Usmle - Biochem

Front 1

What is the purpose of S-adenosyl-methionine?

Back 1

SAM transfers methyl units.

SAM is the methyl donor man.

Front 2

Fomepizole

Back 2

Inhibits alcohol dehydrogenase

Think "foamy" beer

Front 3

Disulfiram

Back 3

Inhibits acetaldehyde dehydrogenase

Front 4

What drugs cause a disulfiram like reaction?

Back 4

Metronidazole, certain cephalosporins, procarbazine, 1st generation sulfonylureas

Front 5

What drugs cause a SLE like reaction?

Back 5

SHIPP - Sulfonamides, Hydrazaline, INH, Phenytoin, Procainamide

Front 6

What is the rate limiting enzyme in glycolysis?

Back 6

Phosphofructokinase-1 (PFK-1)

Front 7

What is the rate limiting enzyme in gluconeogenesis?

Back 7

Fructose 1,6 bisphosphate

Front 8

What is the rate limiting enzyme in the TCA cycle?

Back 8

Isocitrate dehydrogenase

Front 9

What is the rate limiting enzyme in glycogen synthesis?

Back 9

Glycogen synthase

Front 10

What is the rate limiting enzyme in glycogenolysis?

Back 10

Glycogen phosphorylase

Front 11

What processes is NADPH used in?

Back 11

Anabolic processes, respiratory burst, P-450, glutathione reductase

Front 12

Pyruvate kinase deficiency

Back 12

Associated with hemolytic anemia. Inability to maintain activity of Na+-K+ ATPase leads to RBC swelling and lysis.

RBCs metabolize glucose anaerobically (no mitochondria) and thus depend solely on glycolysis.

Front 13

What cofactors are needed by the pyruvate dehydrogenase complex?

Back 13

Tender Loving Care For No one - Thiamine, Lipoic acid, CoA, FAD, NAD

Front 14

Arsenic

Back 14

Inhibits lipoic acid (a cofactor needed for pyruvate dehydrogenase). Causes vomiting, rice water stools, and garlic breat/

Front 15

Pyruvate dehydrogenase deficiency

Back 15

Causes backup of substrate (pyruvate and alanine), resulting in lactic acidosis. Can be congenital or acquired (as in alcoholics due to B1 deficiency). Causes neurologic defects. Treatment includes increased intake of ketogenic nutrients (high fat content or increased lysine and leucine [the only purely ketogenic amino acids]).

Front 16

Cori cycle

Back 16

Allows lactate generated during anaerobic metabolism to undergo hepatic gluconeogenesis and become a source of glucose for muscle/RBCs. This comes at a net loss of 4 APT/cycle.

Shifts metabolic burden to the liver.

Front 17

Why are alanine and glutamine found in such high concentrations in the blood?

Back 17

They are the two major carriers of nitrogen from tissues.

Front 18

What is generally involved in the transamination in the alanine cycle?

Back 18

Transfer of the amino group of an amino acid to alpha-ketoglutarate to form glutamine. The remaining deaminated amino acid is a keto-acid (such as pyruvate) that is used in energy metabolism.

Front 19

2,4 DNP

Back 19

Electron transport chain uncoupling agent

Front 20

Why can't muscle participate in gluconeogenesis?

Back 20

Muscle lacks glucose 6 phosphatase

Front 21

What is the purpose of the HMP shunt?

Back 21

The purpose is to provide a source of NADPH from abundantly available glucose-6-phosphate. Additionally this pathway yields ribose for nucleotide synthesis and glycolytic intermediates.

No ATP is used or produced.

Front 22

NADPH

Back 22

Important in making fatty acids, phagolysosome of macrophages, steroid synthesis, reducing glutathione to prevent oxidative damage, and cytochrome P450 activity.

Front 23

Ribulose 5P

Back 23

Precursor to PRPP, which is used in nucleotide syntheis.

Front 24

Fructose intolerance

Back 24

Hereditary deficiency of aldolate B. Autosomal recessive. Fructose-1-phosphate accumulates, causing a decrease in available phosphate, which results in inhibition of glycogenolysis and gluconeogenesis.

