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UWorld > Biochem > Flashcards

Biochem Flashcards

1
Q

In what reactions is thiamine a cofactor?

A

1) Pyruvate dehydrogenase (Krebs pyr > acetyl coA)
2) a-ketoglutarate dehydrogenase (TCA and branched chain aa catabolism)
3) Transketolase (HMP shunt pentose > glyceraldehyde 3P)

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2
Q

What is the Rx for thiamine deficiency?

A

Glucose + thiamine infusion

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3
Q

What confirms thiamine deficiency?

A

Increased erythrocyte transketolase post infusion

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4
Q

What is the genetic basis of Fragile X?

A

200 + CGG repeats on FMR1 gene (located on X chromo)

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5
Q

What is the pathogenesis of Fragile X?

A

Increased repeats causes hypermethylation

- Inactivates the gene

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6
Q

What are the symptoms of Fragile X?

A

Mental retardation, messed up face, macroorchidism

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7
Q

What steps must occur for mRNA translation to begin?

A

mRNA binds 16S (part of 30S complex)
50S joins
Translation begins

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8
Q

What is the function of 3-5 exonuclease?

A

Proofreading

proofread the opposite way of synth to check

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9
Q

What is the function of 5-3 exonuclease?

A

Allows replacement of nts in repair

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10
Q

What histones make up the nucleosome core?

A

H2A, H2B, H3, H4

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11
Q

What histone binds DNA between histone cores to facilitate compact packaging?

A

H1

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12
Q

What is the fx of N-acetylglutamate?

A

Activates carbamoyl phosphate synthase, the enzyme required for the first rxn of the UREA CYCLE

CO2 + NH4 > carbamoyl phosphate

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13
Q

What are the components of N-acetylglutamate?

A

Acetyl coA and glutamate

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14
Q

What is heteroplasmy?

A

Mixture of 2 types of genetic material, as in mitochondrial inheritance (randomly distributed in mitosis)

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15
Q

What are 3 mitochondrial diseases with penetrance based on heteroplasmy?

A

LHON: Leber’s Hereditary Optic Neuropathy

MERF: Myoclonic Epilepsy with Ragged Fibers

MELAS: Mito. Encephalomyopathy with Lactic Acidosis and Stroke-like episodes

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16
Q

Lysosomal storage disease:

AR lack of sphingomyelinase
Sphingomyelin buildup in CNS

A

Niemann Pick

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17
Q

Lysosomal storage disease:

Foamy histocytes in liver, spleen skin
"Lipid laden macrophages"
HSM
Cherry red spot on macula
Death by 3 years
A

Niemann Pick

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18
Q

Lysosomal storage disease:

AR lack of hexosaminidase A
Accumulation of GM2 ganglioside

A

Tay Sachs

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19
Q

Lysosomal storage disease:

“Onion skin” lysosomes
Neural degeneration
Cherry red spot on macula
Normal development 2-6 mo, then sxs

A

Tay Sachs

Note: no HSM, unlike NP

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20
Q

Lysosomal storage disease:

AR lack of glucocerebrosidase
Accumulate glucocerebroside

A

Gaucher

Rx: recombinant glucocerebrosidase (this one is treatable!)

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21
Q

Lysosomal storage disease:

Wrinkled paper-like macros
HSM
Anemia
Thrombocytopenia
Bleeding
Osteopenia
Bone pain
Fractures
A

Gaucher

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22
Q

Lysosomal storage disease:

XR lack of alpha galactosidase A
Build up ceramide trihexoside

A

Fabry

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23
Q

Lysosomal storage disease:

Peripheral neuropathy of hands and feet
Angiokeratomas
Cardiovascular/renal disease

A

Fabry

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24
Q

Lysosomal storage disease:

AR lack of arysulfatase A
Build up cerebroside sulfate

A

Metachromatic Luekodystrophy

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25
Q

Lysosomal storage disease:

Central and peripheral demyelination
Ataxia
Dementia

A

Metachromatic Leukodystrophy

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26
Q

Lysosomal storage disease:

AR lack of Galactocerebrosidase
Build up Galctocerebroside, psychosine

A

Krabbe

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27
Q

Lysosomal storage disease:

Peripheral neuropathy
Developmental delay
Optic atrophy
Globoid cells

A

Krabbe

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28
Q

Lysosomal storage disease:

AR lack of alpha-L-iduronidase
Build up heparan sulfate, dermatan sulfate

A

Hurler

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29
Q

Lysosomal storage disease:

Developmental delay
Gargoylism
Airway obstruction
Corneal clouding
HSM
A

Hurler

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30
Q

Lysosomal storage disease:

XR lack of Iduronate sulfatase
Build up heparan sulfate, dermatan sulfate

A

Hunter

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31
Q

Lysosomal storage disease:

Mild Hurler + aggressive behavior
No corneal clouding

A

Hunter

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32
Q

What 2 lysosomal storage diseases are XR?

