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USMLE REVIEW > Biochem > Flashcards

Biochem Flashcards

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USMLE® Step 1 flashcards
1
Q

Deamination of cytosine gives you what?

A

Uracil (found in RNA)

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2
Q

How many H bonds between C and G?

A

3

*Higher content of C and G have a higher melting temperature

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3
Q

What is need to make purines? (Adenine and Guanine)

A

“Cats PURRRR until the GAG and Cough on Fur balls”

Glycine
Aspartate
Glutamine

+ tetrahydrofolate (Folic Acid)
+ CO2

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4
Q

4 things needed to make pyrimidines?

A

Aspartate

Carbamoyl phosphate synthetase 2
CO2
Glutamine
ATP

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5
Q

What is the rate limiting step of pyrimidine synthesis?

A

Carbamoyl phosphate synthetase 2

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6
Q

High Orotic acid

High ammonia

A

Ornithine transcarbamylase deficiency

*Disruption of urea cycle

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7
Q

High Orotic acid

NORMAL ammonia

A

Orotic aciduria = deficiency in UMP synthase

Can’t make pyrimidines!

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8
Q

Megaloblastic anemia that does NOT correct when giving B12 or folic acid supplements?

A

Orotic Acid Urea = deficiency in UMP synthase

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9
Q

A boy with self mutilating behavior, intellectual disability, uncontrolled spastic muscles and gout

A

Lesch-Nyhan
HGPRT deficiency
Can’t recycle purines

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10
Q

Rate limiting step in purine synthesis

A

Guanine PRPP amidotransferase

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11
Q

Medication that inhibits ribonucleotide reductase

A

Hydroxyurea

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12
Q

Medication that inhibits dihydrofolate reductase

A

Trimethoprime

Methotrexate

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13
Q

Medication that inhibits thymidylate synthase

A

5-FU

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14
Q

Medication that inhibits inosine monophosphate dehydrogenase

A

Mycophenolate

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15
Q

Medication that inhibitis PRPP amidotransferase

A

6-mercaptopure/ Azothioprine

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16
Q

What accounts for positive charge on histones, and neg charge on DNA?

A

Phosphates in DNA

Histones = lysine & arginine

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17
Q

Alpha DNA pol

A

Lagging strand

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18
Q

Delta DNA pol

A

Leading strand

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19
Q

Beta DNA pol

A

Base excision repair

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20
Q

Gamma DNA pol

A

Mitochondrial DNA

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21
Q

UV radiation damaged DNA

A

Thymine dimers

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22
Q

Mutation found in sickle cell disease

A

Missense mutation = nucleotide substitution resulting in changed amino acid

Significantly changes structural/functional properties

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23
Q

Mutation found in duchenne muscular dystrophy

A

Frameshift mutation

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24
Q

Defective in HNPCC

A

DNA mismatch repair enzyems

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25
Q

DNA pol that synthesizes RNA primer

A

Alpha

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26
Q

3 Stop CODONS

A

UGA
UAA
UAG

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27
Q

Where are ribosomes made?

A

Subunits made in the nucleus and then transported to the cytoplasm

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28
Q

Most abundant type of RNA in body?

A

rRNA (80%)

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29
Q

Aminoacyl tRNA synthetase

A

Enzyme that matches amino acids to tRNA

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30
Q

Anticipation

A

disease onset is younger and younger through each generation

**Huntingtons and trinucleotide repeat dieseaes

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31
Q

Southern Blot
Northern Blot
Western Blot

A 
Western = protein, w/ Ab probe
Southern = DNA w/ DNA probe
Northern = RNA w/ DNA probe
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32
Q

Direct ELISA

A

Testing for antigen in serum

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33
Q

Indirect ELISA

A

Testing for antibody in serum

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34
Q

Diagnosing chromosomal abnormailites

A

Karyotyping

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35
Q

Hardy Weinberg

A

p + q = 1

p^2 + 2pq + q^2 = 1

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36
Q

Enzyme responsible for trapping glucose in cells?