Symptoms include hypoglycemia, jaundice, cirrhosis, and vomiting.

Treatment is to decrease intake of both fructose and sucrose.

Front 25

Essential fructosuria

Back 25

Involves a defect in fructokinase. Autosomal recessive. A benign, asymptomatic condition, since fructose does not enter cells.

Symptoms are fructose appearing in blood and urine.

Front 26

Classic galactosemia

Back 26

Absense of galactose 1 phosphate uridyltransferase. Autosomal recessive. Damage is caused by accumulation of toxic substrates (including galactitol, which accumulates in the lens of the eye).

Symptoms include failure to thrive, jaundice, hepatomegaly, infantile cataracts, mental retardation.

Treatment is excluding galactose and lactose from diet.

Front 27

Galactokinase deficiency

Back 27

Hereditary deficiency of galactokinase. Galactitol accumulates if galactose is present in diet. Relatively mild condition. Autosomal recessive.

Symptoms include galactose appearing in blood and urine, infantile cataracts. May initially present as failure to track objects or to develop a social smile.

Front 28

Von Gierke's disease

Back 28

Glucose 6 phosphatase deficiency

No gluconeogenesis or glycogenolysis. Causes severe fasting hypoglycemia, increased glycogen in the liver, increased blood lactate, and hepatomegaly.

Front 29

Pompe's disease

Back 29

Lysosomal alpha 1,4 glucosidase deficiency

Causes cardiomegaly and systemic findings leading to early death.

Front 30

Cori's disease

Back 30

Debranching enzyme (alpha 1,6 glucosidase deficiency); milder form of Von Gierke's disease with normal blood lactate levels.

Gluconeogenesis is intact but glycogenolysis is inhibited.

Front 31

McArdle's disease

Back 31

Deficit in skeletal muscle glycogen phosphorylase.

Increased glycogen in muscle, but cannot break it down, leading to painful muscle cramps, myoglobinuria with strenuous exercise. Longevity is not affected.

Front 32

What is the rate limiting step in ketone body synthesis?

Back 32

HMG CoA synthase

Front 33

In the liver, fatty acids and amino acids are metabolized into what?

Back 33

Acetoacetate and Beta-hydroxbutyrate

Front 34

Urine test for ketone bodies detects what?

Back 34

acetyl-CoA

Front 35

What is the rate enzyme step in glycolysis?

Back 35

Phosphofructokinase-1 (PFK-1)

Front 36

What is the rate enzyme step in gluconeogenesis?

Back 36

Frustose-1,6-bisphosphonate

Front 37

What is the rate enzyme step in the TCA cycle?

Back 37

Isocitrate dehydrogenase

Front 38

What is the rate enzyme step in glycogen synthesis?

Back 38

Glycogen synthase

Front 39

What is the rate enzyme step in glycogenolysis?

Back 39

Glycogen phosphorylase

Front 40

What is the rate enzyme step in HMP shunt?

Back 40

Glucose-6-phosphate dehydrogenase (G6PD)

Front 41

What is the rate enzyme step in de novo pyrimidine synthesis?

Back 41

Carbamoyl phosphate synthetase II

Front 42

What is the rate enzyme step in de novo purine synthesis?

Back 42

Glutamine-PRPP amidotransferase

Front 43

What is the rate enzyme step in the urea cycle?

Back 43

Carbamoyl phosphate synthetase I

Front 44

What is the rate enzyme step in fatty acid synthesis?

Back 44

Acetyl-CoA carboxylase (ACC)

Front 45

What is the rate enzyme step in fatty acid oxidation?

Back 45

Carnitine acyltransferase I

Front 46

What is the rate enzyme step in ketogenesis?

Back 46

HMG-CoA synthase

Front 47

What is the rate enzyme step in cholesterol synthesis?

Back 47

HMG-CoA reductase

Front 48

What are the cofactors for pyruvate kinase and alpha-ketoglutarate?

