferase

cofactor: B6

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6
Q

Pyruvate —-> Oxaloacetate

What enzyme is responsible?

What cofactors are required?

A

Pyruvate Carboxylase

cofactor: Biotin (B7)

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7
Q

Pyruvate —-> Acetyl-CoA

What enzyme is responsible?

What cofactors are required?

A

Pyruvate Dehydrogenase

cofactor: B1, B2, B3, B5, lipoic acid

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8
Q

Pyruvate —-> Lactate

What enzyme is responsible?

What cofactors are required?

A

Lactic Acid Dehydrogenase

cofactor: B3

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9
Q

Lactate Dehydrogenase Deficiency

  1. How does it typically present?
  2. Why?
A

1.

Exercise intolerance

(Muscle fatigure, pain, cramps with exercise)

2.

They cannot produce lactate and therefore lack anaerobic glycolysis

(LDH is needed to regenerate NAD+)

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10
Q

Pyruvate Kinase Deficiency

  1. How does it present?
  2. Why?
A

Hemolytic anemia with splenomegaly

Pyruvate Kinase converts Phosphoenylpyruvate into Pyruvate while generating 1 ATP in the process.

RBC’s dont have a mitochondria so they heavily rely on this enzyme for energy.

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11
Q

alpha ketoglutarate dehydrogenase

  1. What reaction does it catalyze?
  2. What cofactors does it require?
A

1.

alpha-ketoglutarate —-> Succinyl-CoA

2.

B1, B2, B3, B5, Lipoic acid

(same as pyruvate dehydrogenase)

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12
Q

Which reaction in the Krebs cycle generates GTP?

What is it needed for?

A

Succinyl-CoA —–> Succinate

GTP is required by Phosphoenylpyruvate Carboxykinase (oxaloacetate –> phoesphoenylpyruvate) in gluconeogenesis

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13
Q

What reaction in the Krebs cycle generates FADH2?

What cofactor is needed for this reaction?

A

Succinate —(succinate dehydrogenase)—> Fumarate

Cofactor: B2 (riboflavin)

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14
Q

What are the 2 reactions of the HMP shunt?

A

1. Glucose-6-Phosphate

—(Glucose-6-phosphate dehydrogenase)—>

6-phosphogluconolactone

2. Ribulose-5-Phosphate

—–(transketolase + B1 cofactor)—->

Fructose-6-Phosphate

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15
Q

What is the main function of the HMP shunt?

A

To make NADPH for:

  • glutathione reduction inside RBCs

- Fatty acid synthesis

- cholesterol synthesis

Note: it also make some ribulose for nucleotide synthesis

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16
Q

Essential Fructosuria

  1. Deficient/defective enzyme
  2. Symptoms
A
  1. Fructokinase
  2. Asymptomatic

(other than fructose in urine)

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17
Q

Why is essential fructosuria asymptomatic?

A

Since Hexokinase will take over for fructokinase and convert Fructose into Fructose-1-Phosphate

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18
Q

Hereditary Fructose Intolerance

  1. Deficient Enzyme
  2. Symptoms
A

1. Aldolase B

(converts Fructose-1-P into either DHAP or Glyceraldehyde)

  1. Hypoglycemia, Jaundice, Cirrhosis, Vomitting
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19
Q

Why does Hereditary Fructose Intolerance result in hypoglycemia?

A

Since there is deficient aldolase B, there will be an accumulation of Fructose-1-Phosphate

Phosphate will become less available and gluconeogenesis and glycogenolysis will become inhibited

20
Q

What sugar does the following tests test for:

1. Urine Dipstick Test

2. Copper Reduction Test

A
  1. Glucose
  2. All sugars (glucose, fructose, galactose)
21
Q

What would be the recommended treatment for a patient with Hereditary Fructose Intolerance?

A

Decreased intake of:

  • fructose
  • sucrose (fructose + sucrose)
22
Q

Galactokinase Deficiency

  1. What enzyme is deficient? What accumulates?
  2. Symptoms
A
  1. Galactokinase —> Accumulation of Galactitol

2.

Galactosemia + Galactosuria

Infantile Cataracts

Failure to track objects

Failure to develop a social smile

23
Q

Classic Galactosemia

  1. Deficient Enzyme and accumulated substance
  2. Symptoms
A

1. Galactose-1-Phosphate Uridyltransferase

(Accumulation of Galactose-1-Phosphate and Galactitol)

  1. Severe Galactosemia

Failure to thrive + intellectual disability

Jaundice + Hepatomegaly

Infantile Cataracts

24
Q

Fill in the blanks

Glucose ——-(?????)—–>

Sorbitol —–(?????)—–>

Fructose

A

Aldose Reductase

Sorbitol Dehydrogenase

25
Q

Why do some cells convert glucose to sorbitol and then to fructose?

How can this be dangerous?

A

It is an alternative method of trapping glucose in the cell

Some cells lack sorbitol dehydrogenase which can result in sorbitol accumulation in the cell which can cause osmotic damage

26
Q

Which types of tissue are most susceptible to osmotic damage due to sorbitol accumulation?

