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Step 1 review cards > Biochemistry: Metabolism > Flashcards

Biochemistry: Metabolism Flashcards

1
Q

Why is fomepizole used as antidote for ODing on methanol or ethylene glycol?

A

Blocks alcohol dehydrogenase enzyme from converting ethanol -> acetaldehyde
- doesnt show symptoms if in ethanol stage and is easily excreted

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2
Q

General ethical metabolism cycle

A

Ethanol -> acetaldehyde -> acetate

1) ethanol -> acetaldehyde requires alcohol dehydrogenase enzyme activity
- catalase, NAD+ and CYP2E1 are cofactors in this step, generating water, NADH and ROS in the process
- occurs in cytosol

2) acetaldehyde-> acetate requires acetaldehyde dehydrogenase enzyme activity
- NAD+ is a cofactor in this step, generating NADH in th eprocesds
- occurs in mitochondria

  • acetaldehyde is the product that actually induces alcoholic symptoms*
  • works under zero-order kinetics*
  • NAD+ is rate limiting*
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3
Q

Why is Disulfiram used to discourage alcohol consumption in alcoholics?

A

It blocks acetaldehyde dehydrogenase activity, which leads to a build up of acetaldehyde.

Acetaldehyde produces hangover/alcoholic symptoms in mass, so it becomes uncomfortable to patients.

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4
Q

What are the 4 main consequences of ethanol metabolism in the body?

A
  • ALL due to increased NADH/NAD+ ratio (less NAD+)*

1) lactic acidosis
- increased pyruvate production since TCA is limited

2) fasting hypoglycemia
- decreased gluconeogenesis due to increased malate from OAA production.

3) keto acidosis
- increased ketogenesis and decreased TCA cycle acetyl-CoA usage

4) hepato-steatosis
- increased production of glycerol-3-P

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5
Q

What metabolism is done in mitochondria

A

FA-oxidation (beta-oxidation)

Acetyl-CoA production

TCA cycle

Oxidative phosphorylation

Ketogenesis

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6
Q

What metabolism is done in the Cytoplasm

A

Glycolysis

HMP shunt

Cholesterol synthesis and metabolism

protein production

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7
Q

What metabolism is conducted in both the mitochondria AND the cytosol?

A

Heme synthesis

Urea cycle

Gluconeogenesis

“Takes two to HUG”

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8
Q

What is the function of a kinase

A

Transfers a phosphate group from ATP or NADHP to a substrate

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9
Q

What is the function of a phosphorylase?

A

Adds inorganic phosphate onto a substrate without the use of ATP/NADPH

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10
Q

What is the function of a Dehydrogenase

A

Catalzyes oxidation:reduction reactions

- takes adds or removes hydrogen ions

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11
Q

What is the function of a Hydroxylase

A

Adds hydroxyl (OH) groups to a substrate

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12
Q

What is the function of a carboxylase?

A

Transfers (CO2) groups from a substrate to another

- uses cofactor biotin

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13
Q

What is the function of a mutase?

A

Relocates a functional group on a substrate (but does not remove or transfer it)

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14
Q

What is the function of a synthase/synthetase?

A

Bonds two molecules together using ATP, acetyl CoA or sugar

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15
Q

What is the rate determining enzyme and regulator molecules for glycolysis?

A

Rate determine enzyme: PFK-1

positive regulators:

  • AMP
  • fructose 2,6 BP

Negative regulators:

  • ATP
  • citrate

(negative feedback mechanism)

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16
Q

What is the rate determining enzyme and regulator molecules for gluconeogenesis?

A

Rate determining enzyme:
- Fructose 1,6 BP

Negative regulators

  • AMP
  • fructose 2,6 BP

(Is turned off in the presence of glycolysis, and turned on when glycolysis is turned off)

17
Q

What is the rate determining enzyme and regulator molecules for TCA cycle?

A

Rate determining enzyme:
- isocitrate dehydrogenase

Positive regulators:
- ADP

Negative regulators

  • ATP
  • NADH

(Negative feedback mechanism)

18
Q

What is the rate determining enzyme and regulator molecules for glycogenesis?

A

Rate determining enzyme:
-glycogen synthase

Positive regulators:

  • glucose-6P
  • insulin
  • cortisol

Negative regulators:

  • epinephrine
  • glucagon

(only turned off when you need glucose or are diabetic without insulin)

19
Q

What is the rate determining enzyme and regulator molecules for Glycogenolysis?

A

Rate determining enzyme:
- glycogen phosphorylase

Positive regulators

  • epinephrine
  • glucagon
  • AMP

Negative regulators:

  • glucose 6P
  • insulin
  • ATP

(Turned off when resting)

20
Q

What is the rate determining enzyme and regulator molecules for HMP shunt?

A

Rate determining enzyme:
- glucose 6P dehydrogenase (G6PD)

Positive regulators
- NADP

Negative regulators
- NADPH

(Turned on when you need excess energy and kinase activity)

21
Q

What is the rate determining enzyme and regulator molecules for ketogenesis?

A

Rate determining enzyme:

- HMG-CoA synthase

22
Q

What is the rate determining enzyme and regulator molecules for cholesterol synthesis?

A

Rate limiting enzyme:
- HMG-CoA reductase

Positive regulators:

  • insulin
  • thyroxine
  • estrogen

Negative regulators:

  • glucagon
  • cholesterol
23
Q

Pyruvate dehydrogenase deficiency

A

X-linked recessive disorder that causes a mutation in the E1-alpha gene.

  • Results in low/null pyruvate dehydrogenase activity and decreased production of acetyl-CoA
  • causes TCA cycle impairment and pyruvate accumulation

Pyruvate accumulation leads to increased anaerobic respiration and transformation of pyruvate to lactate and alanine
- results in lactic acidosis

Can be severe ( presents at birth with congenital brain malformations) or moderate (presents in infancy and childhood)

Symptoms/signs:

  • microcephaly
  • blindness
  • mental retardation
    • Leigh syndrome (gray matter degeneration with capillary proliferation)
  • *Cheyne-stokes breathing patterns and dyspnea (results from lactic acidosis)
  • hypotonia
  • ataxia
  • progressive encephalopathy
  • abnormal eye movements
  • increased lactate, pyruvate and alanine levels in serum/urine
  • MRI shows cerebral atrophy, corpus callosum absence and medullary pyramid absence

Treatment:

  • thiamine, carnitine and lipoid acid supplementation
  • keto diet
  • dicholoracetate (synthetic Pyruvate dehydrogenase)
24
Q

What muscle biopsy sign is common in most mtDNA disorders?

A

Ragged-red fibers throughout the myocytes

Step 1 review cards (24 decks)

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