Back 48

Tender Loving Care For No one: Thiamine, Lipoic acid, CoA, FAD, NAD

Front 49

What cofactor for pyruvate dehydrogenase does arsenic inhibit?

Back 49

Lipoic acid

Front 50

What is the rate limiting enzyme in purine synthesis?

Back 50

Glutamine PRPP aminotransferase

Front 51

What is the rate limiting enzyme in pyrimidine synthesis?

Back 51

Carbamoyl phosphate synthase II

Front 52

Hydroxyurea inhibits what enzyme?

Back 52

Ribonucleotide reductase

Front 53

5-fluorouracil inhibits what enzyme?

Back 53

Thymidylate synthase

Front 54

6-mercaptopurine inhibits what enzyme?

Back 54

PRPP synthase

Front 55

Methotrexate inhibits what enzyme?

Back 55

Dihydrofolate reductase

Front 56

Trimethoprim inhibits what enzyme

Back 56

Bacterial dihydrofolate reductase

Front 57

Mycophenilate

Back 57

Immunosuppressant used to prevent organ rejection in transplant. Inhibits inosine monophosphate dehydrogenase in purine synthesis pathway.

Front 58

Orotic aciduria

Back 58

Inability to convert orotic acid to UMP (de novo pyrimidine synthesis pathway) due to defect in either orotic acid phosphoribosyltransferase or orotidine 5'-phosphate decarboxylase. Autosomal recessive.

Findings include increased orotic acid in urine, megaloblastic anemia (does not improve with administration of vitamin B12 or folic acid), failure to thrive. No hyperammonemia.

Treatment is oral uridine administration, in order to bypass the pathway.

Front 59

Adenosine deaminase deficiency

Back 59

Excess ATP and dATP imbalances nucleotide pool via feedback inhibition of ribonucleotide reductase; prevents DNA synthesis and thus decreases lymphocyte count. One of the major causes of SCID.

Front 60

Lesch-Nyhan syndrome

Back 60

Defective purine salvage owing to the absence of HGPRT, which converts hypoxanthine to IMP and guanine to GMP. Results in excess uric acid production. X linked recessive.

Findings are mental retardation, self-mutilation, aggression, hyperuricemia, gout, choreoathetosis.

Treatment is allopurinol for hyperuricemia, but there is no treatment for neurologic symptoms.

Front 61

Anti-SCL70

Back 61

Antitopoisomerase antibody associated with diffuse scleroderma.

CREST scleroderma is associated with anticentromere antibodies.

Front 62

Which DNA repair mechanism is mutated in xeroderma pigmentosum?

Back 62

Nucleotide excision repair

Front 63

Which DNA repair mechanism is mutated in hereditary nonpolyposis colorectal cancer (HNPCC)?

Back 63

Mismatch repair

Front 64

mRNA stop codons

Back 64

UGA, UAA, UAG

Front 65

alpha-amanitin

Back 65

Found in death cap mushrooms; inhibits RNA polymerase II. Causes liver failure if ingested.

Front 66

Where is the amino acid bound on tRNA?

Back 66

The amino acid is covalently bound to the 3' end of the tRNA.

All tRNAs, both eukaryotic and prokaryotic, have CCA at 3' end along with a high percentage of chemically modified bases.

Front 67

What enzyme is responsible for charging tRNA?

Back 67

Aminoacyl-tRNA synthase

Front 68

What is the MOA of tetracyclines?

Back 68

Tetracyclines bind the 30S subunit of tRNA, preventing attachment of aminoacyl-tRNA.

Front 69

Action of aminoglycosides

Back 69

Aminoglycosides inhibit formation of the initiation complex and cause misreading of mRNA.

Front 70

Action of chloramphenicol

Back 70

Chloramphenicol inhibits 50S peptidyltransferase.

Front 71

Action of macrolides

Back 71

Macrolides bind 50S, blocking translocation.

Front 72

Action of clindamycin

Back 72

Clindamycin binds 50S, blocking translocation.

Front 73

What tumor suppressors normally inhibit G1 to S progression?

Back 73

Rb and p53

Front 74

What tumor suppressor normally inhibits the progression from G2 to mitosis?