A

Fabry and Hunter

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33
Q

What is impaired in peroxisomal diseases?

A

Cannot break to VLCFA and some branched chain FA

Build up Phytanic Acid

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34
Q

What is the defect in Zellweger syndrome?

A

Peroxisomal disease

Cannot make myelin

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35
Q

What is the defect in Refsum sundrome?

A

Defect in peroxisomal a-oxidation

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36
Q

What is the cofactor in decarboxylation and transamination reactions?

A

B6

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37
Q

What is the rate limiting step in the Urea Cycle?

A

Carbamoyl phosphate synthase

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38
Q

What is the most common Urea Cycle defect?

A

Ornithine transcarbamoylase

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39
Q

Which bacterial DNA polymerase has 5-3 exonuclease?

A

DNA Pol I

- Used to excise RNA primer

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40
Q

If an amino acid’s pKa > pH, then the amino acid exists in the (protonated/uprotonated) form?

A

Protonated

It’s above it’s comfort zone, so it takes an H no prob

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41
Q

Carnitine deficiency causes:

A

Inability to move acyl coA into the mitochondria for FA oxidation

Myoglobinemia
Weakness post exercise
Increased muscle TGs
Hypoketonimia

42
Q

Acyl coA dehydrogenase deficiency causes:

A

Impaired beta-oxidation of FA

Hypoglycemia
Hypoketonemia

43
Q

Precursor to FMN and FAD

A

Riboflavin

44
Q

Coenzyme for succinyl dehydrogenase (succinate > fumarate rxn)

A

FAD, from B2/riboflavin

45
Q

Where does VLCFA oxidation occur?

A

Peroxisomes (not mito!)

46
Q

What is the role of cytoplasmicP bodies?

A

mRNA regulation and turnover

47
Q

If free energy of products is less than substrates, G is negative and rxn favors:

A

products

48
Q

If free energy of products is greater than substrates, G is positive and rxn favors:

A

substrates

49
Q

What is the GTP producing step of the Kreb’s Cycle?

A

Succinyl-coA to Succinate

This is substrate level phosphorylation, not ox phos

50
Q

What vitamin is contraidincated in pregnancy?

A

Vitamin A –teratogen!

51
Q

What are the effects of Vitamin A on pregnancy?

A 
Microcephaly
Cardiac abnormalities
Early epiphyseal closure
Growth retardation
Spontaneous abortion
52
Q

What is the major aa that transfers nitrogen to the liver for disposal?

A

Alanine

aLa to the Liver

53
Q

Amino groups transferred to a-ketoglutarate form:

A

Glutamate

54
Q

Glutamate processed in the liver forms:

A

Urea, which is then disposed

55
Q

Impact of Fructose 2,6 Bisphosphonate on glycolysis:

A

Activates glycolysis by increasing Phosphofructokinase-1

Inhibits gluconeogenesis by inhibiting Fructose 1, 6 Bis

56
Q

What determines resting membrane potential?

A

The ions most permeable to the membrane

- Generally K+ and Na+ > - 70 mV

57
Q

Biotin is a cofactor to what kind of rxns?

A

Carboxylation

Tin race Car with number 7 painted on the side

58
Q

Biotin is a cofactor what specific rxns:

A
  1. Acetyl coA carboxylase
  2. Pyruvate carboxylase (pyr > oxaloacetate)
  3. Propionyl carboxylase
  4. b-methacronoyl carboxylase

All involved in carb and lipid metabolism

59
Q

Pyridoxine is a cofactor for what kinds of rxns?

A

Transamination and DEcarboxylation rxns with aas

60
Q

Why does B12 deficiency produce MMA?

A

B12 is cofactor in isomerization rxn that transforms MM coA to succinyl coA (before entering Kreb’s Cycle)

61
Q

Small circular DNA in eukaryotic cells that is maternally derived

A

Mitochondrial DNA

62
Q

Function of glycerol kinase:

A

Converts glycerol to G3P in the liver

63
Q

Uses of glycerol by the liver:

A
  1. Triacylglycerol synth
  2. Gluconeogenesis
  3. Intermidate in glycolysis
64
Q

What deficiency causes propionyl acidemia?

A

Propionyl coA carboxylase

Propionyl coA > MM coA

65
Q

What is propionyl derived from?

A

Metabolism of branched chain aas, odd numbered FAs, and cholesterol side chains

66
Q

What enzymes are produced in the SER?

