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UWorld > Biochemistry > Flashcards

Biochemistry Flashcards

1
Q

Three enzymes that use thiamine as a cofactor

A

Pyruvate dehydrogenase
alpha-ketoglutarate dehydrogenase
Transketolase

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2
Q

What is the role of a glycosylase in base excision repair?

A

Recognizes and cleaves abnormal bases

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3
Q

What is the role of a lyase in base excision repair?

A

Completes extraction of the AP site (following endonuclease enzymatic chewing)

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4
Q

What are the fates of pyruvate in the presence of O2 vs with insufficient oxygen

A

O2: pyruvate dehydrogenase converts pyruvate to acetyl-CoA

Limited O2: lactate dehydrogenase converts pyruvate to lactate

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5
Q

Are eukaryotic or prokaryotic mRNA polycistronic?

A

Prokaryotic mRNA is polycistronic

Eukaryotic mRNA is rarely polycistronic

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6
Q

What is the role of ornithine?

A

Ornithine combines with carbamoyl phosphate to become citrulline- part of the urea cycle to eliminate urea

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7
Q

What provides the rubber-like properties of elastin?

A

Extensive cross-linking between elastin monomers, which is facilitated by lysyl oxidase (between lysine residues)

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8
Q

Where does early onset emphysema first appear in people with alpha-1-antitrypsin deficiencies?

A

Early onset, lower-lobe predominant emphysema

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9
Q

What causes the formation of brown stones in the gallbladder?

A

Brown pigment stones arise secondary to bacterial or helminthic infections which leads to the release of beta-glucoronidase.

Beta-glucuronidase hydrolyzes bilirubin glucuronides and increases the amount of unconjugated bilirubin.

The liver fluke chlornochis sinensis cause also cause this

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10
Q

Which is the enzyme responsible for Pompe’s disease?

A

Acid maltase/alpha-glucosidase in lysosomes

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11
Q

High levels of neutral amino acids is indicative of which disease?

A

Hartnup disease

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12
Q

What are the findings of hartnup disease?

A

Impaired transport of neutral amino acids in the small intestine and proximal tubule of the kidney–> pellegara like skin eruptions, and cerebellar ataxia, which occurs as a results of niacin deficiency (derived from tryptophan)

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13
Q

How can you treat Hartnup disease

A

High protein diet (since many amino acids aren’t being absorbed) and supplimentary niacin (derived from tryptophan, which isn’t being absorbed properly)

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14
Q

Which substance directly stimulates the conversion of pyruvate to phosphoenolpyruvate in gluconeogenesis?

A

Acetyl CoA

Levels are high in the presence of fatty acid oxidation

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15
Q

How does pyruvate kinase deficiency lead to splenomegaly and anemia?

A

RBCs don’t have any mitochondria and rely of glycolysis for ATP production

Low pyruvate –> insufficient membrane integrity and inability to maintain erythrocyte structure.

RBCs are eaten up in the red pulp –> red pulp hyperplasia

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16
Q

Pyridoxine (B6) is a cofactor in which type of reactions?

A

Transamination and decarboxylation of amino acids

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17
Q

How does decreased bile acid synthesis lead to cholesterol stones?

A

Bile acids make cholesterol more soluble.

Low bile –> favors cholesterol gallstone formation

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18
Q

What is alkaptonuria?

A

Relatively benign childhood disorder –> severe arthritis as an adult

Deficiency of homogentisic acid dioxygenase

Accumulation of homogentisic acid –> blue/black deposits, urine turns black when exposed to air

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19
Q

Failure of what process leads to ehlers danlos?

A

Failure of cleavage of terminal propeptides in the extracellular space

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20
Q

Which are the two exclusively ketogenic amino acids?

A

Lysine and Leucine.

Use in someone with pyruvate dehydrogenase deficiency to avoid lactate build up

21
Q

Babies with maple syrup urine disease may improve with which suppliment?

A

Thiamine

22
Q

What is the MOA leading to maple syrup urine disease?

A

Inability to break down branched chain amino acids

23
Q

What are the symptoms of wet beriberi?

A

symmetrical peripheral neuropathy

Wet beriberi includes cardiac involvements

24
Q

Musty body odor= which inborn error of metabolism?

A

PKU

Phenylalanine is not converted to tyrosine

25
Q

Which amino acid is the precursor for melanin?

A

Tyrosine

26
Q

What is the enzyme phenylethanolamine-N-methyltransferase responsible for?