Back 74

p53

Front 75

Nissl bodies

Back 75

Rough endoplasmic reticulum; synthesize enzymes and peptide neurotransmitters. Seen in dendrites but not axons.

Front 76

What is the function of the smooth endoplasmic reticulum?

Back 76

Site of steroid synthesis and detoxification of drugs and poisons.

Liver hepatocytes and steroid hormone producing cells of the adrenal cortex are rich in SER.

Front 77

What amino acids are nuclear localization signals rich in?

Back 77

Lysine, arginine, and proline

Front 78

Where are cytosolic and organellar proteins synthesized?

Back 78

Free ribosomes

Front 79

What modification does the golgi apparatus make to asparagine?

Back 79

Modifies N-oligosacchardies

Front 80

What addition does the golgi apparatus make to serine and threonine?

Back 80

Adds O-oligosaccharides

Front 81

What molecule when added to a protein by the golgi apparatus targets the protein to the lysosome?

Back 81

Mannose-6-phosphate

Front 82

COPI

Back 82

Vesicular trafficking protein; used for retrograde movement from Golgi to ER.

Front 83

COPII

Back 83

Vesicular trafficking protein; used for anterograde movement from RER to cis-Golgi.

Front 84

Clathrin

Back 84

Vesicular trafficking protein; brings molecules into the cell and trafficks the vesicle to early endosome.

Receptor mediated endocytosis

Front 85

I-cell disease

Back 85

(Inclusion cell disease) Inherited lysosomal storage disease

Failure of the addition of mannose-6-phosphate to lysosome proteins. Enzymes are secreted outside the cell instead of being targeted to the lysosome.

Results in coarse facial features, clouded corneas, restricted joint movement, and high plasma levels of lysosomal enzymes. Often fatal in childhood.

Front 86

What drugs act on microtubules?

Back 86

Mebendazole, thiabendazole, griseofulvin, vincristine, vinblastine, paclitaxel, colchicine

Front 87

Dynein

Back 87

Retrograde movement to microtubules

Front 88

Kinesin

Back 88

Anterograde movement to microtubules

Front 89

Chediak-Higashi syndrome

Back 89

Microtubule polymerization defect, resulting in decreased phagocytosis. Results in recurrent pyogenic infections, partial albinism, and peripheral neuropathy.

Front 90

What effect does increased cholesterol have on plasma membranes?

Back 90

Increased melting temperature and decreased fluidity

Front 91

Ouabain

Back 91

Inhibits sodium pump by binding to K+ site.

Front 92

What step of collagen synthesis requires vitamin C?

Back 92

Hydroxylation of specific proline and lysine residues. Occurs in the endoplasmic reticulum.

Front 93

What step of collagen synthesis is affected in osteogenesis imperfecta?

Back 93

Glycosylation of pro-alpha-chain lysine residues and formation of procollagen (triple helix of 3 collagen alpha chains).

Front 94

What step of collagen synthesis is affected in Ehlers-Danlos syndrome?

Back 94

Cleavage of terminal regions of procollagen transforming it into insoluble tropocollagen.

Front 95

Ehlers-Danlos syndrome

Back 95

Faulty collagen synthesis causing hyperextensible skin, tendency to bleed (easy bruising), and hypermobile joints. Type III collagen is most frequently affected.

May be associated with joint dislocation, berry aneurysms, and organ rupture.

Front 96

Osteogenesis imperfecta

Back 96

Most common form is autosomal dominant with abnormal type I collagen, causing multiple fractures, blue sclerae, hearing loss, dental imperfections due to lack of dentin.

Type II is fatal in utero or in the neonatal period.

Front 97

Alport's syndrome

Back 97

Due to a variety of gene defects resulting in abnormal type IV collagen. Most common form is X-linked recessive.

Characterized by progressive hereditary nephritis and deafness. May be associated with ocular disturbances.

Front 98

What are the two inherited syndromes which affect elastin?

Back 98

Marfan's syndrome - caused by a defect in fibrillin.