A

Lens —> cataracts

Retina

Kidney

Schwann Cells —> peripheral neuropathy

“Sorbitol LuRKS”

27
Q

What are the Glucogenic amino acids?

A

Methionine

Histidine

Valine

“I met his valentine, she is sweet/glucogenic”

28
Q

What are the ketogenic amino acids?

A

Lysine

Leucine

29
Q

What are the acidic amino acids?

What are the basic amino acids?

A

Acidic:

Aspartic Acid & Glutamic Acid

Basic:

Histidine, Arginine, Lysine

30
Q

Arginase Deficiency

  1. What cant be produced?
  2. How does it present?
A

1.

Urea and Ornithine

(from arginine)

2.

abnormal gait + growth delay

31
Q

Which amino acid transports ammonia (NH3) to the liver so it can enter the urea cycle?

A

Alanine

32
Q

Hyperammonemia

  1. What are the 2 main ways it can occur?
  2. Pathophysiology
A

1.

- Liver disease

- urea cycle enzyme deficiencies

2.

Excess NH3 depletes Glutamate (GABA) which disrupts neurotransmission

33
Q

Hyperammonemia

  1. How does it present?
  2. Treatment
A
  • Asterixis (flapping wrist tremor)
  • Somnolence (desire to sleep)
  • vomitting

-tachypnea

  • cerebral edema

Treatment: limit protein in diet (so there is less a.a. catabolism)

34
Q

Ornithine Transcarbamylase deficiency

  1. What cannot be produced?
  2. What substance builds up?
A

1.

Citruline cannot be produced from ornithine and carbomyl phosphate

2.

Carbomyl phosphate builds up which gets converted to

orotic acid

35
Q

Ornithine Transcarbamylase Deficiency

  1. How does it present?
  2. What is found in blood and urine?
A
  1. Symptoms of hyperammonemia

(asterixis, sleepiness, vomitting, tachypnea, confusion)

  1. Orotic acid

(found in blood and urine)

36
Q

Phenylketonuria (PKU)

  1. What deficiencies result in PKU?
  2. What amino acid becomes essential?
A

1.

  • Phenylalanine Hydoxylase

(converts Phenylalanine to tyrosine)

  • BH4 (cofactor for phenylalanine hydroxylase)
    2. Tyrosine
37
Q

Phenylketonuria (PKU)

  1. How does it present?
  2. Treatment
A

1.

- Musty body odor

- fair/pale complexion

- intellectual disability

- seizures

  1. Increased tyrosine, decreased phenylalanine
38
Q

Maternal PKU

  1. Why does it occur?
  2. How does the infant present?
A
  1. Mother lacks proper dietary therapy during pregnancy
  2. Infant presents with:

- microcephaly

- intellectual disability

- growth retardation

- congenital heart defects

39
Q

Alkaptonuria

  1. What enzyme is deficient?
  2. What substance accumulates?
A
  1. Homogentisate Oxidase

(converts Homogentisic Acid to fumarate which enters TCA)

  1. Homogentisic Acid
40
Q

Alkaptonuria

  1. How does it present?
  2. What are the urinary findings?
A
  1. Bluish/black connective tissue, sclerae and ear cartillage
  2. Urine turns black on prolonged exposure to air
41
Q

Maple Syrup Urine Disease

  1. What enzyme is deficient?
  2. What cofactor is needed for that enzyme?
  3. What proteins cannot be broken down?
A
  1. Branched-chain alpha-ketoacid dehydrogenase
  2. Thiamine (B1)

3. Branched amino acids

(isoleucine, leucine, valine)

“I Love Vermont maple syrup from B1ranched trees“

42
Q

Maple Syrup Urine Disease

  1. Presentation
  2. Treatment
A

1.

Urine smells like maple syrup / burnt sugar

Vomitting

Poor feeding

  1. restrictiction of isoleucine, leucine and valine

Thiamine (B1) supplementation

43
Q

Deficiency of which 2 different enzymes can result in Homocystinuria?

A
  1. Cystathionine Synthase Deficiency

(homocysteine –> cystathione –> cysteine)

  1. Methionine Synthase Deficiency

(homocysteine —> methionine)

44
Q

How does Homocystinuria clasically present?

A

Homocystinuria

Osteoporosis

Marfanoid Habitus

Occular changes (eyes downward and inward)

Cardiovascular effects (thombosis and atherosclerosis)

kYphosis

“HOMOCYsteinuria”

45
Q

What does homocystinuria often result in cardiovascular events such as MIs and strokes?

A

Homocysteine is prothombotic

46
Q

Cystinuria

  1. Where in the kidney does the defect occur?
  2. Which substances cannot be absorbed?
  3. What is the diagnostic test?
A
  1. Proximal Convoluted Tubule (PCT)
  2. Cystine, Ornithine, Lysine, Arginine

“COLA”

  1. Urinary cyanide-nitroprusside test
47
Q

How do cystine stones appear on microscopy? Gross visual appearance?

A

Hexagonal shaped

“SIXtine stone“

Staghorn Calculi

(most commonly in children)

UWorld - Biochemistry (5 decks)

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