A

Conversion of NE to Epi

27
Q

Starting from tyrosine, get to epinephrine

A

tyrosine –> dopa –> Dopamine –> NE –> Epi

also, phenylalanine –> tryosine

28
Q

Where in the cell does heme synthesis occur?

A

Partly in the cytoplasm, partly in the mitochondria

29
Q

FAD acts as an electron acceptor for which enzyme in the TCA cycle?

A

Succinate dehydrogenase

30
Q

Name the two methods by which the lac operon is regulated

A

Positive regulation: cAMP-Cap binds upstream of the promoter region

Negative regulation: the repressor binds to the operator

31
Q

Name the inborn error of metabolism that causes urine to turn black overnight?

A

Alkaptonuria

32
Q

What is the defective enzyme in alkaptonuria? What conversion is inhibited?

A

Homogentisic acid dioxygenase is deficient

Impairs the conversion of tyrosine –> –> –> fumarate

33
Q

Which monosaccharide enters glycolysis after the rate limiting step (bypasses PFK-1) and therefore is most rapidly metabolized?

A

Fructose

34
Q

How does fructose enter glycolysis?

A

Fructose is converted to fructose-1-phosphate by fructokinase.

Fructose-1-phosphate is converted to DHAP and glyceraldehyde by aldolase B

Glyceraldehyde is converted to glyceraldehyde 3 phosphate by triokinase which enters the glycolytic pathway

35
Q

What type of poisoning leads to cholinergic excess?

A

Poisoning with organophosphates (used in agriculture). They act as cholinesterase inhibitors

Treat with atropine and 2PAM

36
Q

Why does septic shock cause lactic acidosis?

A

Septic shock leads to poor tissue perfusion and therefore oxidative phosphorylation is shut down. Anaerobic metabolism occurs.

37
Q

What are “dependent locations” in the lungs, as seen in aspiration pneumonia?

A

The posterior segments of upper lobes and superior segments of lower lobes are dependent and commonly affected by aspiration pneumonia. They are dependent on the patient laying supine.

38
Q

What is the treatment for cyanide poisoning? How does it work?

A

Inhaled amyl nitrite.

The nitrites oxidize the iron in Hb to methemoglobin (3+), which has a higher affinity for CN- . CN- binds to the ferric iron more avidly than the mitochondrial enzymes —> diminishes the toxic effect

39
Q

Where are cytoplasmic P bodies located?

A

Cytoplasm

They are responsible for mRNA translation regulation and mRNA degradation

40
Q

What two things are produced by the pentose phosphate pathway?

A

NADPH- for use in reductive reactions

Ribose-5-phosphate- a precursor for the synthesis of nucleotides

41
Q

What enzyme converts alpha-ketoglutarate to succinyl-CoA? Why is this enzyme particularly susceptible to inhibition in an alcoholic?

A

alpha-ketoglutarate dehydrogenase

This enzyme requires both NAD+ and thiamine for the reaction to proceed.

Ethanol metabolism increases the NADH/NAD+ ratio, and alcoholics are thiamine deficient

42
Q

Vitamin B12 is a cofactor for which two enzymes?

A

methylmalonyl-CoA mutase- converts methylmalonyl-CoA to succinyl-CoA

Methionine Synthase- converts homocysteine and folic acid to methionine

43
Q

Explain the pathology behind maturity-onset diabetes of the young

A

Glucokinase deficiency

Functions as the glucose sensor in beta cells by varying the rate of entry into the glycolytic pathway based on blood glucose levels.

Deficiency –> less ATP and lower insulin secretion

44
Q

Erythrocytosis is a sequelae of what type of shift in the O2 saturation curve?

A

Left shift–

Causes lower O2 delivery to the peripheral tissues

45
Q

Deficiency in uridine monophosphate (UMP) synthase leads to which disease?

A

Orotic aciduria

Supplement with uridine

46
Q

What are the cardiovascular sequelae of homocystinuria? Why?

A

Hypercoagulability and thromboembolic events. Homocysteine is prothrombotic

47
Q

How is methionine connected to cysteine levels?

A

If a patient has homocystinuria, they most commonly have a defect in cynthathinoe synthase. This prevents the conversion of homocysteine to cysteine, and will result in increased methionine levels in the blood as well, as homocysteine is converted to methionine

48
Q

Which DNA polymerase possesses 3’-5’ exonuclease activity?

A

All DNA polymerases. It enables them to identify and remove mismatched bases – proofreading capability

Only DNA polymerase III also has 5’-3’ exonuclease activity which allows them to remove the RNA primer and replace it with DNA

UWorld (4 decks)

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