Alpha1 antitrypsin deficiency - results in excess elastase activity and panacinar emphysema.

Front 99

Prader-Willi syndrome

Back 99

Delection of normally active Paternal allele due to imprinting. Symptoms include mental retardation, hyperphagia (associated with excress ghrelin secretion), obesity, hypogonadism, and hypotonia.

Front 100

Angelman's syndrome

Back 100

Deletion of normally active Maternal (angelMan) allele. Causes mental retardation, seizures, very jerky gait, inappropriate laughter ("happy puppet").

Front 101

Autosomal dominant polycystic kidney disease

Back 101

Formerly known as adult polycystic kidney disease. Always bilateral, massive enlargement of kidneys due to multiple large cysts. Patients present with flank pain, hematuria, hypertension, progressive renal failure. 90% of cases are due to mutation in APKD1. Associated with polycystic liver disease (that's convenient), berry aneurysms, mitral valve prolapse.

Infantile form is autosomal recessive.

Front 102

Osler-Weber-Rendu syndrome (hereditary hemorrhagic telangiectasia)

Back 102

Inherited disorder of blood vessels. Findings include telangiectasia, recurrent epistaxis, skin discolorations, arteriovenous malformations (AVMs). Autosomal dominant. Affects small vessels.

Front 103

What gene mutation are MEN 2A and MEN 2B associated with?

Back 103

Ret gene

Front 104

Neurofibromatosis type I (von Recklinghausen's disease)

Back 104

Autosomal dominant. Findings include cafe-au-lait spots, neurofibromas in skin, neural tumors, Lisch nodules (pigmented iris haratomas). Also marked by skeletal disorders, optic pathway gliomas, pheochromocytoma, and increased tumor susceptibility. Mutated NF-1 gene.

Front 105

Neurofibromatosis type II

Back 105

Autosomal dominant; bilateral acoustic neuroma, juvenile cataracts. NF2 gene mutation.

Front 106

Tuberous sclerosis

Back 106

Autosomal dominant; findings include facial lesions (adenoma sebaceum), "ash leaf" spots on skin, cortical and retinal hamartomas, seizures, mental retardation, renal cysts and renal angiomyolipomas, cardiac rhabdomyomas, increased incidence of astrocytomas. Incomplete penetrence and variable presentation.

Front 107

von Hippel-Lindau disease

Back 107

Autosomal dominant; findings include hemangioblastomas of retina/cerebellum/medulla, renal cell carcinomas, angiomatosis, pheochromocytoma; associated with deletion of VHL gene resulting in constitutive expression of HIF (transcription factor) and activation of angiogenic growth factors.

Front 108

What concentration of Cl- in a sweat test is diagnostic of cystic fibrosis?

Back 108

> 60 mEq/L

Front 109

What is the longest known human gene?

Back 109

Dystrophin gene (DMD)

Dystrophin helps anchor muscle fibers, primarily in skeletal and cardiac muscle.

Front 110

How are muscular dystrophies diagnosed?

Back 110

Increased CPK (creatine phosphokinase) and muscle biopsy

Front 111

FMR1 gene

Back 111

Gene codes for FMRP which is a cytoplasmic protein found in the brain and testes; it is involved in mRNA translation of axons in dendrites.

Fragile X syndrome is an x-linked defect affecting the methylation and expression of the FMR1 gene. Associated with chromosomal breakage (hence, the name "fragile" X).

Front 112

Which diseases are trinucleotide repeat expansion diseases?

Back 112

Huntington's disease (CAG), myoTonic dystrophy (CTG), Friedreich's ataxia (GAA), and fraGile X syndrome (CGG)

Front 113

Edward's syndrome

Back 113

Trisomy 18; infant with microcephaly, rocker-bottom feet, and structural heart defect; death usually occurs within 1 year of birth.

Front 114

Patau's syndrome

Back 114

Trisomy 13; cleft lip, cleft palate, holoprosencephaly, polydactyly; death usually occurs within 1 year of birth.