A

Hexokinase
Glucokinase

Glucose –> glucose 6 phosphate

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37
Q

Differences between Hexokinase and glucokinase?

A

Glucokinase =

  • found in liver
  • induced by insulin
  • high Km
  • High Vmax

Hexokinase =

  • Low Km (high affinity)
  • Low Vmax (low capacity)
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38
Q

Rate limiter of glycolysis?

A

Phosphofructokinase 1

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39
Q

2 molecules that stimulate phosphofructokinase 1?

A

AMP (low energy)

fructose 2,6 bisphosphate

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40
Q

2 molecules that inhibit phosphofructokinase 1?

A

ATP (high energy)

Citrate (substrate of TCA cycle, indicates overwhelming TCA cycle)

41
Q

How does insulin help regulate glycolysis?

A

Stimulates PFK-2 in the fed state

Produce more Fructose 2,6 BP

Stimulates PFK1

42
Q

How does glucagon help regulate glycolysis?

A

Stimulates fructosebisphosphatase 2

Converts Fructose 2,6 BP back to fructose-6P

43
Q

What is the clinical consequence of a glycolytic enzyme deficiency?

A

Hemolytic anemia

RBC must do anerobic metabolism because they do not have mitochondria… Can’t do glycolysis, no ATP, Na+/K+ pump not working, influx of water, swelling, bursting

44
Q

Irreversible enzymes involved in gluconeogenesis

A

Pyruvate carboxylase
PEP-CK
Fructose 1,6 bisphosphatase
Glucose-6-phosphatase

45
Q

Rate limiting step in gluconeogenesis?

A

Fructose 1,6 bisphosphatase

46
Q

Glycogen phosphorylase deficiency

A

McArdle

Type 4

47
Q

Glucose-6-phosphatase Deficiency

A

Von Gierke

Type 1

48
Q

Lactic acidosis
Hyperlipidemia
Hyperuricemia

A

Von Gierke

Type 1

49
Q

alpha-1,6-glucosidase deficiency

A

= debranching enzyme
Cori Disease
Type 3

50
Q

alpha-1,4-glucosidase deficiency

A

Pompe Disease

Type 2

51
Q

Cardiomegaly in a glycogen storage disease

A

Pompe Disease

Type 2

52
Q

Glycogen storage disease with diaphragm weakness leading to respiratory failure

A

Adult type pompe disease

Type 2

53
Q

Painful muscle cramps

Myoglobinuria with strenuous exercise

A

McArdle Disease

Type 4

54
Q

Glycogen storage disease with severe hepatosplenomegaly

Enlarged kidneys

A

Von Gierke

Type 1

55
Q

Cofactors required for pyruvate dehydrogenase?

A

“TLC For Nobody”

Thiamine pyrophosphate
Lipoic Acid
Coenzyme A
FAD
NAD
56
Q

Vomiting
Rice water stools
Garlic Breath

A

Arsenic

Which inhibits lipoic acid (a cofactor for pyruvate dehydrogenase) = acquired pyruvate dehydroenase deficiency

57
Q

Substances that increase permeability of inner mito membrane, decreasing ATP synthesis but increasing heat generation??

A

2,4 Dinitrophenol
Aspirin
Thermogenin

58
Q

What 4 things inhibit complex 4 of the electron transport chain?

A

Cyanide
N3-
CO
H2S

59
Q

Major regulatory enzymes of TCA cycle

A

CItrate Synthase = starts TCA cycle

Isocitrate dehydrogenase = rate limiting

alpha ketoglutarate dehydrogenase = heavily regulated due to cofactors (same as pyruvate dehydrogenase)

60
Q

2 main nitrogen transporters in the blood?

A

Alanine

Glutamine

61
Q 
"FLAMES"
Fatty Liver
Anemia
Malnutrition
Edema
Skin Lesions
A

Kwashiorkor Disease = protein deficiency

62
Q

Rate-limiting enzyme in Fatty Acid Synthesis?