A

Steroid and phospholipid biosynthesis

All steroid producting cells (adrenals, gonads, liver) contain abundant SER

67
Q

What enzymes are produced in the RER?

A

Secretory, lysosomal, and membrane proteins

68
Q

What is the fx of Vitamin E?

A

Vitamin E is an antioxidant

Lack = increased susceptibility of neuron and erythrocyte membranes to oxidative stress, increased FA oxidation

69
Q

What are the CNS sx of Vitamin E deficiency?

A

Loss of vibration and proprioception due to dorsal column and spinocerebellar tract = ataxia

70
Q

What enzyme is missing in Classic Galactosemia?

A

Galactose uridyl transferase (FAB GUT)

71
Q

Short term presentation of Galactosemia

A

Vomiting after breast feeding, lethargy

Decreased glucose in blood after mlik

72
Q

Long term presentation of Galactosemia

A

Galactitol in lens and liver, permanent damage

73
Q

What enzyme is missing in Alkaptonuria?

A

Homogentisate Oxidase

74
Q

What rxn does homogentisate oxidase perform?

A

Tyr > fumarate

75
Q

Where does homogentisic acid accumulate?

A

Urine, tendons/cartilage, ears, nose, cheeks > black pigment

76
Q

What is pantothenic acid?

A

B5 = coA

77
Q

What does RNA pol I make?

A

18S, 5.8S, ad 28S ribosomal units

78
Q

What does RNA pol II make?

A

mRNA (proteins)
snRNA (splicing)
micro RNA (silencing)

79
Q

What does RNA pol III make?

A

tRNA (link codons to aas)

5S ribosomal unit (component of 60S)

80
Q

What is palmitoylation?

A

Anchoring of GPCRs to plasma membrane

Attaches FA of the GPCR to a cysteine of the PM

81
Q

N-terminal hydrophobic residues serve as:

A

Signal peptides: stop translation in the cyto and target to RER

82
Q

What is the x intercept on a Lineweaver Burke plot?

A

1/Km

83
Q

What is the y intercept on a Lineweaver Burke plot?

A

I/Vmax

84
Q

DNA methylation does what to transcription?

A

Silences

85
Q

Area of DNA rich in CG repeats means it’s…

A

methylated, and silenced.

86
Q

What is the cause of cell swelling after injury?

A

Buildup of Na because of lack of Na/K ATPase (no ATP)

87
Q

What are the sx of abetalipoproteinemia?

Fat Betting Pirate says AAR

A
  1. Fat buildup
  2. a-Beta
  3. Pigmented retinopathy (can’t see in low light)
  4. Acanthocytes
  5. Ataxia
  6. Retardation
88
Q

Rx for methanol poisoning:

A

Ethanol or Fomepizole

89
Q

What is the MOA of ethanol or fomepizole in methanol poisoning?

A

Inhibit alcohol dehydrogenase and prevent buildup of formaldyehyde and formic acid

90
Q

What happens in a lack of myeloperoxidase?

A

Less respiratory burst to kill bacteria

Less hydroxyl halide (HOCl-) from H2O2

91
Q

Muscle weakness, lack of proprioception, and retinal damage are signs of what vitamin def?

A

E

92
Q

What are secondary structures of proteins, and what type of bond is responsible?

A

alpha helix, beta sheet, H bonds

93
Q

What bonds are responsible for the tertiary structures of proteins?

A

Ionic bonds

94
Q

What is the order of proteins at work in base excision repair?

A
  1. Glycosylase
  2. Endonuclease
  3. Lyase
  4. Polymerase
  5. Ligase
95
Q

What types of corrections does base excision repair make?

A

Corrects single base DNA defects induced spontaneously or by exogenous chemicals

96
Q

Megalobastic anemia
Neuro abnormalities
Growth retardation
Orotic acid in urine

Diagnosis?

A

Orotic aciduria

97
Q

What is the disorder underlying orotic aciduria?

A

Pyrimidine metabolism

98
Q

What is the Rx for orotic aciduria?

A

Uridine, to feedback inhibit carbamoyl phosphate synthase II

99
Q

What are TATA and CAAT boxes?

A

Promoters of transcription in eukaryotic cells
25-80 bases upstream of start site
Serve as binding site for RNA pol II, aka “transcription initiation sites”

100
Q

What are 3 DNA binding protein domains?

A

Leucine Zipper
Helix-loop-helix
Zinc Finger

101
Q

Where in the cell does purine/pyrimidine synth take place?

A

Cytosol

102
Q

What are some hydrophobic aa?

A

Val, ala, isoleucine, met, phe

  • These are often transmembrane domains of proteins

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