Front 115

Cri-du-chat syndrome

Back 115

Congenital microdeletion of short arm of chromosome 5; causes microcephaly, moderate to severe mental retardation, high-pitched crying/weeping, epicanthal folds, and cardiac abnormalities.

Front 116

Williams syndrome

Back 116

Congenital microdeletion of long arm of chromosome 7 (deleted region includes elastin gene).

Findings include "elfin" facies, mental retardation, hypercalcemia (increased vit D sensitivity), well-developed verbal skills, extreme friendliness with strangers, CV problems.

Front 117

Which two syndromes are associated with 22q11 deletions?

Back 117

DiGeorge syndrome (thymic, parathyroid, and cardiac defects) and Velocardiofacial syndrome (palate, facial, and cardiac defects)

Front 118

What is an increased erythrocyte transketolase activity upon addition of thiamine indicative of?

Back 118

Vitamine B1 (thiamine) deficiency

Front 119

Wet Beriberi

Back 119

Dilated cardiomyopathy (high output cardiac failure), edema, and polyneuropathy; due to thiamine (B1) deficiency.

Front 120

Dry Beriberi

Back 120

Only polyneuropathy (toe-drop, wrist-drop, foot-drop, muscle weakness, hyporeflexia, areflexia); due to thiamine (B1) deficiency.

Front 121

What are the signs of riboflavin deficiency?

Back 121

Vitamin B2 (riboflavin) deficiency is characterized by cheilosis (inflammation of the lips, scaling and fissures at the corners of the mouth), corneal vascularization, glossitis, dermatitis.

Front 122

What is the function of vitamin B2

Back 122

Vitamin B2 (riboflavin) is a cofactor in oxidation and reduction (e.g. FADH2).

Front 123

What deficiencies are associated with cheilosis, glossitis, and stomatitis?

Back 123

Iron, riboflavin, niacin, folate, and B12

Front 124

How is niacin (B2) created?

Back 124

From tryptophan, in a reaction requiring pyridoxine (B6)

Front 125

What is pellagra?

Back 125

Dermatitis, dementia, and diarrhea due to niacin (B3) deficiency; can be due to Hartnup disease, malignant carcinoid syndrome (increased tryptophan metabolism), or INH (decreased vitamin B6).

Front 126

Hartnup disease

Back 126

An autosomal recessive disorder characterized by defective neutral amino acid transport on renal and intestinal epithelial cells. Causes tryptophan excretion in urine and absorption from the gut, which can lead to pellagra (dermatitis, diarrhea, and dementia).

Front 127

Pantothenate

Back 127

Vitamin B5; essential component of CoA (a cofactor for acyl transfers) and fatty acid synthase.

Deficiency results in dermatitis, enteritis, alopecia, and adrenal insufficiency. There is, however, no deficiency disease.

Front 128

Vitamin B6

Back 128

Pyridoxine (pyridoxal phosphate in active form); a coenzyme for numerous enzymes including those of amino acid metabolism (transaminations and deaminations).

B6 deficiency has the same findings as riboflavin deficiency plus convulsions, hyper-irritability, and peripheral neuropathy.

Front 129

What enzymes is cobalamin a cofactor for?

Back 129

Homocysteine methyltransferase (SAM pathway) and methylmalonyl-CoA mutase.

Front 130

What is the active form of folic acid?

Back 130

Tetrahydrofolate

Front 131

What is the function of biotin?

Back 131

Biotin is a cofactor for carboxylation enzymes.

Front 132

What are the symptoms of vitamin C deficiency?

Back 132

Scurvy - swollen gums, bruising, anemia, and poor wound healing

Front 133

What is the function of vitamin K?

Back 133

Catalyzes gamma-carboxylation of glutamic acid residues on various proteins concerned with blood clotting. Synthesized by intestinal flora.

Necessary for the synthesis of clotthing factors 2, 7, 9, 10, protein C, and protein S.

Front 134

What are the symptoms of zinc deficiency?

Back 134

Delayed wound healing, hypogonadism, decreased adult hair (axillary, facial, pubic), dysgeusia, anosmia. May predispose to alcoholic cirrhosis.