A

Acetyl-CoA carboxylase

63
Q

Rate-limiting enzyme in Fatty acid degradation?

A

Carnitine Acyltransferase 1

64
Q

Dark connective tissue
Brown pigmented sclerae
Urine turns black on prolonged exposure to air
Debilitating arthralgias

A

Alkptonuria

Congenital deficiency of homogentistate oxidase (degrative pathway of tyrosine to fumarate)

65
Q 
Intellectual disability
Growth retardation
Seizures
Fair skin
Eczema
Musty body odor
A

PKU

Deficiency of phenylalanine hydroxylase

High phenylalanine gets converted to phenylketone

Tyrosine becomes essential

66
Q

Two ways to have Albinism?

A

Defective tyrosinase activity or defective tyrosine transport

NORMAL NUMBER OF MELANOCYTES

**Vitiligo is autoimmune destruction of melanocytes

67
Q 
Intellectual disability
Tall Stature
Osteoporosis
Kyphosis
Atherosclerosis
Subluxation of the lens (downward and inward)
A

Homocystinuria

NOTE: Marfan syndrome has subluxation of the lens UPWARD

68
Q

Urine smells sweet….. blocked degradation of what amino acids?

A

Maple Syrup Urine Disease

alpha-ketoacid dehydrogenase deficiency

Blocked degradation of branched amino acids
Isoleucine, Leucine, Valine

“I Love Vermont maples syrup from maples trees with branches”

69
Q

Defective alpha ketoacid dehydrogenase

A

Maple syrup urine disease

70
Q

Household fire
Bright red vessels in eyes
Smell of bitter almonds on breath

A

Cyanide Poisoning
Inhibits Complex 4 in electron transport chain (cellular respiration)

Bright red vessels due to absent tissue oxygen extraction

71
Q

What is a palindromic sequence in DNA?

A

Reading 5’-3’ on one strand matches reading the complimentary strand 5’ to 3 ‘ in the other direction

*TGTACA

72
Q

What is the only DNA polymerase with 5’ to 3’ exonuclease activity (removal of RNA primers)

A

DNA pol I

73
Q

Enzyme deficient in Fructose intolerance

A

Aldolase B = Fructose 1 phosphate accumulates causing a decrease in phosphate available for glycogenolysis and gluconeogeneis

Symptoms present after eating fruit, juice, honey

Hypoglycemia, jaundice, cirrhosis, vomiting

74
Q

Enzyme deficient in essential fructosuria

A

Fructokinase = benign, asymptomatic

Fructose appears in blood and urine

75
Q 
FTT
Jaundice
Hepatomegaly
Infantile cataracts
Intellecutal disability
A

Classic Galactosemia

Deficient Galactose-6-uridyltransferase

Build up of products (Galactitiol which accumulates in lens)

76
Q

HYPOKETOTIC hypoglycemia would indicate what?

A

Defect in fatty acid B-oxidation in the mitochondria

77
Q

Most common defect causing impaired B-oxidation?

A

acyl-CoA dehydrogenase

78
Q

Mutations at different loci can produce a similar pheontype (Albinism)

A

Locus heterogeneity

79
Q

Different mutations in the same locus produce the same phenotypes (B-thalassemia)

A

Allelic heterogeneity

80
Q 
hyperphagia
Obseity
Intellectual disability
Hypogonadism
Hypotonia
A

Prader-Willi Syndrome

Maternal silent/imprinted
Paternal gets mutated or deleted

81
Q

Inappropriate laughter
Seizures
Ataxia
Severe intellectual disability

A

AngleMan Syndrome

Paternal silent/imprinted
Maternal gets mutated or deleted

82
Q

Common associations with Down SYndrome

A 
GI:
Duodenal Atresia
Hirschprung
Annular Pancreas
Celiacs

ASD
ALL and AML
Alzheimer (APP is on chromosome 21)

83
Q

Decreased AFP
Increased B-hCG
Decreased estriol
Increased Inhibin A

Increased nuchal transleuceny

A

Down SYndrome

84
Q

Describe G6PD deficiency and what you see on a peripheral smear

A

G6PD deficiency = can’t produce NADPH in HMP Shunt

No NADPH means we cannot reduce glutiathione

No reduced glutiothione means we can’t detoxify H2O2 in RBCs

H2O2 oxidizes hemoglobin - which precipitates as Heinz bodies

Heinz bodies eaten by MACs in the spleen to produce bite cells

85
Q

What does decreased NAPDH in RBCs produce?

A

Hemolytic anemia due to poor RBC defense against oxidizing agents

Fava beans
Sulfonamides
Primaquine
Anti TB durgs

86
Q

Most common human enzyme deficiency?

A

G6PD deficiency

More common in blacks - refers malarial resistance

87
Q

Fructose appears in blood and urine

Otherwise a benign, asymptomatic condition

A

Essential Fructosuria

Deficiecny = Fructokinase

Normally takes fructose to fructose1-P

88
Q

Hypoglycemia
Jaundice
Cirrhosis
Vomiting

After consuming fruit, juice, or honey

A

Fructose Intolerance

Deficiency = Aldolase B

Fructose-1-P cannot get broken down
P gets trapped there, less available

Need phosphate to do glycogenolysis and gluconeogenesis

89
Q 
FFT
Jaunidice
Hepatomegaly
INFANTILE CATARACTS
intellectual disability
A

Classic Galactosemia

Deficiency of galactose-1-phosphate uridyltransferase

Causes accumulation of toxic substances

90
Q

How does high glucose or galactose cause cataracts?

A

Glucose –> sorbitol by Aldolase reductase
Glacatose –> Galacticol by Aldolase reductase

Sorbitol/Galacticol converted back by Sorbital dehydrogenase

If tissue lacks sorbital dehydrogenase, can get accumulation of Galacticol/Sorbitol and cause osmotic damage

91
Q

What tissues ONLY have aldolase reductase and are at risk for osmotic damage if high glucose or galactose?

A

Schwann cells
Retina
Kidneys
Lens

92
Q

Dark connective tissue
Brown pigements sclerae
Urine turns black on prolonged exposure to air
Debilitating Arthralgias

A

Alkaptonuria

Deficiency = Homongentisate Oxidase

Can’t degrade tyrosine, homogentisic acid accumulates in tissues

Autosomal recessive

93
Q 
Increased homocysteine in urine
Intellectual disability
Osteoporosis
Marfanoid habitus
Kyphosis
Lens subluxation (downward)
A

Homocystinuria

Defect - cystathionine synthase

Can’t convert homocysteine to cystathionine

94
Q

Recurrent precipitation of hexagonal radiolucent renal stones in children

A

Cystinuria
+ sodium cyanide nitroprusside test

Defect in renal PCT, prevents reasborption of cysteine, ornithine, lysine, arginine

Tx = alkalinization of urine

95
Q

Inheritance pattern of all lysosomal storage disease (except Fabry)?

A

Autosomal Recessive

96
Q 
GM2 ganglioside accumulation
Development delay
Cherry red spots on Macula
Lysosomes with onion skin
NO HEPATOSPLENOMEGALY
A

Tay-Sachs

Deficiency of Hexosaminidase A

97
Q 
Accumulations of shingomyelin
Progressive neurodegeneration
HEPATOSPLENOMEGALY
Foam cells
Cherry red spots on Macula
A

Neimann-Pick disease

Deficiency of Sphingomyelinase

98
Q 
Hepatosplenomegaly
Pancytopenia
Osteoporosis
Aseptic necrosis of femur
Bone Crises

Lipid-laden macrophages resembling crumpled tissue paper

A

Gaucher Disease

Deficiency Glucocerebrosidase

Accumulations of glucocerebroside

**Most common

USMLE REVIEW (25 decks)

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